EPA-460/3-73-001
                     DEVELOPMENT
                  OF LOW EMISSION
     POROUS-PLATE  COMBUSTOR
EOR AUTOMOTIVE GAS TURBINE
   AND RANK1NE CYCLE  ENGINES
        U.S. ENVIRONMENTAL I'KOTKCTION \(,KNO
            Office of Air ami \\ at<-r Programs
        
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                                      EPA-460/3-73-001.
DEVELOPMENT OF LOW EMISSION
   POROUS-PLATE  COMBUSTOR
FOR  AUTOMOTIVE GAS TURBINE
 AND RANKINE CYCLE ENGINES
                      by

               Mr. Richard J. Rossbach
                General Electric Co .
               Energy Systems Programs
                  P.O. 13ox 15132
                Cincinnati, Ohio 45215

                Contract No. 68-01-0461
                 Project Officers:

          Mr. Thaddcus S. Mroz (NASA - Lewis)
              Mr. William C. Cain (EPA)

                   Prepared lor

        U.S. ENVIRONMENTAL PROTECTION AGENCY
            Office of Air and Water Programs
         Office of Mobile Source Air Pollution Control
        Alternative Automotive Power Systems Division
              Ann Arbor , Michigan 48105

                    September

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This  report  is  issued by  the Office of Mobile Source Air Pollution
Control, Office of Air and Water Programs, Environmental Protection
Agency, to report technical data of interest to a limited number of
readers.  Copies of  this  report are available free of charge to
Federal employees, current contractors and grantees, and non-profit
organizations - as supplies permit - from the Air Pollution Techni-
cal Information Center, Environmental Protection Agency, Research
Triangle Park, North Carolina  27711 or may be obtained, for a
nominal cost, from the National Technical Information Service,
5285  Port Royal Road, Springfield, Virginia  22151.
This report was furnished to the U.S. Environmental Protection Agency
by The General .Electric Company in fulfillment of Contract No.
68-01-0461 and has been reviewed and approved for publication by the
Environmental Protection Agency.  Approval does not signify that the
contents necessarily reflect the views and policies of the agency.
The material presented in this report may be based on an extrapolation
of the "State-of-the-art."  Each assumption must be carefully analyzed
by the reader to assure that it is acceptable for this purpose.  Results
and conclusions should be viewed correspondingly.  Mention of trade
names or commercial products does not constitute endorsement or
recommendation for use.
                     Publication No. EPA-460/3-73-001
                                   11

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                               CONTENTS

                                                                  Page
SUMMARY	    1

INTRODUCTION	    5

ABSTRACT	   17

CONCLUSIONS AND RECOMMENDATIONS	   19

GAS TURBINE COMBUSTOR	   31

     Discussion	   31
     Combustor Loading and Emission Analysis 	   33
     Combustor Concept Feasibility Development 	  105
     Fuel-Air Mixture Supply Development 	  147
     Porous Plate Combustor Fabrication Development	167
     Combustor Configuration and Engine Integration Design . . .  180

RANKINE CYCLE COMBUSTOR	189
                                     /

     Discussion	. .	. • . •  189
     Preliminary Burner-Vapor-Generator Design .........  191
     Bench Tests	200

REFERENCES	232

APPENDIX	235

ACKNOWLEDGEMENT	244
                                  iii

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                           LIST OF FIGURES

Figure No.                                                        Page
     1    Schematic of Porous Plate Burner	   9
     2    Effect of Unburned Gas Superficial Velocity and
          Equivalence Ratio Upon Flame Temperature	11
     3    NO Formation Rate From Hot-Air Mechanism	13
     4    Calculated W>2 Formation Rates as a Function of Porous
          Plate Superficial Velocity and Equivalence Ratio. ...  14
     5    Air-Cooled Porous-Plate Burner Concept	21
     6    Schedule for Gas-Turbine Porous-Plate Combustor ....  22
     7    Conceptual Design of Porous-Plate Burner-Vapor Generator
          for Rankine System	26
     8    Schedule for Rankine Porous-Plate Combustor 	  28
     9    Low NOX Frit Plate Gas Turbine Combustor (Fuel Inside).  34
    10    Fuel Scheduling of Base Line Engine	37
    11    Hot-Side Burner Temperature:  Primary Air from Com-
          pressor Discharge	38
    12    Hot-Side Burner Temperature:  Primary Air from Com-
          pressor Discharge	39
    13    Hot-Side Burner Temperature:  Primary Air from Re-
          generator Discharge	   41
    14    Hot-Side Burner Temperature:  Primary Air from Re-
          generator Discharge	42
    15    Hot-Side Burner Temperature 	  43
    16    Effect of Emissivlty on Burner Temperatures 	  45
    17    Burned Gas Temperature of Radiation Cooled Combustor
          at Steady State Points	48
    18    Burned Gas Temperature of Radiation Cooled Combustor
          at Steady State Points	49
    19    Burned Gas Temperature of Radiation Cooled Combustor
          at Steady State Points	50
    20    Burned Gas Temperature of Radiation Cooled Combustor at
          FDC Points	51
    21    Burned Gas Temperature of Radiation Cooled Combustor at
          FDC Points	52
    22    Burned Gas Temperature of Radiation Cooled Combustor at
          FDC Points	53
    23    Burned Gas Temperature of Radiation Cooled Combustor at
          Steady State Wide Open Throttle Points	54

                                   iv

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Figure No.                                                        Page

    24    Burned Gas Temperature of Radiation Cooled Corabustor at
          Steady State Wide Open Throttle Points	„  55
    25    Burned Gas Temperature of Radiation Cooled Combustor at
          Steady State Wide Open Throttle Points	56
    26    Surface Temperature of Radiation Cooled Combustor at
          Steady-State Points 	  57
    27    Surface Temperature of Radiation Cooled Combustor at
          Steady-State Points 	  58

    28    Surface Temperature of Radiation Cooled Combustor at
          Steady State Points 	  59
    29    Surface Temperature of Radiation Cooled Combustor at
          FDC Points	60

    30    Surface Temperature of Radiation Cooled Combustor at
          FDC Points. . .  i	61
    31    Surface Temperature of Radiation Cooled Combustor at
          FDC Points.	62

    32    Surface Temperature of Radiation Cooled Combustor at
          Steady State Wide Open Throttle Points	63

    33    Surface Temperature of Radiation Cooled Corabustor at
          Steady State Wide Open Throttle Points	64
    34    Surface Temperature of Radiation Cooled Combustor at
          Steady State Wide Open Throttle Points	„ .  . .  65
    35    Surface Temperature of Radiation Cooled Corabustor at
          Steady State Points 	  66
    36    Surface Temperature of Radiation Cooled Combustor at
          Steady State Points 	  67

    37    Surface Temperature of Radiation Cooled Combustor at
          Steady State Points 	  68
    38    Surface Area of  Radiation Cooled Combustor at FDC
          Points	69
    39    Surface Temperature of Radiation Cooled Corabustor at
          FDC Points	70
    40    Surface Temperature of Radiation Cooled Combustor at
          FDC Points	71
    41    Surface Temperature of Radiation Cooled Corabustor at
          Steady State Wide Open-Throttle Points	72
    42    Surface Temperature of Radiation Cooled Combustor at
          Steady State Wide Open Throttle Points	73
    43    Surface Temperature of Radiation Cooled Combustor at
          Steady State Wide Open Throttle Points	74
    44    Superficial Velocity Along Steady State Power Match
          Line	76

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Figure No.                                                        Page
    45    Combustor Temperature Along Steady State Power Match
          Line	77

    46    NOX Emission Index Along Steady State Power Match
          Line	78

    47    CO Emission Index Along Steady State Power Match
          Line	79
    48    Nodal System for Transient Thermal Analysis 	  82

    49    Time-Dependent Gas Generator Speed During 3 Wide-Open-
          Throttle Transients (WOT) at 85°F	85

    50    Fuel Scheduling of Base Line Engine During the Four
          Transients	86

    51    Configuration or Materials in Porous Burner (for
          Transient Analysis) 	  88
    52    Schedule of Burner Area and Equivalence Ratio During
          the 4 Transients	89
    53    Calculated Thermal Response of the Porous Combustor
          During WOT From Idle	  90

    54    Undiluted Burned Gas Temperature During the WOT
          Transient From Idle to 100% Gas Generator Speed of the
          Base Line Engine	92
    55    Conditions at the Burner Surface During WOT From Idle
          to 100% Gas Generator Speed	93
    56    Heat Fluxes Back to the Burner Surface  During WOT
          from Idle to 100% Gas Generator Speed	94
    57    Thermal Response of Porous Combustor to a Hypothetical
          Transient	96
    58    Calculated Thermal Response of the Porous Combustor
          During the WOT Transient from 40% Engine Power	97
    59    Burned Gas Temperature During the WOT Transient from
          40% Engine Power of the Base Line Engine	98

    60    Calculated Thermal Response of the Combustor During
          the WOT Transient from 60% Engine Power of Base Line
          Engine. . „	99
    61    Burned Gas Temperature During the WOT from 60% Engine
          Power of the Base Line Engine	100
    62    Comb us tor Response to Cold Start Transient	101

    63    Burned Gas Temperature During Cold Start Transient
          of Base Line Engine	102
    64    Predicted N02 Emissions Index Based on the Hot Air
          Mechanism	103

    65    Predicted CO Emissions Index	104

    66    Gas Turbine Porous-Plate Combustor Test Section .... 106
    67    SIC Spring Loaded Configuration 	 108

                                  vi

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FIKure No.                                                        Page
    68    Metallic Corabustor Configurations	o  .  .  .  «  110
    69    Kanthal-Wrapped Burner	112
    70    Kanthal-Wrapped Burner with Zirconia Cloth and
          Cerapaper Insulation	113
    71    Emission Measurements from Burner S/N 102	117
    72    Configuration With SiC Rings Over Mullite Cylinder.  .  .  118
    73    Schematic of Preignition Test Setup	119
    74    Preignition Test Rig Hardware	120
    75    Upstream Face Temperature Leading to Preignition at
          3 Atmospheres 	  124
    76    Impending Preignition at P = 4 Atmospheres	125
    77    Radiant Heat Flux From A Burner	128
    78    Calculated Maximum Wall Temperatures for Air-Cooled
          Burner for Cooling Air Initial Temperature, 400°F „  .  .  129
    79    Calculated Maximum Wall Temperatures for Air-Cooled
          Burner for Cooling Air Initial Temperature, 1400°F.  .  .  130
    80    Heat Flux Back to the Porous Burner as a Function of
          Pressure and of Superficial Gas Velocity (V2J	132
    81    Design of Air-Cooled Porous Burner 106	  133
    82    Air-Cooled Burner #106 During Fabrication 	  136
    83    Schematic of Gas Turbine Corabustor Test Facility.  .  .  .  138
    84    Scott Exhaust Gas Analyzer	140
    85    Emissions from Air-Cooled Burner S/N 106 at 1  Atm.
          Pressure	142
    86    N02 Measurements at 1 to 4 Atmospheres on Air-Cooled
          Burner	143
    87    Burner 107 Pressure Drop	144
    88    Measurements of CO and NOV Emissions on Burner 107.  .  .  146
                                   X
    89    Measured CO Emissions on Burner 108M with Both Heated
          and Unheated Mr	148
    90    Measured NOX Emissions on Burner 108M with Both Heated
          and Unheated Air	149
    91    Fuel Vaporizer for Gas Turbine Combustor	151
    92    "Sonicore" Fuel Vaporizer	153
    93    Estimated Performance of Fuel Vaporizer for Gas Turbine
          Corabustor ...>..........•••••••••  157
    94    Vaporizer and Inlet and Exhaust Lines 	  159
    95    Vaporizer and Inlet and Exhaust Lines 	  161
    96    Vaporizer Air .and Fuel Supply System	162
    97    Experimental Vaporization Quality as a Function of the
          B Group Parameter 	  166
                                  vii

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Figure No.                                                        Page
    98    Weight Gain of Fe-25Cr-4Al-Y Alloy During Oxidation
          Testing in Air	174
    99    Poroloy Permeability Retention After Exposure at 1800
          and 2000°F (982 and 1093°C) in Air.  Alloys GE 1541 and
          H 875	175
   100    Nichrome Porous Cylinder No. 3 As Sintered at 2350°F. . 181
   101    Porous Cylinder No. 3 with Tube Sheets Brazed on Each
          End	182
   102    Air-Cooled Porous-Plate Burner Concept	185
   103    Conceptual Design of Porous-Plate Burner-Vapor
          Generator for Rankine System	192
   104    Fuel-Air Mixer and Fuel Vaporizer Double-Swirl
          Carbureting Concept 	 195
   105    Preliminary Installation Configurations . . 	 196
   106    Rankine Engine Fuel-Air Mixer Cup Flow Characteristics. 198
   107    Estimated Vaporizer Performance 	 199
   108    Half-Filled Copper Shot Burner, Illustrating Burner
          Construction and Coolant Tube Manifolding 	 201
   109    Schematic Diagram of Burner Test and Gas Sampling
          Arrangement	202
   110    Burner Heat Flux Back to the Burner from the Flame;
          Propane-Air Mixtures	213
   111    Burner Heat Flux Back to the Burner from the Flame;
          Gasoline (EPA)-Air Mixtures 	 214
   112    Comparison of Gasoline (EPA) and Propane-Air Burned
          Gas Temperatures	215
   113    CO Analyses from Two Flames	220
   114    CO Experimental Measurements on Water-Cooled Burners
          with 20 Milliseconds Residence Time	222
   115    Variation of NO Formation Rate from "Hot-Air" Mechanism
          as a Function of Reciprocal Absolute Temperature.  NO
          Formation Rate Adjusted to 2% Molar 0	224
   116    N02 Experimental Measurements on Water-Cooled Burners
          with 20 Milliseconds Residence Time .	230

   A-l    GDF I Combustor Test Facility	236
   A-2    Test Cell Heaters and Flow Metering Sections	237
   A-3    Fuel Storage and Pumping	239
   A-4    Heater Control Console	240
   A-5    Facility Control Console	241
   A-6    Scott Exhaust Gas Analyzer	„ 243

                                  viii

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                            LIST OF TABLES

Table No.                                                         Page
    1     Base Line Engine Combustor Test Points	    36
    2     Summary of Calculations	    47
    3     Silicon Carbide Combustor Configurations 	   109
    4     Metallic Combustor Configurations	114
    5     Preignition Tests	122
    6     Parts List of Air-Cooled Porous Burner Shown in
          Figure 81	134
    7     Air-Cooled Burners (Cylindrical) 	   137
    8     Gas Turbine Fuel Vaporizer Test Data	165
    9     Porous Combustor Materials 	   168
   10     Candidate Alloys for Combustor Components	170
   11     Tensile Properties of Candidate Alloys for Combustor
          Components	   173
   12     Critical Thermal Properties of Selected Ceramics .  . .   176.
   13     Porous Rankine Combustor 	   193
   14     Rankine Model Burner Test Results	216
   15     Rankine Model Burner Emission Results	219
                                  ix

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                                SUMMARY







      The requirements of the 1970 Clean Air Act Amendments were that the



Environmental Protection Agency enforce stringent exhaust emission standards



for new automobiles on unburned hydrocarbons and carbon monoxide in the



1975 model year and on nitrogen oxides in the 1976 model year (although



these requirements may be relaxed for a time).  As the standards originally



stood, the most difficult standard to meet was that relating to NO ,
                                                                  A


especially since it is difficult to obtain low NO  and low CO together.
                                                 X


Experiments with porous-plate combustors previous to this contract had



shown very low NO  levels, so further development work was undertaken.
                 X


The purpose of this contract was to evaluate analytically and experi-



mentally the use of the porous-plate combustor for use in the gas-turbine



or Rankine-cycle advanced automobile engines to control exhaust emissions.



      By providing a uniform mixture of fuel and air (pre-mixed) and



passing it through a porous plate, combustion is initiated and a uniform



flame can be stabilized on the downstream surface of the porous material.



Because of the closeness of the flame to the plate and short flame height



(1-4 mm), heat is transferred from the flame to the plate, cooling the



flame and preventing the adiabatic flame temperature from being attained.



The heat transferred to the plate must be removed by radiation or a



coolant in the case of the gas-turbine combustor and by the working fluid



in the case of the Rankine-cycle combustor.  This combustion process



virtually eliminates unburned hydrocarbon emissions as long as there is

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a small excess of oxygen.  The reduction of the flame temperature from



the adiabatic to some lower temperature dramatically reduces the NO



emissions.  The CO emission can be traded off with the very low NO



emissions in terms of residence time to make them low also.



THE GAS TURBINE COMBUSTOR



      The following conclusions were drawn concerning the porous-plate



gas turbine combustor from the work described herein:



      1.  Analytical work indicates that the combustor equivalence ratio



          and the porous-plate burner area must be variable in order




          for the engine to operate between the steady-state level-road



          load fuel requirements and the wide-open-throttle acceleration



          fuel requirements.




      2.  The operational temperature of the downstream side of the



          porous plate must be limited to a specific value at the higher



          power levels to prevent flashback through the porous plate



          and pre-ignition of the fuel air mixture.  Air cooling of the



          porous plate matrix, in addition to radiation cooling, is re-



          quired to avert this condition.



      3.  Models of air-cooled porous-plate combustors have successfully



          been made from sintered nichrome and tested.



      4.  Emission measurements with propane-air mixtures at inlet tem-



          peratures of approximately 400°F and one atmosphere were



          favorable.  The NO  emission index was below the 1976 Federal
                            Jk


          Standards and the CO emission index was below the Standards



          at combustor conditions corresponding to light engine loads



          but somewhat above it at heavier loads.  The unburned hydro-




          carbon values were at about the detection level which is much



          below the Standard.

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      5.  Tests of a fuel atomizer and vaporizer using an air assist



          fuel nozzle spraying into a swirling flow resulted in all but



          a few points having 93% or more of the fuel vaporized.



      Based upon these results, a full size porous-plate combustor con-



cept has been developed for the Baseline Engine having a total porous


                    2
plate area of 2.2 ft  and which extends only 2 inches higher vertically



than the conventional combustor for the engine.  In this concept, the



total porous surface is made up of a number of air-cooled wedge-shaped



flat-plate segments.  It is recommended that this combustor be designed,



fabricated, and tested with gasoline.



THE RANKINE CYCLE COMBUSTOR



      The following conclusions were drawn concerning the porous-plate



Rankine-cycle combustor from the work described herein:



      1.  The Arrhenius plots of superficial velocity versus reciprocal



          absolute flame temperature at constant equivalence ratio which



          are used to design porous-plate combustors were confirmed for



          five fuels including gasoline.



      2.  Both the emissions indexes for NO  and CO increased with super-
                                           X.
          ficial velocity at constant equivalence ratios and for li



          fuels were only below the Standard at conditions corresponding



          to moderate engine loads.



      3.  The unburned hydrocarbon emission indexes were very low, about



          at the detection level.



      A.  The fuel atomizer and vaporizer developed for the gas turbine



          combustor are adequate for the Rankine combustor.  All but a



          few of the test points indicated 93% or more fuel vaporization.

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      The original Rankine-cycle combustor concept is unchanged.  Since




the sintered copper water-cooled porous-plate combustors are success-




fully being made by the General Electric Company and based upon the




above results, it is recommended that the full-size water-cooled Rankine




combustor be designed, fabricated,  and tested using gasoline.

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                             INTRODUCTION








     The purpose of the work under this contract was to evaluate the




use of the porous plate combustor systems for gas turbine and Rankine




cycle advanced automotive engines.




     Evaluation of this unique combustion system included emission levels,




burning limits, air and fuel requirements, response to transients, general




operating characteristics, start up, durability, sensitivity to degree




of inlet fuel vaporization, and pressure drop.  This work was intended




to provide proof of feasibility of use of porous plate burners by demon-




strating adequate performance in the following areas:




     •  Emission characteristics of the model or segments as developed




     •  Definition of start up characteristics




     •  A complete combustor operating map sufficient to define full




        scale combustor designs.  The information to be generated in-




        cludes mixture quality control requirements, mixture distribu-




        tion requirements, corabustor active area control, means of con-




        trolling equivalence ratio, etc.




     The approach to the gas turbine and Rankine cycle combustor develop-




ment included the following tasks:




                   Gas Turbine Combustor Development




          IB.  Combustor loading and emission analysis




         IIB.  Combustor configuration and engine integration design




        TUB.  Combustor concept feasibility development

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         IVB.  Fuel-air mixture supply development




          VB.  Porous plate combustor fabrication development




         VIB.  Prepare recommendations




                  Rankine Cycle Combustor Development




          IR.  Preliminary burner vapor generator design




         IIR.  Bench tests




        IIIR.  Engineering test unit




         IVR.  Prepare recommendations




     The development of the Rankine Cycle Combustion system was performed




in parallel to the gas turbine combustor development.  A complete inter-




change of technology was made, generated on either gas turbine or Rankine




cycle burners.




     The requirements of the 1970 Clean Air Act Amendments are that the




Environmental Protection Agency enforce stringent exhaust emission standards




for new automobiles on unburned hydrocarbons and carbon monoxide in the




1975 model year and on nitrogen oxides in the 1976 model year.  The




original 1976 standards are as follows:




               Unburned hydrocarbons, grams/mile    0.41




               Carbon monoxide, grams/mile          3.4




               Nitrogen oxides, grams/mile          0.4




Although the automobile industry is attempting to meet the emission




standards with the conventional automobile reciprocating engine, there




are several other promising engine types which have a high potential of




meeting the 1976 emission Standards.  Both the gas turbine and the Rankine




cycle engines have the potential for low exhaust emissions.  The combustor




for each engine can be designed separately for efficient and controlled

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(1,2,3)
combustion while still being integrated into the engine configuration.



Currently, combustors designed for these two engine types still have



emissions problems, especially with difficulty in obtaining low NO



emissions.  Many conventional combustors burn from sprayed droplets.



The result is that large variations in the local equivalence ratio can



exist in the primary combustion zone due to inefficient atomization and



mixing; for an overall lean equivalence ratio, part of the combustion



can occur at near-stoichiometric conditions, resulting in high peak flame



temperatures, with attendant high NO  production rates, while the rest
                                    X


of the combustion occurs at a very lean equivalence ratio at lower flame



temperatures with lower NO  production rates.  The overall result is



high NO , since the NO  production rate increases logarithmically with
       X              X


temperature; the areas of low NO  production cannot balance the areas of
                                X


high NO  production.
       X


     In order to minimize NO  emissions, both the flame temperature and



the residence time at temperature must be controlled.  The flame tempera-



ture determines the NO  production rate, while the residence time is the



time over which the NO  production rate is operative.  The flame tempera-
                      X


ture should not be excessively depressed; if the flame temperature •*?> too



low, then the CO decay rate is also low, and not enough CO will be burned



off to form CO , for a given residence time.  Similarly, flame temperatures



that are too low will also result in high emissions of unburned hydro-



carbons, since the burn-off rates depend strongly on flame temperature.



     Previously, experiments with a porous plate combustor had shown



very low NO  levels, so further development work was undertaken.  By
           X


providing a uniform mixture of fuel and air and passing it through a

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porous plate, a uniform flame can be stabilized on the downstream surface



of the porous material.  Because of the closeness of the flame to the



plate, heat is transferred from the flame to the plate, cooling the flame



and preventing the adiabatic flame temperature from being attained.  The



heat transferred to the plate must be removed by radiation or a coolant



in the case of the gas-turbine combustor and by the working fluid in the



case of the Rankine-cycle combustor.  The evenness of the flame virtually



eliminates unburned hydrocarbon emissions as long as there is a small



excess of oxygen.  The reduction of the flame temperature from the adiabatic



to some lower temperature dramatically reduces the NO  emissions.  The
                                                     X


emission of CO can be traded off with the very low NO  emissions in terms
                                             J       x


of residence time and flame temperature to make them low also.



     The porous burner is shown schematically in Figure 1.  Premixed



fuel and air pass through a porous matrix.  A substantial amount of heat



is conducted from the flame back to the cooled porous matrix, since the



flat laminar flame is maintained close to the metal surface.  The burned



gas (flame) temperature obtained with the porous burner varies from the



adiabatic flame temperature down to about 1500°F (2340°F) as the super-



ficial velocity is decreased from the adiabatic flame velocity.  NO  pro-
                                                                   A


duction rates decrease logarithmically with burned gas temperature;



hence, since burned gas temperatures with the porous combustor are lower



than the adiabatic flame temperature, NO  production rates are advantageously



lower than in conventional combustors at the same combustion rates.



     The characteristics of flames burning on cooled porous plugs have



been discussed from various points of view. *• » » '  The operating principle



of the porous combustor relative to NO  production rates is that a very
                                      A

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SINTERED
POROUS
METAL
              BURNED GAS
              T        0
Figure 1.  Schematic of Porous Plate Burner

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uniform, flat, laminar flame, about 1 mm high, is formed on the surface



of the porous combustor.  This flame is non-adiabatic, with a predictable



and appreciable fraction of its heat release being transferred from the



unburned side of the flame back to the porous plate.  Since the flame is



non-adiabatic, the burned gas temperature can be selected by design at



a value below the adiabatic temperature so as to control NO  production



rates; NO  production rates are extremely temperature dependent, and re-
         X


ductions in burned gas temperatures result in significant reductions in



NO  production rates.  The heat absorbed by the porous plate can be re-
  X


moved either by allowing the plate to operate at a high temperature such



that heat removal is accomplished by thermal radiation and preheating of



inlet unburned gas mixture or by incorporating cooling tubes in the



porous matrix for compressor discharge air in the case of the gas turbine



or for the working fluid in the Rankine application.



     Measurements of burned gas temperature (T) with the porous burner



are related to superficial unburned gas velocity through the burner (V_,-)



and equivalence ratio (R) by straight lines on a log V.^ versus 1/T plot,



yielding a single line for each value of R; data from Kaskan    is shown



in Figure 2.  The four porous burner combustion lines are independent of



gas inlet temperature, to a first approximation.  The lines at which



adiabatic combustion occurs are also shown for two different unburned



gas inlet temperatures.   The inlet temperature of the fuel-air mixture



has a significant effect on the maximum velocity above which the flame



lifts off the porous surface.  The points of intersection of the adiabatic



and porous burner lines determine the unburned gas velocities at which



the flat flame will begin to lift off the porous plate, the upper limit
                                  10

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                               Temperature,  °F
              4000   3800   3600  3400   3200
              —i	1	1	1	r
                               3000
                              —r
            2800
100
 10
                                              Estimated  Liftoff  Limit  for
                                              Inlet  Fuel-Air  of  1200°F
                                                                 Liftoff  Limit
                                                                 for  Inlet  of  77°F
                                 Porous Burner
                                 Combustion Lines
                                                             Equivalence  Ratio
           Note:
               I
V_5 is at P - 1 atm.
             I
I
           4 x 10"4                       5  x  10~4
                      Reciprocal Absolute Temperature,  (1/°K)
                                                      6 x 10
                                                            .-*
     Figure 2.   Effect  of Unburned Gas Superficial Velocity and Equivalence  Ratio
                Upon  Flame Temperature.
                                       11

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of operation.  The lower limit of operation (or flame extinguishment) is



the gas velocity at which the burned gas temperature drops below that



required to sustain the flame reaction, which occurs at about 4 cm/sec.





     As seen in Figure 2, the flame temperature obtained with the porous



burner can be considerably below the adiabatic flame temperature by varying



the unburned gas velocity, independent of equivalence ratio.




     Shown in Figure 3 are NO formation rates based on the "hot-air"



mechanism.  These rates are derived from the basic kinetic data used by



Fenimore   .  It can be seen that significant reductions in NO formation



rates can be achieved by lowering the actual flame temperatures by only



several hundred degrees.  For example, a temperature reduction of 360°F



(200°C) reduces the NO production rate by a factor of 20.



     The porous burner produces a very uniform, stable flame; hydrocarbon



and particulate emissions from lean flames on this burner have been



measured, and are approximately zero.  CO emissions can be kept at a low



level by providing sufficient burned gas residence time at temperature



to allow decay to CO .  However, the gas temperature after dilution must



be low enough so that the NO  production rates are low.  The emissions
                            X


design of the porous plate burner therefore simplifies at first approxi-



mation to selection of a flame temperature low enough to limit NO forma-



tion.  The NO production rates of Figure 3 can then be used to compute



NO formation rates as a function of superficial velocity V-_ from the



flame temperature data of Figure 2; Figure A presents the NO  formation



rates thereby estimated as a function of V...  The extreme reductions of



NO  that can be obtained with the porous combustor are apparent.
                                12

-------
 10.0
3200    3000
2800
                    800  3600
                                                     (for N   -  0.1)
               NO Formation Rate by
               Hot Air Mechanism
               r =    .; Normalized to 2200K
                    dT
               At 1 Atn Total Pressure and No  -0.1
                                             2
               J. Experimental Data from Various Flames
              I     _ I _ I
0.001
              4              4.5             5              5.5
               Reciprocal Absolute Temperature  (1/T) x 10*,  (1/°K)

                 Figure  3.  NO Formation Rate From Hot-Air Mechanism.
                                       13  '

-------
                        Equivalence Ratio R -  1.0
                                                        0.7
                        Full Load
 10
1.0
                                                             Adlabatic Plane
                                                             1200°F Inlet
Adiabatlc Flame
77 F Inlet
            Typical Mean
            Load
    Note:  V2  Is at P-l atm
                  10       20          50       100
                     Superficial Gas Velocity,  V   (cm/sec)

     Figure  4.   Calculated N0£  Formation  Rates  as a Function of Porous Plate
                Superficial Velocity  and  Equivalence Ratio.

-------
     Until analytical ami experimental techniques were employed to evaluate




tin.' feasibility of the porous-plate combustor for both gas turbine and




Kankino atitomohM c- engines.  As regards the gas turbine application,  this




i,-purl  contains ana.l yt leal results on the burner area requirements for




the various operating conditions of the-Baseline Engine as well as exhaust




eni.ssi.on predictions.  The design concept of an air-cooled, variable-area




combustor for this engine is presented.  Operational and emissions data on




several experimental combustors are presented along with the fabrication




development leading to these combustors.  Finally the demonstration results




for a full-scale fuel-air mixture system are presented.




     With regard to the automotive Rankine engine application, heat load




and emissions data are presented for propane and four liquid fuels.   Although




the fuel-air mixture system developed for the gas turbine combustor is




directly applicable, alternate systems were.investigated.  Finally




recommendations for the development of both gas turbine and Rankine




combustors are presented.
                                    15

-------
                              ABSTRACT






     Experiments with porous-plate combustors previous to this contract



had shown very low NO  levels, so further development work was under-
                     X


taken.  The purpose of this contract was to evaluate analytically and



experimentally the use of the porous-plate combustor for use in the gas-



turbine or Rankine-cycle advanced automobile engines to control exhaust



emissions.



     For the porous-plate combustor for the gas turbine, the following



conclusions were drawn:  (1) Analytical work indicates that the burner



area must be variable in order to meet the fuel flow requirements for



operation between steady-state load and wide-open-throttle acceleration;



(2) Air-cooling of the porous burner (in addition to radiation cooling)



is required to avoid flashback; (3) Models of air-cooled porous-plate



combustors have been successfully built from nichrome and tested; (4)



Emission measurements of NO , CO and unburned hydrocarbons with propane-



air mixtures at inlet temperatures of approximately 400°F and one atmosphere



were favorable; (5) Tests of a fuel atomizer and vaporizer resulted in



all but a few points having 93% or more of the fuel vaporized.



     For the porous plate combustor for the Rankine-cycle expander, the



following conclusions were drawn:  (1) The Arrhenius plots of superficial



velocity versus reciprocal absolute flame temperature at constant equiv-



alence  ratio were confirmed for five fuels including gasoline; (2) Both



the emission indexes for NO  and CO increased with superficial velocity
                           A




                                  17

-------
at constant equivalence ratios and for liquid fuels (including gasoline)




were only below the Standard at conditions corresponding to moderate




engine loads; (3) The emission indexes for unburned hydrocarbons were at




about the detection level, well below the Standards; (4) The fuel atomizer




and vaporizer developed for the gas turbine combustor are adequate for




the Rankine combustor.
                                  18

-------
                   CONCLUSIONS AND RECOMMENDATIONS








THE GAS TURBINE COMBUSTOR




     The following conclusions were drawn concerning the porous-plate




gas turbine combustor from the work described herein:




     1.  Analytical work indicates that the combustor equivalence ratio




         and the porous-plate burner area must be variable in order for




         the engine to operate between the steady-state level-road load




         fuel requirements and the wide-open-throttle acceleration fuel




         requirements.




     2.  The operational temperature of the downstream side of the porous




         plate must be limited to a specific value at the higher power




         levels to prevent flashback through the porous plate and pre-




         ignition of the fuel air mixture.  Air-cooling of the porous




         plate matrix, in addition to radiation cooling, is required to




         avert this condition.




     3.  Models of air-cooled porous-plate combustors have successfully




         been made from sintered nichrome and tested.




     4.  Emission measurements with propane-air mixtures at inlet tem-




         peratures of approximately 400°F and one atmosphere were favorable.




         The NO  emission index was below the 1976 Federal Standards and




         the CO emission index was below the Standards at combustor con-




         ditions corresponding to light engine loads but somewhat above




         it at heavier loads.  The unburned hydrocarbon values were at




         about the detection level which is much below the Standard.






                                  19

-------
     5.  Tests of a fuel atomizer and vaporizer using an air-assist fuel



         nozzle spraying into a swirling flow resulted in all but a few



         points having 93% or more of the fuel vaporized.



     As a result of these accomplishments, it is recommended that the



full scale air-cooled porous-plate combustor shown in Figure 5 for the



Base Line Engine be designed, fabricated and tested with gasoline in the



General Electric Combustor Test Facility described in Appendix A.  A



schedule for the recommended work is shown in Figure 6.



     The full size porous-plate combustor concept shown in Figure 5 and


                                                                         2
developed for the Baseline engine has a total porous plate area of 2.2 ft



and extends only 2 inches higher vertically than the conventional com-



bustor for the engine.  In this concept, the total porous surface is



made up of a number of air cooled wedge-shaped flat-plate segments.



Development Plans



     The air-cooled porous-plate combustor for the automotive gas turbine



engine has been developed thus far by means of 1/5 scale models.  Tests



to date (at lower values of combustor inlet temperature than would be



the case in the engine) have shown NO  emission levels considerably be-
                                     X


low the Federal Standard and UHC levels at or below the detection level.



CO emissions are either below or above the Standard depending upon operat-



ing conditions.  By adjusting residence time and/or dilution staging,



the CO values can be lowered with the expectation that the NO  emissions



will increase somewhat but still be below the Standard.  It is now ap-



propriate to test a module of the full-scale porous plate combustor at



combustor inlet conditions commensurate with engine operating conditions,



followed by testing of the full-scale combustor.  The recommended work



would be carried out in the following four tasks:




                                   20

-------
•  TO
   C
  re
  D.
  o
  ft
  o
  C
  o>

  fa
  3
  a
  ft

  n
  o

  n
 n
•v

-------
Master Schedule Sheet
BASE LINE ENGINE FULL SIZE POROUS COMBUSTOR DEMONSTRATION

fMn, Months


Design
Analysis
Configuration
Shop Drawings

Fabrication
Sintering Trials
Sinter Wedges
Sheet Metal Parts
Assembly
Installation
Design Adapters
Fabricate Adapters
Prepare Facility

Check Out
Propane
Gasoline

Test
Plan
Map Burner
Demonstrate

Evaluate Data
Reduce and Plot
Compare to Prediction

Summary Report

1




































































—





























































































2









































































































































3


































































































































4
































































































































































5

























































—





































































6











































































































































































































































































































































































































































































































































































































































































































































































































































































































































































Figure 6.  Schedule for  Gas-Turbine  Porous-Plate Combustor

-------
Task I - Design and Fabrication of the Full Scale Combustor - Making use




of the design analysis and the test results on the air-cooled porous




plate combustor described above, a full scale combustor will be designed




to the operating conditions of the Base Line Engine.   More than one com-




bustor will be fabricated having cooling tubes embedded in the sintered




nichrome porous surface.  Modules of the full-scale porous plate com-




bustor will also be designed for the purpose of confirming emission




measurements and module integrity under cycle conditions.   In addition,




all adapters will be made for installation in the General  Electric GDF-I




Combustor Facility described in the Appendix.  In the fabrication of the




combustor, care will be taken to properly control particle size distribu-




tion, sintering temperature, braze proportions and mixing  and dimensions.




Completion of the corabustor will include the integrated fuel-air mixture




supply, Joining of the porous plates to the remainder of the corabustor




structure and insulation upstream of the porous plate to prevent pre-




ignition of the fuel-air mixture.




Task II - Installation and Checkout - After assembly of the full scale




combustor it will be installed in the ESP GDF-I corabustor  test facility.




Adapters and complete instrumentation will be provided to  the faciiicy.




Provisions for measurement will include inlet flow rates,  temperatures




and pressures, outlet temperatures and emissions.  The emissions will be




measured using the Scott Dilute Exhaust Gas Emission Analyzer which is




capable of accurately measuring, on a continuous basis, NO, NO, CO, CO




and unburned hydrocarbons.  The facility will provide 2.5  Ibm/sec of air




flow in two streams, one being capable of being heated and controlled to




temperatures up to 1400°F and the other to 500°F.  The facility provides




air at the test section at pressures up to 4 atmospheres.





                                   23

-------
     Following installation of the combustor and calibration of the in-



strumentation, exploratory tests of the combustor will be made to assure



that all required conditions of the test can be met and that all facility



controls are functioning properly.  The necessary adjustments to the



facility will be made that are required for the test program.



Task III - Test and Evaluation - The operating performance of the com-



bustor, including pressure drop, exit temperature, and emissions will be



mapped over the appropriate ranges of burned gas velocity (V__)t equivalence



ratio, temperature and pressure level.  Testing of full-scale modules of



the combustor will precede testing of the full-scale combustor.  After



this, the test points delineated in EPA Test procedure for Low NO  Com-
                                                                 A


bustor Final Evaluation will be established and full measurements in-



cluding emissions will be made.  These data will be obtained at the air-



flow and fuel-flow rates, inlet temperature and pressure values specified



in the EPA Test Procedure for Low NO  Combustor Final Evaluation.  The
                                    X


appropriate equivalence ratio established for each test point will also



be set.



     The reduced test data will be evaluated in terms of the Base Line



Engine requirements.  The exhaust emissions data will be interpreted in



terms of emission index for the combustor performance map.  However, for



the points specified by the EPA Test Procedure for Low NO  Combustor
                                                         X


Final Evaluation, the data will be presented in terms of grams of pollutant



per mile, using the mutually agreed upon schedule of fuel economy.



Task IV - Summary Report - The analysis, design and combustor test data



will be documented at the end of the program along with appropriate draw-



ings and specifications.
                                  24

-------
THE RANKINE CYCLE COMBUSTOR




     The following conclusions were drawn concerning the porous-plate




Rankine-cycle combustor from the work described herein:




     1.  The Arrhenius plots of superficial velocity versus reciprocal




         absolute flame temperature at constant equivalence ratio which




         are used to design porous-plate combustors were confirmed for




         five fuels including gasoline.




     2.  Both the emissions indexes for NO  and CO increased with super-




         ficial velocity at constant equivalence ratios for all fuels




         tested and for liquid fuels were only below the Standard at




         conditions corresponding to moderate engine loads.




     3.  The unburned hydrocarbon emission indexes were very low, about




         at the detection level.




     4.  The fuel atomizer and vaporizer developed for the gas turbine




         combustor are adequate for the Rankine combustor.  All but a




         few of the test points indicated 93% or more fuel vaporization.




     The tin-coated copper porous-plate burners tested on this program




were available from previous General Electric research programs.  It




was not necessary to develop the sintering techniques because they are




established and available for use.  The liquid-cooled porous-plate burner




operates at temperatures below 700°F and as a result the thermal stresses




are moderate.  The Rankine cycle porous-plate combustor operates at at-




mospheric pressure which limits the heat flux conducted back to the porous




plate from the flame, limiting the heat load.




     Based on the above accomplishments, it is recommended that the full-




scale water-cooled porous-plate combustor shown in Figure 7 for the
                                  25

-------
                               Cxluuit

                               0»t»» Out
                                                                                                                                 Air rroa bp*Dd«:
                                                                                                                                 Driven Co>pr«»o>
to
o\
                                                                                                        -."..'X     '.>, T
                                                                                                 ',.     •   ,  "••/ > • •-,;' ' '•"' \, ":l
       Cbabujtloo
         Volua*
       ru«l/Alr Htalfold
                                               Figure   7.    Conceptual  Design of  Porous-Plate Burner-Vapor
                                                               Generator for Rankine System
                         A-A

-------
Rankine-cycle engine be designed, fabricated, and tested with gasoline.



The schedule for the recommended work is shown in Figure 8.



Development Plans



     The water-cooled porous-plate combustor for the automotive Rankine-



cycle engine has been developed thus far by means of bench tests on flat



burner models.  Tests to date suggest NO  emission levels below the
                                        A


Federal Standard at most points and unburned hydrocarbon levels at or



below the detection level.  CO emissions may be either below or above



the Standard depending upon operating conditions.  By adjusting residence



time and/or dilution staging, the CO values can be lowered with the ex-



pectation that the overall average of NO  emissions over the cycle will
                                        X


increase somewhat but still be below the Standard.  It is now appropriate



to test a full-scale porous-plate combustor.  The recommended work would



be carried out in the following four tasks:



Task I - Design and Fabrication of the Full Scale Combustor - Making use



of the design analysis and the test results on the water-cooled porous-



plate combustor described above, a full-scale combustor will be designed



to the operating conditions of a specified full-size Rankine engine.



The combustor will be fabricated having cooling tubes embedded in the



sintered copper porous surface.  In the fabrication of the combustor,



care will be taken to properly control particle size distribution,



sintering temperature, braze proportions and mixing and dimensions.



Completion of the combustor will include the integrated fuel-air mixture



supply including the air preheater, joining of the porous plates to the



remainder of the combustor structure, and a tube bundle.



Task II - Installation and Checkout - After assembly of the full scale



combustor, it will be installed in a test facility which can supply air,




                                  27

-------
Master Schedule Sheet
Event
Design
BASE LINE ENGINE FULL SIZE POROUS COMBUSTOR DEMONSTRATION

Months



Analysis
Configuration
Shop Drawings

Fabrication
Sinter Modules
Sheet Metal Parts
Assembly

Installation
Prepare Facility

Check Out
Propane
Gasoline

Test
Plan
Map Burner
Demonstrate

Evaluate Data
Reduce and Plot
Compare to Prediction

Summary Report



1




































































—




























































































2






































































































































3


































































































































4

















































































—













































































5






















































u








































































6











































































































































































































































































































































































































































































































































































































































































































































































































































































































































































Figure 8.  Schedule for Rankine Porous-Plate ComLustor

-------
water, and fuel at the appropriate conditions.  Provisions for measure-




ment will include inlet flow rates, temperatures and pressures, outlet




temperatures and emissions.  The emissions will be measured using the




Scott Dilute Exhaust Gas Emission Analyzer which is capable of accurately




measuring, on a continuous basis, NO, NO , CO, CO  and unburned hydro-




carbons.




     Following installation of the combustor and calibration of the in-




strumentation, exploratory tests of the combustor will be made to assure




that all required conditions of the test can be met and that all facility




controls are functioning properly.  The necessary adjustments to the




facility will be made that are required for the test program.




Task III - Test Evaluation - The operating performance of the combustor,




including pressure drop, exit temperature, and emissions will be mapped




over the appropriate ranges of burned gas velocity (V_,.), equivalence




ratio, temperature and pressure level.  After this, mutually acceptable




test points covering the expected range of operation of a specified




Rankine cycle engine will be established and full measurements including




emissions will be made.  The appropriate equivalence ratio established




for each test point will also be set.




     The reduced test data will be evaluated in terms of the specified




Rankine cycle engine requirements.  The exhaust emissions data will be




interpreted in terras of emission index for the combustor performance map.




Task IV - Summary Report - The analysis, design and combustor test data




will be documented at the end of the program along with appropriate




drawings and specifications.
                                  29

-------
                       GAS TURBINE COMBUSTOR





DISCUSSION



     Conventional combustors for the gas turbine engine often have low



emissions of CO and unturned hydrocarbons at high power levels; but the



NO  emissions are often high.  In conventional gas turbine combustors,



fuel from atomizing nozzles is sprayed into the primary combustion zone,



and combustion occurs as the fuel vaporizes off the dropletSo  The local



equivalence ratio of this combustion is uncontrollable, and the NO  pro-
                                                                  X


duction rates are high because of the variable local equivalence ratio.



The equivalence ratio has a string effect on flame temperature.  Since NO
                                                                         X


production rates have a logarithmic temperature dependence, the NO  rates
                                                                  X


at low temperatures can not offset the NO  rates at high temperatures.
                                         X


Furthermore, for regenerated cycles, the combustor inlet temperature is



usually the regenerator exit temperature; this high temperature also re-



sults in high NO  production rates, since the resulting flame temperature
                X


is high.



     With conventional combustors, efforts to reduce the NO  emissions
                                                           X


often result in increased emissions of CO and unburned hydrocarbons.  At



the same equivalence ratio and inlet air temperature, the flame temperature



with the porous-plate combustor can be independently controlled and main-



tained below the adiabatic flame temperature.  This independent control



of flame temperature is not possible with conventional combustors.



     With a porous plate combustor, the lean uniform flame eliminates



unburned hydrocarbons; the controllable reduction in flame temperature


                                  31

-------
below the adiabatic flame temperature results in reduced emissions of



NO  and allows design freedom in controlling the CO.  The flame temperature
  X


can be controlled so that the NO  production rates are very low, while



the CO decay rates are high enough with the available residence time to



reduce the CO in the exhaust gas.



     There are several design problems with the porous-plate combustor



for the gas turbine application.  At pressure levels of four atmospheres,



the heat flux back to the burner which must be removed by the heat sink



can be large, depending on the operating point.  Possible cooling methods



to remove this heat flux include independent air cooling with tubes em-



bedded in the matrix and also radiation to a sink.  The cooling can be



done with cold-side regenerator discharge air, which is cooler  than the



flame temperature. A value of equivalence ratio approaching unity without



violating the temperature limitations of the burner materials is desirable



from the standpoint of minimum flow bypass around the regenerator. As the



equivalence ratio increases towards unity, the amount of compressor discharge




air required for combustion is favorably reduced,  but the hot-side burner



temperatures increase toward material limitations.  In addition to ma-



terials limitations at the higher equivalence ratios, the problem of pre-



ignition upstream of the burner also increases.  Insulation on the up-



stream side of the burner is employed to prevent pre-ignition.  Materials



for both the porous burner matrix and the insulation must be suitable for



high temperature operation.   The porous-plate combustor also requires a



fuel vaporizer,  since a pre-mixed fuel-air charge is necessary for opera-



tion.



     Another problem that must be met for combustors for the automotive



gas turbine is that there is a wide range of fuel flow required to meet


                                  32

-------
all of the transient flow conditions.  For the porous plate combustor,



this means a wide range in superficial velocity (V_-) of the fuel-air



mixture, and hence a wide range in heat flux back to the burner which



must be removed by the cooling sink.  Because of the fact that the flame



can lift off the porous-plate burner if the superficial velocity becomes



too high, sufficient porous-plate surface must be provided for the com-



plete operating range of the engine.



     Illustrated in Figure 9 is the general design concept of a cylindrical



porous combustor for the gas turbine.  The pre-mixed fuel-air mixture



provided by a device which atomizes and vaporizes the flow is introduced



to the inside of the combustor.  The laminar flat flame burns on the out-



side of the cylinder where it is immediately quenched by the diluent air.



The porous plate made either of metal or ceramic material radiates the



heat removed from the flame to the diluent baffle, which is cooled by



the diluent air.  Also shown in Figure 9 are tubes embedded in the matrix



of the porous combustor for air cooling in the event that radiation heat



transfer can not provide enough cooling.



COMBUSTOR LOADING AND EMISSION ANALYSIS



     In order to investigate the burner temperatures during operation



and the limits imposed by the allowable range of superficial velocity,



a steady-state combustor performance analysis was done.  Estimates were



made of the exhaust emissions of NO  and CO.  Then, the thermal response
                                   Ji


of the combustor to four engine transients was calculated.



Steady-State Combustor Performance Analysis



     The results of a combustor performance analysis in parametric form



are based upon the Test Procedure for Base Line Engine Combustor Final



Evaluation on the Test Rig provided by EPA which specified the combustor



                                   33

-------
Figure 9.     Low NO  Frit Plate Gas Turbine Combustor (Fuel Inside)

-------
test points shown in Table 1.   Later,  the transient fuel-flow map of the

Base Line Engine, shown in Figure 10 became available.   Steady state calcu-

lations for the points shown on Figure 10 were then done.

     A computer code for the thermal analysis of radiation-cooled porous

combustors was developed and used to perform parametric analyses.  The

assumptions made to calculate temperatures of the porous burner include:

     •  One dimensional, steady-state heat transfer

     •  Experimental relationship between superficial velocity, V2_, burned-

        gas temperature, and equivalence ratio according to Kaskan

     •  Lift off at the adiabatic flame velocity

     •  Configuration:  Hollow cylinder

     •  Engine data from the Base Line Engine.

     The following values were assigned for the parametric study of burner

temperatures with the computer code:

     Porous Plate Emissivity                        0.9

     Radiation Receptor Emissivity                  0.9

     Gas Emissivity                                 0.0

     Minimum Stable Flame                           4.0
     Superficial Velocity, cm/sec

     Burned Gas Specific Heat, Btu/lb-°F            0.38

     Porous Material                                SiC

          Porous Plate Thickness, in.                0.125

          Porous Plate Effective Conductivity,      13.8
          Btu/(hr-ft-°F)

          Pore Size, microns                        100

          Porosity, %                               20

Shown in Figures 11 and 12 is the hot-side burner temperature as a function

of burner area for equivalence ratios (R) of 0.7, 0.8, and 0.9 with primary

                                   35

-------
Table 1.  BASELINE ENGINE COMBUSTOR TEST POINTS
BE.l Simulated Federal Driving Cycle
Fuel
Flow
Wf
(pph)
Heat
Exchanger Turbine
Comb us tor Exit Inlet
Pressure Temperature Temperature
PI Tl T2
(psig) (°F) (°F)
6 27 1380 1450
10 8 900 1100
12 8 1000 1250
13 8 1100 1370
16 10 1380 1680
65 16 1100 2100
BE. 2 Steady Speed Mode
Wf
(pph)
12
PI Tl T2
(pslg) (°F) (°F)
8 1100 1350
lU 8 1200 1490
16
25
31
39
48
59
69
82
10
16
20
25
29
35
40
47 i
1500
1590
1620
1680
1730
1780
1810
f 1850
Total
Air
Flow
Wa
(Ib/sec)
1.50
0.85
0.85
0.85
0.95
1.15
Wa
(Ib/sec)
0.85
0.85
0.95
1.15
1.30
1.45
1.60
1.80
2.00
2.30

Veh. Speed
(MPH)
30
40
50
60
70
80
90
100
108
119
                      36

-------
  160
  140
  120
  100
5  80
   60
   40-
   20-
            85°F Inlet
                 Preferred Metering
                 at Upper Limit
                                                               Points  to
                                                               Simulate Wide
                                                                    Throttle
                                                                         Points  to
                                                                         Simulate
                                                                         Steady
                                                                         State Speed
                                                                                         Steady State
                                                                                         Match Power
                                                              Minimum Steady Fuel Flow During Engine
                                                              Braking
              10
20        30       40        50        60

                   Gas Generator Speed,  %

   Figure 10. Fuel  Scheduling of Base Line Engine
70
80
90
100

-------
                                   0.7
oo
         4000
            Equivalence Ratio
        0.8
          3000
       0)
       M
       0)

       §•
       3
       m
       co
       I
          2000
          1000
            0
                                          Typical Design  Line
Flame Extinguishment

(No. 1 only)
    (119 MPH)

    Design Point
                                                                                           Typical Design Line
       Design Point

       (119 MPH)
—Flame Extinguishment
                                                                                                 FDC Point
              Figure 11.   Hot-Side Burner Temperature:
                    0                1
                           2
            Burner Area, ft


            Primary Air from Compressor Discharge

-------
    4000
    3000
0)
M
3
0)
§•

-------
 air  to  the  combustor  coming  from the  compressor  discharge.   Shown are




 lines for  the  six  Federal  Driving Cycle (FDC)  points  as  well as the De-




 sign Point  (119  raph)  taken from Table 1.   The  maximum area  above which




 flame extinguishment  is  assumed to occur  (V_,.  =  4  cm/sec) is shown;  the




 problem of  flame extinguishment occurs only with the  first  FDC  point.




 Also shown  is  the  minimum  area  to avoid lift-off.   The velocity,  V^  ,  is




 the  superficial  velocity of  the unburned  gas based on the porous  plate




 upstream area, and referred  to  the density of  the  fuel-air  mixture at




 25°C (76°F)  and  at pressure.  A typical design line corresponding to a




 fixed area  is  shown on  the figures.   The  conclusions  from Figures 11 and




12 with  the  primary air being  compressor discharge  are that:




     •   Decreasing equivalence  ratio  from 0.9  to 0.7  generally  increases




         required burner  area  and decreases the hot-side  surface tempera-




         ture level.




     •   A given  design  (fixed area) usually cannot be accommodated by a




         constant equivalence  ratio.




     Similarly,  the variation of hot-side burner temperature is shown in




 Figures 13 and  14 as a function  of burner  area  for  equivalence ratios of




 0.5, 0.7, 0.8  and  0.9 when the  primary air is  from the regenerator dis-




 charge;  an  equivalence  ratio  of less  than 0.7  is required to keep the




 burner  temperatures below  2000°F.




     Shown  in  Figure  15  is a  comparison of the case of primary  air at




 R =  0.7 being  the  compressor  discharge from Figure 11 and of  the case of




 the  primary  air  at R  =  0.5 being the  regenerator discharge  from Figure 13.




 From Figures 13 and 15,  it  can be concluded that:




     •   At  an  equivalence  ratio of 0.5 using regenerator air, the hot-




         side surface  temperatures are generally  higher than for an




                                    40

-------
     4000
                                0.5
          Equivalence Ratio
                                                                                    0.7
0)
3
4-1
2
0)
I
H
M

I
O
     3000
     2000
     1000
                                 — Typical Design Line
                           I
(119 MPH)  Design
          Point

    Flame  Extingui;
    (No. 1 Only)
               6
               1
                                               Lift Off
 I
                                                             hment
                                                                                    — Typical Design Line
                                                                                            (119 MPH) Design
                                                                                                      Point
                                                                                       FDC Point
                                                                                           6
                                                                                             Plane
                                                                                             Extinguishment
                                                                                             (No. 1 Only)
                                                                                 Lift Off
                                                                                               I
                           12012
                                                                   2
                                                    Burner Area, Ft

                   Figure 13.  Hot-Side Burner Temperature:Primary Air From Regenerator Discharge

-------
                                                           Equivalence Ratio
             4000
             3000
NJ
         s
         hi
         0)
         E
        •3
        •H
        CO
2000
             1000
                                      R - 0.8
                                                                            R - 0.9
                                            Typical Design  Line
                                                  Design Point
                                                  (119 mph)
                                       Flame Extinguishment
                                       (No. 1 only)
                              "Liftoff
                                                                               	1	
                                                                              *— Typical Design Line
                                                                                       Design Point
                                                                                       (119 mph)
                                                                                'Liftoff
                                                           Burner Area, ft'
                           Figure 14& Hot-Side Burner Tenperature:  Primary Air From  Regenerator Discharge

-------
CO
      o>
      M

      4J
      03
      t-i
      
-------
        equivalence ratio of 0.7 using compressor discharge air.


     •  Decreasing equivalence ratio generally increases burner area


        and decreases surface temperature level.


     •  A variable equivalence ratio permits limiting surface tempera-


        tures, while staying within (V«5) velocity limits.

                                                               2
     Calculated burner temperatures at one burner area (1.15 ft ) are


shown in Figure 16 for the FDC points and the steady-state vehicle speed


points for the Base Line Engine for an SIC burner operated at an equiva-


lence ratio of 0.8.  The peak hot-side burner temperature occurs at 119

                                                               2
mph at this burner area.  With the burner area fixed at 1.15 ft , the


first FDC point has a V   at 4.2 cm/sec, which is near flame extinguish-


ment; the sixth FDC point has a V   above the adiabatic lift-off data

          / o \
of Dugger.   '


     The effect of emissivity on hot-side temperature is shown in Figure


16.  If the emissivity is only 0.75 instead of 0.9, then the hot-side

                                                                 2
burner temperature is about 2544°F at this burner area of 1.15 ft  (or


almost 300°F higher than the case of 0.9 emissivity).


Combustor Analysis Using Base Line Engine Fuel Schedule - The code for


steady-state analysis of burner temperatures mentioned previously was


used to perform parametric analyses of 18 engine cycle points.  These


points are:  a) six steady-state operating points from idle to full


power, b) the six Federal Driving Cycle (FDC) points, and c) six engine


points simulating wide-open-throttle (WOT).  Figure 10 is the fuel flow


map for the Chrysler Base Line Engine which shows the six steady-state


operating points selected and the six engine points simulating wide-open


throttle; the six FDC points are shown in Table 1.  The corresponding air
                                   44

-------
3000
w.
s

V
kl
01


*
H
2000
1000  -
    >
            Actual Flame
            Temperature (R*v-0.8)
                  Hot-aide Burner
                                         BLE Conditions
                                                          ft
                                              Bum   *'

                                             Enlaalvlty  G_   • 0.0
                                                          Gas

                                             'Burner ' eSink " °'9  '


                                             'Burner " €Sink "
                 Cold-side Burner
                            SIC  Burner

                                Particle  size,  100 alcrons

                                Porosity, 20Z

                                1/8"  thick

                                Effective conductivity,  13.8 BTU/hr ft F
                 I     I
                               I     1  J  1     I
*
I     i
I     I
                                   30
                                                 50
        70
   90
                                        110
          Simulated FDC Modes
                                                  Steady-State Vehicle Speed oph
        Figure 16.   Effect of Baisslvlty on Burner Temperatures

                                       45

-------
flow rates and temperatures shown for each engine point are used in the


analysis.  Compressor discharge air is used as the primary air for com-


bustion, and the diluent air is cold-side regenerator discharge air.  The


analysis for each of the three sets of six operating points was done for


emissivities of the burner and radiation receptor of 0.9 and 0.7, and for


equivalence ratios of 0.9, 0.8 and 0.7.  At each of the 18 operating points,


the burner area was varied from areas that correspond to flame extinguish-


ment (at superficial velocity, V-,- = 5 cm/sec) to areas that correspond


to the lower of either 50 cm/sec or the lift-off velocity for each condi-


tion (as determined from the combustor inlet temperature and the equivalence


ratio).  These calculations are for mixtures of propane-air, since data


for V   versus 1/T with gasoline were not available.  The specific heat


of the burned gas in the flame was taken as 0.38 Btu/lbm-°F.


     Table 2 summarizes the calculations of burned gas temperatures which


are given in Figures 17 to 25 and of hot-side burner temperatures which


are given in Figures 26 to 43.  The burned gas temperature is determined


solely by the superficial velocity V._ and the equivalence ratio, R,


according to available data; hence, the emissivity of the burner has no


effect on the burned gas temperatures.


     The values of V   at the operating points are indicated by the ap-


propriate symbol on each of the figures.


     On the figures of hot-side burner temperatures, operating envelopes


corresponding to a hot-side temperature limit of 2300°F and of burner

                  2           2
areas between 1 ft  and 2.5 ft  are shown. The 2300°F limit for steady-


state operation on the hot-side is selected based on results from flash-


back tests at Energy Systems Programs and Corporate Research and Develop-


ment which indicated that hot-side burner temperatures in the range of

                                                                         2
2000°F to 2732°F (1500°C) can cause flashback.  Burner areas up to 2.5 ft


are considered reasonable for packaging considerations.


                                   46

-------
Table 2.  SUMMARY OF CALCULATIONS

Steady-State
Operating Points
Equivalence Burned Gas
Ratio Emissivity Temperatures
0.9 0
0.8
0.7
0.9 0
0.8
0.7
9 Fig. 17
18
19
7 17
18
19
Hot Side
Burner
Temperatures
Fig. 26
27
28
35
36
37
FDC
Burned Gas
Temperatures
Fig. 20
21
22
20
21
22
Points
Hot Side
Burner
Temperatures
Fig. 29
30
31
38
39
40
WOT
Burned Gas
Temperatures
Fig. 23
24
25
23
24
25
Points
Hot bide
Burner
Temperatures
Fig. 32
33
34
41
42
43

-------
    4000
    3000
u,
o
 3
 J-)
 (3
 Id
 01
 Q.

 01
 H

 05
 a
 o

 •a
 v

 M

 33
2000
    1000
                                          Superficial Velocity
                                           25
                                               cm/
                                              sec
                                          50     6U       70       80

                                                 Gas Generator Speed,
                                                                         9U   100
                   Radiation Cooled Conbustor

                   Steady State Points

                   Emissivity of Burner and Sink, 0.9  and 0.7

                   Equivalence Ratio, 0.9
                                       Burner Area, ft



        Figure 17.    Burned Gas Temperature of Radiation Cooled Combustor at

                      Steady State Points
                                            48

-------
                 3000
            c*
            o
            §
            4J
            2
            01
            a
2000
vo
             o>
                 1000
                                                    Superficial Velocity
                                                    V  ,  cm/sec
                                                        50        toO        70       80

                                                              Gas Generator Speed, %
                                                                                90
                 Radiation Cooled Combustor
                 Steady State Points
                 Emissivity of Burner and  Sink,  0.9 and 0.7
                 Equivalence Ratio, 0.8
                     01         23         456         78          9

                                                        Burner Area, ft2
                     Figure  18-.   Burned Gas Temperature of Radiation Cooled Combustor at Steady State Points

-------
   3000
§
4J
a
M
0)
u
•o
0)

§
a)
   2000
   1000
                                                     Superficial Velocity
                                                        , cm/sec
                                                50
                                        60          70        80

                                         Gas Generator Speed, %
90
Radiation Cooled Combustor
Steady State Points
Emissivity of Burner and Sink, 0.9 and 0.7
Equivalence Ratio, 0.7
                                                       5         6
                                                     Burner Area, ft2
                                                                8
         10
11
         Figure  19.   Burned Gas Temperature of Radiation Cooled Combustor at Steady State Points

-------
   4000
   3000

-------
          4000
Oi
K)
          3000
       2
       4J
       0)
      C3
      •O

      I
      aq
          2000
          1000
                                                 i  '  T
                                                                                 Superficial Velocity
                                                                                    ,  cm/sec
                                              2345
                                        FDC Points
Radiation Cooled Combustor
FDC Points
Emissivlty of Burner and Sink, 0.9 and 0.7
Equivalence Ratio, 0.8
             0
             0.1
                                                                               X	I
                           1.0
10
20
                        Figure 21*
                            Burner Area, ft

           Burned Gas Temperature of Radiation Cooled Combustor at  FDC Points

-------
Co
           4000
           3000
       0)
       M
       4J
       
-------
   4000
   3000
0)
0)
   2000
o
0>
I
   1000
                                                                            I  1  I
                                                                                Superficial Velocity
                                                                                       , cm/sec
                                                               50
                                                                  100       90,80,70,60

                                                         Gas Generator Speed, %
Radiation Cooled Combustor
Steady State Wide Open Throttle
Emlsslvity of Burner and Sink, 0.9 and 0.7
Equivalence Ratio, 0.9
                               j	L
                                                   1     I    I
       0.1
                              1.0
10
30
                Figure  23.
                                  Burner Area, ft

              Burned Gas Temperature of Radiation Cooled Combustor at Steady State
              Wide Open Throttle Points

-------
       4000
                                                                      I     '
3000-
    P*
    o
    2
       20001-
                                                                                    Superficial Velocity
                                                                                           ,  cm/sec
                                                                                 30
                                                                                         25'
                                                                                    25
                                                                                       20
                                                                                           15
                                                                                            10
                                                                                       100      90,80,70,60

                                                                             Gas Generator Speed,  %
Oi

1000-
                     Radiation Cooled Combustor
                     Steady State Wide Open Throttle
                     Emissivlty of Burner and Sink, 0.9 and 0.7
                     Equivalence Ratio, 0.8
                                                                              J	i	I
           0.1
                                           1.0
10
                                                      Burner Area,
                   Figure  24,   Burned  Gas  Temperature  of  Radiation Cooled Combustor at  Steady State
                                Wide Open Throttle  Points
30

-------
  4000
  3000
0)
9-2000
s
o
1000
          i   I  I  I  r
                                       i     i    i
                                                   1   '  ''  I
                                                                  Superficial Velocity

                                                                     , cm/sec
                                           50                100       90,80,70,60
                                                 Gas Generator Speed, %
              Radiation Cooled Combustor
              Steady State Wide Open Throttle
              Emlssivlty of Burner and Sink, 0.9 and 0.7
              Equivalence Ratio, 0.7
                                                  I
                                                        J I
                                   I     I    I
l  i
      0.4
                   1.0
              10
               2
Burner Area, ft
     100
              Figure  25,  Burned Gas Temperature of Radiation Cooled rombustor at Steady State
                           Wide Open Throttle Points

-------
                   T   i   r  i
    3000
                                                          Gas Generator
                                                              Speed,  Z
                                                                 °0
                        100
    2000
u.
e
 0)
 a
 §
 H
 01
 u
 (0
 IM
 t-t
 3
    1000
             Radiation Cooled Combustor
             Steady-State Points
             Emissivity of Burner and Sink, 0.9
             Equivalence Ratio, 0.9
 Superficial Velocity
         on/sec
O   5
A  10
D  15
O  20
V  25
e  30
A  35
•  40
•  45
V  50
                                                       Lift Off
                                                                       i  i  i
         0.3                    1.0                2                         10
                                    Burner Area, ft
                Figure 26.  Surface Temperature of Radiation-Cooled Cotnbustor
                            at Steady-State Points
                                        57

-------
   3000
                                                          Gas Generator
                                                             Speed, Z
   2000
Ch
e
 »
HI
3

-------
   3000
             I     I   I   I   I
                             1  I
                                                               I    I   I  I   I
   2000
Operating
 Limit
01
t-i
3
i-
01
H
0)
u
10
D
t/3
                          50
        60 70 80
   1000
                                                              Gas Generator
                                                                Speed, %
           Radiation Cooled Combustor
           Steady-State Points
           Emissivity of Burner and Sink, 0.9
           Equivalence Ratio, 0.7
Superficial  Velocity
    Vyet  cm/sec
O  5
A 10
D is
O 20
V 25
• 30
A 35
• 40
• 45
V 50
* Lift Off
   i	i   i   i   i  i  i
       0.3                    1.0                                           10
                                                 2
                                  Burner Area, ft
              Figure 28-  Surface Temperature of Radiation Cooled Combustor
                          at Steady State Points
                                    59

-------
  2800
T
  l  '
   2000
1
4J
2
0)
0)
o
   1000
                                               1  i  '
                                                       Radiation Cooled Comluustor
                                                       FDC Points
                                                       hmissivity of Burner and Sink, 0.9
                                                       Equivalence Ratio, 0.9
                                              Operating
                                              Limits   \
T
                                         l   i
                                                                               Superficial  Velocity
                                                                                   V25,  cm/sec
                                                                              O  5
                                                                               D15
                                                                               O20
                                                                              V25
                                                                              • 30
                                                                              A 35
                                                                              040
                                                                              • 45
                                                                                 50
 Of      I
i   ill
       0.07  0.1                                    1.0     2                                10
                                             Burner Area, ft
                    Figure  29,  Surface Temperature of Radiation Cooled Combuator at FDC Points
                   20

-------
  2500
  2000
I
4J
CJ
H
0)
  1000
                          T     I    I   I
             Radiation Cooled Combustor
             FDC Points
             Emlsslvlty of Burner and Sink,  0.9
             Equivalence Ratio, 0.8
                                                 I     T
                                                                    Operating
                                                                    Limits
I   I  |  T
                                                        Superficial Velocity
                                                            V-e,  cm/sec


                                                        O  5
                                                       A10

                                                       015
                                                       Q20

                                                       V25


                                                       A 35
                                                       • 40
                                                                            50
                          (    iii
                                           j	i
                                                                                 Off
                                                j	I
                                                                               I  I  I  I
       0.1
                            1.0                                      10
                                       2
                        Burner Area, ft

Figure 30.  Surface Temperature of Radiation Cooled  Combustor  at  FDC Points
                    20

-------
         25UO
         2000
      ft,
      o
      §
tsi
      H
      «  1000
      VI
             0.1
                     Radiation Cooled Combustor
                     FDC Points
                     Emlssivlty of Burner and Sink, 0.9
                     Equivalence Ratio, 0.7
I     I    I
                                            ,   ,  , ,  I
                    1.0
                                                                      ^Operating
                                                                         Limits
10
                                                 Burner Area, ft

                         Figure 310  Surface Temperature of Radiation Cooled Combustor at FDC Points
20

-------
   4000
Pu
o
I
g  2000
0)
 8
 0
CO
   1000
          Superficial Velocity
              V, cm/sec
       P 5
       Aio
       Dl5
3000»-  020
       V25
       • 30
       A 35
       • 40
       • 45
       ¥50
                                                     100 Z Gas Generator Speed
                 Off
                                                              Radiation Cooled Combustor
                                                              Steady State Wide Open Throttle
                                                              Emissivlty of Burner and Sink, 0.9
                                                              Equivalence Ratio, 0.9
                                        I  I  i
      0.1
                                           1.0
                                           Burner Area,
10
40
                 Figure  32o
                          Surface Temperature of Radiation Cooled Combustor at Steady State
                          Wide Open Throttle Points

-------
  4000
  3000
Q>
M


2 2000
0)
u
4
W
  1000
                   I       I     I
           Superficial Velocity
'25'
                    cm/sec
 O  5
A 10
 D is
 O 20
V 25
• 30
A 35
•   40
• 45
V 50
•fr Lift Off
                  Operating
                  Limits
                                   I   I  I
                                                           1   I
                                                          Radiation Cooled Combustor
                                                          Steady State Wide Open Throttle
                                                          Emissivity of Burner and Sink, 0.9
                                                          Equivalence Ratio, 0.8
                                                            90  70
                                                           I   I  i
                                                                                                Gas
              Generator
             Speed, Z

               90
      0.1
                               1.0
10
                                                  Burner Area, ft'
                Figure  33.  Surface Temperature of Radiation Cooled Combustor at Steady State
                            Wide Onen Throttle Points
                                                                                                     40

-------
                4000
Ul
                3000
            0)
            p
            3
            V
            8-
            0)
            H
            0)
            O
            09
            en
2000
                1000
                        Superficial Velocity
                             25'
                                 cm/sec
 O  5
 A 10
 D15
 O 20
V 25
• 30

A 35
B 40

• 45
V 50
  . Lift Off
                        Operating
                        Limits-
                                                                   T
                                                             I   I
                                                Radiation Cooled Combustor
                                                Steady State Wide Open Throttle
                                                Emissivity of Burner and Sink, 0.9
                                                Equivalence Ratio, 0.7
                                                                                  Gas
Generator
      %
                    0.2
                                1.0
                                                     Burner Area,  ft
                                                                10
          40
                             Figure 34,   Surface Temperature  of  Radiation Cooled  Combustor at  Steady State
                                         Wide Onen Throttle Points

-------
                           	I
                                                                Gas Generator

                                                                   Speed, Z
    3000
                                100
   2000
V
(J
3
4J
18
hi
O
o.


I


s

-------
                                                                      i   i  r
   3000 -
   2000
[b
O
 tO
 M
 01
 01
H

 0)
 O
 d
 3
w;
   1000
                           Gas Generator
                             Speed, Z
            Radiation Cooled Combustor
            Steady State Points
            Emissivlty of Burner and Sink, 0.7
            Equivalence Ratio, 0.8
                       Superficial Velocity
                           V, en/sec
                         O  5

                         A 10

                         D 15
                         O 20

                         V 25
                         • 30

                         A 35
                         • 40

                         • A5

                         T 50
                         -- Lift Off
                      i	i
                                                                      i   i
       0.3
1.0
10
                                   Burner Area, ft
             Figure  36.   Surface Temperature of Radiation Cooled Combustor
                          at Steady  State Points
                                       67

-------
    3000
    2000
w
cfl
i-
01
o
rt
CO
    1000
       0
        0.4
                Operating
                Limits	1
                                                          i    i   i
                                                      Gas Generator
                                                        Speed,  Z
                Radiation Cooled Combustor
                Steady State Points
                Emissivity of Burner and Sink,0.7 •  *°
                Equivalence Ratio, 0.7            •  AS
                                     Superficial Velocity
                                         V25,  cm/sec
                                      O  5

                                      A 10
                                      D  15

                                      O 20

                                      V 25
                                      •  30

                                      A 35
                                                  T 50

                                                 •# Lift Off
j	I
                      I	i
             1.0
10
                                  Burner Area, ft
              Figure 37.  Surface Temperature of Radiation Cooled Combustor
                          at Steady State Points
                                      68

-------
   3000
Pb
o
8  2000
 8
 «0
M
   1000
          I   I
                                I   i  r
                          I   I
                                                             Radiation Cooled Combustor
                                                             FDC Points
                                                             Emissivity of Burner and Sink, 0.7
                                                             Equivalence Ratio, 0.9
                                                  .  .
                                                                     Superficial Velocity
                                                                         V2^, cm/sec
                                                                     O  5

                                                                     A 1°
                                                                     D "

                                                                     O 20

                                                                     V "
                                                                     • 30

                                                                     A 35
                                                                     B 40

                                                                     • «5
                                                                     V 50
                                                                     -j. Lift Off
                                                                     I   I  i  i   i I	
       0.05
o.i
1.0
10
20
                                             Burner Area, ft
                Figure 3&. Surface Area of Radiation Cooled Combustor at FDC Points

-------
   3000
fe   2000
e

I
4J
cd
o»
CO
    1000
        0.1
                                    I   i   i
                                                                                  i  I  '
                                                                                        T
                                                    Operating
                                                    /Limits
                                                        Radiation Cooled Combustor
                                                        FDC Points
                                                        Emissivity of Burner and Sink,  0.7
                                                        Equivalence Ratio 0.8
                                                                            Superficial Velocity
                                                                                      cm/ sec
                                                                                  -e
                                                                             O  5
                                                                             A 10
                                                                             D 15
                                                                             O 20
                                                                             V 25
                                                                             • 30
                                                                             A 35
                                                                                40
                                                                                50
                                                                                Lift Off
                                                1.0
10
                                            Burner Area,  ft  .
               Figure 39.   Surface  Temperature  of Radiation Cooled  Combustor at FDC Points
20

-------
  2000
4)
2
S  1000
OT
                          I      I
               Radiation  Cooled  Conbustor
               FDC Points
               Emissivlty of  Burner and  Sink,  0.7
               Equivalence Ratio,  0.7
                           I
I    I   I   I
                              Superficial Velocity
                                  V2^, cm/sec
                              O 5
                              A10
                              Dl5
                              O 20
                              V25
                              • 30
                              A 35
                              • 40
                              • 45
                              T50
                              4|frLift Off
                             I  i   i  i  l
        0.1
1.0
                                                                                       10
                                                 Burner Area,  ft
                 Figure 40.  Surface Temperature  of  Radiation  Cooled  Combustor at FDC Points
                                                                          30

-------
   4000
    3000
i
4J
2
0)
2000
8
a
<4-4
14
CO
    1000
  Superficial Velocity
      V25» cm/sec

  O 5
  A10
_D15
  Q20


  • 30
  A 35
  • 40
      T50

      * Lift Off
                                       i   i  i  i
                                                                                      Gas Generator
                                                                                         Speed, Z
                                                             Radiation Cooled Combustor
                                                             Steady State Wide Open Throttle
                                                             Emlssivlty of Burner and Sink, 0.7
                                                             Equivalence Ratio, 0.9
                                                                   .     ...... I
        0.1
                                           1.0
                                                                               10
                                                Burner Area,  ft

                    Figure 41.   Surface Temperature of Radiation Cooled Combustor at Steady State
                                 Wide Open Throttle Points
30

-------
  4000
  3000
s
4J
2
2000
  1000
 Superficial Velocity
     V.-, cm/sec
 O  5
 A 10
 D15
 O 20
 V 25
 • 30
 A 35
 B 40
 e 45
 V 50
^ Lift Off
                                                                                           Gas Generator
                                                                                             Speed, %
                                                                   Radiation Cooled Combustor
                                                                   Steady  State Wide Open Throttle
                                                                   Emlsslvity of Burner and Sink, 0.7
                                                                   Equivalence Ratio, 0.8
                                     ,   ,  .  .1
      0.1
                                           1.0                                    10                       40
                                           Burner Area,  ft
                Figure  42C  Surface Temperature  of Radiation  Cooled  Combuetor at Steady State Wide Open  Throttle
                            Points

-------
   4000
   3000
g
4J
cd
H
   2000
8
CO
   1000
                                       i   I
           Superficial Velocity
                '25'
                    cm/sec
O   5

A  10

D  15
O  20
V  25
•  30
A  35
•  40
•  45
V  50
Iff  Lift  Off
Operating
Limits —i
                                                                                                Gas Generator
                                                                                                  Speed, Z
                                                                   90
                                                                      Radiation Cooled Combustor
                                                                      Steady State Wide Open Throttle
                                                                      Emissivity of Burner and Sink, 0.7
                                                                      Equivalence Ratio, 0.7
                                       I	I
                                                                                  I  1
        0.1
                                     1.0
                                                  10
                                                Burner Area, ft
                   Figure  43.  Surface Temperature of Radiation Cooled Combustor at Steady State  Wide  Open
                               Throttle Points
40

-------
Examination of the operating envelopes shows that all 18 operating points


fall within the envelopes over a range of equivalence ratios from 0.7 to

                                                       2
0.9 and over a range of burner areas from 1.0 to 2.5 ft .


     For the plots of hot-side burner temperature for the WOT, the hot-


side burner temperature shown in the plots would be reached only if the


burner were to remain in the steady-state at these pressures and fuel


flow rates.

                                               2
     An analysis was made at an area of 1.15 ft  and an equivalence ratio


of 0.8 along the steady state power matching line of Figure 10.  Figure 44


shows the range of V_,. over the range of power from idle to full power,


on the line of steady-state match points.  The operating velocity of 38.3


cm/sec at 100% gas generator speed is below the lift-off velocity of 48.3


cm/sec.  Shown in Figure 45 are the burned gas temperatures, the hot-


side burner temperatures, and the inside burner temperatures, all at


steady state.  The burner has a high-conductivity outer layer of 1/8"


thick silicon-carbide (K about: 10 Btu/hr-ft-°F) and an Inside layer of


1/8" thickness and low thermal conductivity (K about 1.5 Btu/hr-ft-°F).


Figure 46 shows the emission index for NO. emission; the calculation


uses the hot-air model for N02 production rates, as shown earlier in


Figure 3.  Prompt N02 is not included in the calculation.  A stratified-


plug flow model is used to estimate residence time, with a six-inch

                                               2
residence length and an exit flow area of 34 in .  This simplified model


with stratified plug-flow assumes that the velocity profile is uniform,


with the primary air from the flame and the secondary air assumed to be


unmixed while in the combustor.  In reality, the flows would be mixed,


with the mixture at a lower temperature; the lower mixture temperature


would have a lower N02 production rate.  Figure 47 shows the 00 emission


index, calculated with a 00 decay rate based on the flame temperature



                                   75

-------
u
V
0)
o

 •
>>
u
o
   30
                Equivalence Ratio, 0.8

                Burner Area, 1.15 ft2

                Emissivity of Burner and Sink, 0.9
o.
   20
                                                Pull  Power
          Idle Power
  10
                               I
                          _L
      50
60
 70          80

Gas Generator Speed, Z
90
100
              Figure 44,  Superficial Velocity Along Steady State Power

                          Match Line


                                        76

-------
   3000
   2000
u,
o
0)
^
•s
u

-------
   1.40
                                                EPA Standard
                                                (Based on 10 mi/gal.)
   0.20
I

1
 x
 0)
•o
 c
M

 C
 o
Tt
 tn
 w
•H

W

 X
o
   0.10
                                                                        s
Equivalence Ratio, 0.8

Burner Area, 1.15 ft2

Emlssivlty of Burner and Sink, 0.9
               Idle Power
                                                   Full Power-
                                            I
       50
   60
70          80

Gas Generator Speed, %
90
100
                Figure 46.   NOx Emission Index Along Steady State Power
                            Match Line
                                        78

-------
  30
                T
            T
T
            Equivalence Ratio, 0.8
            Burner Area, 1.15 ft2

            Emlssivlty of Burner and Sink, 0.9
  20
                                              Pull Power
               Idle Power
C
o
fl
05
CO
                           EPA Standard  (Based on 10 mi/gal.)
  10
                             I
                         I
             I
                                                    I
     50
60
                        100
               70          80          90

                Gaa Generator Speed, %

Figure 47.   CO Emission Index Along Steady State Power Match Line
                                      79

-------
and with the stratified plug-flow model for residence time.  For both


Figures 46 and 47 the Federal Standard is indicated for the case of an


average fuel consumption of 10 mpg.  Although all of the steady-state


NO  points are lower than the Standard, the 00 values are higher.  By
  X

increasing the residence time and/or staging the diluent air the low


NO  values can be traded off with the high 00 values.  It is characteristic
  X

of porous-plate flames that only traces of unburned, hydrocarbon are pro-


duced as long as there is some excess air.


Transient Combustor Performance Analysis


     A computer code for the transient thermal response of radiation-


cooled burners was developed and used to analyze three Wide-Open-Throttle


(WOT) accelerations and a cold start transient.


Analytical Methods - The approach was to use a finite difference marching-


time (or explicit) formulation.  The burner slab was divided into nodes,


and a heat balance was written on each node to include conduction through


the matrix, the enthalpy fluxes, and the heat from the flame for the case


of the node on the hot-side surface.  For the node on the cold-side sur-


face, the heat out was balanced with the temperature increase in the gas


just upstream of the burner by conduction in the gas.  The code allows


for 2 layers of porous materials with different properties to be used in

                                                        ( 9 )
a composite burner.  Following the approach of Schneider    , the local


gas temperature within the porous material was taken as equal to the local


metal temperature, because of the good heat transfer coefficient and the


high volumetric density of heat transfer area in the matrix.  Furthermore,


the initial steady-state temperature profile in the solid was calculated

                                           ( 9 )
using the steady-state results of Schneider     for a cooled porous plate.
                                   80

-------
The initial condition for each of the transients is assumed to be the



steady state condition when the transient begins; for example, the initial



condition of the WOT acceleration is the gas generator at 50% speed and



at a fuel flow of 10 Ibm/hr.



     Looking at the nodal system as shown in Figure 48, the transient



heat going into the hot-side node at an instant of time is:
                        QIn - 'Air + 'PI - QRAD
The first term on the right-hand side of Eq. 1 is:
CPg (TB(1> ~ TAJ
                         = WPri  Pg




The transient heat rate, Q   , is the heat that is required to heat the
                          Air


primary air flow, W   , from its combustor inlet temperature, T   ,
                   L n                                         A _
                                                                in

(which is the compressor exit temperature) to the hot-side burner exit



temperature which is taken as identical to the hot-side burner temperature,



T'(l).  The prime refers to the temperature of the node at the previous



instant of time, since very small time increments with a typical size of



0.01 seconds are used in the marching time solution.  (L,  is the specific



heat of the unburned fuel-air mixture.



     The second term is:





                          QF1 = WPri                          (3)



This transient heat rate, Q  , represents the net cooling of the flame



by the sink and is calculated from Kaskan's data     as a function of the



superficial gas velocity, V.,., and the equivalence ratio, R.  The enthalpy



difference of the fuel-air mixture in the parentheses is the enthalpy h*



at the adiabatic flame temperature less the enthalpy h at the actual flame




                                   81

-------

                                                                    -'RAD
                                                                     -
               QF1 - WPri
                'RAD
                        iurn
                            a F
                           - T
                              Sink
Figure  48. Nodal System for Transient Thermal Analysis
                            82

-------
 temperature which is  a function of V   as  shown earlier in Figure 2.



      The third term is the transient radiation flux from the hot-side



 burner temperature, T'(l), to the sink, I    , , and is calculated with:
                                                                     (4)




 a  is the  Stefan-Boltzraann constant,  and F is  the overall view factor



 (including emissivities)  from the burner to the sink.   A,.    is the frontal
                                                         Burn


 area of  the burner.



      The  conduction  flux  out of  node 1 into node 2 is  approximated in the



 finite difference approach with  Fourier's conduction law as:



                                     Tl(l) - T'(2)

                     Q,  2  = K_ A_    -5	j=-S	                   (5)
                      1-z     B Burn       AX
 where K^  is the effective thermal conductivity of the burner,  and AX is



 the node  thickness  and also the thickness  over which the gradient T'(l)
                                                                    D


:T'(2) is  obtainedo
  o


      The  enthalpy flux of the air flow out of node 1 is:
                    QW)out  ~ WPri Sg (TB(1)  - TRef)
 while the enthalpy flux of the air flow into node 1 is taken as:
                                                      \


                                                   Ref )
 The  temperature,  T   ,  is an arbitrary reference temperature for the



 enthalpy which drops out of the calculation method.



      Then,  since  the "heat in" less the "heat out" represents the heat



 left to increase  the temperature of the node, the following heat balance



 holds:




                                    83

-------
         'in + Qw)m - Qi-2 * 

where At is the increment in time.  For this half-node, the burner mass
is M., = pn TT^ A,,   .  The effective density and specific heat of the burner
    D    B 2.   Durn
material are p_ and Cnr>, respectively.  The burner temperature of the node,
              B      rti
Tn(l) is the new temperature of the node at the end of the time increment,
At; T'(l) is the temperature of the node at the beginning of the time
     o
increment.  Hence, the transient heat balance results in the following
algebraic equation for the node temperature at the current instant of time
in terms of the known temperatures from the previous instant of time:
             '-a,
                                                                     (9)
                                     {lj(l) - 1
                     WPri CPB At
                     Vrn ** PB CPB

     For the interior nodes, similar heat balances are applied which also
result in algebraic equations for temperatures of the nodes; the heat
fluxes in and out of the interior nodes are calculated with Fourier's
conduction equation.
Input Data - Time-dependent values of fuel flow, total air flow, and tem-
peratures were taken from the supplied Chrysler Base Line Engine data.
For the WOT acceleration from Idle, the gas generator speed is shown in
Figure 49 as a function of time as supplied for the Chrysler Base Line
Engine; this plot in conjunction with the plot of fuel flow as a function
of gas generator speed shown in Figure 50 was used to obtain the time
dependent fuel flow.  Similar plots were utilized to obtain the time
dependent values of pressure level, total gas flow, compressor exit tern-
                                   84

-------
     45
           WOT from
           60% Power (Assumed)
CO
 o
K
S
g>
 ij
 O
     35
          WOT from
          40% Power (Assumed)
u)
«
a
     30
     25
                             •WOT from Idle
                                                6th Generation Engine

                                                100% GG Speed = 44,610 RPM
     20
                      _J	
                       0.4
                              _J	
                               0.6
Jj	
 0.8
                                                 I
	I
"TTT
               0.2
         1.0     1.2

Elapsed Time, seconds
1.4
2 0
           Figure  49.  Time-Dependent Gas Generator Speed During 3 Wide-Open-Throttle
                       Transients  (WOT) at 85°F
                                            85

-------
       160
        140
        120
fi
.0
oo
fa
iH
0)
        100 h
     *   80 U
                                                          Gas Generator
                                                          Acceleration Schedule
                                                                                                   60% Power
                                                                                                  (Assumed)
                                              WOT from
                                              Idle
                                                                     WOT  from
                                                                     40%  Power
                                                                     (Assumed)
                                                 Cold Idle
                               old Start
                                                                                               Steady State
                                                                                               Match Power
                                                                  Minimum Steady State. Fuel Flow
                                                                  During Engine Braking
                                                   40       50        60
                                                Percent Gas Generator Speed
                                                                                                             100
                        Figure 50,  Fuel Scheduling of Base Line Engine During the Four Transients

-------
perature, and regenerator exit temperature.  The gas generator speed during



the cold start transient was also supplied.



     For the WOT transients from 40% engine power and 60% engine power,



the transient gas generator speeds were approximated as shown in Figures



49 and 50 since they were not supplied.



     For the transient calculations discussed herein, the configuration



of materials and their thermophysical properties are shown in Figure 51.



On the flame side of the burner is a slab of Silicon Carbide (SiC) of



1/8" thickness; it is selected because of its high-temperature capabilities.



On the air inlet side is a slab of low-conductivity material which acts



as an insulator to prevent auto-ignition upstream of the burner; the thick-



ness of this slab was arbitrarily taken as 1/8", but the thickness may



need to be increased to prevent auto-ignition of gasoline which has a



lower ignition temperature than propane.



     The schedules of burner area and of equivalence ratio during the



four transients are shown in Figure 520  These arbitrary schedules were



selected to avoid both lift-off and flame extinguishment during the



transients; the steady-state temperatures at both the beginning and the



end of the transient with these schedules are sufficiently within ma-



terials limitations.  At the start of the transient, the equivalence



ratio undergoes a step increase to 1.0 from 0.8, and the burner area has


                                       2             2
a simultaneous step increase to 2.20 ft  from 1.15 ft .  At the end of



the transients, the equivalence ratio undergoes a step decrease to 0.8,


                                  2
as does the burner area to 1.15 ft .



Results - Shown in Figure 53 is the calculated thermal response of the



porous combustor at three locations during the WOT fuel transient from
                                   87

-------
                               1/8"
                    1/8"       Thick
                    Thick      Low-Conductivity
                    SiC        Material
   Flame
Thermal Conductivity  10

Specific Heat          0.3

Density              162.
                                                Cold Air Inlet
  1.5  BTU/hr-ft-°F

  0.3  BTU/lbm-°F

112.   lbm/ft3
 Figure 51.  Configuration of Materials in Porous Burner
             (for Transient Analysis)
                            88

-------
  2.0 _
M
cu
c
                                    Time, sec.
                                                                        10
                                                        Legend
                                                            Cold Start
                                                  	 WOT from Idle

                                                  	 WOT from 40% Engine Power

                                                 	 WOT from 60% Engine Power
  1.0 _



—
i\
v <
1

^_]
I1

D
F-


L^



l
1
l
l
i
i
1
1



-\
\
'j /—Transients over
I)./ at 1.53 seconds
\\t-

WOT from 60% Engine Power Begins at 0.67 sec
WOT from 40% Engine Power Begins at 0.48 sec
WOT from Idle and Cold Start Begin at 0 0 s«
1
5
Time, sec.

/Cold Start over
at 8.75 sec.

•
ap
1
10
      Figure  52.  Schedule of Burner Area and Equivalence Ratio During the

                  <•» Transients
                                     89

-------
                                                                              T
2500 _
2000
1500-
100
              Transient over at 1.53 seconds
                                                                  WOT  From  Idle
                                                                  Hot-Side  Surface Temp'erature
                                                                  Interface Temperature
                                                                                        T
                                                                  Cold Side Surface Temperature
                     10
                                        20
                                                                              40
                                                                                                 50
                                            30

                                     Time,  seconds
Figure  53.  Calculated Thermal Response of the Porous Combustor During WOT From Idle

-------
idle of the Base Line Engine to full gas generator speed. The fuel transient




ends after 1.53 seconds.  Figure 54 shows the undiluted burned gas tem-




perature during this transient.  From the theory of the porous combustor,




only the superficial gas velocity, V_s, and the equivalence ratio, R,




determine the flame temperature; hence, the burned gas temperature re-




mains constant after the transient is over at 1.53 seconds because both




V   and R remain constant.




     To examine the time-dependent behavior of the hot-side surface tem-




perature during the WOT, Figure 55 is shown in which the time rate of




change of temperature of the hot-side surface node as well as the hot-side




surface temperature for the first 8 seconds of the WOT transient are




plotted.  Similarly, Figure 56 shows the time-dependent behavior of the




three surface fluxes as defined earlier:  P^/A^n* QFl/ABurn' QRAD/



A^   .  When the burner finally reaches steady state after approximately




80 seconds for this transient, the equality holds that:








                              "RAD - 'FI                           (10)




For this transient, the value of Q.   /A-    is about 10 times as large




as QBAT/A^    for most of the transient.  The overshoot in temperature




above the final steady-state value for this transient occurs because the




dT/dt of the surface node is still a large positive number when the hot-




side burner temperature first goes through the value that corresponds to




the final steady-state value.   Because of the selected schedule of burner




area, the flux that heats the incoming air, Q .  /A_   , undergoes a step




increase at 1.53 seconds, which is a large disturbance in the flux boundary




condition at the surface; the burner is unable to instantaneously conduct
                                  91

-------
    4000
    3500
    3000
                                 Burned Gas Temperature, °F
                                       (Undiluted)
0)
M

4J
rt
M
0)
    2500
                          10
20
30
                               Time, seconds
         Figure 54,.  Undiluted Burned Gas Temperature During the

                     WOT Transient From Idle to 100% Gas Generator
                     Speed of the Base Line Engine
                                   92

-------
u

00
c
m
x
u

01
V-i
3
0)
D-
E
0>
H
01
4-1

,3

0>
e
     500
     400 -
 300 -
                                      Time Rate of Change of Hot-Side

                                      Surface Temperature During WOT from

                                      Idle to 100% Gas Generator Speed
    -100
                           Flow Transient Over at 1.53 Seconds
1
1 1 1 1 1 1
0)
M
3
o>
a,


-------
3
u
CO
TO
0)
                  —  Flow  Transient Over  at  1.53  Seconds
                                                      QAlr/AB
                                                             urn
                                                     QRAD/AB
                                                             urn
                                                            urn
                                                                    10
                                    Time,  seconds
         Figure  56,   Heat  Fluxes  Back to  the Burner Surface During WOT from

                      Idle  to  100% Gas Generator Speed

-------
away this step increase in heat flux with the current gradient, so the




surface node begins to heat up in order to provide the necessary tempera-




ture gradient to conduct away the heat flux.




     A hypothetical transient was run to investigate the calculated




thermal response further.  For this case, the initial temperature profile




was selected such that the temperature gradient in the solid was com-




parable to the final steady-state value of the WOT transient; the initial




temperatures were selected at about 200°F lower than the final steady-




state values.  The results of this transient calculation are shown in




Figure 57«  There is no overshoot of the hot-side surface temperature,




and the time-rate of change of the hot-side surface temperature is an




order of magnitude lower than that of the real WOT shown above in Figure




55 because the initial temperature profile is steep enough to conduct




away the incoming heat flux.  The transient temperature is asymptotically




approaching the steady-state value without overshoot because the time




rate of change of the hot-side surface temperature is asymptotically




approaching zero.




     The transient burner temperatures and the undiluted burned gas tem-




perature for the WOT transient from 40% engine power are shown in Figures




58 and 59.  The corresponding information for the WOT transient from 60%




engine power is given in Figures 60 and 61, while the corresponding in-




formation for the Cold Start transient is given in Figures 62 and 63.




     Estimates of NO™ produced by the hot-air mechanism during the 4




transients are shown in Figure 64, as a function of gas generator speed.




Estimates of CO decay are shown in Figure 65,  The calculations are quasi-




steady-state; the NO^ calculations are made using the NO- production rate
                                   95

-------
 o
 
-------
3000
2000
1000
                                                                                WOT from 40% Engine Power
                                                               Hot-Side Surface Temperature
                                                               Interface Temperature
                                                               Cold-Side Surface Temperature
                -Transient Begins at 0.48 seconds
                -Flow Transient Over at 1.53 seconds
             J_
_L
J.
_L
                                              _L
_L
_L
-L
_L
                      10
                   20
                                                40
                                                        50
                                                       30
                                                Time,  seconds

Figure  58.  Calculated Thermal Response of the Porous Combustor During the WOT Transient from 40% Engine  Power

-------
    3500

-------
       3000
       2000
   PL,
   e
    M
    0)
vO
       1000
                                                                                  WOT from 60% Engine Power
                                                                   Hot-Side Surface Temperature
                                                                      Interface Temperature
                                                                   Cold-Side Surface Temperature
          0
                          -Transient  Begins  at  0.67 seconds
                          "Flow Transient  over at  1.53 seconds
                                                 _L
                             JL
                   J_
            0
10
20                 30


        Time, seconds
40
50
              Figure  60.  Calculated  Thermal  Response  of  the  Combustor  During  the WOT Transient  from 60% Engine

                          Power of Base Line  Engine

-------
   4000
   3000
t!  2000
0)
H
   1000
                                       Burned Gas Temperature (Undiluted)
                                       WOT from 60% Engine Power
                   -Transient Begins at 0.67 seconds

                   •Flow Transient Over at 1.53 seconds
                              20
60
                                    Time, seconds
       Figure 61.  Burned Gas Temperature During the WOT from 60% Engine Power
                   of the Base Line Engine
                                          100

-------
   400
   300
0)
M
3
0)
a
e
0)
H
   200
   100
                                               Cold Start
                                       -Flow Transient Over at 8.75 seconds
                               I
                  I
I
I
             Figure 62.
     10                      20

              Time, seconds

Combustor Response to Cold Start Transient
                                                                             30
                                          101

-------
   4000
   3500 -
   3000 -
   2500
fe.

o
 0)
 u


 %  2000
 1-1
 0)
 a
 E
 v
 H
   1500
    1000
     500
                                 Burned Gas Temperature  (Undiluted)
                                          Cold  Start
                                       -Flow Transient Over at 8.75 seconds


                                           I	I	I	
                               10                     20

                                     Time, seconds
30
            Figure  63. Burned Gas Temperature During Cold Start Transient

                        of Baseline Engine
                                          102

-------
-J
CJ
O
O
O
O


e

rH
^x


x"
•z.
O
CO
CO
 CSI
O
2
  CN
 O
       2.0
      1.0
FEDERAL STANDARD

(0.4 gm/mi)

(Based on 10 mi/gal)
                                            FUEL
      0.1
     0.01
    0.001
   0.0001
                                   I
                                              BASED ON STEADY-STATE

                                              CALCULATION AT THE
                                              TRANSIENT POINTS
                              I
I
                     20
                 40          60          80


               PERCENT GAS GENERATOR SPEED
           100
             Figure 640   Predicted N02 Emissions Index Based on  the Hot Air  Mechanism

                                             103

-------
     100
u:
e
.a
c
c
c
8
X
w
c
2
     10
 8
                                                                          i
              FEDERAL STANDARD (3.4 gra/mi)

              (Based on 10 mi/gal)        -
                                          BASED ON  STEADY-STATE

                                          CALCULATION  AT  THE

                                          TRANSIENT POINTS
   2.0
                                I
                           I
                  20
 40          60          80


PERCENT GAS GENERATOR SPEED
100
                      Figure 65.  Predicted CO .Emissions Index

                                          104

-------
with the "hot-air" mechanism shown in Figure 3 and are made with flame




temperatures based on the instantaneous values of superficial gas velocity,




V  , and of equivalence ratio, R.  The stratified plug-flow model was




used to estimate residence times in the combustors.  Also shown for com-




parison in Figures 64 and 65 are the Federal Standards.




COMBUSTOR CONCEPT FEASIBILITY DEVELOPMENT




     The object of this task was to fabricate a porous plate burner model




(approximately 1/5 size) which could be run over the combustor operating




conditions of the Base Line Engine and to fully test this burner so as




to obtain emissions and operational data.




     First, initial screening work on radiation-cooled geometries was




done.  However, cracking and preignition occurred  a number of times, and




tests  to examine this phenomenon were conducted.   Because of the occurrence




of preignition, attention was turned to air-cooled combustors.  A design




analysis of air-cooled combustors was done, and several were built and




tested.




Initial Screening of Radiation-Cooled Combustors




     Screening tests of various porous plate combustor configurations




were carried out with models one-fifth the size of the combustor for the




Base Line Engine application.  The combustor configurations tested in-




cluded porous ceramics, porous metals, and burners made up of layers of




screens and insulating materials.  These configurations are radiation-




cooled geometries.




     The combustor test rig used for these screening tests is shown in




Figure 660  The primary air-fuel mixture enters the test rig through the




pipe at the left.  The secondary or diluent air enters through the fitting
                                   105

-------
Figure 66.    Gas Turbine Porous-Plate Combustor Test Section

-------
at the top left of the drawing.  The cylindrical burner (about two inches




in diameter and six inches long) is surrounded by a conical screen which




is a radiation sink for the burner and which is cooled by the secondary




flow.  The hexagonal shape is a view port which permits visual observa-




tion of the burner during testing.  Another view port downstream of the




flange is used to detect the presence or absence of flames or plumes




from the burner.   Farther downstream is the water injection nozzle which




is used to cool the gas stream ahead of the valve which controls  the




pressure level in the system.




Ceramic Combustors - The first screening tests were done with porous




silicon carbide cylinders in a typical configuration shown in Figure 67.




Since it was recognized prior to the present contract that high service




temperatures were required for the porous plate, SiC cylinders were pro-




cured with the largest porosity (15 to 20%) commercially available.  In




a combination of bench and rig testing, all 4 of the cylinders tried




were fractured with each cylinder having a different test history.  It




was tentatively concluded that the fractures were related to non-uniform




density  (porosity).  The silicon carbide tests are summarized in Table  3.




Metallic Combustors - A porous stainless steel burner is shown in Figure




68.  During the first test with a metal burner, the surface of a bare




porous stainless steel burner became too hot at high heat fluxes and was




damaged.  To increase the temperature  capability, the burner was wrapped




with a layer of Kanthal wire screen, but preignition  was still a problem.




Ignition inside the burner did not occur until the temperature of the




Kanthal  screen on the outside of the burner was in excess of 2100°F, as




indicated by an optical pyrometer.  The results indicate  that a higher




temperature differential between the burner surface and the  inside  surface





                                   107

-------
o
oo
                                             SIC CYLINDER
                                                                                          WIRE SCREEN
                                            I    I    I
                                           ® - 


-------
           Table 3.  SILICON CARBIDE COMBUSTOR CONFIGURATIONS
          Description

   Lavite End Caps
   High Temp. Gaskets
   Spring Loaded
•  Bolt Loaded
•  No Diluent Screen

•  Bolt Loaded
•  Flat Steel End Caps
•  High Temp. Gaskets

•  Attached TC's Inside Burner
•  Flat Inconel End Plates

•  Bolt Loaded
•  Flat Inconel End Caps
•  High Temp. Gaskets
             Results

•  Two hours of operation
•  Atmospheric lift-off data
•  Shattered next day after 30 rain.
   operation

•  Burner shattered as soon as
   ignited

•  8 cycles in shop vise 1200-1400°F
   to room temp.
•  6 cycles in test rig

•  Burner shattered after 15 min.
   operation

•  Temperature gradients observed
   during vise tests
•  Stress relieved at 1800°C,  1 hour.
•  Burner shattered while being fired up

-------
          DESCRIPTION
•  POROUS STAINLESS STEEL BURNER
        RESULTS

•  AT PEAK HEAT FLUX AND AT PRESSURE
   POROUS PLATE EXCEEDS ALLOWABLE
   TEMPERATURE (2000°F)
      if.-...'. -
                    Figure  68.  Metallic  Combustor Configurations

-------
i;; needed to avo.id internal ignition.




     Hence, a layer of ceramic high-temperature porous insulation was




pj.u-eii hiMwtu-ii HH- Knnthal screen and the porous steel burner in an




attempt to provide this temperature differential.  A sketch of  this con-




figuration is shown in Figure 69.  Tests were run with exit gas velocities




up t:o JOO ft/sec.  In most cases, the reason for termination of the test




was tlu1. presence of a hot spot on the outer stainless steel cover pipe.




Post-test inspections revealed that the burners had melted opposite the




hot spot.




     Several  muJ i i-.Layer burner configurations were constructed of porous




riptal with various types of insulation and Kanthal screening.   In most




cases,  the burner would function satisfactorily for about 10 to 15 minutes




with a uniform red glow and no plume, and then the burner would fail due




to hot spots, and/or holes in the insulation.




     A burner shown in Figure 70 was assembled of Kanthal screen, four




layers of Cerapaper and two layers of zirconia cloth insulation and




Kantlial screen.  The burner ran successfully for about two hours at 8




psig and V   around 10-15 cm/sec.  Three days later, the burner was re-




started to measure NO , but the burner did not operate properly and a




hot spot was observed.  Disassembly revealed that the burner end cap on




the inlet side had failed.




     This burner was rebuilt and tested in the rig.  At a typical FDC




condition, the NO was measured at 15 ppm with low diluent flow.  After further




testing,the burner deteriorated, and disassembly revealed that  the in-




sulaiLor: had shrunk away from the end plates.




     The metallic combustor screening tests are summarized in Table 4.
                                   Ill

-------
                          DESCRIPTION



                9  POROUS  STAINLESS STEEL BURNER



                •  TWO LAYERS OF CERAPAPER INSULATION



                •  ONE LAYER OF KANTHAL SCREEN
                    RLSULTS



        NO PREIGNITION AT OUTSIDE TEMPERATURE


        OF 2150°F (OPTICAL PYROMETER)



        FLAME NOT EXTINGUISHED AT AS HIGH AS


        130 FPS AXIAL VELOCITY
                                                    POROUS STAINLESS STEEL

                                                   .CYLINDER CO.62  WALL)
 H-
oo
 e
 H
 vo
01
•o
•a
(6
a.
(D
l-t
                                                                       2  LAYERS OF CERAPAPER

                                                                       CO.62 THK)
                                                                                                     KANTHAL

                                                                                                     SCREEN
         2.OO  D!A
6.0 O

-------
                   KANTIIAL
                   SCREEN    __,        ;	  4 LAYliRS       	 2 LAYERS
                                           CERAPAPKK     /    ZIRCONIA CLOTK
\ttti,
tttttt
                                                                           1J *• * f/fff f
                                                                              -* * * Fs* *^-
RESULTS:  Ran well for about two hours  at  8 psig, and superficial velocity of
          15 on/sec.  Burner was restarted 3 days later to measure NOX emissions
          but hot spot appeared.  Burner end cap at inlet had failed.
Figure 70.     Kanthal-Wrapped Burner  with Zirconia Cloth and Cerapaper Insulation

-------
                    Table 4.   METALLIC COMBUSTOR CONFIGURATIONS
          Description
•  Porous Stainless Steel Burner
   Porous Stainless Steel Burner
   One Layer Kanthai Screen Around Burner
   Porous Stainless Steel Burner
   Two Layers of Kanthai Screen Around Burner

   Porous Stainless Steel Burner
   Two Layers of Cerofelt Insulation
   One Layer of Kanthal Screen
•  Porous Stainless Steel Burner
•  Two Layers Cerofelt Insulation
•  One Quarter Inch High Fences; Spacing:
   0.25 and 0.5 Inches

•  Porous Stainless Steel Burner
•  Two Layers of Cerofelt Insulation
•  Two Layers Ranthai Screen 1/8 Inch Apart
             Results

   At peak heat flux and at pressure
   porous plate exceeds allowable
   temperature (2000°F)

   Porous plate runs cooler
   Preignition at high heat flux
   Kanthal raises allowable temperature  (2400*F)

   Operation unchanged
•  No preignition at outside temperature
   of 2150"F (Optical Pyrometer)
•  Flame not extinguished at 130 fps axial
   velocity

•  Fences shield flame from axial velocity
•  Cerofelt fails due to required pressure
   drop
   Flame not extinguished at 200 fps axial
   velocity
   Inner Kanthal screen operating temperature
   raised

-------
                  Table 4.   METALLIC COMBUSTOR CONFIGURATIONS
                 	(Cont'd.)	
          Description

•  Porous Inconel Burner
•  Two Layers Cerapaper
•  One Layer Kan thai Screen

•  Porous Inconel Burner
•  Two Layers Cerapaper
•  One Layer Kanthal Screen
•  Better End Cap Design

•  Porous Inconel Burner
•  Two Layers Irish Refrasil
•  One Layer Kanthal Screen
•  Kanthal Screen
•  Three Layers Cerapaper
•  Kanthal Screen
•  Same as above
•  Kanthal Screen
•  Four Layers Cerapaper
•  Two Layers Zirconia Cloth
•  Kanthal Screen

•  Same as above
          Results

Ran well for 10-15 min., then "clink"
sound, large plume
Downstream end of burner failed

Ran well for 30 min.
Burner operation changed, plume appeared
Inconel was intact, Kanthal and stainless
steel diluent screen had few holes

Developed hot spot after 10-15 min.
Insulation had split and there were large
holes in Inconel and Kanthal screen, small
hole in diluent screen

Ran well for 10-15 min., then chugging sound
and plume
Outside of burner like new
Inside Kanthal screen melted
Five or six small holes in insulation

Ran veil for 15 min.
Developed hot spot
Inner Kanthal screen melted
Multiple holes in Insulation
Several holes in diluent screen

Ran well for 2 hours
Burner was restarted after weekend but hot
spot appeared
Burner end cap at inlet had failed

Ran well for about 30 min.
Measured NO « 15 ppra at typical FDC condition
with low diluent flow.  Then observed high NO
and plume.
Insulation had moved away from end cap

-------
     Emission Measurements on Burner 102 - Burner S/N 102, which consisted



of a porous inconel matrix with ZrO  cloth insulation on the inside di-



ameter, was tested on the bench and in the test rig.  Tests on the bench



were run at equivalence ratios of 0.7 and 0.8 over the full range of un-



burned gas velocities.  A few test points were obtained at an equivalence



ratio of 0.9.  The burner was then installed in the test rig.  Emission



measurements (CO and NO ) were made at atmospheric pressure for an equiva-
                       X


lence ratio of 0.7 over the full range of unburned gas velocities.  The



Emission  Index (El) as calculated from the ppm measurements is shown in



Figure 71.  The data is not corrected for water content.  Also shown are



estimates of NO  production from the "hot-air" mechanism and CO decay



which use a residence time calculated from a stratified plug-flow model.



Composite Ceramic Burner - A ceramic burner of SiC rings over a mullite



cylinder shown in Figure 72 was run on the bench for about thirty minutes



over a range of V  .  Then the burner became cooler on the downstream



ond and the cooler area gradually increased as the pressure drop through



the burner decreased from 15 to 7 psi.  Disassembly revealed that the



SiC rings were intact but the mullite cylinder had multiple cracks.



1'reignition Tests



     During the initial screening tests of the cylindrical radiation-



cooled burners described previously, a number of occurrences of pre-



i(-;nition were observed.   In these instances,  the fuel-air mixture was



ignited upstream of the burner by the hot inner surface of the burner.



In order to determine the operating conditions which lead to preignition



in this type of burner,  a special test fixture was designed and built.



Figure 73 is a sketch of the fixture and Figure 74 shows the completed
                                  116

-------
                   '76  Fed.  St'ds.  (10 MPG)
                   CO	
                                                                  CO Measured
     10
    1.0
0)
£
o
o
o
                                          Predicted CO

                                            Equilibrium  for  the  Flame
                                            Temperature  and  Residence
                                            Time
o
C-

6C
X
o
-c
c
c
o
    0.1
                                   NO
                                   Converted from Measured NO
             Residence Times Calculated
             with Stratified Plug Flow
             Model, and 6 inch Residence
             Length
   0.01
                                 Predicted NO
  0.001
                                                        2/20/73 Data
                                                        Measured CO
                                                        Measured NO
                                                                   x
                                                        I	I
                                                                      D
          Figure  71.
                               10          15          20
                           Superficial Gas Velocity, V25» cm/sec
                       Emission Measurements from Burner S/N 102
                                                                   25
30
                                         117

-------
                                          SiC Rings
                                                                Mullite  Cylinder
                  7711   I   I   I
I   I   I   I—T~     ~\U
                          -e—0—o — o —e—e—e—e—e—  o— o —©—9—e-
TTT—(17
                        \   \\  T JLJ—I—I—I—I—I—I—I	i   ''   '   i
                   Figure 72.   Configuration With SiC Rings Over Mullite Cylinder

-------
       Porous
       Incone1
       Plate
Rex Radiant
   Burner
Water Jacket
                                             Fuel-Air Mixture  Inlet

                                                         Spring
                  Figure  73.  Schematic of Preignition Test Setup
                                      119

-------
K>
o
                         -
                                               Figure 74.  Preignition Test Rig Hardware

-------
parts.  The test burner was a commercial product of Rex Radiant Company



and consisted of a flat, circular 3-inch-diameter disc with an overall



thickness of 0.6 inches.  The disc was a composite in which the layer



at the burning surface was composed of 0.1 inch thickness of porous SiC,



backed by raullite which performed the function of a thermal insulation in



order to keep the upstream surface cool while the burning surface was



running at high temperature.  A porous Inconel plate was installed at



the upstream face of the ceramic burner and four thermocouples were at-



tached to the plate in order to measure the upstream surface temperature.



These thermocouples were used as a measure of impending preignition.



The fuel-air mixture was fed into the plenum upstream of the burner as



shown.  After passing through the porous burner, the mixture was burned



near the downstream surface and the combustion products flowed out through



a water-cooled passage to the exhaust.  A water cooled valve in the ex-



haust was used to control the burner operating pressure.  Table 5 sum-



marizes the tests performed in the preignition rig.



     Tests were completed on the bench at one atmosphere pressure and



an equivalence ratio of 0.9 over a range of unburned (superficial) gas



velocities (V?c.) from 15 cm/sec to 40 cm/sec.  In these tests, the up-


stream surface temperature remained essentially at the temperature of the



incoming fuel/air mixture and no preignition occurred.  The test section



was then installed in the pressurized rig and the same tests were con-



ducted at one and at two atmospheres pressure.  No preignition was ob-



served.



     The system pressure was next increased to three atmospheres with R = 0.9



and V«_ ^ 10 cm/sec. The measured upstream surface temperature of the
     25 "\>
                                  121

-------
                                              Table  5.  PREIGNITION  TESTS
N>

Test
FB-1


FB-2



FBr-3





FB-4



Section R
Rex Radiant burner 0.9
0.9
0.9
Rex Radiant burner 0.9
backed with two
layers of ZrO?
cloth
Rex Radiant burner 0.9
backed with two
layers of ZrO^
cloth plus two
layers fiber-
chrome
Rex Radiant burner 0.7



Inlet
Temp.
°F Press, Atmos
55 1
55 2
46 3
60 3



45 3





65 1
65 2
65 3
65 4
V , cm/sec
15 - 40
15 - 40
40-32
40 - 32



40 - 32





15 - 40
15 - 40
15 - 40
40 - >15
Result
No preignition
No preignition
Preignition
Preignition



Preignition





No preignition
No preignition
No preignition
Preignition

-------
burner began to rise rapidly and when the temperature reached about 1400°F,




preignition occurred and the fuel was immediately shut off.  Another




attempt was made to establish this point with the same result.  It was




then decided to set three atmospheres pressure and 40 cm/sec.  At this




high velocity, the flame was near liftoff and little heat was transferred




from the flame to the burner.  The objective was to reduce the unburned




gas velocity (and increase the heat flux to the burner) in steps until




the preignition condition was established.  This plan was successful and




a preignition point was established.  Figure 75 is a plot showing the




temperature recorder behavior as the preignition condition was established.




In order to determine the effect of insulation on the preignition condi-




tion, two layers of ZrO_ cloth were installed between the upstream face




of the burner and the inconel plate.  This had no effect on the pre-




ignition results.  An additional two layers of 1/U in. thick Fiber-




chrome insulation were installed with no effect on the preignition re-




sults.  Examination of the ceramic burner used in the above tests re-




vealed that it had hairline cracks extending from the outer edge along




generally radial lines.




     Based on the above results it was concluded that operation at four




atmospheres pressure would be possible only if the equivalence ratio




were reduced.  A new SiC/Mullite burner was installed and tests were




conducted at R = 0.7.  No preignition occurred at a pressure of three




atmospheres over the full velocity range.  At a pressure of four atmos-




pheres, the upstream face temperature increased to about 950°F and




stabilized for V   ^ 15 cm/sec.  Figure 76 is a recorder chart trace




showing this condition.  At this condition, very slight changes in fuel-
                                  123

-------
   1600
   1400 f-
             Data Taken March 2, 1973

         Pressure,?  =  3 atm.

Equivalence Ratio.R  %  0.9

Fuel-air Inlet Temperature,  46°F
   1200
   1000
    800
01
Id
3
i-l
n)
U
0)
a


I
    600
    400
    200
                                                        Preignition
                                                             1550°F
               u
               Ol
U
01
n
                                 0»
                                  •
                                 00
U
01
o>
                                                «M
                                                co

                                                 B
                         to
                                                 CM
                        Q)
                        CO
                         (U
                        (A
               41
               0}
                                             _L
                                            12

                                       Time, Minutes
                                                16
                                    20
             Figure  750  Upstream Face Temperature Leading to Preignition at
                         3 Atmospheres
                                           124

-------
      iOOO
       800
Pu
e
 0)
 h
 3
 4J
 a
 \->
 a»
600
       400
                              0
                              0)
                              a
       200
              0)
              a
              o
              s

             r
              IT)
                                                           u
                                                           o>
                                                           00


                                                           u
                                                                                            m
                                                                                            01
                                                                                           CO
                                                                              Data Taken March 3, 1973


                                                                         Pressure, P » 4 atm


                                                               Equivalence Ratio,  R % 0.7


                                                               Fuel Air Inlet Temperature, 65°F
                                                    _L
                                                                                    1
                                                                                                J_
       12           16          20



                    Time, minutes


Figure  76.   Impending Preignition at P
                                                                                    24           28
                                                                                  4 Atmospheres
                                                                                                     32
36

-------
air ratio caused large effects on the upstream face temperature.  Post-




test examination of this second burner revealed the same type of hairline




cracks as those observed in the first burner.




     The temperature of the downstream surface (combustion side) of the




burner was not measured during the preignition tests. However, using the




theoretical heat flux from the flame to the burner, a surface temperature




required to radiate this heat away can be calculated.  For a pressure




of 3 atmospheres and an equivalence ratio of 0.9, the calculated surface




temperature is 2120°F.  For a pressure of 4 atmospheres and an equivalence




ratio of 0.7, the calculated temperature was about 2050°F.  The emissivity




was taken as 0.9.  Within the accuracy of the measurements and the un-




certainties in the calculations, these two temperatures can be considered




equal.  A tentative conclusion is that at a certain hot-side surface tem-




perature, the flame propagates against the flow of fuel-air mixture in




the porous plate and eventually reaches the upstream surface igniting the




fuel air mixture prematurely.  The phenomenon labeled "flashback" is




postulated to occur at a fixed hot-side surface temperature which probably




depends on such things as porosity and pore size of the porous material.




Air-Cooled Combustor




Design Analysis - In order to solve the problem of preignition or flash-




back experienced in radiation-cooled burners, some preliminary calcula-




tions were performed to determine the effect of air cooling on the tem-




perature of a metallic burner.  The configuration examined had cooling




tubes embedded in the porous plate matrix, using air as the cooling medium.




With the temperature limitations of a metallic burner, neither radiation




cooling alone nor air cooling alone could reject the heat load from the






                                   126

-------
flame at all operating conditions.  The calculations were made to determine


if the combination of radiation and air cooling could reject the heat.


Some available combustor loading calculations indicated that the maximum


steady state heat flux from the flame to the porous plate was on the


order of 70,000 Btu/hr-ft2.


     Figure 77 is a plot of the radiation heat flux between two long con-


centric cylinders.  The inner cylinder (surface 1) represents the burner


surface radiating to a heat sink (surface 2).  At a burner surface tem-


perature of 2000°F, the radiant heat flux ranges from about 28,000 Btu/

     2                    2
hr-ft  to 37,000 Btu/hr-ft , depending upon the sink temperature.  Thus


for an air cooled combustor, the difference between the heat flux of

                2
70,000 Btu/hr-ft  and the radiated flux must be removed by cooling, or


the burner temperature will exceed 2000°F.   An analysis was performed


to determine the temperature distribution in a burner with embedded cool-


ing tubes.  It was assumed that the heat flux from the flame to the


burner surface is uniform and that there is no temperature variation


through the thickness of the burner.  The resulting nonlinear differential


equation describing the burner temperature distribution was solved


numerically for a number of possible operating conditions.  For each of


these cases, the solution yielded the axial temperature distribution in


the burner.  The maximum calculated temperature for each case was used


as a measure of cooling effectiveness.  The cooling air fractional pres-


sure drop (AP/P) was held constant at 5%.  Figure 78 shows the calculated


maximum wall temperature as a function of heat flux from the flame to the


burner with burner operating pressure as the parameter.  The cooling air


inlet temperature was taken as 400°F which is about the maximum compressor


discharge temperature.   Figure 79 is the corresponding result for a cool-
                                  127

-------
     10'
.. 3
 _l
33
 -   10
 c
 3
 -a

 OS
                                     Burner Surface
                                     at T
                   1400
        1000           1500           2000          2500

                                Burner Temp., T.,  F


              Figure  77. Radiant Heat Flux Fran A Burner
3000
                                           128

-------
       3000
       2000
    0)
    n
    V

    I
NJ

VO
       1000
                      Di = 0.1  inch, Tube  Inside  Diameter



                      TA - 400°F, Cooling  Air  Initial  Temperature



                      AP/P = 0.05, Fractional  Pressure Drop



                      TCTMV = 1400°F, Sink Temperature
                       a INK


                      L = 6 inches, Length
          10,000     20,000
30,000     40,000      50,000      60,000      70,000     80,000      90,000     100,000

          Heat Flux to Combustor,  Btu/hr-ft^
            Figure 78.    Calculated Maximum Wall Temperatures for Air-Cooled Burner for Cooling Air Initial

                         Temperature,  400°F

-------
   3000
u,  2000
o
2
I

8
   1000
                D, =0.1 inch,Tube Inside Diameter



                T. = 1400°F, Cooling Air Initial Temperature



                AP/P - 0.05, Fractional Pressure Drop



                TSINK = 1400°F,  Sink Temperature



                L = 6 inches, Length
       10,000    20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,0
                                         Heat Flux to Combustor, Btu/hr-ft'
          Figure  79.  Calculated Maximum Wall Temperatures for Air-Cooled Burner for Cooling Air Initial

                      Temperature, 1400°F

-------
ing air inlet temperature of 1400°F which is about the maximum regenerator


discharge temperature.  In order for these plots to have meaning, the


heat flux from the flame to the combustor porous surface must be known.


Figure 80 is an estimate of that flux as a function of superficial gas


velocity for several burner pressures and an equivalence ratio of 0.9.

                                                                     2
Taking the peak heat flux for 4 atmospheres, namely 108,000 Btu/hr-ft ,


results in maximum combustor surface temperatures of 1520°F and 2200°F


for cooling air temperatures of 400°F and 1400°F, respectively.  Based


on these encouraging results, the decision was made to fabricate an air-


cooled burner made up of sintered nichrome powder with 1/8 inch OD cool-


ing tubes embedded in the matrix.  Design of this burner was completed


and fabrication development work was done.  That development work is


described in the Section on Porous Plate Fabrication Development.


Mechanical Design - Figure 81 shows the design of the first air-cooled


burner which was designated as 106. Table 6 is a Parts List for this burner.


The basic burner is a porous cylinder with a 2.25 inch outside diameter


(O.D.) and 1.75 inch inside diameter (I.D.).  The porous matrix is made


up of nichrome powders bonded together by brazing as described in the


Section on Porous Plate Fabrication Development.  A total of 24,  1/8 inch


O.D.  cooling tubes are embedded in the porous matrix and run parallel to


the burner centerline.  Insulation held in position by a screen is installed


on the inner cylindrical surface of the burner.  The end plate is insulated


with a disc of insulation.  The fuel-air mixture enters the burner through


the large tube at the center, passes through the screen, the insulation,


and the porous nichrome and is ignited on the outer cylindrical surface.


Cooling air discharges from four inlet tubes into a cooling air manifold.


From this manifold, the cooling air enters the cooling tubes where it is


                                   131

-------
   110,000
   100,000
    90,000
    80,000
 I
 u
^   70,000
 3
 _i
13
 «   60,000
    50,000
    40,000
    30,000
    20,000
    10,000
                    Nominal Limit for
                    Flame Extinguishment
                                                       Equivalence Ratio, 0.9
                                                 •Lift Off Limit
                                                  with Inlet Air
                                                  at 76°F
Figure 80.
                                  20                     40

                            Superficial Gas Velocity, V^t cm/sec


                             Heat Flux Back to the Porous Burner as a
                             Function of Pressure and of Superficial Gas
                             Velocity (V25)
                                                                   60

-------
..x MOD- SWA&ELOK TO
~>)     BUTT IME.LD ELBOW
        CAT MO. 400-Z-ZVvJ 3l(.
              = 1/1
                                                                                                            BOTH ENDS,
                          Figure  81. Design of Air-Cooled  Porous Burner 106

-------
        Table 6.  PARTS LIST OF AIR-CQOLED POROUS
                  BURNER SHOWN IN.FIGURE 81
Item 1.    Assembly

     2.    Fuel-Air Inlet Tube

     3.    Cooling Air Fitting

     4.    End Plate

     5.    Side Wall of Cooling Air Manifold

     6.    Upstream End Plate

     7.    Insulation Retainer Screen

     8.    Zirconium Oxide Insulation

     9.    Porous Burner

    10.    Insulation Retainer Plate

    11.    Zirconium Oxide Insulation

    12.    Downstream End Plate

    13.    Flow Distribution Screen
                           134

-------
heated by the heat transferred from the flame back to the burner.  The




heated cooling air discharges from the cooling tubes at the end of the




burner and mixes with the combustion products.  Figure 82 is a photograph




of burner 106 during fabrication.




     Table 7 is a list of the air-cooled burners which were tested on




this program.  Burner 107 was a modification of 106 in which the porous




matrix was made thicker and the tubes were embedded in the center of the




matrix instead of at the inner surface.  Burner 107 has an outside diameter




of 2.5 inch and an inside diameter of 1.75 inch and contains 27 cooling




tubes.  All of the air-cooled burners had a burning surface length of




6 inches.




Air-Cooled Burner Tests




     Tests of air-cooled burners were made to map their operational range,




determine their emission characteristics and establish their durability.




Test Procedures and Facilities - The general procedure for testing model




burnerr, was to perform a bench checkout test followed by tests in the




pressurized rig.  The purpose of the bench test was to observe the flame




uniformity and to check for defects such as leaks.  During the bench




tests, the pressure drop across the porous matrix was measured as a




function of superficial velocity (V?c)«




     Figure  83 is a schematic diagram of the gas turbine burner test




rig.  The burner being tested is installed in the pressure cylinder as




shown.  Separate streams of primary, secondary and cooling air are sup-




plied from a plant air system at 100 psig pressure.  The fuel used in




the burner development tests was propane.  The primary air passed through




a rotameter and then througn an electrical heater where it could be




heated to temperatures simulating the compressor discharge temperature




                                 135

-------
Figure 82.  Air-Cooled Burner #106 During Fabrication
                           136

-------
                          Table 7.  AIR-COOLED BURNERS (CYLINDRICAL)
Burner
         Description
  Tests
 106
 107
 108
Brazed nichrome, 2.25" O.D. x 1.75" I.D.
  24 cooling tubes

Brazed nichrome, 2.50 O.D. x 1.75" I.D.
  27 cooling tubes

Same as 107
Bench tests
Pressure rig tests

Bench tests
Pressure rig tests

Bench tests only
 109
 108M
Same as 107 except with slotted surface.
Burner 108 modified with insulation
  and screen on outer surface.
Bench tests
Limited pressure rig
  tests.

Bench tests
Pressure rig tests
  with heated combustion
  and cooling air.

-------
   Air Supply
   at 100 psig
00
Electrical
  Heater
                                                       Burner  Cooling
                                                            Air
                Flowmeter
                        Control
                         Valve
                                    Electrical
                                      Heater
         Primary
         Air
                     i
                                                             Sampling Port
                  Fuel Air
                  Mixture
                                                                 :~   Combustor j
              Fuel
              Tank
                                                                                                          Exhaus t
                                                                                                          to Atmosphere
                                                                    Diluent
                                                                    Secondary
                                                                    Mr
Valve to
Control
Combustor
Back-pressure
         Secondary
         Air
                           Figure 83.   Schematic of Gas Turbine Combustor Test Facility

-------
(about 400°F) of the gas turbine.  Fuel flow was measured with a rota-




meter and was then injected into the primary air stream.  The fuel-air




mixture then entered the burner where it was burned.  Surrounding the




burner was a conical screen which served as a heat sink for radiation




from the burner surface.  The heat sink screen was cooled by the secondary




air which flowed radially inward through the screen and mixed with the




combustion products.  Cooling air passed through a rotameter and an




electrical heater, where it could be heated to about 400°F, and into the




cooling air manifold in the burner.  After passing through the cooling




tubes, the cooling air mixed with the combustion products and the diluent




secondary air.  The combined burner exhaust then flowed out through a




water-cooled valve used to control the burner operating pressure level.




Samples of the exhaust gases were taken through a sampling line down-




stream of the burner.  Measurements of CO, CCL, NO, NO- and unburned




hydrocarbons were made with a Scott Research Laboratories, Inc., Model




108H Exhaust Gas Analysis System which was purchased by the General




Electric Company.  Figure 84 is a photograph of the Scott equipment.









Burner 106 - This was the first of the air-cooled burners to be tested




in the pressurized rig.  Before installing the burner in the rig,



a bench checkout was performed.    The equivalence  ratio was held




constant at 0.8 and the superficial gas velocity (V?(.) was varied from




10 cm/sec to about 45 cm/sec.  During this operation, several small hair-




line cracks appeared on the surface.  The cooling air flow rate was set




equal to the combustion air flow rate.  No flashback was observed.




     The burner was then installed in the pressurized rig in order to




measure emissions and to determine the effectiveness of the air cooling.



                                  139

-------
-P-
O
                                            Figure 84.  Scott Exhaust Gas Analyzer

-------
Tests were conducted with room-temperature air at burner pressure of



one, two, and three atmospheres before a flashback occurred and the test



was stopped.  These tests imposed the most severe conditions, in terms



of heat  flux to  the burner, of any burner tested to that time.




     Figure 85 is a plot of the emission index for the measurements of




CO and NO  from burner 106 as a function of superficial velocity.  The



solid points are the measurements and the open points are the correspond-



ing prediction; for NO , the calculation uses the "hot-air" mechanism.
                      X


All of the measured NO  values were well below the 1976 Federal Standard.



The CO values exceeded the standard at a V ,. of around 20 cm/sec.



     Figure 86 shows the measured N0« emission index for the tests at




pressures up to four atmospheres.  No definite trend with pressure is



evident.




     Post-test examination of the burner revealed the existance of several



cracks.  The appearance suggested that the flashback probably occurred



through one of these cracks.  The pressure surge associated with flash-



back split the burner along four axial cracks located approximately 90°



apart.   A new air-cooled burner (designated as burner 107) was designed



and built,  This burner was 50% thicker (0.375 in.  wall) and placed



more of the sintered powder behind the tubes.




Burner 107 - Air-cooled burner 107 was tested on the bench, both for



pressure drop and for uniformity of flame.  Figure 87 is a plot of the



measured pressure drop as a function of unburned gas velocity, V  .



Measurements were made both with and without burning.   The increased



pressure drop during burning is probably due to changes in burner porosity



due to heating and reduced gas density.
                                    141

-------
40

10


cl
_o
— i
o
0
0
£ 1.0
u
1
•—I
C
E
•— i
X*
CJ
TJ
C
i— I
co
o
CO
0)
— ' 01
E "
U




' 0.01
5
1 1 1 |i
? *
8
r '
-
w
.
 & (3.4 gm/mi) I
(Based on 10 mi/gal)
i

!>
N02 Fed. Std
(0.4 gm/mi)
A
" 4 ^2 A A "
t t t &

•taMMM

•
*»

H«
Z
=• i i -
A 	
—
A
Solid - Measured
Open - Predicted with
Stratified Plug - -
Flow Model
i
1 II 1 l
10 15 20 25 30 3!
V_5, cm/sec
Figure 85.
Emissions from Air-Cooled Burner S/N 106 at 1 Atm. Pressure
                 142

-------
     1.4
                                         I
         Federal Standard
         (0.4 gm/mi)
o
c
 CNI
g
O
•O
C
 c
 o
 V.
 •ft
    0.6
    0.4
"  °'3
    0.2
    0.1
                        D
                       X


                       O

                                                          I
                                      Burner 106

                                          A R = 0.79 + 0.01, 1 atm

                                          Q R = 0.74 + 0.05, 1.98-2.36 atm

                                          O R • 0.75 + 0.01, 3.0-3.1 atm

                                          X R - 0. 72 + 0.005, 4.09 atm
                               JO
                                       0
                                                0
                                     -&

                        10              20               30

                         Superficial Velocity,  V _,  on/sec
                                                                          40
         Figure  86.  N0« Measurements at 1  to  4 Atmospheres on Air-Cooled  Burner

                                           143

-------
0.5
0.4
o.   0.3
o
Q
0)
3
W
M
O
0.2
0.1
                Operating Pressure,  1 atm.
                                  A
                                A
                             A
                      A
                 A
            A
                                                             A
                                                   A
                                         A
                                             Burner 107 Pressure Drop
                                          A With Combustion
                                             Without Combustion
              10
                              20
30
40.
50
60
                       Superficial Velocity, V?_, cm/sec
                     Figure  87.   Burner 107 Pressure Drop
                                     144

-------
     Kigure 88 shows the CO and NCL measurements for burner 107.  The




NO  values were below the Federal Standard over the full range of super-




ficial gas velocity.  The CO values exceeded the standard above about




15 cm/sec.  This is probably due to the relatively cool exhaust tempera-




ture associated with unheated inlet air.  Subsequent tests with heated




inlet air with burner 108M described below tend to confirm this hypothesis.




     Tests with these burners showed that the unburned hydrocarbons (HC)




emissions were essentially zero when the burner was intact.  It was soon




learned, in fact, that indications of unburned HC was a definite indica-




tion of a burner defect.  Testing with burner 107 was terminated when




there were indications of hydrocarbons.  Post-test examination of the




burner revealed longitudinal cracks similar to those observed with burner




106.  The cause of the cracks was hypothesized to be due to hoop stresses




associated with the radial temperature gradient through the burner.




Burner 108 - This burner was identical to burner 107.  Since 107 cracked




during tests, 108 was checked out on the bench only.




Burner 109 - In order to avoid the problem of cracking, the decision was




made to machine longitudinal slots in the burner extending radially in-




ward from the outer surface of the burner to the top of the tubes (one




slot for each tube).  This slotted burner was designated as 109 and was




checked out on the bench.  During preliminary tests in the pressurized




rig, the burner cracked and this test was terminated before any emissions




data was obtained.




Burner 108M - Burner 108 was modified into burner 108M by wrapping the




cylindrical surface with a layer of Fiberchrome insulation held in posi-




tion with a Kanthal screen.  Tests were conducted in the pressurized rig




first with unheated combustion and cooling air and later with these air





                                   145

-------
     10
T
                          >
                                     o
                                               O
                                                        CO Federal Standard
                                                        (3.4 go/mi)
                     CO
c
2   i.o
X
01
•o
CO
c
o
•rl
CO
CO
•H
    0.1
                L
                       Predictions with  Stratified
                       Plug Flow Model
                *
                                       N0» Federal  Standard
                                         j,(0.4 gin/mi)
                                         O
                               Air-Cooled Burner  #107

                                  1 Atm. Pressure


                                     • R = 0.89

                                     A R - 0.82

                                     O R " 0.71

                                    Slash (/) is  Prediction

                                    Inlet Fuel Air Mixture
                                    at  70°F
   0.01
                                1
                            1
1
                  II          20            30           40          50

                          Superficial Gas Velocity, V5-»  on/sec

            Figure M.   Mtasurements of CO and NO^ Emissions  on Burner 107

                                         146

-------
streams heated to temperatures approximating compressor discharge tem-




perature (400-600°F).   Figure 89 shows the CO emissions and Figure 90




shows the NO  data.  The CO emissions are lower with heated air (open
            X



points) than with unheated air (solid points), as would be expected with




the higher exhaust temperatures associated with the heated air; with the




higher exhaust temperatures, the CO decay rates are higher which result




in reduced CO.  For the same reason, it is not surprising that the NO
                                                                     X


values increased with the air heating, since higher exhaust temperatures




also mean higher NO  production rates.  However, all the data were be-




low the Federal Standards.




FUEL-AIR MIXTURE SUPPLY DEVELOPMENT




     Because the porous plate combustor requires a uniform mixture of




fuel and air upstream of the porous plate, it was necessary to design,




fabricate and test a fuel-air mixture supply system.




Design and Fabrication




     The technical literature indicated that, within reasonable geometrical




restraints, complete vaporization of the required quantities of gasoline




could be accomplished only if more than one of the following vaporization




mechanisms were used:




     1.  Preheating the fuel prior to injection into the airstream.




     2.  Pressure atomization.



     3.  Air atoraization, including shearing and sonic atomization.




     4.  Evaporation of droplets by the heat of the primary airstream.




     5.  Evaporation of droplets centrifuged onto a plate heated by heat




         losses from the combustion zone.




     All of the above mechanisms could be utilized when combustion is in




progress.  The cold starting problem dictated that a sonic air atomizer



                                   147

-------
      10
0)
ft,

.1
O
O
O
8
J
 8
     1.0
s
c
O
•H
Ul
W
•H

I

O
u
    0.1
Federal Standard
(3.4 gm/mi)

(Based on 10 mi/gal)0
                      A   A
                                                      O
                                             A
                                                 O
                   A
                                 A
    O

     O
                                        O
  D
      D
Burner //108M

CO Data at 1 Atmosphere

  Primary Inlet, 390 to 550°F
  Coolant Inlet, 390 to 600°F

      Q   R * 0.9

      A  R ~ 0.8

      O   R ^ 0.7

  Solids are with Unheated Air
                    10
                 20
        30
40
                     Superficial  Gas  Velocity,  V__,  cm/sec
        Figure 89.   Measured  CO  Emissions  on Burner 108M with Both
                     Heated  and Unheated Air
                                      148

-------
0)

3

(JL,
o
o
o
§
u
w

-------
be utilized to produce the fuel spray.  This type of injector is also
capable of meeting the high turndown ratio required with reasonable air-
flow and air and fuel pressure requirements.
Fuel-Vaporizer Test Assembly - A gas turbine fuel vaporizer test assembly
shown in Figure  91 was      fabricated, instrumented, and tested.  This
assembly comprises the following elements.
     Burner Model - The cylindrical surface is provided with sixteen
0.04 in. inner diameter tube fittings, and the end is provided with one
of the same.  These fittings are used to pass the thermocouple wires through,
to control the flow area and thus model the porosity of the porous matrix;
and the tubes attached to the fittings are used for pressure taps.  The
cylinder and end outer surfaces are wrapped with electric heating wire
to partially model the operating temperature of the porous matrix.  The
end plate contains a centerbody and flow director to assist the fuel-
air mixture in making a 180° turn.  Three thermocouples are staggered
within the model of the porous matrix to measure its inside wall tempera-
ture.
     Vaporizer Plate - An internal heated cylinder enclosed within a
cone acts as a vaporizer plate.  The cylinder is closed on one end ex-
cept for a hole through which the fuel nozzle protrudes and six flow-
directing louvers.  When used with the louvers, the air flow area is
variable in order to produce a constant fuel-air ratio.  A high tangential
velocity is produced, which effectively creates an airflow path much
longer than the axial length of the cylinder.  The vaporization of the
fuel is enhanced by the longer exposure of the fuel droplets to the
sensible heat of the air.  Also, the larger droplets are vaporized by the
heated cylinder wall when they contact it either by impaction of the
                                  150

-------
                                                                Type of 17
                                                                Fittings
\\\\\\\x\x\\x\
                    	\_
                    Primary Air
                    Flow Path
Air Actuated
Fuel Nozzle
 Upstream  Flow
 Meter  and Pressure
 Gauges for Both
 Fuel and  Primary
 Air
                                                           Heater Wires
                                                         Vaporizer Plate
 Air  Supply
 Tube
 \\\\ \
                                                                Simulated
                                                                Burner Surface
                                                                                      V   Thermocouple Locations

                                                                                           Pressure Measurement
                            Figure  91.  Fuel Vaporizer for Gas Turbine Corabustor

-------
spray or by centrifuging.  The cone acts as a flow director and as a


radiation barrier between the model of the porous matrix and the vaporizer


cylinder.  Two thermocouples measure the vaporizer cylinder wall tempera-


ture.


     Fuel Nozzle - Sonicore 156K and 125K atomizer nozzles made by the


Sonic Development Corporation have been tested.  The actuating air as


shown in Figure 92 enters the center of the nozzle through a 1/4 in. pipe


ell.  The fuel enters a chamber surrounding the air chamber through a


1/8 in. pipe connector.  It is injected into the airstream through fixed


orifices of 0.032 in. diameter.  The spray Immediately enters a zone


wherein a resonator cup creates soundwaves which break the spray into a


soft mist of droplets which are expected to be about 20 microns or less


under most operating conditions.


     Thus, the assembly utilizes the principles of low-pressure atomiza-


tion, air shearing and sonic atomization, evaporation of droplets by the


heat of the airstream, and evaporation of droplets centrifuged onto a


plate heated by combustion zone heat losses.  Other methods which can be


incorporated into this assembly include preheating of the fuel, the in-


sertion of a device into the vaporizer cylinder which will increase the


passage length and time of exposure of the fuel to the hot air, and in-


serts around the nozzle tip to create more turbulence or change the


quantity of air passing through the spray.


Summary of Fuel Nozzle Tests - The fuel nozzles were assembled in a rig


which contained an air supply with electric heater, flowmeter and gauge


which read the pressure at entry into the nozzle.  The fuel system con-


tained a pressurized tank, flowmeter, and gauge which read fuel pressure


at entry into the nozzle.  The spray was exhausted into atmospheric air


and was observed visually.
                                  152

-------
                      RESONATOR CHAMBER
     LIQUID
                                    CENTER OF
                                    IMPLOSION
                 AIR OR GAS
Figure  92.    "Sonlcore" Fuel Vaporizer
                   153

-------
     Since the air orifices were nozzles of fixed throat diameters, the




air flow rates could be set at any given level below choked flow by




varying the air supply pressure.  At low fuel supply rates, the presence




of the fuel had no appreciable effect.  At fuel supply rates above 50




Ib/hr, the air flow rates decreased.




     Since the fuel orifices were of fixed number and diameter, the fuel




flow rates could also be controlled by varying the fuel supply pressure.




Low fuel supply rates could be achieved by the aspiration of the air-




stream, with greater aspiration achieved at a given air flow rate by the




smaller 125K nozzle.




     The intent of the nozzle calibrations was to determine whether the




spray from either nozzle was satisfactory and what combinations of air




and fuel flows were best.  Since the greatest amount of energy available




for atomization was supplied by the air, smaller droplets are produced




by larger air flow rates at constant fuel flow rates, and by smaller




fuel flow rates at constant air flow rates.  A "wet" spray - "dry" spray




boundary was established by varying the fuel flow at constant air flows




and temperatures.  The boundary was a straight-line variation with pres-




sure, being about 7 Ib/hr for the 125K nozzle and about 6 Ib/hr for the




156K nozzle, both at 15 psi air pressure differential and essentially




invariant with air temperature.




      A criteria  which  showed more  distinction between  the  two nozzles was




 the  stable  combustion  limit.   By setting  the nozzle  air flow and increasing




 the  fuel  flow, a point was reached at which a flame would  not blow out




 after the ignition  source was  removed.  At 10 psi air  pressure differential,




 the  stable  combustion  limit was about 34  Ib/hr fuel  flow for the 156K nozzle




 and  about 10  Ib/hr  fuel  flow for the 125K nozzle. The  appearance of the






                                   154

-------
flames also favored the 125K nozzle, since its flames could be made to


appear virtually invisible, indicating good vaporization very close to


the nozzle.  The 125K nozzle appeared to have a distinct advantage with


respect to quick vaporization because it produced smaller drops.


     The distribution of the 125K nozzle was also superior, since under


most operating conditions the spray angle was larger than that of the


156K nozzle.  The larger spray angle and the softer spray assists in


distributing the spray into the high tangential swirl of the combustion


air and in impacting the larger drops onto the vaporizer hot plate.


     The 125K nozzle was chosen for further testing.


Summary of Vaporizer Fluid Flow Tests - By varying the setting of the


movable louvers and the air pressure differential across them, the ef-


fective louver flow area and the tangential swirl velocity could be cal-


culated.  The effective burner flow area was variable by closing some


of the seventeen Swagelok fittings of the burner model.  Pressure was


measured through one of the nozzle supply tubes and the port on the end


of the burner model.  The supply air was at ambient temperature and the


conditions at the burner model exit were ambient.  A fuel injector was


not installed during the tests.


     with a louver air pressure differential of 1 psi (tangential velocity,


270 fps) and the louvers nearly completely closed, a choked air flow of

                                                                  2
160 Ib/hr was delivered with a model burner flow area of 1 to 2 in .


With the louvers fully open, an air flow of 1080 Ib/hr was delivered


(variable with burner area).
                                   155

-------
Calculations of Degree of Vaporization - The test conditions used for

tests of the fuel-air mixture supply were those specified for the Base

Line Engine in Table 1.  Using the data summarized by Graves and Bahr

and the most severe air conditions specified in Table 1 as far as high

flow rate/low air temperature conditions are concerned (the Federal

Driving Cycle point with a fuel flow of 65 Ib/hr), estimates were made

of the degree of vaporization which could be achieved by the sensible

heat of the air alone.  The contact time and length of air flow path

given in Figure 93 were based upon the vectorial path length using tan-

gential swirl velocities and axial through-flow velocities.

     It was expected that droplet sizes would be produced by the sonic

injector which would be at least as good as those of a simple orifice

at 300 psi fuel pressure differential, and that 300 ft/sec tangential

velocity would be achievable with reasonable air pressure differential.

Therefore, it was expected that 93 percent vaporization could be achieved

through air sensible heat alone.  All other test points except the one

with a fuel flow of 65 Ib/hr require less tangential velocity and. could

tolerate coarser sprays to achieve the same degree of vaporization.
                                       ^
     A thermal analysis has shown that the vaporizer plate would operate

at about 1200°F inside an operating porous burner if it were not shielded

from radiation.  With the present shielding, its operating temperature

would be closer to 200°F.  Therefore, by proper design of the shielding,

the vaporizer plate could be designed to operate between these extremes.

The heating wires within the vaporizer plate allow the vaporizer plate

temperature to be controlled as a test variable.

     A plot of the heat required to heat the required quantities of fuel

from 100°F to 425°F and to vaporize 100% of the fuel can have superimposed

                                   156

-------
   100
    90
s-t
g   80
H
g


s
W
    70
    60
    50
                          100



                          SIMPLE ORIFICE

                          EQUIVALENT SPRAYS
                                                           MOST SEVERE AIR CONDITIONS
           16 PSIG
                                                           W  - 1200 LB/HR
      237°F
                         Wf - 65 LB/HR
                             100
200
300
400
                                            AIR VELOCITY, FT/SEC
        Figure  93.    Estimated Performance of Fuel Vaporizer for Gas Turbine Combustor

-------
upon it the heat provided by convection from the plate to the combustion




air at constant equivalence ratio.  The heat required rises linearly with




the amount of fuel while the heat provided decreases hyperbolically.  The




net result is that 100 percent of the fuel can be vaporized by the plate




up to a fuel flow of 20 Ib/hr (provided it is placed upon the plate)* The




vaporized fraction decreases to 50 percent at a fuel flow of 30 Ib/hr,




11 percent at 65 Ib/hr, 8 percent at 85 Ib/hr, and 2 percent at 160 Ib/hr.




     The 11 percent vaporized at 65 Ib/hr by the plate plus the 93 per-




cent vaporized by the sensible heat of the air exceeds 100 percent.  Also




it is not expected that as much as 10 percent of the fuel will be pre-




sent on the vaporizer plate.




Fuel Vaporizer Tests - The objective of the tests was to determine the




degree of fuel vaporization for typical combustor operating conditions.




     Test Apparatus - The test apparatus shown in Figure 91 is shown in-




stalled in the test facility in Figure 94«  The combustion air comes




from the left into the vaporizer which is covered with insulation.  The




injector (heated) air and fuel lines are shown at the location where




they enter the test device.  Four manifolds can be seen leaving the




vaporizer.  Each manifold collects the fuel mixture from four fittings




along an axial line on the simulated porous surface (see Figure 91).




Three of these lines simply discharge the fuel-air mixture.  The fourth




discharges to a 15-inch diameter porous-plate, water-cooled combustor.




The line to this burner is water cooled to arrest further vaporization.




Thermocouples to the inside of the simulator/combustor surface, the




cylindrical vaporizer tube, and the lines used to carry pressure signals




to the manometers are also shown.
                                  158

-------
Ul
                                                                             Vaporiz(
                                                                             Beneath,
                                                                            Insulation
                                            Figure 94.  Vaporizer and Inlet  and Exhaust Lines

-------
     Figure  95  is another view of  the vaporizer.  Shown on the figure




are  the heater  wires around  the simulated porous surface and on the down-




stream end of the test piece.  Also shown are the mixture sampling ports




located approximately 1.75 and 5.25 in. from the closed end of the simulated




combustor surface.  Samples  were taken from the 1.75 in. location  (open




in the figure).



     Shown in Figure 96  is the apparatus upstream of the vaporizer.  Shown




are the flow meters and pressure gauges for the fuel,  injector air and




combustion air.   Pressure lines to the manometers are shown on the right.




The injector air and combustion air heaters and insulated lines are shown




in the lower part of the figure.   The fuel tank and the pressurized




ambient-temperature air line are shown at the lower left.




     In order to analyze the fuel-air mixture in the vaporizer,a Scott




Model 108-H  Dilute Exhaust Emission Measurement System purchased by the




General Electric Company was used.  This console has provisions for




measuring total hydrocarbons, NO,  NO., CO, and C0?.




     Testing Technique - In  order  to measure the fraction of the fuel




that was vaporized, two samples were taken through the total hydrocarbons




analyzer, an isokinetic and  a non-isokinetic sample.  The former determines




the  total hydrocarbon content by sampling all of the mixture in a given




streamline;  the latter the amount  of unvaporized fuel by allowing the




vapor to spill  out of the streamline because the sample Is extracted at




lower velocity.




     In order to provide low pressures to the Scott analyzer because it




was  feared that the existing pressure regulator was not capable of with-
                                   160

-------
                           '  Thermocouples
                      Vaporizer Beneath Insulation
                                                                 Cooling Water
Injector \AirJ
                                                      Mixture to 15" Diameter Burner





                                                                      Mixture
                                       :  •  -    ' " •'.'-. •'--
          Figure  95.   Vaporizer and Inlet  and Exhaust  Lines

-------
ro
                                                    Injector Air Flowmeter and Pressure Gauge
                                                               Combustion Air Flowmeter  and Pressure Gauge
                          Flowmeter and
                      Pressure Gauge
                                                                                                         Lines to Manometers
                                    Combustion Air Heaters

                               Pressurized  Anbient-Tenperature
                                                    Figure  96.  Vaporizer Air and  Fuel  Supply System

-------
standing the full compressor discharge pressures, the combustor air was




maintained at about 1 psig.  It was assumed that the combustion air pres-




sure effect on vaporization was small, and anticipated that this could




be checked later.  The injector air and combustion air temperatures and




flow rates and the fuel flow rate were held at the conditions specified




for each engine operating point.




     Although the vaporizer outer diameter and closed end were insulated




to prevent heat loss, the vaporizer heaters were not activated.  All of




the vaporization tests were run with the primary air louvers fully open,




which gave the minimum amount of tangential swirl at each combustion air




flow setting.  The conditions tested, therefore, represented approximately




the most severe expected as far as providing vaporization energy to the




spray and heat from the combustion process were concerned.




     Test Points - The points 1-6 for the fuel-air mixture supply simulate




the six Federal Driving Cycle points in Table 1.  Test points 7 and 14-18




simulate the steady speed mode:




                     Test Point      Vehicle Speed (MPH)




                         14                  70




                         15                  80




                         16                  90




                         17                 100




                         18                 108




                          7                 119




     The operating conditions at steady state speeds of 30-60 MPH almost




duplicated the conditions of test points 3, 4, 5, and 14.
                                   163

-------
Fuel flow rates of both 69 and 84 lb./hr were run under test point 7.



The lower figure represents the most air flow (at R J\» 0.8) which could



be heated to the desired temperature.  The higher figure represents the



desired fuel flow rate at the maximum air temperature which could be



achieved.  For each of the test points,the injector air and combustion



air temperatures were set approximately equal to the calculated compressor



discharge temperature.  For any given engine condition, an equivalence



ratio of about 0.8 was set using the appropriate air and fuel flow rates.



The vaporizer pressure was set at approximately 1 psig and the air pres-



sure differential across the nozzle was varied to give a reasonable range



of calculated mean droplet sizes.  The injector air flow rates were those



which resulted from the air pressure differentials.



     Test Results - The test data are presented in Table 8 and plotted



in Figure 97.  In the figure the vaporization quality in percent is



plotted against a group parameter similar to that of Graves and Bahr



and which relates all of the pertinent terms associated with spray drop-



let: evaporation.  The group parameter is:




                                 ^0.8  /  v-1.2 /   vO.42

                   I   a  I    la

               B =
where  T      combustor primary air inlet temperature, °R
        O


       U      primary air velocity in mixing region, ft/sec
        3.



       P.     pressure of air leaving injector, psia




      APf     equivalent fuel pressure drop through a 0.030-inch

              orifice, psi




The fuel pressure drop APf is the equivalent drop in the Graves and Bahr




apparatus.  Most of the data fall between 93 and 99 percent of the fuel




vaporized, although some data were as low as 87 percent.  The data seem




                                  164

-------
Table  8.   GAS.TURBINEiFUEL VAPORIZER TEST DATA

Test
Point
1

u W
Hr a
lbf/hr
1428 $ 6.043
1450 (7 ^

1500 :75.944
2

3
4

1003 I 10.01
1040 (2) ^
i
1054 A ll. 94
1117 4>12.88
1125 4>

1135  V
5
6

7




14

15


16
1234 dj 15.85
0943 C|364.99
0955 (|j >
lr
1407 &>69.25
1438 £>
1448 (>
1458 £> >
1507 fc> 84


'

1320 /d> 30.71
1334 X$> J
i
1352 OJ 38.73

1403 0) 1

/
1020 4)48.05
1037 faQ 47.75


17
18
1047 VS)
1057 if) '

i
1130 |>58.94
1154  69.25
1315 <3> 68.85


1332 <3>
1340 <5> \

i
P2
psig
1.01
1.00
1.15
1.09
1.01
1.01
1.07

V
1.22
0.84
0.85
1.00
1.15
1.10
1.15
1.16
2.18
2.18
3.68+

3.42
0.56
0.57
0.58
0.56
0.76
1.04
1.01
0.94
1.01
Tl
°F
320
310
286
176
177
175
164
i
I
V
177
237
241
411
390
401
393
376
269
267
300
312
314
323
321
316
323
354
373
367
377
371
Wa
tot
Ib /hr
d
119.4
vl
128.7
189.5
187.7
221.4
241.5
!
V
292.1
1210
1215
1234
1330
1282
1307
1366
518.3
523.2
680.4

695.6
915.2
908.3
932.0
897.5
1024
1269
1221
1189
1219
Wa/wf
19.76
i
21.66
18.93
18.76
18.54
18.75
1
1
18.43
18.62
18.70
17.81
19.20
18.52
18.88
16.26
16.88
17.04
17.98

17.96
19.05
19.02
19.52
18.80
17.38
18.31
17.73
17.27
17.71
R
0.748
^
0.683
0.781
0.789
0.798
0.789
1
1
0.802
0.794
0.791
0.831
0.770
0.799
0.784
0.910
0.876
0.868
0.823

0.824
0.777
0.778
0.758
0.787
0.851
0.808
0.834
0.856
0.835
AP .
ai
psi
1.01
1.03
9.26
3.83
2.28
3.05
3.51
0
3.51
4.72
17.7
24.4
22.9
22.6
29.5
15.4
21.2
9.60
14.9
12.3

19.9
15.2
20.5
24.1
9.65
17.4
21.8
23.3
30.8
15.1
SMDo.i
M
45
41
1
1
25
22
21
OO
21
23
97
26
80
100
23
OO
CO
23
9
29

9
30
14
10
OO
125
130
85
18
00
Vap.
_
93.5
95.3

96.5
97.9
93.9
90.8
87.7
94.8
96.8
97.0
94.6
96.3
97.3
96.3
93.7
97.1
99.0
93.8

94.5
97.1
97.1
97.2
95.8
97.1
_
90.4
87.4
88.3
1000 B
20
19
68
50
15
19
18
0
18
22
61
105
176
154
280
0
0
59
87
77

128
131
174
199
0
96
125
137
258
0

-------
ON
           100
            95
3
o-


§   90
•H
4J
tO
N
•H
M
O


I
            85
           80
                                 0.05
                                                                         Data Key In Table 8
                                         0.10
0.15
0.20
0.25
0.30
                                B Group Parameter  B
                                                             4-*u   °-8
                                                                                 0.42
              Figure 97e   Experimental Vaporization Quality  as  a  Function of  the B Group Parameter

-------
to fall in a band which increases in vaporization quality as the group




parameter B increases, indicating the correct influence of the individual




variables in the parameter.  Except for some extraneous points it appears




that the fuel mixing device developed produces a mixture with a high




degree of vaproization.




POROUS PLATE COMBUSTOR FABRICATION DEVELOPMENT




Introduction




     The basic combustor material considerations are that the material




must:  (a) have structural and chemical stability at the maximum-use




conditions which includes the temperature of use and the ability to with-




stand the anticipated thermal cycling, (b) be suitable for fabrication




into the desired design for the engine, (c) be compatible with other




materials of the engine design, and (d) be economically feasible for mass




production as a combustor component.




     The materials which are presently available and feasible for use in




a porous combustor for an automobile gas turbine are outlined in Table 9,




which shows the usable temperature range and the reasons for the tempera-




ture limitation.  The final resolution of material selection will require




more detailed test data than are available at the present, both from the




design requirements and from material behavior measurement.








     These material considerations are outlined below in more detail in




terras of the metals and the ceramics.  Most of these are available com-




mercially but need more detailed crucial laboratory tests to more




accurately define the behavior characteristics for this porous combustor




application.  The initial selection for detailed development was a com-
                                  167

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                     Table  9.  POROUS COMBUSTOR MATERIALS
       Material


Ni Alloys

Fe-Cr-Al Alloys

A1203-S102 Glass Fibers

Si02 Glass Fibers

SiC
ZrO
Probable Use
  Temp. *F


  1600-1800

  1800-2200

  1700-1900

  1800-2000

  2200-2700

  2400-2700

  2400-3000

  2400-3200
          Limitations
Sintering, Oxidation

Oxidation

Sintering(a\ Devitrification

Sintering***, Devitrification(b)
         (A\
Oxidationv/

Sintering

Sintering

Sintering
a.  Sintering of glass structures is obviously a liquid phase phenonenun and
    may be accelerated by pressure due to contact surface Increase as a result
    of plastic deformation at the higher temperatures where the viscosity is
  -  decreasing.

b.  Devitrification is simply crystallization  of the glass(which is, of course,
    a supercooled liquid) with the result in loss of glass fiber structure.

c.  The oxidation of SIC is complex because of the presence of fuel and air
    which means that SiC, SiO, SiOo, hydrocarbons, H2, H^O, (OH), 00, C02 and
    02 are all present.  This could mean, for example, that if the SIO species
    is formed in preference to CO, there may be a high rate of oxidation at
    temperatures above 2400"F.  Also, the oxidation of SIC also can conceivably
    cause loss of permeability due to pore blocking by the SiC^ formed.  The
    resolution of this problem probably will depend on measuring the oxidation
    kinetics in the various temperatures of Interest.
                                         168

-------
bustor using a silicon carbide (SiC) burner face backed with mullite

(3 Al_0_-2SiO_) to provide the necessary thermal insulation to keep the

temperature of the cold side of the burner (which faces the incoming fuel-

air mixture) below the ignition temperature.  However, after limited

testing of commercially available materials in radiation-cooled burners,

it became obvious that additional cooling was required at higher loading

and that an air-cooled design was essential which would have to be based

on a metal system; the preignition tests which lead to the air-cooled

design were described earlier.

Metals

     The candidate alloys for combustor components are shown in Table 10,

which lists compositions of both the Ni-base alloys and the Fe-Cr-Al

alloys.  These listed alloys were selected primarily on the basis of their

excellent oxidation resistance at elevated temperatures.  For the stain-

less steels, in which chromium is the only alloying element, a generalized

relationship has been established between the Cr content and the maximum

use temperature in standard combustion gases.  This relationship is shown

in the following tabulation:

                                       Max.  Service Temperature
                 % Cr                  in Combustion Gases, °F

                  0                             1050

                  4                             1200

                  8                             1300

                 12                             1400

                 16                             1450

                 20                             1650

                 24                             1900

                 28                             2100


                                  169

-------
Table  10. CANDIDATE ALLOYS FOR COMBUSTOR COMPONENTS

CRYSTAL STRUCTURE
ALLOY MATRIX
AISI 442
AISI 446
GE-1541
Hoskins 875
Amco 18SR
AISI 310
Incoloy 800
Inconel 601
Rolled Alloys
333
Hastelloy X
Kanthal A-l
BCC
BCC
BCC
BCC
BCC
FCC
FCC
FCC
FCC
FCC

Fe
Bal
Bal
Bal
Bal
Bal
Bal
Bal
14
18
19
Bal
COMPOSITION, %
Cr Ni Co Mo W Al Ti Si
20 -------
27 -------
15-___4_-
23 - - - - 6 - -
18 - - - 2 0.4 1
25 20 ----- -
20 32 - - 0.4 0.4
23 Bal - - - 1.4 -
25 Bal 3 3 3 0 1.2
22 Bal 1.5 9 0.6 - - 0.5
22 0.5 - - 5.5 -
Y
-
-
1
-
-
-
-
-
-
-
_
                            170

-------
On this basis, the recommended maximum service temperatures under cyclic




conditions for AISI 310 SS (24Cr-20Ni) and AISI 446 SS (27Cr) have been




reported as 1900°F and 2100°F, respectively.




     Significant improvement in oxidation resistance of iron-chromium




and nickel-chromium alloys can be achieved by the addition of Al or Al




and Y (yttrium) as exemplified by the 1541 iron base alloy developed by




General Electric and the nickel-base Inconel 601 alloy (Table 10)„ In




the Fe-Cr-Al system, one of the main advantages of increased Cr content




is to reduce the amount of Al required for the selective oxidation to




form the protective A1.0_ film; 15-25% Cr has been found to be optimum.




A minimum of 2% Al is required to produce the Al?0  -layer-in the 15-25%




Cr-Fe alloy.  Al content  above 5% result in alloys'that are brittle




and difficult to fabricate.  It was found that additions :of yttrium to




Fe-Cr-Al alloys result in improved oxidation resistance under cyclic con-




ditions because of increased oxide adherence.  The mechanism by which




yttrium improves oxide adherence has been postulated that it may result




from subscale formation of YJD  which either promotes sintering of the




surface oxide Al-0  or provides a locking affect for the.surface oxide.




A form of a locking mechanism of the surface oxide layer by a uniform




network of internally penetrating oxides has also been suggested as




playing a role in achieving the excellent oxidation resistance in the




Al containing nickel base alloy Inconel 601.  Spalling resistance of the




oxide layer is credited to the similar coefficients of thermal expansion




of the alloy and the surface oxide.




     The oxidation resistance of the Fe-Cr-Al-Y alloys is such that a




0.020 inch thick sheet can resist destructive oxidation for more than
                                   171

-------
 2000 hours at  2300°F, 1400 hours at 2400°F, and 400 hours at 2500°F.  The




 Fe-Cr-Al-Y alloys are as oxidation resistant at 2300°F as the nickel




 base non-aluminum containing Hastelloy X is at 2000°F.  The use of nickel




 base alloys requires that they be resistant to hot gas corrosion due to




 sulfur containing environments.  For this reason, it is necessary that




 the Cr content be in excess of 15%.  Hastelloy X (22% Cr),for example,




 shows rather good resistance to hot gas corrosion.  However, high Cr plus




 aluminum additions (Inconel 601) provides still further improvement to




 hot gas corrosion.




     The strength properties of the ferritic (BCC) stainless steels and




 the more oxidation resistant ferritic iron base alloys at temperatures




approaching 2000°F are very low (Table 11).  If strength requirements for




 the structural components exceed the limits of the ferritic iron alloys,




it will be necessary to utilize the higher strength austenitic (FCC) iron




or nickel ba«e alloys.  It is well known and documented that the face




centered cubic lattice (FCC) is more resistant to creep than the body




 centered cubic lattice.   Limited testing data on these Fe-Cr-Al alloys




are shown in Figure 98 for typical oxidation curves at temperatures of




 2000°F to 2600°F, and loss in permeability of porous plates at 1800°F




and 2000°F shown in Figure 99.




Ceramics




     The most promising ceramic materials for the porous combustor are




SiC as the burner face and mullite as an insulator immediately adjacent




 to the SiC.  The crucial thermal properties of these and other potential




ceramic materials are shown in Table 12*  Since high thermal conductivity




and low thermal expansion improve resistance to thermal shock, the selec-




 tion of SiC is obvious.   This selection is further supported by the high




emittahce factor which enhances radiation heat transfer*  The choice of



                                   172

-------
Table 11.   TENSILE PROPERTIES OF CANDIDATE ALLOYS
                  FOR COMBUSTOR COMPONENTS

TENSILE PROPERTIES
Alloy
AISI 446


GE-2541



Annco 18SR


AISI 310



Incolor 800


RA 333

Inconel 601


Hast. X



Temp. ,°F
RT
1800
2000
RT
1800
2000
2200
RT
1800
2000
RT
1800
2000
2200
RT
1800
2000
RT
1800
RT
1800
2000
RT
1800
2000
2200
0.2% Y.S., ksi
51.5
-
-
50.8
2.2
1.2
1.0
65.0
-
-
36.5
8.0
5.0
3.0
47.7


50.0
15.4
49.0


52.2
16.0
8.0
3.7
Ult, ksi
83.0
2.9
1.5
76.7
3.5
2.0
1.8
85.0
2.0
1.1
84.0
14.0
8.0
6.0
87.7


100.0
18.4
107.0


114.0
22.5
13.0
5.4
El, %
29.0
_
-
14.0
135.0
154.0
161.0
29.0
—
-
50.0
52.0
35.0
35.0
42.0


50.0
53.0
45.0


43.0
45.0
40.0
31.0
                          173

-------
                                                               (a)   GE,  0.160 In.  dia rod
                                                                    static air.  Isothermal
                                                                    IITRI,  0.010 in.  sheet
                                                                    cyclic  exposure

                                                               (c)   GE,  0.030 in.  sheet
                                                                    static  air.  isothermal
                                                       2400°F(a)
Cracking of
Oxide
                                                     2200°F(a)
            Figure 98,
                        10/20
                 Time,  Hours x 10

Weight Gain of Fe-25Cr-4Al-Y Alloy During  Oxidation  Testing  in Air
                                                                                                  100

-------
  100
                                           1800°F
   75
=  50
o  25
                100
                        H 875
                        GE 1541 	
                                         I
                          I
200          300         400

   EXPOSURE TIME - HOURS
                                                                500
600
           Figure 99S  Poroloy Permeability Retention After Exposure at 1800 and,.
                      2000°F  (982  and 1093°C) in Air.  Alloys GE 1541 and H 875U  '
                                     175

-------
Table  12.  CRITICAL.THERMAL.PROPERTIES.OF.SELECTED CERAMICS

THERMAL CONDUCTIVITY THERMAL EXPANSION NORMAL TOTAL
IN BTU/(hr)(ft)(°F) COEFFICIENT EMITTANCE
MATERIAL
Al.O,
MgO
Zr02
Zr02-Si02
SiC
3Al.,0,-2SiO,
200eF
18
35
1.0
3.8
90
3.5
2000°F x 10~6/°F (to 2000-2200°F) AT 2200°F
3.4 5.0 0.41
3.5 8.8 0.3
1.0 6.7 0.5
2.5 3.1
10 2.7 0.85
2.4 2.9 0.6
                            176

-------
mullite as an insulator for SIC is based on (a) the close match of thermal



expansion plus (b) the fact that SiC forms SiO  upon oxidation and the



film of this material will bond the SiC to 3Al203-2SiO .  It is to be



noted, however, that the possibilities of using mullite alone or the use



of AlpO- may become economically attractive by using a Cr 0 additive to



increase the emittance factor.



     The thermal stability of SiC at very high temperatures may impose



undesirable limitations on its use as a porous combustor as compared to,



for example, Al-0 .  The oxidation of SiC is not known in sufficient de-



tail to make an accurate prediction at this time.  For example, the



published data on oxidation^  '    are not readily applicable to the porous



combustor because these data were measured on powders of unknown ratios



of surface area to volume.  As noted in Table 9, there is need for more



detailed test data to apply to this specific application.



     The readily available fabricated ceramic materials which were used



entirely or in part to construct porous combustors for testing are as



follows:



     1.  ZrO  (Y?0  stabilized) cloth is made by Union Carbide Corpora-
            £•   £3


         tion.  This material is reported to be made by saturating an



         organic fiber cloth with suitable zirconium - yttrium salts and



         then thermally removing the organic accompanied by converting



         the zirconium-yttrium salts to the oxides.  Initial tests on



         this material show that it begins to become stiff after about



         one hour at 2400°F, suggesting that sintering and/or crystallite



         growth is occurring.



     2.  SiC - mullite porous combustor plates are available from sources



         such as Rex Radiant.  These plates are about 1/8" of SiC bonded




                                   177

-------
         to about 1/2" of mullite.  Both substances are of about 16 mesh



         particle size, probably bonded with some Al 0_-SiO  substance.
                                                    £ J    £


         Heating to 2600°F for 4 hours shows an increase in grain-to-



         grain bond.



     3.  Porous SiC-bonded SiC cylinders are available from the Norton



         Company.  Tests on the cylinders have resulted in fracturing



         presumably because of non-uniformity in the porosity and/or non-



         homogeneity in fuel injection; however, limited testing of 1/4"



         rings shows no evidence of fracture.



     4.  Porous Al^O.-SiO- cylinders are available from Coors Porcelain



         Company.  Initial tests were on a "P-6" type porosity which has



         a lAl-O -ISiO  composition with a thermal expansion similar to



         A1203.



     In addition to the above, limited studies were undertaken to develop



porous ceramic parts of SiC and Mullite in which four fabrication approach



were considered.  The first technique studied was to use coarse particles



of SiC and of mullite made from fine grained powders.  These particles



are composed of fine grains (i.e., generally below 10 microns); this com-



position gives much higher strength than the commercially available single



crystal particles (such as Rex Radiant uses in their porous combustor).



A second approach was to use a volatile organic particle in fine grain



compacts to produce the desired porosity.  This process will result in a



fine grain structure of optimum strength for the high porosity.  A third



method was to use large single crystal particles and sinter these much



the same as the Rex Radiant porous material.  The reason for this latter



approach was that there may be a porosity loss in use because of sintering



at the use temperature which will be minimized by the large grains.  A



                                   178

-------
fourth possibility was to use a material with high emissivity for radia-




tion heat transfer, for example, one of the above ceramics incorporating




a high emissivity material such as chromium oxide (Cr.0_) or cerium oxide




(Ce02).





     However, porous metal materials for combustors were selected as the




main effort when it became obvious heat removal by cooling air was essential.




Initially these were commercially available alloys in a sheet or plate




form.  Subsequently, the most crucial work was directed to fabrication




of porous metal combustors with air cooling tubes using 80Ni-20Cr powders




and 310 stainless steel tubes.




Fabrication of Porous Air-Cooled Burner




     The initial porous-plate air-cooled burner designed for development




tests was 2.25 inches in outside diameter and 1.25 inches in inside




diameter and 6 inches long with 24 coolant tubes 0.125 inch in diameter




imbedded on the surface of the inside wall of the porous surface.  The




porous-plate material was 80% Ni-20% Cr alloy in the form of coarse




powder in a particle size range of 25 to 50 mesh which was procured as




the only readily available powder in this size range.  By making sample




pieces, it was found that coarse particles could be sintered in hydrogen




at 2400°F to form a soft porous surface.  The mixing of 5 to 10 percent




of GE-81 braze material with powder was found to improve the strength of




the sintered plate and permitted the use of a lower sintering temperature.




     A total of nine porous cylinders of approximately the aforementioned




dimensions were made and tested on this program.  Problems that had to




be solved included mold design to minimize the effects of differential




expansion between mold and part, mesh size, elimination of density varia-




tions in the porous structure by vibration of the mold during filling,



                                   179

-------
 the  choice of  the  correct proportion of braze powder to be added, uni-




 formly mixing  the  braze powder with the powdered metal.  Shown in Figure




100 is the sixth porous cylinder after sintering.  Some disproportionate




 braze distribution areas can be seen on the surface.  Shown in Figure 101




 is the same porous cylinder with the tube sheets brazed on.  This porous




 combustor (No. 6)  was fabricated with an outer diameter increased to




 2.50-inches and the 27 coolant tubes located on a 2.125-inch diameter




 ring so as to  be imbedded in the 0.375-inch thick frit wall.  This re-




 quired a new mold  design with the 27 coolant tubes held in position by




 temporary tube sheets of GE-1541 alloy which was pre-oxidized to prevent




 bonding to the porous material.  The coolant tubes were coated with braze




 to improve the bond with the porous material.  The -35 mesh NiCr powder




 was  pre-treated in hydrogen at 2000°F to reduce the oxygen content and




 improve sinterability and then mixed with 5 percent of GE-81 braze.  This




 assembly was initially sintered at 2300°F and after removal from the mold




 was  resintered at  2370°F for 4 hours.  The dimensions of this porous-




 plate unit were 2.45-2.80 inch outside diameter, 1.70-inch inside diameter,




 with a wall thickness of 0.35 to  0040-inch0  Radiographic examination




 of this porous cylinder revealed that considerable improvement in uni-




 formity of density was achieved by vibrating the mold during loading of




 the  NiCr powder, although some layering effect was noted as a result of




 incremental additions of the powder.  This cylinder was fitted with tube




 sheets and the joints were brazed at 2250°F using GE-81 braze powder.




 COMBUSTOR CONFIGURATION AND ENGINE INTEGRATION DESIGN




     The accomplishments on the several tasks described above have pro-




 duced results  which can be synthesized into a porous-plate burner design

-------
00
                       .'
                     re-
                  •m.
                      •••'••':.-
                              Figure 100.  Nichrome Porous Cylinder No. 3 As Sintered at  2350°F

-------
Figure 101.  Porous Cylinder No.  3 With Tube Sheets Brazed on Each End
                                182

-------
concept for the Base Line Engine.  An important result stemming from the


Combustor Loading and Emission Analysis is that the porous plate area

                        2
must change from 1.15 ft  for operation along the vehicle level road-

                   2
load line to 2.2 ft  for wide open throttle accelerations in order for


the combustor to operate between values of superficial velocity (V«-)


which correspond to flame extinguishment and to lift-off at the two limits.


During such operation, the equivalence ratio must be varied to help limit


superficial velocity and to limit porous-plate hot side temperature with-


in the temperature capabilities of available porous materials.  Because


of the excessive heat flux conducted back to the porous plate from the


flame at elevated pressure levels (4 atm.) which heat results in surface


temperatures beyond available material limits, it is necessary to cool


the burner porous plate by means of embedded air-cooling tubes.  The


thermal stresses in the air-cooled porous material must be reduced for


part integrity by employing a series of flat plates instead of a hollow


cylinder.  Adequate fuel atomization and vaporization can be obtained


by spraying the fuel into compressor discharge-temperature air with an


air-assisted nozzle while at the same time avoiding preignition of the


fuel.  Emission testing with propane indicated that NO  emission index


values were below the Federal Standards.  CO emission index values were


below the Federal Standards at superficial velocity (V2,-) levels corres-


ponding to low engine load and slightly above at conditions corresponding


to high loads.  The unburned hydrocarbon emissions were barely detectable


and,  therefore,  adequately low.  Prompted by these results, a design


concept for a porous-plate combustor for the Base Line Engine was formulated


and is described below.
                                  183

-------
Combustor Conceptual Design


     Figure 102 illustrates the air-cooled porous plate burner concept


which is proposed for application to the gas turbine Base Line Engine.


Figure 102 was prepared using a drawing of the Base Line Engine.  The


porous plate combustor shown extends vertically above the engine center


line only 2 inches more than the standard combustor for this engine and

                        2
provides the full 2.2 ft  of porous-plate surface required for wide open


throttle acceleration.  The flat-plate porous burner elements made of


sintered nichrome are grouped in five rings of V-shaped burners arranged


inside a circular shell which is enclosed within the combustor outer


casing.  Passages for the flow of primary air,bled from the compressor


discharge, and of secondary air from the regenerator discharge are pro-


vided in the annular space between the burner support shell and the outer


casing.  Primary air entering the top of the combustor is admitted through


sixteen controllable (on-off) butterfly valves to the vaporization tubes.


In each of the vaporization tubes, an air atomizing fuel nozzle is lo-


cated immediately downstream of the air valve.  Vaporization and fuel-


air mixing occur during passage of the fuel and air down the length of


the 6-inch vaporization tubes.  The fuel is vaporized in these tubes by


heat from the primary (compressor discharge) flow and from the secondary


flow (regenerator discharge) which surrounds the vaporization tubes.  At


the end of these tubes, the fuel air mixture reverses flow direction and


passes down channels formed between the V-shaped burners and the burner


support shell.  From these channels the fuel-air-mixture flow is admitted


to the upstream faces of the porous burners.


     Secondary air flowing oppositely to the primary air passes between


the vaporization tubes and is admitted to the porous burner cooling tubes.


                                  184

-------
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     c
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     a.
     o
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     g1
     o
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     a.
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     to
     rt
     n
     a
     n
     o
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    •s
                                                                                                                                                                                                                       MCOMQMT1 MCI

-------
The V-shaped burners are axially segmented into short sections which are




scaled by end plates.  This prevents severe distortion under the radial




temperature gradient existing in the burner porous surfaces.  All of tho




burners in a given .line, are attached to the sides of one of the fuel-air




mixture distribution ducts.




     Burning occurs on the outer surfaces of the wedge—shaped burners in




the space between opposing burners.  Power modulation involves variations




in air flow rate and equivalence ratio and in addition involves shutting




burners on and off by means of the butterfly air valves.  Only the most




extreme transient operating condition requires all burners in operation.




Non-operating burner surfaces continue to be cooled by secondary air




flow through the embedded tubes, and thus serve as radiation heat sinks




for the opposing operating burners.




     Because of the short length and close spacing of the embedded air-




cooling tubes the cooling effectiveness will be quite high.  Since this




burner concept employs both radiation and air cooling, the surface will




run cooler than the values reported in the Section on Loading and Emission




Analysis.




Combustor Concept Development




     As reported above, cylindrical porous nichrome burner models with




embedded air-cooling tubes have been run, mostly at one atmosphere, and




have indicated favorable emission results.  It is expected that the use




of flat plate segments instead of complete cylinders of porous material




will alleviate the cracking problem experienced at elevated pressure




levels where the heat release rates are increased over the atmospheric




case.  The sintering parameters must be optimized and the joining methods




must be specified which will assure a good product.




                                   186

-------
     The design concept shown in Figure 102has the flexibility of varying


                                                            2           9
the active area of the burner in eight steps between 1.15 ft  and 2.2 ft"



or in as few as one step.  This flexibility will be useful in transient



operation because when more than half of the burner area is being used



at least some of the wedge-shaped segments will have no radiation sink.



By controlling the active area and the equivalence ratio, the superficial



velocity (V9r) can be made high enough so as to limit the heat flux back



to the porous plate to a value that can safely be removed by cooling air



alone.  This, of course, will have to be balanced against the increase



in NO  because of the smaller reduction in flame temperature.
     X


     It is desirable to use regenerated air instead of compressor air for



the primary flow from the standpoint of engine fuel mileage.  In



previous work     an analysis of an engine with and without regenerator



bypass for the combustor primary air flow was made for the case of a



constant equivalence ratio of 0.9.  For the Federal Driving Cycle the



fuel mileage values with and without regenerator bypass were 10.6 and 12.8


                                         (23)
tnpg.  There is some evidence, for example   '  that the atomization and



vaporization of gasoline can be carried out in a time interval smaller



than the ignition delay using regenerator air, thus eliminating the re-



generator bypass.  A compromise would be mixing compressor and regenerator



discharge flow for the combustor primary flow, thus reducing the fuel



mileage penalty without using an extreme temperature that might lead to



preignition.   For the porous-plate combustor,  since the flame temperature



is set by the superficial velocity (V-r) independent of the burner inlet



temperature,  no adverse effect on NO  emission index would be expected



with the elevated primary air temperature.



                                   187

-------
     Another means for improving fuel mileage is to use advanced sintered




materials having higher operational temperatures.   By so doing,  the




equivalence ratio of the burner could be increased, thereby reducing the




regenerator bypass; this bypass could be zero, in  the limit.   To utilize




materials with higher operational temperatures than nichrome,  materials




processing methods must be worked out which avoid  producing the  protective




oxide coating of the sintering material before sintering.




     In light of the present status of the air-cooled porous  plate burner




for the gas turbine automobile engine, it is important to fabricate a




full-size combustor and test it on gasoline over the expected operating




range it would have in the Base Line Engine.  Because of at least partial




success with the nichrome air-cooled burners, nichrome should be utilized




in the full size burner.  This will require finalizing the sintering




parameters for this material and establishing the  joining techniques to




be used between the porous material and the remainder of the  combustor




structure.
                                   188

-------
                         RANKINE CYCLE COMBUSTOR








DISCUSSION




     \-Jhen any fuel is burned with air, some nitric oxide is almost in-




evitably formed in the hot product gases; of the contributors to air




pollution from combustion processes, it may be the most difficult to




eliminate or control.  The principal mechanism of its formation is that




of the hot-air reaction; and until recent years, this was thought to be




the only important process.  It is now known that in some circumstances




NO can evidently be made in hydrocarbon-air flames by other processes  '




and in amounts that are significant in terms of the low source emission




goals now established.




     The main problem in NO  reduction is still that of controlling the
                           A



high temperature ("thermal or hot-air") production of NO.  The rate of




the process unfortunately becomes appreciable just in the range of burned




gas temperatures common to most combustion processes.  It has a very




large temperature dependence; the rate is approximately doubled by a 90°F




increase in temperature so that any preheating (for example, by precom-




pression in an engine cycle) drastically increases NOX emissions.  Con-




versely, any effective scheme for reduction of the maximum temperature,




as well as the residence time at that temperature, can result in sub-




stantial decrease in NOX emission, for which various approaches have been




conceived and are being pursued.




     The work described here is based on one such idea:  limiting the






                                   189

-------
maximum temperature of a premised flame by heat removal from the unburned



gas, in effeet,before the mixture is burned, so that it is equivalent to



precooling the mixture.  The concept is derived essentially from the



cooled porous-plug burner or flameholder, first investigated by Botha



and Spalding  '  and by Kaskan   .   Burners of this kind have since been



used extensively in flame studies, and have also been applied in various


                                      (18 19 20}
forms in practical combustion devices.   '  *     The background and



rationale of the concept were discussed above.



     For the corabustor boiler in a Rankine-cycle automotive engine, the



porous plate combustor is attractive for three general reasons:



     1.  It appears certain to be readily controllable to yield products



         low in NO  and hydrocarbons and acceptable in CO content.



     2.  It is conceptually well matched to such a cycle, since its re-



         quired coolant can simply form part of the working-fluid path,



         with complete recovery of the heat necessarily absorbed by the



         burner prior to its passage to the boiler.



     3.  Although it requires a reasonably uniform premixture, the prepara-



         tion of the fuel-air mixture in this application should be fairly



         straightforward.



     The approach taken is a combination of analytical and detailed ex-



perimental work to determine the feasibility of the porous-plate combustor



for the Rankine Cycle engine.  Furthermore, since the porous-plate com-



bustor requires the fuel and air to be premixed, concepts of a fuel vapor-



izer were examined.



     It was the purpose of the work described here to examine experi-



mentally porous plate combustion particularly with respect
                                   190

-------
to emissions, and to obtain test data that is relevant to the design of




this combustor for a Rankine Cycle engine.  Preliminary designs of both




the combustor and the vaporizer suitable for the Rankine Cycle were first




made.




     While the approximate distribution .of heat absorption between the




burner and the rest of the boiler system can be roughly estimated from




available data, it is desirable to determine this with some accuracy for




the anticipated range of flame conditions.  Many such burner heat flux




measurements were made for this purpose, as well as for indirectly es-




timating or checking the actual burned gas temperature.




     Further, measurements of oxides of nitrogen, carbon monoxide, and




unburned hydrocarbons were made over the range of operating conditions




at the atmospheric pressure of the Rankine Cycle.  These measurements




were made on flames with air and five different fuels-(EPA'gasoline, AMOCO,




propane, toluene, and n-heptane).




PRELIMINARY BURNER-VAPOR-GENERATOR DESIGN




Preliminary Rankine Combustor Design




     Figure 103 shows the conceptual design of the Rankine Engine burner




and vapor-generator.  Combustion air from the blower passes through a




preheater where it is heated by the hot exhaust gases.  The preheated




air flows through a mixing device where the fuel is injected and atomized.




Vaporization of the fuel takes place in the flow ducts leading to the




transpiration burners.




     The specifications and preliminary design of a porous Rankine burner-




vapor-generator with the configuration of Figure 103 are summarized in




Table 13C  This component has an overall diameter of 18 inches; there is







                                  191

-------
Air fro* Expander
Driven
Superheated
     Out
                                                                                    Air Controlled
                                                                                   Preaaure Reaervolr
                                                                                     •nd »• If old
                                          =    Air      —
                                          —  Preheeter   —
                                          j^ (Plate-Mo Type) =
  fu.l/Alr fcnlfold
                                           Figure 103,   Conceptual Design of  Porous-Plate  Burner-Vapor
                                                            Generator for Ranklne System
               auction A-A

-------
                  Table 13.  POROUS RANKINE COMBUSTOR
SPECIFICATIONS
      Combustor Heat Load                        1.87 x 10  Btu/hr
      Feedwater Temperature                      200°F
      Steam Flow                                 Max. 1296 Ibm/hr
                                                 Min.   40 Ibm/hr
      Fuel Flow                                  101 Ibm/hr
      Feedwater Pressure                         1200 psi
DESIGN
      Equivalence Ratio                          0.9
      Fuel/Air Flow Rate                         1801 Ibm/hr
                                             2
      Burner Area                        5 ft  with V-_     =40 cm/sec
      Minimum Area to Avoid Lift-off             3.9 ft2
        at Maximum Flow
      4 Concentric Burner Plates                 1/2 in. Thick
      Overall Diameter of Burner                 18 in.
      Burned Gas Exit Velocity with 1/2"         65 ft/sec
        Radial Gap for Each Exit Plate
      Pressure Drop at Design Condition          105 psi
        (215 Microns Pore Size, 35% Porosity)
      3 Stages Required to Meet Turndown Requirement of 32.4:1 with
      Individual Burner Turndown of 5:1
                                   193

-------
a 1/4 in. radial gap for each of the 4 concentric burner plates, which


gap results in a burned gas exit velocity of 65 ft/sec.  Three stages are


required to supply an overall turndown ratio of 32.4:1, since the maximum


turndown of the individual burners is approximately 5:1.  The package

                                                    2
shown in Figure 103 has a porous burner area of 5 ft .


 Preliminary Fuel Supply Design


      In conventional combustors using liquid fuel,  the fuel is typically


 injected into the combustion zone in the form of small liquid droplets


 which are subsequently vaporized and burned.   The porous-plate burner


 requires that the fuel be vaporized and well mixed with air before en-


 tering the porous structure of the burner.


      Figure 104 shows the fuel-air mixer and fuel vaporizer concept which


 is similar to that used in a current advanced aircraft engine development


 program.  The fuel enters the mixer through the  central tube and is in-


 jected radially into the primary air stream through the small orifices.


 The primary vanes impart a swirling motion  to the air which then passes


 through a venturi section.  Additional air  is introduced through a radial


 inflow counter-rotating secondary swirler.   The  intense shear region be-


 tween these counter-rotating flows provide  good  atomization of the fuel


 which is then vaporized on the downstream duct.


      The turndown ratio compatibility of a  single burner is in the order


 of 5:1 for constant pressure and equivalence ratio.  In order to achieve


 the required 20-30 turndown ratio,  staging is required.


 Figure 105 shows two possible installation  configurations for the fuel/


 air mixers.  Preliminary calculations were  made  to estimate pressure drop


 as a function of cup dimensions and degree  of fuel vaporization as a


 function of air velocity, air preheat temperature and length of vaporizer.
                                    194

-------
Figure 104.  Fuel-Air Mixer and Fuel Vaporizer
             Double-Swirl Carbureting Concept
                            195

-------
       CONFIGURATION I
F/A Mixers
                            Control
                            Valves
                                             1
Fan
       CONFIGURATION  II
    Figure 105.  Preliminary Installation Configurations
                                   196

-------
The pressure drop results for the design point are shown in Figure 106



and the degree of fuel vaporization is shown in Figure 107.   The fuel


                                                     (21)
vaporization predictions are based on the correlation     previously de-



veloped.  Since the liquid droplets in those experiments were relatively



large, the predictions for this mixer (in which the droplets will be



small) are believed to be conservative.



     After completing the above analyses, the vaporization tests were



run on the gas turbine combustor fuel-air mixture supply reported above.



As indicated in Figure  97,  most of the data indicated 93% or above of



the fuel was evaporated.  The tests were run at atmospheric pressure



similar to Rankine burning conditions.  The inlet air temperature was in



the range of 164 to 411°F.  These temperatures  are   easily attainable



in a Rankine cycle air preheater required for an efficient engine.  The



equivalence ratio of the data was 0.8, only slightly lower than contemplated



for the Rankine combustor.  Thus, the test data can be seen as applicable



to the Rankine fuel-air mixture supply.



     Reference to Figure  91  indicates that a tangential flow of primary



air is created in a central tube by variable louvers around the inlet



end.   A "Sonicore" air-actuated fuel nozzle sprays gasoline in a 90°



conical spray down the center line of the central tube.  The spray nozzle



creates a spray with a 20-50 micron mean drop diameter which quickly



evaporates due to the warm primary air introduced into the central tube.
                                   197

-------
                                   = 0.49 PPS
                                 TA=  205 °F
                                 PA =  16 PSiA
                           N = NO  OF CUPS TOTAL

                                   1
     4   5   6    8    10          20
     CUP PRESSURE DROP , AP/P $
30
40
60  80  100
Figure  106.  Rankine Engine Fuel-Air Mixer Cup
            Flow Characteristics
                    198

-------
VO
         ion
          90
          80
          70
          60
O
s-
M   50
          40
          30
          20  h
          10
             0
                       200
                                         _L
                                                         T -  540 F
400
600
                                                                                                  T
                                                                                          Primary Air Temperature
                                                                                               T -  350 F
                                                                                                    T - 205 F
                                                                                                    T - 100 F
                                                                                        Developed Flow Length
                                                                                800
                                                                                           1000
                                                        Velocity, ft/sec

                                  Figure  107.   Estimated  Vaporizer Performance

-------
The smaller drops follow the streamlines and are evaporated due to the


presence of the warm air.  It takes only a configurational study to


adopt this tested concept to the Rankine combustor


BENCH TESTS


Test Apparatus


Burner and Auxiliary Equipment - To meet the design requirements of a


real engine, the individual modular burners will probably have to be other


than flat, but a satisfactory evaluation of the quantities of interest


here can equally well be made with a flat burner.  An available unit made


of sintered copper shot and with a 5.5 in. x 5.5 in. burner surface,


about 0.4 in. thick and with about 35% porosity, was used in this work;

                          2
the burner area of 30.3 in  is reasonable for laboratory bench tests


and is large enough for adequate precision in the desired measurements.


The scale factor relative to the specified engine parameters is approxi-


mately 1/30.  Figure 108 shows an essentially identical sample unit,


made only half-filled with the sintered copper shot to illustrate its


construction.


     A schematic diagram of the test set-up is shown in Figure 109.  The


burner is secured to a flanged plenum, primarily to reinforce the rec-


tangular water manifolds of the burner which had been made entirely of


copper and thoroughly annealed during the sintering of the copper shot.


(The manifolds had to sustain a water pressure of as much as 120 psi to


suppress boiling, with the preheating required to avoid condensation of


pre-vaporized fuels.)  The water preheater (Figure 109) is an identical


sintered copper burner, and both have manifolded parallel water tubes as


in Figure 108, rather than the monotubes in some of the proposed engine


designs.

                                   200

-------
ro
O
                                                                                   ».  ^m
                                                                                      ^l,...

                                                                                                           .'
                                                                                                                  r
                               Figure  108.   Half-Filled Copper Shot Burner,  Illustrating Burner

                                             Construction and Coolant Tube Manifolding

-------
 Air (^ 150 psi)
           Pressure
           Gage
        i—o—i
N>
O
N5
Flow
Meter
 Propane or
 Methane
                                          Differential
                                          Thermopile
                                                                                                     NO  Monitor
                    Critical
                    Flow
                    Orifice
                                            Calrod
                                            Heater
                                                                                                          PDS
                                                                                                    To     Sample
                                                                                                    Vac    Flasks
                                                   Porous  Plate
                                                   Test  Section
                         Inlet
                         Temperature
                         T/C
                                                                                                                   Pressure
                                                                                                                   Gage
                     Figure  109.  Schematic Diagram of Burner Test and Gas Sampling Arrangement

-------
                                                               _2
     The water flow appropriate to this scale is about 1.1 x 10   Ibm/sec;


it was metered with a calibrated differential  pressure orifice, and de-


livered from the pressurized reservoir shown.  On the preheater, a methane


(or propane)-air mixture is burned at a composition and flow adjusted to


give the temperature rise required (up to 180°F) to match approximately


the preheated air temperature and to avoid condensation of the prevaporized


liquid fuel (for example, gasoline) in the burner pores.  The air pre-


heater is a Variac controlled 1 KW Calrod immersion heater in about 2

                                                             /   *3
feet of 2-inch pipe.  It can heat a steady flow of 1.76 x 10~  ft  (STP)/


sec of air to 230°F.


     The combustion air was fed from the 150 psi plant supply and metered


with a calibrated critical flow orifice meter; when propane was used as


the fuel, it was taken from a regulator on a standard container of chemically


pure (CP) propane.  It was metered with a critical flow orifice, as were


also the fuel and air to the preheater when used.


     When a liquid fuel was used, it was taken from the reservoir, pres-


surized to a few psi above system pressure with N_, through a rotameter


and delivered by the adjustable Zenity metering pump to a simple spray


nozzle (Monarch or Delavan; 0.6 gallons per hour).  The rotameter was


calibrated with each of the three liquids used.


     Many earlier attempts had been made to operate the system with pre-


vaporized fuel at temperatures up to 306°F, using the single spiral coolant


tube in another small porous-plug burner as the heater; it appeared to


be a satisfactory and readily adjustable source of the vaporization heat,


but pulsations seemed to be very difficult to avoid with any reasonable


feed-system modification, and steady flames were seldom obtained with


this arrangement.  It was finally abandoned for the simpler arrangement


                                   203

-------
discussed below.  To ensure complete vaporization of the liquid fuels,




the air was usually preheated to about 212°F, as measured at the entry




to the plenum (Figure 109).  All of the apparatus downstream of the fuel




injection was well insulated with glass wool, and the water temperature




at the burner inlet was maintained at about 212°F or higher to avoid




possible condensation of the fuel.  The spray nozzle, (facing downstream),




mounted in the center of the pipe, discharged into the preheated air




stream ahead of the mixer.  Satisfactory performance of the burner was




thus obtained; ignition was prompt and reliable to a steady flame of




uniform appearance, which extinguished promptly when the pump was stopped




with no evidence of residual unvaporized fuel.




     The heat flux to the burner was obtained from the water flow, its




specific heat and the temperature rise; calibration of the ten-element




thermopile  with which the temperature rise was measured agreed well with




standard copper-constantan tables.  One of the 1/8 inch diameter stain-




less steel sheathed junctions of this device contains a separately wired




single-junction thermocouple.  This end was mounted at the burner inlet




to monitor the water temperature as delivered by the preheater.  The




temperature rise across the main burner was frequently as much as 144°F,




so that the exit water was usually flashing to steam beyond the back pres-




sure valve (Figure 109).  When a steady flame could be established quickly




(for example, with propane-air mixtures), the system would come to equili-




brium in a few minutes.




     Burned-gas temperature measurements were made with 0.005 in. butt-
 Virtis Corp., Gardiner, N.Y.
                                  204

-------
welded platinum platinum-(10 percent) rhodium, silica cooled thermocouples;




the methods used in their preparation and in computing the radiation




correction were those described by Kaskan    .  In the case of the EPA




gasoline, such gas temperature measurements were made for the entire




range of conditions of interest.  For a few flames, the thermocouple was




placed at many locations above the burner surface to learn whether there




were significant lateral variations in temperature attributable to velocity




nonuniformity; none larger than about 18 to 36°F were found even though




the appearance of near-lifted flames that occur with weak mixtures, for




example, did show an observable effect of the proximity of the cooling




tubes to the surface of the sintered copper.  In all the reported measure-




ments, the thermocouple was located at or as close as possible to the




point of maximum temperature in the direction of the hot gas flow, usually




about 0.2 to 0.4 in. above the burner surface.




     Some of these conditions, particularly wherein the burned gas tem-




perature exceeds the melting point of platinum, are rather severe for




the survival of these thermocouples, and it is fairly tedious to make




them.  The gas temperature was frequently obtained from the heat flux




and a careful enthalpy balance; when it was measured in both ways, there




was good agreement between them and with previous data   .




Gas Sampling and Analysis - The burned gas was withdrawn through a quartz




probe 0.04" I.D. x 0.12" O.D. x 1.18" long; it was joined to a 1.18 in.




length of 0.4 in. O.D. quartz tubing, which was connected and sealed to




a 10 in. length of 1/4 in. O.D. thin-walled metal tubing.  The height of




the probe tip above the burner could be adjusted and measured; its lateral




position could also be varied, keeping the quartz-to-metal seal outside




the flame gas column.  From the dimensions and approximate temperature




of the probe and the sample flow rate, it was estimated that the sample



                                  205

-------
cooling rate was approximately 1800°F/msec.  The metal tube was jacketed


with plastic tubing and fittings for water-cooling, and was connected


by polyethylene tubing to a glass trap (to remove liquid condensed from


the sample), and to the inlet of the sampling system.  By placement of


the probe at various distances from the burner, the hot-gas residence


time of the sampled gas could be varied and computed from the burned gas


velocity (which was calculated from the mass velocity and the burned


gas density) and the distance from the probe to the burner.


     The sample could be pumped to the various analytical devices as


shown in Figure 109, using a small diaphragm compressor in the Stack


Sampling Unit that accompanied the NO  monitor referred to later.
                                     A
                                                   3
Typically, the probe sampling rate was about 0.2 in /sec.   This unit


also contained an aftercooler for the compressor, a gas distribution


manifold and a small rotameter which monitored the flow actually de-


livered for analysis.  This flow was generally about  0.1 in /sec, the


balance of the sampled flow being discarded beyond the compressor.


     The 0_ content of the gas was measured with a Beckman E-2 analyzer.


It was done primarily to confirm the actual equivalence ratios, for ex-


ample, when the input fuel flow was uncertain.  The °?/N2 rati° was also


determined by gas chromatography together with carbon monoxide using a


13-X column, helium carrier and a thermal conductivity detector.  It had


been calibrated with CO/O^/N  mixtures prepared from metered flows of


the gases.
                                 206

-------
     A  second  gas  chroraatograph was used  to examine the gases for hydro-



 carbons,  employing a Poropak-N column and a flame ionization detector.



 It  had  been  calibrated with a number of light hydrocarbons; the sensitivity



 was  equivalent  to  1 ppm or less of, for example, CH , C H- or C H,.



     For  nitrogen  oxide measurement by the phenol-disulfonic (PDS) acid


                                                    3          3
 procedure, the  pumped samples were taken  into 180 in  or 300 in  evacuated



 flasks  containing  the required hydrogen peroxide - sulfuric acid solution.



 The  gas sample  pressure was brought to 0.5 atmosphere and the pressure



 was  then  raised to 1 atmosphere with oxygen.  The analysis was made by


                 (22)
 the  PDS procedure



     Measurements  of total NO  were also made with an electrochemical
                             x


 NO   monitor  that was available.  The calibration or span gas used was
  X


 stated  to be 196 ppm NO in N?.  The instrument ±8 convenient since it



 gives a result  in  a few minutes and is far less tedious to use than the



 well-accepted PDS procedure.  The sample pumping and conditioning assembly



 (provided for passing the sample continuously to the monitor) could also



 be  used for  all of the other analytical sampling as well.







     The  instrument is supposedly immune to interferences from other gas



 components including possible hydrocarbons.  In the course of earlier



work, it was noted, however,  that the electrochemical monitor does respond



 strongly  to both acetylene and ethylene,  and if present they will seriously



 interfere.   In a few experiments with unintentionally rich flames in



 the present work, this effect could be quite clearly seen.   Therefore,
 Dynasciences Corp., Chatsworth, Calif.; model NX-130
                                   207

-------
it was used only as a guide in confirming trends.  Though its indications



generally did not grossly disagree with the PDS determinations, they did



tiend to he higher by about 20 percent.  This could not have been due to



hydrocarbons, since they were eventually shown to be entirely negligible;



it now seems likely that the calibration or span gas used was in error



(low in NO) by this amount, since a subsequent PDS analysis of this gas



suggested that its NO content in N  was only about 150 ppm.  It is,



therefore, possible that the instrument itself was performing satisfactorily.



     Emissions measurements of practical interest would actually be made



on the engine exhaust, or in this case at least downstream of the boiler,



and therefore on gas which has been quenched to some extent at a rate



not easily determined.  Such quenching should be very effective on the



NO formation process owing to its large temperature dependence, and the



result will be close to what is actually present in.the hot gas before



the boiler, and also to what is measured by the sampling method used


                                                        (23)
here.  Freezing the CO concentration is much less likely    , and a



measurement on the boiler exhaust is certain to be lower than on samples



obtained with much faster cooling, such as that in the sampling pro-



cedure used here.  But in any case, the measured concentration may well



be low.



     It was not feasible nor considered essential to provide a cooler



equivalent to the boiler for the present work, so the [CO] determinations



no doubt represent levels intermediate between the true values at the



high temperature and the values of ultimate practical interest.  Thus,



they represent upper limits to the emissions levels that would be ob-



served in practice, but lower limits to what is actually present at the



burned gas conditions.




                                  208

-------
Fuels - CP propane was taken from a standard 100 Ib liquified petroleum



gas container and the toluene was also CP reagent.  Prior to receipt of



the specified EPA gasoline, some work was done with AMOCO Super Premium



(no lead, no phosphate).  Its specific gravity was 0.76 at 76°F suggest-



ing a considerable content of aromatic material; it was not analyzed for



hydrogen-carbon (H/C) ratio, but based on a subsequent inquiry of the



manufacturer's representative, it was taken to be about 50% toluene,



50% paraffins, with a gross composition equivalent to C7H   for approxi-



mate stoichiometry estimates.  Similarly, the specific gravity of the



EPA gasoline was 0.755, and though its aromatic content is specified to



be lower, its allowable olefin content is much higher (about 30%), so



its combustion stoichioraetry was expected to be very close to that of



AMOCO, which also accords with subsequent 0  analyses of the combustion



products.



     These three liquid fuels were analyzed for bound nitrogen with these



results:



                  AMOCO Super Premium         11+5 ppm N



                  Toluene                     24+5 ppm N



                  EPA Gasoline                33+5 ppm N



     This N content could account for at most a few ppm of NO  in the



burned gases    , which would be within the likely error of the analysis



and was ignored in considering the emission results.



     Near the conclusion of this work, some NO  formation measurements,
                                              X


also reported here, were made with one other liquid fuel (CP n-heptane)


                        2
using a smaller (15.5 in ) but similar water-cooled burner, in which the



burned-gas temperature was directly measured.  The intent was to examine
                                   209

-------
 for NO  formation some flames of a fuel with H/C ratio near that of
       K


 propane,  but of molecular weight in the range of the other fuels.



 Data Reduction and Correction - Where preheated air was used,  a correction



 to the measured heat flux was applied to obtain the values presented



 which are referred to an initial condition of 76°F.  This correction can



 be shown to be:





                       6F = 2.13 V   (T    -76) Btu/hr-ft2          (12)
 with sufficient accuracy.   The unit of the terms in Eq.  12 are V?_ in



 en/sec and T    in °F.   For example,  with T    = 230°F and V   = 25 cm/sec,
             Ai r                            AT r              2.J

                    2
 6F = 8200 Btu/hr-ft .   Although it is at most  only a few percent of the



 total enthalpy flux, it is a significant fraction of the measured heat



 flux.  (The burner heat flux,  F,  is only 10 to 30% of the total combus-



 tion flux, but it must  contain all of the effect of the preheat, so long



 as the burned gas temperature depends only on  the mass velocity (V_,.);



 6F/F can therefore be as high as 25%.)



      The heat-balance calculation of the burned gas temperature from the



 heat flux thus corrected was done as follows.   For the calculated adiabatic



 flame temperature (T )  of the mixture initially at 76°F, a value of the
                     3


 enthalpy of the mixture was obtained, from which was subtracted this



 correction, Ah:
             Ah = (Fb/V25) x   ^    = hT - hT  (Btu/lb gas)         (13)

                               m        a    b



 in which F,  is the corrected burner heat flux, m is the average molecular
           b


 weight of the burned gas and the constant is a conversion factor to ob-



, tain the result in the engineering units usually tabulated.  The enthalpy



 at the calculated adiabatic flame temperature is h  , while the enthalpy

                                                    a

                                    210

-------
                                                   (24)
at the burned gas temperature is h  .  These tables     have been com-
                                  Tb
piled for various fuel-air mixtures which generally do not correspond
                     •»
exactly to the fuels and compositions encountered here.  But we are

only interested in enthalpy differences which do not vary significantly

with the H/C ratio of the fuel for a given equivalence ratio, R, and

temperature interval, and it is readily shown that the temperature decre-

ment is obtained in this way with ample accuracy.  Thus, with the quanti-

ties h   and Ah, h   is obtained and the corresponding burned gas tem-
       a           b
perature, T , is read or interpolated from the table.

     In view of the fairly low H/C ratios of toluene and the two gaso-

lines, some attention was given to estimates of the adiabatic flame tem-

peratures, or at least how much they should differ from that of propane-

air for a given equivalence ratio.  The difference (mainly due to the

stoichiometry) would not be expected to be large; but owing to the great

sensitivity of NO  formation rate to temperature and the way in which
                 X

T  was used when the actual gas temperature was estimated from the heat
 3

flux, it seemed desirable to compute the difference with some care.  The

unit heating value of the stoichiometric mixture of air with the vapors
                                                                2
of each of the three liquid fuels was computed to be 94.5 Btu/ft  + 0.11

(76°F, 1 atm) for all of them, or 4.5% higher than the corresponding
                                  3
value for propane-air (90.6 Btu/ft ).

     A correlation can be made between the trends of these unit heating

values with accurately calculated adiabatic flame temperatures, for

various classes of hydrocarbons of varying H/C ratio and molecular weight.

It shows that the 4.5% difference should result in a 45 to 54°R higher

value of T ; for stoichiometric propane-air (R = 1), T  is 4091°R, so

for the three liquids at R = 1 in air, a value of 4140°R is estimated.

                                  211

-------
There are also available a  few  calculated values  for  toluene,  benzene,


                                                                       (25)
cyclohexane,  etc., mostly for various  rich mixtures  (R =  1.05  to  1.17)



that can be  compared with the corresponding values for propane-air;  this



comparison also  indicates a difference of about 45°R.  The  value  of  4140°R



for R = 1 was therefore assumed,  and with similar estimates of the dif-



ference for  lean mixtures,  a plot of T vs. R was made from the computed
                                       cl


values for propane-air mixtures.  In no case is the estimate believed



to be in error by more than +^ 9°F.



Measurements  of  Heat Flux and Burned Gas Temperatures



     Figures  110 and 111 summarize  the heat flux  data, corrected  to  76°F



in the manner previously described, for propane-air mixtures and  for EPA



gasoline-vapor air mixtures.



     The burned-gas temperatures, largely computed from the heat flux



data,  are shown in Figure 112 for propane and EPA gasoline, and other



data derivable in part from  these plots are also summarized in Table 14.



Similar data giiTnma-Hp.fi for  the toluene  and AMOCO gasoline-air mixtures



are also shown in Table 14.   In the case of the EPA gasoline,  direct



measurements of  the gas temperature by  thermocouple, as well as the



indirect measurements from  the heat flux data, were generally  made; on



the whole, these were in very good agreement (within 54°R)  and the lines



shown in Figure  112 average  these temperatures.




     The data for propane-air mixtures in Figure  112  can  be compared with



those of Kaskan     and the agreement  is excellent.  There  are no data



in the literature with which the  results for the  other fuels could be



compared.  The heat flux data were  in  this case extended  further  toward



the adiabatic flame condition, well beyond the range  of interest  for this



application.  Although it has no  practical consequences in  the present




                                  212

-------
         40,000
N>

I-"

U>
     \->
    jz

     P
     OJ


     M


     PQ

     QJ
     O
     4-1
         30,000
20,000
         10,000
     id
     0)
                                                                                                          R = 1.0
                                                                                                   =  0.9
                                                                                   R = 0.8
                                        10
                                                       20
30
                                                 Superficial  Velocity,  V  ,  era/sec
                                        Figure  110.
                                             Burner Heat Flux Back to the Burner from

                                             the Flame; Propane-Air Mixtures
40

-------
    40,000
    30,000
I
                                                                                    R = 0.9
M
OJ
C
M
0)
.C
id
PQ
cd
0)
a:
    20,000
    10,000
                      R = 0.8
                R = 0.7
                                  10
20
                                           Superficial Velocity,  V   ,  cm/sec
30
40
                              Figure 111«  Burner Heat Flux  Back to  the Burner from the

                                           Flane; Gasoline  (EPA)-Air Mixtures

-------
   100
                             Absolute Temperature, T, °R
u
•H
U

o
n)
•rJ

0
O

§•   10
                  o
                  o
                  o
                  I
                 o
                 o
                                          CM

                                          CO
             o
             o
             o
             P-I
                     Propane-Air
             o
             r»
             r^
             CM
                                                               Gasoline-Air
                                                       Data From:

                                             Thermocouple       Heat Flux
Gasoline (EPA)-Air Flames R = 0.7

                          R » 0.8

                          R =• 0.9
                                                                    O

                                                                    D
             Propane-Air Flames
                          R " 0.8	

                          R - 0.9	
                              I
                                                       I
                 4.5
                5.0
5.5
6.0
6.5
                   Reciprocal Absolute Temperature,  [1/T(°K)  x 10 ]
        Figure 112. Comparison of Gasoline  (EPA)  and Propane-Air Burned Gas

                    Temperatures
                                         215

-------
                            Table  14„ RANKINE MODEL BURNER TEST RESULTS

Fuel
C3H8

Toluene


AMOCO

EPA
Gasoline

R
0.83
0.95
1.0
0.68
0.78
0.86
0.88
1.0
0.70
0.80
0.90
Btu/ft3
76.1
86.0
90.6
64.4
73.7
81.3
83.1
94.5
66.2
75.6 .
85.1
F
raax _
Btu/hr-ft
23200
31500
36500
15900
23900
34500
27900
41800
19200
25200
37200
V25,ra
cm/sec
15
18
20
12
16
18
17
19
15
17
19
p
0.18
0.17
0.17
0.18
0.18
0.20
0.17
0.20
0.17
0.17
0.20
max
°R
3330
3550
3640
3060
3310
3490
3510
3600
3130
3310
3492
T
a
°R
3760
4010
4090
3330
3710
3890
3940
4140
3440
3730
3960
S
u
cm/sec
37
42
43
24
35
38
41
43
30
39
43
E
Btu/
( Ibm-mole)
99000
97200
95400
108000
110000
97200
108000
89100
99000
97200
93100
Stoichiometric (R = 1.0) F/A ratios by weight:
     Propane 0.0641     (0.0420 by volume)
     Toluene 0.0740
   Gasolines 0.0703

-------
context, an interesting incidental observation is that the heat  flux



apparently does not tend toward zero as V_,. approaches the adiabatic



burning velocities for these mixtures.  There would evidently be a  resi-


                                      2

dual heat flux of about 8200 Btu/hr-ft  which is no doubt due mainly  to



radiation from the flame to the cold burner surface.  From the emissivity



of such flames (estimated as about 0.03), the radiative flux in  such  a



geometry should be approximately of this magnitude.  If it is computed



for each condition and subtracted from the measured values, the  remainder



then does tend to zero as the unburned gas velocity, V-,, approaches  the




adiabatic burning velocity, S .



     In Table 14, h is essentially the lower heat of combustion  of  the



(gaseous) fuel per unit volume of the mixture (76°F, 1 atm).  F
                                                               D ^ITlcOt


and Voc   are respectively the maximum heat flux and the unburned mix-
     /j,m


ture velocity at which it occurs.  The fraction  6  ( F,     /h      )
                                                  m    b.max  v,...
                                                               25,m

is the fraction of the enthalpy flux rejected to the burner at the maxi-



mum heat flux.  The maxima, as seen in Figures 110 and 111, are  of  course



rather flat, so that the designation of Voc   and 3  are somewhat arbi-
                                         25,m      m


trary; they are included as possibly useful for design purposes.  T

                                                                    max

is the flame temperature at which the heat flux back to the burner  is



a maximum.



     T  is the calculated adiabatic flame temperature and S  is  the normal
      H                                                    U


burning velocity of the mixture (that is, Su is the value of V25 which occurs



at the temperature,  T ) obtained by extrapolation (Figure 112) and
                     a



noted as a matter of general interest.  E is the apparent "activation



energy" indicated by the slopes of these lines:  E = -4606 R (d(log _V  )/



d(l/T)).  R is the universal gas constant, R = 1.9859 Btu/°R Ibm-mole.



The last three columns would suffice to determine the temperature de-




                                  217

-------
pendence of V  .   For a given V   and R, there is little difference in




the actual burned-gas temperature for a given fuel.   At least, for the




hotter flames (near R = 1), the higher initial enthalpy content (h) of




the higher molecular weight fuels seems mostly to enhance the burner




heat flux rather than the burned gas enthalpy.




     It is worth noting that, where both were measured, comparison of




the directly measured temperatures and those computed from the heat flux



                                                                 ( 6 )
shows little, if any, of the kind of disagreement noted by Kaskan     in




comparing his results with other data computed from heat flux measure-




ments    .  To the extent that combustion is not entirely complete in




the flame itself, it might be expected that those temperatures calculated




from the heat flux would be somewhat higher; but if there is such a con-




sistent difference here, it appears to be no more than about 54°R which




is about the expected uncertainty in the temperature anyway.  Similarly,




any calorimetric losses associated with the heat flux measurements would




also result in a higher computed gas temperature.  It appears that neither




source of error could have been significant.




Emissions Measurements




Carbon Monoxide - The analytical results are given in Table 15 as the




measured concentrations in samples taken about 20 msec from the flame.




Many of them are at or below the equilibrium concentrations corresponding




to the burned gas conditions.  Some analyses were also made on samples




taken closer to the flame where [CO] was found to be considerably higher




than equilibrium, and the expected decay behavior could be qualitatively




observed as shown for a few cases in Figure 113,




     No quantitative interpretation or kinetic analysis of the measure-




ments was attempted for reasons discussed below; but the measurements do


                                   218

-------
                     Table   15c  RANKINE MODEL BURNER EMISSION RESULTS





W
d[NO]
dt
ppm/msec



C H





AMOCO

Toluene



Gasoline
(EPA)








R
Dim.
0.93
0.93
0.93
0.83
0.83
0.83
0.96
0.88
0.95
0.86
0.78
0.68
0.89
0.88
0.86
0.77
0.78
0.76
0.78
0.70
0.68
v
V25
cm/sec
25
20
15
25
20
15
25
25
—
20
20
20
25
20
15
25
20
15
15
25
20
T
Xb
°R
3690
3570
3430
3540
3440
3330
3780
3690
—
3470
3370
3260
3650
3560
3380
3490
3350
3200
3130
3420
3220
[Measured]
Ppra
n D Prompt [NO]
NO
Meas.
0.95
0.25
0.17
0.56
0.27
0.05
8.0
7.5
—
1.8
1.0
0.3
3.4
—
—
1.0
—
0.06

—
—
"NO
Calc.
0.64
0.26
0.05
0.22
0.10
0.03
1.2
0.86
—
0.23
0.07
0.02
0.47
—
—
0.19
—
0.02

—
—
Meas.
(Approx.)
25
15
10
7
6
5
—
—
—
30
15
10
25
—
—
35
—
15

— -
—
Pred.
1 Est.
15
12
10
5
5
5
25
20
—
15
*\j j
% 0
20
—
—
•HO
—
% 5

—
—
ppra
[NO]
20M
sec
ppm
[CO]

PDSa) (DYN)b)20M sec
44
20
14
19
12
6
160
150
—
65
35
15
90
—
—
55
—
18

—
—
(38)
—
—
—
—
—
—
—
—
(69)
(31)
(31)
(77)
(77)
(51)
(59)
(38)
(25)

(38)
(21)
500


150
	
	
1500
	
1500



1200
800
400
600
400
< 100

200
^ 100
[CO]ea
eq.
(T }
(v
1100


700


3000

1200



1200
720
300
600
350
145

200
65
a)
   Phenol disulphonic acid method
b)
   Dynasciences electrochemical NO  monitor
                                  X

-------
    2200
    2000
     1800
e
o.
Q.
O
    1600
     1400
     120C-
                         A
                         A
                                           Gasoline/Air


                                           Equivalence Ratio


                                           R * 0.9
                                  25 cm/sec, T * 3600°R
c
0)
o
c
o
100(
•o
0)
3

W)
      80(
      60C-
                     D
                                       D
                                           Propane


                                           R ~ 0.9
                                                D

                                                D
      20(
                         A
                                  A
                                                Propane/Air
                                                        I
                    5          10          15           20


                         Residence Time, Milliseconds




                   Figure 113,  CO Analyses from Two Flames



                                        220
                                                               25

-------
adequately show that, with this hot gas residence time, and a practically


attainable quenching or cooling rate in the boiler, the CO emission would


be less than the specified level, which is equivalent for the average


operating condition to about 800 ppm.  A few of the measured values in


Table 15 apparently exceed this level, but they too would certainly fall


below 800 ppm in the boiler; the values given represent an upper limit


to what can be expected of the engine.

                                                        (jfi\
     In this connection, it has been shown in other work     with a


geometrically similar burner system, that a large reduction in [CO] does


occur across such a downstream heat exchanger; it was found to decrease


by more than an order of magnitude to values typically corresponding to


equilibrium at temperatures lower than 3240°R.  Whatever the analysis


or interpretation of this process may be, as a practical matter,  a


similar reduction must occur in any similar device.


     The CO data given in Table 15 was converted to the Bnission Index


and is plotted for all the fuels tested in Figure 114.  The bulk of the


data falls below the level corresponding to the original 1976 Federal


Standard, especially at the lower values of superficial velocity (V~c)


or lower power levels.  At some of the higher values of superficial


velocity (V25) and hence higher power levels, the measurements are above


the level of the Standard for gasoline burned at an equivalence ratio


of 0.9.  However, it is expected that the CO emissions averaged over a


duty cycle would be below the Standard since a large fraction of the


duty cycle occurs at the lower power levels.

Hydrocarbons - Most of  the  sampling  for  this  purpose was done at residence


times  of 10  to 20 msec;  in  no  case with  any of  the  fuels was any hydro-


carbon detected; it is  concluded  that with any  reasonable excess air


there  will be essentially  zero  (<1  ppm)  emission  of hydrocarbons from


                                  221

-------
100
 10
1.0
            FUEL
          •  C3H8
          V  AMOCO
          D  GASOLINE (EPA)
          •  GASOLINE (EPA)
          [|  GASOLINE (EPA)

          1 ATMOSPHERE
                I            I
               EQUIVALENCE
                  RATIO

                   .83

                   .93

                   .96

                   .68-.70
                   .76-.78
                   .86-.89
CO FEDERAL STANDARD
(3.4 GM/MI)
                   GASOLINE
                            I
                            I
I
                           10          15           20

                       SUPERFICIAL VELOCITY, V25/ CM/SEC
                                                    25
   Figure  114.  CO Experimental Measurements on Water-Cooled Burners
                with 20 Milliseconds Residence Time
                                    222

-------
burners of this kind.  In fact, it was generally observed that  the normal

background CH, concentration  (1.0 to 1.2 ppm) was, if anything, decreased

by the flame.

Oxide of Nitrogen - Most of the results summarized in Table 15, were ob-

tained at conditions similar  to but not necessarily identical with those

in the thermal tests just described, since they were not usually done

simultaneously.  The main interest here is in the NO  formation data,

compared in Table 15 and Figure 115 with the computed values to be ex-

pected by the thermal or hot-air mechanism; with the assumption of [0] =

[0]  , the equation of the solid line was obtained; for combustion products

at 1 atm with 0_ mole fraction (N  ):


                               18   -136.500

      RJJQ E d[NO]/dt = 3'3 *  10   e    RT     (NQ )1/2 (ppm/millisec)  (14)


from the same basic kinetic data used by Fenimore    .  The present estimate

of the NO formation rate in Eq.14 is about 30% higher than the original

estimate given in Figure 3; this correction was made after more careful

consideration of the relevant kinetic data.  The line (practically straight

in this temperature interval) was calculated for an oxygen mole fraction,

N   = 0.02, and the data were adjusted or normalized to this oxygen content
 U2
to facilitate comparisons at a fairly representative excess air condition.

This oxygen content corresponds to an equivalence ratio of R = 0.91.

      The individual rates were obtained from the slopes of linear plots

of the analytical results versus the time from the burner, and the "prompt

NO" was obtained from the intercept at zero time in essentially the manner

described by Fenimore    .  The "predicted estimate" of the prompt NO was

made from Fenimore's data with the assumption that it would be the same for

all hydrocarbon fuels at the same equivalence ratio.
                                    223

-------
                              Temperature,  °K
           00
           o   o
           in   »»
           IN   CM
                           0
                           o
                           ro
O
O
CM
CM
O
O
O
O
o
O
o
O
o
00
Q.
Q.
0)
4J

10
C
O
10
e
o
u,
to
    10
   1.0
   0.1
  0.01
                                             Equation 14
	  Original Line    y

-    From Fig.  3	A
      Data Adjusted to

      2%  02 Mole Fraction
             O  Propane

             Q  Heptane

             ^  Toluene

             X  EPA Gasoline

                AMOCO
                              4.5
                                               5.5
                  Reciprocal Burned Gas Temperature,  [1/T(°K)  x 10 ]
        Figure 115. Variation of NO Formation  Rate from "Hot-Air" Mechanism as

                    a Function of Reciprocal Absolute  Temperature.  NO Formation
                    Rate  Adjusted  to 2% Molar 0^

                                        224

-------
     The errors in both the thermal NO  derived from the slopes, and in
                                      x                     *  '


the intercepts are no doubt large.  There were usually too few observa-



tions to warrant any assumption other than linearity or constant R^  at



a given condition; in no case were there more than three sampling posi-



tions (for example, at 1.0, 2.0 and 3.0 cm from the burner) and frequently



only two were taken.  The uncertainty in R^  may be as much as 50%



and the intercepts may be in error by 5 or 10 ppm,  (though there was



no case in which there appeared to be no intercept at all), but the



tabulated values at 20 msec in Table 15 would be in reasonable accord



with a measurement at that residence time (taken as appropriate for the



present application and representing what would be found in the engine



exhaust), whatever the distribution between prompt and thermal NO  may
                                                                 A


be.  The uncertainty in these values of [NO ] at 20 msec is estimated
                                           X


as no more than 30%.



     With these reservations concerning their accuracy, the data may be



compared with the calculated line, bearing in mind this also has a likely



uncertainty of about + 30%.  The data for propane-air flames may be said



to agree reasonably well;  they lie within a factor of two of the calculated



values,  and this may be little outside the combined errors.



     For the other four fuels, a single line could represent well enough



all the data, but everywhere it would be just about an order of magnitude



higher;  alternatively, the disagreement with the predicted line is equiva-



lent to about 270°R for a given rate, or by 180°R relative to the propane



data.   In any case, it is too large to be accounted for by experimental



errors in either the analyses or in the temperature measurements.  (The



possible contribution of fuel nitrogen had been anticipated, but the



analyses mentioned earlier showed that it could account for at most only




                                  225

-------
a few ppm in the burned gases.)



     Thus, the measured formation rate of NO, at least for the fuels of



high average molecular weight exceeds by about an order of magnitude the



rate expected or calculated with the assumption that [0] = [0]  .  The



conclusion seems inescapable that the actual [0] averaged over the resi-



dence time (^ 20 msec) must in fact be higher by a factor of five or



more.  Since the oxygen concentration must be decreasing toward equili-



brium and would be expected to attain [0]   in this time, the oxygen



concentration nearer the flame would have to be still larger.  It should



be noted that the plotted data do not include the contributions, shown



in Table 15, of the intercepts or prompt NO.  Had they been arbitrarily



included in averaging the rate, the results would be somewhat higher



still.  It seemed reasonable to separate its contribution however, since



it does appear to be real and generally agrees satisfactorily with data



though the possibility that it too results from excess [0] cannot be en-



tirely ruled out by these results.



     There have been many investigations of the emission of nitrogen



oxides from combustors and engines with a variety of fuels, including



some similar to those used in this work; unfortunately, there appears



to have been none with preraixed flames of hydrocarbons higher than



propane, with which the data given here can be directly compared.  There


                                                        f 26 ^
has been reported one rather detailed experimental study     and analysis



of NO formation in a preraixed, quasi-one-dimensional propane-air flame



system,, With near-adiabatic flames of one equivalence ratio (R = 0.8),



estimates were made of the variation of the rate with time for up to 15



msec from the main zone of flame reactions.  The maximum instantaneous



rate a few msec from the flame appeared to be an order of magnitude or



                                  226

-------
more higher than would be predicted from Eq.14, generally decreasing



thereafter.



     For the same burned gas temperature, and for roughly comparable



burned gas conditions, an average d(NO)/dt computed over a residence



time comparable with that considered here (about 20 msec) would be about



a factor of two higher than that measured in the present work; it would



more nearly agree with the data for higher hydrocarbons (Figure 115 and



Table 15).  In view of the differences in equipment and approach, the



agreement may be reasonable; but from either set of results, it has to



be concluded that the NO formation rate is considerably higher than



Eq.14 would suggest, whatever the detailed interpretation may be.



     The failure of the approximation or assumption that [0] = [0]   in



the burned gases of hydrocarbon flames has been discussed by others in



the context of NO formation; it formed the basis for interpretation of


                        (2ft)
the data just mentioned,     and in the following generally similar dis-


                                                                   (27)
cussion, its connection with CO and its afterburning is considered.



     That higher-than-equilibrium concentrations of free radicals do



occur in post-flame gas has been shown in many experimental studies.



The nature of the chemical processes involved, the partial equilibrium



state, and the subsequent relatively slow radical recombinations are

                /2g\

well established     and need not be elaborated here; but it is worth



notinp, that the slow decay or "afterburning" of CO in lean hydrocarbon-



air flame gases is intimately connected with such excess radical con-



centrations.  It is known that the afterburning is really a recombination


       (27 29)
process   '    in which CO is in effect one of the radicals in excess



of equilibrium.  It is connected with the others through the equilibrium
                                  227

-------
constant for the balanced reaction:




                         CO + OH =• CO  + H                          (15)


And through similar relations for the other balanced reactions, in


effect:



                         CO + 02 = C02 + 0                          (16)


is also balanced.  In the products of lean flames [CO] must then be just


proportional to [0] or [0]/[0]   = CO/[CO]   and will always be greater than


unity during the afterburning of carbon monoxide; the rate of formation of NO


will then be larger by this ratio also.



     For reasons discussed previously, the [CO] measurements summarized


in Table 15 may have no really quantitative meaning; the true [CO]  in


the burned gas must be higher than that measured owing to uncertainties


in the sampling procedure.  But even from these data it is qualitatively


clear that [CO] does, as expected, decrease from levels considerably


higher than equilibrium.

                                                      (29)
     There appears to have been only one investigation     in which ex-


cess radical concentrations were determined and directly related to [CO]


and its decay in the burned gas of a lean hydrocarbon flameo It was an


ethylene-air flame at 3528°R at an equivalence ratio of 0.82, and  [CO]/[CO]e


about 1 msec after the main reaction zone of the flame was approximately


10, decreasing to approximately 5 in the 6 msec period observed.  This


ratio might have approached unity in roughly the time of interest here


(20 msec), during which its average value and therefore [0]/[0]


evidently would have been about 5.                  •   ...


      If  it is assumed that this ratio (deduced from only one set of data)


applies to the lean burned gases of other hydrocarbons, and that the



                                 228

-------
ratio has no temperature dependence, a line parallel to the predicted




line (Figure 115) could be drawn; the data would generally lie within a




factor of two of this adjusted prediction.  Within the likely errors of




the data, this could then be considered fair agreement.




     The fairly consistent difference between the results for propane




and the other fuels (Figure 115) is still unexplained.  Assuming the




validity of and extending the argument above, it would be inferred that




[CO]/[CO]   following the main reaction zone is appreciably higher in




flames of these higher hydrocarbons.  There is some indication of such




a tendency in data obtained here; but it would be worthwhile to investi-




gate this point (using, for example, optical techniques   '   ) that




would permit an unequivocal determination of [CO] or its equivalent in




the actual burned gas conditions of such flames.




     The NO  data shown in Table 15 was converted to Emission Index and
           X



is plotted for all the fuels in Figure 116,  as a function of superficial




velocity, V  ,  and equivalence ratio.  Some of the individual NO  values




for gasoline burned at an equivalence ratio of 0.9 are above the level




of Federal Standard at high values of V  ; however,the NO  values at the




lower values of V - (or lower power) are well below that of the Standard,




and it is expected that the N0_ emissions averaged over a duty cycle would




be below the Standard since a large fraction of the duty cycle occurs




at the lower power levels.




Summary and Conclusions From Bench Tests




     The thermal and emissions characteristics of some non-adiabatic




hydrocarbon-air flames at 1 atmosphere have been determined for use in




the design of a transpiration (cooled porous metal) burner for the com-




bustor boiler of a low-NO  Rankine cycle engine.  Flames of mixtures
                         X


                                 229

-------
     10
o
o
     1.0
2;
O
UJ
 CSI
O
     0.1
[J
FUEL
C3H8
SH8
AMOCO
AMOCO
TOLUENE
TOLUENE
TOLUENE
GASOLINE (EPA)
GASOLINE (EPA)
GASOLINE (EPA)
                                            I
                                 EQUIVALENCE
                                    RATIO
             N0? FEDERAL STANDARD
        	  CO. 4 GM/MILE)
                           GASOLINE
            SYMBOLS WITH FLAGS C U ) ARE NO
            DATA MEASURED WITH DYNASCIENCE
            ELECTROCHEMICAL MONITOR
                    I
                               10
                           15
                                          20
25
                            SUPERFICIAL VELOCITY, V    CM/SEC
          Figure  116.  NC>2  Experimental  Measurements  on Water-Cooled Burners With
                       20 Milliseconds Residence  Time
                                               230

-------
of air with propane and with prevaporized toluene, heptane and two gaso-


                                  2
lines were stabilized on a 30.3 in  water-cooled porous copper burner.



Burned gas temperature as a function of mixture mass velocity and equiva-



lence ratio was determined for each fuel, and other related flame para-



meters were computed and summarized.  The temperature was obtained either



from direct thermocouple measurements or from the measured burner heat



flux and a heat balance; when both were made on the same flame, they



agreed well.



     Determinations of NO , CO and hydrocarbons were made on probe



samples with hot gas residence times up to about 20 millisec.  Hydro-



carbons were found to be <1 ppm and thus negligible from any flame ex-



amined (R £ 0.95).  The absolute concentration levels of carbon monoxide



as measured are of doubtful significance, but the decay of [CO] from



values much higher than equilibrium could be observed.  The levels es-



timated for practical engine exhaust conditions are expected to be



satisfactorily Iower0



     From the measured NO  concentrations, the rate of the thermal or
                         x


hot-air formation of NO in the burned gas was estimated and correlated



with the measured burned-gas temperatures.  It was compared with the



prediction from accepted kinetic data, with the assumption that [0]  =



[0]   ; the measured rates are all higher than predicted, and for the
   equ


fuels of higher molecular weight,  by about an order of magnitude at all



observed temperatures (3240°R-3780°R).



     It is concluded that the average [0] must correspondingly exceed



[0]   and the probable connection between this excess and [CO] is dis-
   eq


cussed.
                                  231

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                              REFERENCES






(1)  Amann, C.A., W.R. Wade, and M.K. Yu.  Some Factors Affecting Gas




Turbine Passenger Car Emissions.  SAE Paper 720237. 1972.




(2)  Wade, W.R., P.I. Shen, C.W. Owens, and A.F. McLean.  Low Emissions




Combustion for the Regenerative Gas Turbine:  Part 1 - Theoretical and




Design Considerations.  ASME Paper 73-GT-ll.  1973.




(3)  Azelborn, N.A., W.R. Wade, J.R. Secord, and A.F. McLean.  Low




Emissions Combustion for the Regenerative Gas Turbine:  Part 2 - Experi-




mental Techniques, Results, and Assessment.  ASME Paper 73-GT-12.  1973.




(4)  Wohl, K.  Quenching, Flashback, Blow-off - Theory and Experiment.




Fourth Symposium on Combustion.  1953.  p. 68-89.




(5)  Botha, J.P. and D.B. Spalding.  The Laminar Flame Speed of Propane




Air Mixtures with Heat Extraction from the Flame.  Proc. Roy. Soc.




(London).  A225; 71-96, 1954.




(6)  Kaskan, W.E.  The Dependence of Flame Temperature on Mass Burning




Velocity.  Sixth Symposium on Combustion.  1957.  p. 134-143.




(7)  Fenimore, C.P.  Formation of Nitric Oxide in Premixed Hydrocarbon




Flame.  Thirteenth Symposium on Combustion.  1970.  p. 373-380.




(8)  Barnett, H.C. and R.R. Hibbard, (ed.).  Basic Considerations in the




Combustion of Hydrocarbon Fuels with Air.  NACA Report 1300.  1957.  p. 135.




(9)  Schneider, P.J.  Conduction Heat Transfer.  Addison-Wesley, 1955.




p. 218-221.




(10) Barnett, H.C. and R.R. Hibbard, (ed.).  Basic Considerations in the




Combustion of Hydrocarbon Fuels with Air.  NACA Report 1300.  1957. p. 1-31.





                                   232

-------
(11)  Wukusick, C.S. and J.F. Collins.  An Iron-Chromium-Aluminum Alloy




Containing Yttrium.  Materials Research and Standards.  December  1964.




(12)  Cundiff, J.W.  Superalloy Improves Anti-Smog Devices  for  Autos.




Metal Progress.  September 1972.




(13)  Madsen, P. and R.M. Rusnak.  Oxidation Resistant Porous Material




for Transpiration Cooled Vanes.  NASA CR-1999.  1972.




(14)  Adarasky, R.F.  Oxidation of Silicon Carbide in the Temperature




Range 1200°F to 1500°F.  J. Physical Chemistry.  £3:  305-307.  1959.




(15)  Jorgensen, P.J., et al.  Oxidation of Silicon Carbide.  J.  Am.




Cer. Soc. 42;  613-616.  1959; Effects of Oxygen Partial Pressure on




the Oxidation of Silicon Carbide.  J. Am. Cer. Soc. 43;  209-212.   1960.




(16)  Automobile Gas Turbine-Optimum Cycle Selection Study.  General




Electric Report GESP 730 FS.  June 1972.




(17)  Fenimore, C.P.  Formation of Nitrogen Oxides from Fuel Nitrogen




in Ethylene Flames.  Combustion and Flame, 19;  289.  1972.




(18)  Siegler, M. and G.E. Moore.  Flame Recombination of Oxygen  and




Hydrogen.  Chem. Engrg. Prog. Symp., ,66.:.l.  1970.




(19)  U.S. Patent 3,589,184 (1971) (Continuous Flow Gas Calorimeter).




G.E. Moore.




(20)  U.S. Patent 3,672,839 (1972) (Exothermic Gas Generator).  G.E. Moore.




(21)  Bahr, D.W.  Evaporation and Spreading of Iso-octane Sprays  in High




Velocity Air Streams.  NACA-RME 531.14.  November 1953.




(22)  Oxides of Nitrogen in Gaseous Combustion Products (Phenoldisulfonic




Acid Procedure).  ASTM Test Method Specifications Designation D-1608-GO,




reapproved 1967.




(23)  Halpern, C. and F.W. Ruegg.  A Study of Sampling of Flame Gases.




J. Res.  NBS, 6_0:  29-37.  1958.




                                  233

-------
(24)  Fremont, H.A. et al.  Properties of Combustion Gases - System




C H  -Air.  General Electric Co., Cincinnati, Ohio.  1955 and Kutzko, G.G.




Properties of Combustion Gas-System CH.-Air.  General Electric Company.




R68AEG161.  1968.




(25)  Fristrom, R.M. and A.A. Westenberg.  Flame Structure.  McGraw-Hill,




1965.  p. 22-23.




(26)  Williams, G.C., A.F. Sarofim, and N. Lambert.  Nitric Oxide Forma-




tion and Carbon Monoxide Burnout in a Compact Steam Generator.  Symp.




on Emissions from Continuous Combustion Systems.  Plenum Press, 1972.




p. 141.




(27)  Schott, G.L.  Comments on Article by Robert F. Sawyer and Trilochan




Singh.  Co-reactions in the Afterflame Region of Ethylene/Oxygen Ethane/




Oxygen Flames.  Thirteenth Symposium on Combustion.  1970.  p. 403-415.




(28)  Fenimore, C.P.  Chemistry in Premixed Flames.  Macmillan, 1964.




(29)  Kaskan, W.E.  Excess Radical Concentrations and the Disappearance




of Carbon Monoxide in Flame Gases from Some Lean Flames.  Combustion and




Flame (London).  J3:49-60.  1959.




(30)  Kaskan, W.E.  The Source of the Continuum in Carbon Monoxide-




Hydrogen-Air Flames.  Combustion and Flame (London).  _3:39-48.  1959.
                                   234

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                                APPENDIX A








                        COMBUSTOR TEST  FACILITY








     The combustor test facility is located in the Gas Dynamic  Facility




No. 1 of Bldg. D and is shown in simplified schematic form  in Figure A-l




     The facility was designed  for l/5th or full scale automotive gas




turbine combustor testing.  The design  criteria are as follows:




     1.  Primary Air Flow 0.031 - 0.4 pps to 400°F




     2.  Secondary Air Flow .75 - 2.25 pps to 1400°F




     3.  Fuel Flow (Gasoline) - 6 Ib/hr to 75 Ib/hr ambient temperature




     The plant air supply (100 psig) is fed through a filter from which




it is split to provide air to both the primary and secondary flow metering




stations.  Pressure regulating valves ahead of the metering tubes (sharp




edge orifice type) control the orifice upstream pressures.  The primary




metering system consists of three orifice metering tubes in parallel to




cover the 13:1 flow range required.  Remote operated pneumatic actuated




valves are used to direct air flow through the proper orifice.  A down




stream flow control valve can be used in conjunction with the combustor




back pressure valve to control combustor pressure and primary air flow.




Shown in Figure A-2are the test cell flow metering sections and the pri-




mary and secondary flow heaters.




     The primary  heater is electrically powered from an adjacent substation.




The power control system consists of ignitions with firing rate varied




to control voltage and current to the resistance type air heaters.




     The secondary air system is basically the same as the primary, how-





                                 235

-------
Figure A-l
 GDFI

-------
N3
                                       Figure A-2.  Test Cell Heaters and Flow Metering  Sections

-------
ever only one orifice metering station is required to cover the air flow




range.




     Cooling water is injected into the corabustor discharge gas stream




prior to entering the butterfly type back pressure valve.  Water flow is




automatically controlled to maintain a maximum temperature of 500°F




entering the back pressure valve.  An exhaust silencer discharges the




gases and water vapor vertically to the atmosphere.




     The fuel system consists of a 250 gallon storage tank equipped with




a float for level indication and located outside of the test area.  A




saall BOtor driven gear type pump with pressure regulating valve and by-




pass return to the tank Is located adjacent to the storage tank.  Fuel is




fed into the test cell to a control station where a remote operated valve




controls the flow to the combustor.  A turbine type flowmeter senses fuel




flow.  Shown in FigureA»U3 is the fuel storage and pumping system.




     The control room houses all controls and instrumentation.  Operation




is controlled completely from the control consoles in this area.  Shown




in Figures  A-A and A-5are the heater and facility control consoles re-




spectively.  All pertinent parameters are indicated and if necessary re-




corded.  An automatic fuel-air ratio control system is capable of holding




a constant fuel-air ratio over a range of primary air flows.  The ratio




type system also allows changes in the fuel-air ratio to be made.  The




system will then hold the new fuel-air ratio over a range of air flows.




     To operate a combustor of the l/5th scale size, the inner valves of




pressure regulating and control valves are changed and smaller orifice




plates are installed in the flow metering tubes.  The turbine type fuel




flow sensor is also replaced with a smaller unit.  The portable Scott




Research Laboratory Inc. Model 108H Dilute Exhaust Gas Analysis System




                                 238

-------
U>
                                                 Figure A-3.  Fuel Storage and Pumping

-------
N3
•e-
o
                                                 Figure A-4.  Heater  Control  Console

-------
Figure A-5.  Facility Control Console

-------
purchased by General Electric shown in Figure A-6 is available for use




in the Gas Dynamic Facility No. 1 (GDF-I).  It has provisions for measur-




ing NO, N02, CO, C0_, 0- and total hydrocarbon emissions.




     The facility has been given a mechanical checkout.  Both heater units




have been tested and operate satisfactorily.  A complete checkout will be




made after the installation of a combustor.
                                  242

-------
NJ
                                           Figure A-6.   Scott  Exhaust Gas Analyzer

-------
                            ACKNOWLEDGEMENT



     Contributions to the work reported herein were made by a number of

people in the Energy Systems Programs and the Corporate Research and

Development components of the General Electric Company.  The main con-

tributions are listed below:
     Combustor Loading and Emission Analysis
     and Report Editing

     Combustor Concept Feasibility Development


     Testing Operations


     Fuel-Air Mixture Supply Development


     Porous Plate Combustor Fabrication Development



     Combustor Configuration and Engine
     Integration Design

     Preliminary Burner-Vapor Generator Design

     Bench Tests
C.W. Deane
J.A. Bond
G.C. Wesling

R.A. Fuller
H. Bradley

J.A. Bond
B.L. Moor

R.G. Frank
J.F. White
J.F. Collins

A.W. Schnacke
J.R. Peterson

G.E. Moore
B.E. Cans
These contributions are gratefully acknowledged.

     The contributions to the program by T.S.  Mroz and W.C. Cain, the

EPA Project Officers are also gratefully acknowledged.
                                  244

-------
                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
   EPA-A60/3-73-001
                                                           3. RECIPIENT'S ACCESSION-NO.
 4. TITLE ANDiuBTITLE
   Development of Low Emission  Porous-Plate Combustor
    for  Automotive Gas Turbine  and  Rankine Cycle Engines
                                     5. REPORT DATE
                                        September  1973
                                     6. PERFORMING ORGANIZATION CODE
 7. AUTHOR(S)
                                                           8. PERFORMING ORGANIZATION REPORT NO.
   Richard '^J.  Rossbach
 9. PERFORMINqOR~ANIZATION NAME AND ADDRESS
  General  Ellectric Company
  Energy Syjstems Programs
  P.  0.  Box! 15132
  Cincinnati ,  Ohio  ^52 15
                                                           10. PROGRAM ELEMENT NO.
                                     11. CONTRACT/GRANT NO.
 12. SPONSORING',AGENCY NAME AND ADDRESS
   U.S.  ENVIRONMENTAL PROTECTION  AGENCY
   Office of Air and Water Programs
   Alternative Automotive Power Systems  Division
   Ann Arbor,' Michigan   ^8105
                                     13. TYPE OF REPORT AND PERIOD COVERED
                                     14. SPONSORING AGENCY CODE
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT
 The  purpose  of this contract was to evaluate  analytically and experimentally  the use
 of the  porous-plate combustor for use  in  the  gas-turbine or Rank!ne-cycle  advanced
 automobile engines to control exhaust  emissions.  As regards the gas  turbine  applica-
 tion, this  report contains analytical  results  on  the burner area requirements  for the
 various  operating conditions of the Baseline  Engine as well as exhaust  emission pre-
 dictions. The design concept of an air-cooled, variable-area combustor  for this engine
 is presented.   Operational and emissions  data  on  several experimental combustors are
 presented along with the fabrication development  leading to these combustors.  Finally
 the  demonstration results for a full-scale  fuel-air mixture system are  presented. With
 regard  to the automotive Rankine engine  application, heat load and emissions  data are
 presented for propane and four liquid  fuels.   Although the fuel-air  mixture  system
 developed for the gas turbine combustor  is  directly applicable, alternate  systems were
 investigated.  Finally recommendations  for the  development of both gas turbine  and Ran-
 kine  combustors are presented.
 7.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
                                                  c.  COSATI Held/Group
 Air  polIut ion
 Development
 Combustion  chamber
 Automotive  engines
 Rankine  cycle
 Fabri cat i on
 Exhaust  emissions
Hydrocarbons
Carbon monoxide
Propane
Gasoli ne
N i ch rome
Oxi des of ni trogen
Porous plate combustor
Burner-vapor generator
Fuel atomizer
13B
2lB
21E
 3. DISTRIBUTION STATEMENT

        UnIi mi ted
                        19. SECURITY CLASS (This Report)
                        Unclassified
                                                                         21. NO. OF PAGES
                                              20. SECURITY CLASS (This page)
                                              Unclassified
                                                                         22. PRICE
EPA Form 2220-1 (9-73)
                                           245

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