US. Department
of Transportation
Federal Aviation
Administration
Nitric Oxide
Measurement Study
Office of Environment
and Energy
Washington, D.C. 20591
Comparison of Optical
and Probe Methods
Volume
Report Numbers:
FAA-EE-80-30
USAF ESL TR-80-14
NASA CR-159863
USN NAPC-PE-39C
EPA-460/3-80-015
MAY 1980
M.F. Zabielski
L.G. Dodge
M.B. Colket, II
D.J. Seery
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This document is disseminated under the joint sponsorship
of the Federal Aviation Administration, U.S. Air Force,
U.S. Navy, National Aeronautics and Space Administration,
and the Environmental Protection Agency in the interest of
information exchange. The United States Government assumes
no liability for the contents or use thereof.
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Technical Report Documentation Page
1. Report No.
FAA-EE-80-30
2. Government Accession No.
3. Recipient s Catalog Nc
4. Title and Subtitle
Nitric Oxide Measurement Study
and Probe Methods - Volume III
Comparison of Optical
5. Report Dote
March 31, 1980
6. Performing Organization Code
7. Author-s!M_
D. J. Seery
, M. B. Colket, III
8. Performing Organization Report No.
R80-994150-3
9. Performing Orgomzotion Nome ond Address
United Technologies Research Center
Silver Lane
E. Hartford, CT 06108
10. Work Unit No. (TRAIS)
M. Controcf or Grant No.
DOT FA77WA-4081
13. Type of Report and Period Covered
12. Sponsoring Agency Nome ond Address
U.S. Department of Transportation
Federal Aviation Administration
Office of Environment and Energy
Washington. DC 20591
4, Sponsoring Agency Code
is. Suppiementory Notes punciing for this study was provided by an Interagency Committee.
Contributing agencies and report nos. are: DOT-FAA (FAA-EE-80-30); USAF (ESL TR-80-
14); NASA (CR-159863); USN (NAPC-PE-39C); EPA (EPA-460/3-80-015).
16. Abstract
Nitric oxide (NO) was measured in the exhaust of three different combustion systems
by in si tu ultraviolet absorption and by chemiluminescent analysis after gas sampling
with several probe designs. The three combustion systems were: (1) a flat flame
burner fueled with CA^/^2/^2' (2) a research swirl burner fueled with C-^Hg/air; and,
(3) a modified FT12 combustor operated on Jet A/air. Each combustion system was
run at several different conditions so that probe and optical measurements could be
obtained over a wide range of exhaust environments encompassing products from lean,
stoichiometrie, and rich flames, laminar to turbulent flows, and temperatures at
centerline from 600 K to 1800 K. The results obtained with the metallic, water-cooled
probes of different designs (all expansion-type) agreed with the optical results to
within 25 percent. Some small losses of NO (10-15 percent) were observed in a l<.-an
methane flame at 1800 K with an uncooled stainless steel probe, but under: fuel-rich
conditions up to 80 percent NO destruction was observed. Experimental facilities
are described, previous results are discussed, and a summary of the major findings
of this study is given.
The Nitric Oxide Measurement Study is in three volumes:
Optical Calibration - Volume I;
Probe Methods - Volume II;
Comparison of Optical and Probe Methods - Volume III.
17. Key Words
Nitric oxide, ultraviolet absorption,
probe sampling, chemiluminescent analysis
combustion.
18. Distribution Statement
Document is available to public througr
, the National Technical Information
Service, Springfield, VA 22161
19. Security Cloisif. (of this report)
Unclassified
20. Security Clossif. (of this poge)
Unclassified
21. No. of Pages
95
22. Pr
Form DOT F 1700.7 (8-72)
Reproduction of completed page authorized
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ACKNOWLEDGMENTS
This contract was administered by the Federal Aviation Administration.
Funding for this work was provided by an Interagency Committee representing
the Federal Aviation Administration (FAA), Air Force, Navy, National
Aeronautics and Space Administration (NASA), and the Environmental Protection
Agency (EPA).
The assistance, in this third phase of the study, of Mr. D. L. Kocum
and Mr. R. P. Smus during the experimental portions of this work is grate-
fully acknowledged. The authors also would like to acknowledge the contribu-
tions of the following UTRC staff: Mrs. B. Johnson and Mr. R. E. LaBarre
for data reduction; Mr. P. N. Cheimets, Mr. M. E. Maziolek, Mr. W. T. Knose,
and Mr. M. Cwikla for facilities support. Since the third phase of this study
was based on the results of the first two phases, the prior contributions of
Mr. J. Dusek, Mr. L. J. Chiappetta, and Dr. R. N. Guile are acknowledged.
In addition, we extend our thanks to Mr. J. D. Few and his colleagues at
Arnold Research Organization for their cooperation during their measurements at
UTRC. Also, we extend our thanks to Dr. D. Gryvnak of Ford Aerospace for his
infrared gas correlation measurements.
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R80-994150-3
ABSTRACT
Nitric oxide (NO) was measured in the exhaust of three different combustion
systems by in situ ultraviolet absorption and by chemiluminescent analysis
after gas sampling with several probe designs. The three .combustion systems
were: (1) a flat flame burner fueled with CH^/^/C^; (2) a research swirl
burner fueled with C^Hg/air; and, (3) a modified FT12 combustor operated on
Jet A/air. Each combustion system was run at several different conditions so
that probe and optical measurements could be obtained over a wide range of
exhaust environments encompassing products from lean, stoichiometric, and rich
flames, laminar to turbulent flows, and temperatures at centerline from 600 K
to 1800 K. The results obtained with the metallic, water-cooled probes of
different designs (all expansion-type) agreed with the optical results to
within 25 percent. Some small losses of NO (10-15 percent) were observed in a
lean methane flame at 1800 K with an uncooled stainless steel probe, but under
fuel-rich conditions up to 80 percent NO destruction was observed. Experimental
facilities are described, previous results are discussed, and a summary of the
major findings of this study is given.
ii
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R80-994150-3
Nitric Oxide Measurement Study:
Comparison of Optical and Probe Methods
TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS i
ABSTRACT ii
TABLE OF CONTENTS iii
LIST OF FIGURES v
LIST OF TABLES vi
I. INTRODUCTION 1-1
II. APPARATUS II-l
A. General II-l
B. Flat Flame Burner II-l
C. Large Scale Combustor Test Section II-4
1. IFRF Burner H-4
2. FT12 Burner Can II-8
3. Temperature Measurements II-8
D. Sampling Systems 11-12
1. Scott Exhaust Analyzer 11-12
2. TECO Analyzer 11-13
E. Probes 11-13
1. Flat Flame Burner 11-14
2. Large Scale Combustors 11-14
iii
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R80-994150-3
TABLE OF CONTENTS (Cont'd)
Page
F. Optical Apparatus 11-20
1. Flat Flame Burner 11-20
2. Large Scale Combustors 11-22
III. RESULTS III-l
A. General III-l
B. Flat Flame Burner III-2
1. Probe Measurements III-2
2. Optical Measurements 111-10
a. Narrow Line Lamp 111-10
b. Continuum Lamp 111-13
C. IFRF Burner 111-14
1. Probe Measurements III-lA
2. Optical Measurements 111-21
U. FT12 Combustor 111-21
1. Probe Measurements 111-21
2. Optical Measurements 111-26
IV. DISCUSSION IV-1
A. Introduction IV-1
B. Comparison of Optical and Probe Results (Task III) .... IV-1
C. Recent Related Studies IV-2
D. Original Studies: Comments IV-3
V. SUMMARY AND CONCLUSIONS V-l
A. Optical Calibration (Task I) V-l
B. Probe Methods (Task II) V-3
C. Comparison of Probe and Optical Methods (Task III) .... V-4
REFERENCES R-l
APPENDIX A - Measuring NO In Aircraft Jet Exhaust by Gas-
Filter Correlation Techniques, Task III:
D. A. Gryvnak A-l
IV
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R80-994150-3
LIST OF FIGURES
Fig. No. Title Page
II-l Top View of Flat Flame Burner and Assembly II-2
II-2 Atmospheric Pressure Combustion Facility II-5
II-3 Swirl Burner Assembly II-6
II-4 FT12 Assembly II-9
II-5 Pt-Pt/13% Rh Aspirated Thermocouple 11-11
II-6 Drawing of Miniprobe 11-15
II-7 Stainless Steel Tipped Miniprobe 11-16
II-8 Drawings of Macroprobes 11-17
II-9 Tip of Reference Probe 11-18
11-10 Reference Probe 11-19
11-11 Water Cooled Hollow Cathode Lamp 11-21
III-l Horizontal Temperature Profile over CH^/02/N2
Flat Flame III-4
III-2 Vertical Temperature Profile over CH,/02/N2
Flat Flame III-5
III-3 Normalized Nitric Oxide Profiles over CH4/02/N2/NO
Flat Flame III-7
III-4 Vertical Profiles of Nitric Oxide over Flat Flame
Burner III-9
III-5 Temperature Profile Across IFRF Cotnbustor 111-16
III-6 Normalized Nitric Oxide Profiles Across IFRF
Combustor 111-19
III-7 Temperature Profiles Downstream of FT12 Combustor . . 111-24
III-8 Normalized Nitric Oxide Profiles Across Optical
Axis for FT-12 Combustor 111-27
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R80-994150-3
LIST OF TABLES
Table No. Title Page
II-A Operating Conditions for Flat Flame Burner II-3
II-B Operating Conditions for IFRF Burner II-7
II-C Operating Conditions for FT12 Combustor 11-10
III-A Mole Percent of Stable Species for Flat
Flame Burner III-6
III-B Measured Concentration of NO (PPM) Using
Uncooled, Stainless Steel Probe Over
Flat Flame Burner III-ll
1II-C Comparison of Nitric Oxide Results Obtained with
Water-Cooled Probes and Narrow Line
Ultraviolet Absorption: Methane
Flat Flames 111-12
III-D Spectral Lines Used in High Resolution NO
Measurements in Methane Flat Flames 111-13
III-E Comparison of Nitric Oxide Results Obtained
With Water-Cooled Probes and Continuum
Ultraviolet Absorption: Methane
Flat Flames 111-15
III-F Mole Percent of Stable Species for
IFRF Burner 111-17
111-G Comparison of Nitric Oxide Measurements
Using the Reference Probe: IFRF Combustor .... 111-20
III-H Comparison of Nitric Oxide Results Obtained
With Water-Cooled Probes and Narrow
Line Ultraviolet Absorption: IFRF Combustor . . . 111-22
III-l Comparison of Nitric Oxide Results Obtained
With Water-Cooled Probes and Narrow Line
Ultraviolet Absorption: FT12 Combustor 111-25
VI
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R80-994150-3
LIST OF TABLES
Table No. Title
III-J Comparison of Nitric Oxide Measurements Using
the Reference Probe - FT12 Combustor 111-28
III-K Comparison of Nitric Oxide Results Obtained
with Water-Cooled Probes and Narrow-Line
Ultraviolet Absorption: FT12 Combustion 111-29
IV-A A Comparison of Corrected Model Results
with Original Model and Verifying
Experimental Results: An Example IV-4
IV-B T-56 Measurements by ARO Reexamined with
Corrected Spectral Model IV-6
vii
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R80-994150-3
I. INTRODUCTION
Since Johnston (1971) and Crutzen (1970, 1972) independently suggested
that the injection of nitric oxide (NO) into the upper atmosphere could signif-
icantly diminish the ozone (0.,) concentration, an accurate knowledge of the
amount of NO emitted by jet aircraft has been a serious concern to those
involved in environmental studies. This concern intensified when McGregor,
Seiber, and Few (1972) reported that NO concentration measured by ultraviolet
resonant spectroscopy were factors of 1.5 to 5.0 larger than those measured by
extractive probe sampling with subsequent chemiluminescent analysis. These
initial measurements were made on a YJ93-GE-3 engine as part of the Climatic
Impact Assessment Program (CIAP) which was one of four studies (CIAP, NAS,
COMASA, COVOS (see References)) commissioned to determine the possible environ-
mental consequences of high altitude aircraft operation, especially supersonic
aircraft. After those studies were initiated, economic factors strongly
favored the production and operation of subsonic aircraft. Nevertheless, since
the subsonic aircraft fleet is large and does operate as high as the lower
stratosphere, interest in the causes of the discrepancies between the two NO
measurement methods continued. Few, Bryson, McGregor, and Davis (1975, 1976,
1977) reported a second set of measurements on an experimental jet combustor
(AVCO-Lycoming) where the spectroscopically determined NO concentrations were
factors of 3.5 to 6.0 higher than those determined by the probe method. In
this set of measurements, optical data were obtained not only across the
exhaust plume but also in the sample line connecting the probe with the chemilum-
inescent analyzer. The sample line optical data seemed to agree with the
chemiluminescent analyzer data; hence, it was suggested that the discrepancies
were due to phenomena occurring in the probe. These results stimulated a third
set of measurements involving ultraviolet spectroscopy (Few et al, 1976a,
1976b), infrared gas correlation spectroscopy (D. Gryvnak, 1976a, 1976b) and
probe sampling on an Allison T-56 combustor. The measured ratios of the
ultraviolet to the probe values typically ranged between 1.5 and 1.9 depending
on the data reduction procedure. The ratios of the infrared to the probe
values varied between 1.1 to 1.5 also depending on the method of data reduction.
In addition to these engine and combustor data, evidence supportive of the
accuracy of the ultraviolet spectroscopic method, i.e., calibration data and
model predictions, was presented by McGregor, Few, and Litton (1973); Davis,
Few, McGregor and Classman (1976); and Davis, McGregor, and Few (1976).
Nevertheless, it was still not possible to make a judgment on the relative
accuracy of the spectroscopic and probe methods. The most significant reasons
for this were: the complexity of the spectroscopic theory and computer model
required to infer concentration from optical transmission; the inadequate
treatment of probe use; and the incomplete exhaust temperature and pressure
data which are necessary for a valid comparison of the methods. Recently,
Oliver et al (1977, 1978) as part of the High Altitude Pollution Program has
ranked these discrepancies as a major and a continuing source of uncertainty in
atmospheric model predictions.
1-1
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R80-994150-3
The purpose of this investigation was to identify and determine the
magnitude of the systematic errors associated with both the optical and probe
sampling techniques for measuring NO. To accomplish this, the study was
divided into three parts. The first was devoted to calibrating the ultraviolet
and infrared spectroscopic methods. This entailed developing procedures which
could provide known concentrations of NO over a wide range of temperatures and
pressures, and also reviewing and correcting the ultraviolet spectroscopic
theory used in the engine and combustor measurements cited above. The results
of this part are presented in TASK I Report entitled Nitric Oxide Measurement
Study: Optical Calibration by Dodge et al (1979). The second part of this
study was focused on sample extraction, transfer, and analysis of chemilumi-
nescent instrumentation. The sampling methods were used on three successively
more complicated combustion systems starting with a flat flame burner and
culminating with a jet combustor. The results are presented in TASK II Report
entitled Nitric Oxide Measurement Study: Probe Methods by Colket et al (1979).
In the third part of this study, optical measurements were made on the same
three combustion systems operated at the same conditions used for the probe
measurements. The results of the optical and probe measurements were compared
and are given in this the TASK III Report entitled Nitric Oxide Measurement
Study: Comparison of Optical and Probe Methods.
The main elements of this report, i.e., TASK III, are the following.
First, the flat flame burner, swirl combustor, and jet combustor are described,
and typical NO concentration and temperature distributions are given. The
probes, both sampling and temperature, used to obtain these distributions are
also described. Second, the details of both ultraviolet and infrared spectro-
scopic systems are provided. The procedures for interpreting the optical data
are reviewed. Third, the results of the optical measurements are compared with
the probe sampling results for all three combustors. Fourth, a review is pre-
sented of previous work in which optical and probe sampling measurements of NO
were compared. Finally, a summary of the major conclusions of this study are
given.
1-2
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R80-994150-3
II. APPARATUS
II. A General
As part of the method to identify the relative merits of probe and
optical measurements of NO in the exhaust of aircraft engines, three com-
bustion systems of varying degrees of complexity were used. These systems
were :
1. CH^/C>2/N2 flame over a flat flame burner:
* = 0.8, 1.0, 1.2, P = 1 atm, m- ^ 2.75 g/sec
2. CoHg/Air flame in a swirl burner:
* = 0.8, 1.0, 1.2, Swirl = 0.63, and 1.25, P = 1 atm, ^Q-^^ /> 71g/sec
3. Jet A/Air flame in a modified FT12 combustor: Idle, Cruise,
and Maximum Continuous, P = 1 atm, ^0^-,^ >/ 470g/sec.
Physical details and operation of the flat flame burner are described
in TASK I Report (Dodge, et al . , 1979); consequently-, only a brief overview
will be presented here. For the other two flames, each burner assembly could
be installed separately into a single combustor housing with the associated
fuel lines and flow controls modified accordingly. This facility and the
burner assemblies are described in detail in this chapter. In addition,
techniques for temperature measurements with corrections for radiation and
conduction, sample gas transfer and analysis, are presented.
II.B Flat Flame Burner
The flat flame burner is made of sintered copper and has two zones: the
main zone (containing the main flame seeded with nitric oxide) with dimensions
o
of 17.5 x 9.2 cm or 161 cm and the (unseeded) buffer zone with an area of 76
r\
cm . A methane flame was burned above the buffer flame to provide a hot zone
in the wings of the flame. The burner was enclosed by a stainless steel
shroud/chimney with optical ports to separate windows (quartz or salt) from the
flame. The ports were purged with nitrogen at room temperature to reduce the
local nitric oxide concentrations within these ports. A top view of the burner
is shown in Figure II-l. Temperatures were measured using a butt-welded, Ir/60%
Ir-40% Rh thermocouple coated with a mixture of Yttrium and Berylium oxides.
The diameter of the bead and coating was approximately 90 microns (0.0035
inches). Gases were individually metered using critical flow orifices.
Separate mixes of gases (N2> 0^, CH^, NO, H2, Ar) were blended for the
main and buffer flows. Details of these facilities are provided in the Task I
Report (Dodge, et al, 1979). The flames examined in this program are listed in
Table II-A.
II-l
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TOP VIEW OF FLAT FLAME BURNER AND ASSEMBLY
I
ro
BUFFER ZONE-
SS. SHROUD
INERT
GAS PURGE
II
)
I
MAIN GAS FLOW "^
(SEEDED W/NO)
X
'
\
\
\
'
/
>
QUARTZ WINDOWS v
,1 \
t
f
^^-DEAD SPACE
ID
I
O
Ul
b
I
SCALE
t 1 tt 1
5 cm
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^80-994150-3
TABLE 11-A
OPERATING CONDITIONS FOR THE FLAT FLAME BURNER*
Test Condition Bl B2 B3
I"N2 (g/sec) 2'15 2-2° 2-07
m ^ (g/sec) 0.512 0.466 0.494
m ^ (g/sec) 0.103 0.116 0.149
T inlet (K) 285 285 285
P (psia) 14.7 14.7 14.7
4> 0.8 1.0 1.2
Without Seed
II-3
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R80-994150-3
II.C Large Scale Combustor Test Section
The combustor test section used for the swirl burner and FT12 combustor
is shown schematically in Fig. II-2. It consists of a water-cooled, double-
walled chamber 50 cm in diameter (i.d.) and 150 cm long. Four (4) rows of
eight (8) viewing ports are provided in the combustor section at 90 intervals.
It was constructed at UTRC specifically to investigate flame phenomena with
various optical and probing techniques. The two burner systems were designed
to fit inside the burner housing. One is a swirl burner and is a scaled down
version of the burners designed at the International Flame Research Foundation
(IFRF). The second is a modified FT12 burner and shroud. The optical axis
used for subsequent optical measurements was the center of the third window
from the far right in Fig. II-2. All probes (sample and thermocouple) were
designed to translate across this axis.
II.C.1 IFRF Burner
The IFRF burner assembly, as shown in Fig. II-3, is a model of those burners
described by Beer and Chigier (1972) and consists of a central fuel nozzle and
an annular air supply. A movable vane block arrangement provides variable air
swirl intensity from a swirl number of 0 to 2.5; in this case, the swirl number
is defined as the ratio of the tangential to the axial momentum divided by the
radius of the exit quarl. The swirl number was calculated using the appropriate
equations in the text by Beer and Chigier (1972) and, as they demonstrate,
experimental and theoretical values agree fairly well for this type of burner.
An axially adjustable, 19 mm diameter, fuel feed tube can be equipped with
various pressure atomizing or air-assisted fuel spray nozzles.
This swirl burner has been tested previously during internal programs at
UTRC and has been used recently to study the combustion of a coal/oil slurry
(Vranos, et al, 1979). In this study, gaseous propane was used for fuel and a
nozzle was constructed to inject the fuel radially into the swirling air flow.
Six stable operating conditions were selected for these tests and provide three
stoichiometries and two swirls. Input conditions are listed in Table II-B.
The optical axis and the probe tips were located 87.5 cm downstream of the
quarl exit.
The two swirl levels used in these tests (0.63 and 1.25) were selected by
performing a series of tests on flame stability. At lower swirl numbers, the
propane flame was relatively long and unstable and was not considered to be
suitable for this series of tests. Beer and Chigier argued that below a swirl
number of 0.6 axial pressure gradients are insufficient to cause internal
recirculation; however, at higher swirl intensities a recirculating zone in the
central portion of the je-t is required to support a strong adverse pressure
gradient along the axis. Since recirculat ion zones tend to stabilize the
flame and increase the intensity of reaction, the ability to achieve stable flame
conditions only above swirl numbers of 0.6 in this research program is in agreement
with Beer and Chigier's analysis.
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ATMOSPHERIC PRESSURE COMBUSTION FACILITY
TRANSITION DUCT
AIR
SWIRL BURNER
4 ROWS OF 8 QUARTZ WINDOWS
WATER-COOLED, DOUBLE-WALLED, CONSTRUCTION
-COMBUSTOR SECTION (60 IN. LONG X 20 IN. DIA)-
CO
I
o
CTl
I
I
Ul
-------
SWIRL BURNER ASSEMBLY
r-7
cr
»
I
QUARL
SWIRL VANE ADJUSTMENT/INDICATOR
AERODYNAMIC I
PROBE I
LJ
SWIRL VANE
ARRANGMENT
AIR
STATIC PRESSURE
STATIONARY VANES
MOVEABLE VANES
FUEL
COOLING WATER
O
CO
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R80-994150-3
TABLE II-B
OPERATING CONDITIONS FOR THE IFRF BURNER
Test Condition
mair
P (psia)
Tinlet
*fuel
1, 4+
66.7
14.7
290
3.40
0.8
2, 5+
66.7
14.7
290
4.26
1.0
3, 6+
66.7
14.7
290
5.11
1.2
*
Gaseous propane
+ Swirl number (see definition in text) was 0.63 for test conditions 1-3
and 1.25 for test conditions 4-6.
II-7
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R80-994150-3
II. C. 2 FT12 Burner Can
A modified FT12 combustor can used in this program was 29.5 cm in length
(11.5 cm shorter than the original can) and 13.0 cm in diameter. It was
altered to make all air addition holes symmetric. This can was welded at its
exit to a shroud and was placed in the test section with the swirl burner
removed. As shown in Fig. II-4, a flow straightener was placed in the burner
housing upstream of the combustor can and appropriate fuel lines and cable for
spark ignition were fed through the housing. A standard fuel nozzle for the
FT12 (Pratt & Whitney Part No. 525959) was used in this series of tests.
Three flight conditions, i.e. idle, cruise, and maximum continuous, were
simulated. A simulation was necessary since the test section could only
sustain a maximum pressure of four atmospheres, while the cruise and maximum
continuous flight conditions required pressure above six atmospheres.
In addition, since gas sampling and accurate definition and examination
of the optical path is simplified by operating at one atmosphere, all experiments
were performed at one atmosphere. Simulated flight conditions at this lower
operating pressure, were calculated by equating Mach numbers. This is a common
test procedure and is useful in simulating equivalent fluid flow patterns and
heat transfer. In this case, the mass flow rate was reduced appropriately to
maintain the chamber pressure at one atmosphere and the inlet temperature was
identical to the flight conditions. The simulated flight conditions are listed
in Table II-C. The optical and probe axis was 78 cm downstream from the exit
of the FT12 burner can.
II. C. 3 Temperature Measurements
Exhaust temperatures from the IFRF and FT12 combustors were made using a
water-cooled, double shielded, aspirated thermocouple probe with a bead made of
Pt/Pt-13/.Rh. The probe was manufactured by Aero Research Instrument Co. (Part
Number T-1006-6 (25) R) according to specifications described by Glawe, et al.
(1956) but was modified (by water cooling and material substitution) to increase
the temperature range to above 1370 K (2000°F). A photograph of this probe
is shown in Fig. II-5. Radiation and conduction corrections were made according
to equations supplied by the manufacturer. For the measurements made in this
study (P = 1 atm, Mach No. « 1), these equations can be written
Tgas
-------
FT12 ASSEMBLY
-FLOW STRAIGHTENER
I
VD
L7
O
O
O
O
O
O
MODIFIED FT12
BURNER CAN
Ml
FUEL
IGNITER
CABLE
AIR
ID
I
O
I
3
~1/3 ACTUAL SIZE
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R80-994150-3
TABLE II-C
OPERATING CONDITIONS FOR THE FT12 COMBUSTOR
mair
P (psia)
T
inlet
m*
fuel
f/a
Idle
485
14.7
335
5.15
.0106
Cruise
463
14.7
515
6.62
.0143
Maximum
Continuous
454
14.7
524
6.92
.0152
Jet A
11-10
-------
Pt-Pt/13% Rh ASPIRATED THERMOCOUPLE
(0
I
o
oo
yi
I
CD
-------
R80-994150-3
and M is the Mach number. For the FT12, no correction was made since
A TRC was negligible « 10 K). For the IFRF burner, corrections were
typically on the order of 50 K. Additional description on the operation of
aspirated probes is given by Land and Barber (1954).
II.D Sampling Systems
Two instrumentation systems were used for measuring the products of
combustion. The first is the Scott Exhaust Analyzer used in the Task I of this
program and the second is a chemiluminescence analyzer made by Thermo Electron
Corporation (TECO). The Scott system was used during the initial tests with
the flat flame burner to obtain concentrations of the major species. The Scott
system was thereafter dedicated to the larger scale combustor tests and the
TECO instrument was used for subsequent measurements of N0/N0x over the flat
flame burner. The Scott system was dedicated to the combustor measurements for
two reasons. First of all, it was impractical to move this system between
facilities and secondly it was determined that the Scott package (under the
conditions of the flat flame tests) did not satisfy the Federal requirements
for total instrument response time and could not be easily modified to meet
those requirements.
II.D.I Scott Exhaust Analyzer
The Scott Model 119 Exhaust Analyzer provides for the simultaneous anal-
ysis of CO, C02, NO or N02, 02 and total hydrocarbons (THC). The analyzer is
an integrated system, with flow controls for sample, zero and calibration gases
conveniently located on the control panel. The incoming gas sample passes
through a refrigeration condenser (""275K), to remove residual water vapor. As
the sample passes from the condenser, it is filtered to remove particulate
matter. The system is comprised of five different analytical instruments.
Becktnan Model 315B Non-Dispersive Infrared (NDIR) Analyzers are used to measure
the CO and C02 concentrations in the gas sample. Concentration ranges
available on the CO analyzer were from 0-200 ppm to 0-15% on several scales.
Concentration ranges available on the C02 analyzer were 0-4% and 0-16%. The
accuracy of the NDIR analyzers is nominally + 1% of full scale. A Scott
Model 125 Chemiluminescence Analyzer is used to measure the NO and N0~
concentrations in the gas sample. Concentration ranges available with this
instrument were from 0-1 ppm to 0-10,000 ppm on several scales, with a nominal
± 1% of full scale accuracy. The thermal converter used in the chemilumi-
nescent analyzer was stainless steel, and was operated at a temperature of
approximately 1000 K. A Scott Model 150 Paramagnetic Analyzer is used to
measure the 02 concentration in the gas sample. Concentration ranges avail-
able with this instrument were from 0-1% to 0-25% on several scales, with a
nominal accuracy of + 1i of full scale. A Scott Model 116 Total Hydrocarbon
11-12
-------
R80-994150-3
Analyzer is used to measure the hydrocarbon concentration in the gas sample.
This analyzer utilizes an unheated flame ionization detection system to provide
for measurement of hydrocarbons (as methane) in concentration ranges from
0-1 pptn to 0-10%, with a nominal accuracy of + 1% of full scale. Output
signals from the various analyzers are displayed on chart recorders and a
digital display.
The sample line was teflon-lined aluminum. The typical operating tempera-
ture was 380 K. When sampling from the large combustors, water was removed
from the sample by two traps cooled to 3° C. The first was located 6 ft.
beyond the probe exit and the second was housed in the Scott analyzer.
11. D.I a IMjmp_iiig_ Req^jirem£^it_s
Two problems specific to this sampling/probe system were encountered.
First of all, the orifice diameter of the macroprobes (2mm) was sufficiently
large that a separate vacuum pump (17.5 cfm) was required to reduce the back
pressure of the probe to the very low values ( >^l/10th of an atmosphere)
required in this program. This vacuum pump was attached directly to the probe
via a line one inch (2.54 cm) in internal diameter and three feet (90 cm) long.
The second requirement was that, at the reduced pressures, the pumping capacity
of the sampling system must be sufficient to deliver flow to the analytical
instrumentation. To accomplish this task, a MB-301 pump and two MB-118 pumps
(metal bellows) were assembled in a series/parallel arrangement. These pumps
were in addition to the two MB-118 pumps in the Scott analyzer and the vacuum
pump associated with the CLA. Even with this pumping capacity the deliverable
flow was marginal at the lowest of probe back pressures.
II.D.2 TECO Analyzer
The Thermo Electron Corporation (TECO) Model 10AR Chemiluminescent N0/N0x
analyzer was used for the reported data for the flat flame burner. This
instrument has a stated minimum detectable concentration of 50 ppb and a
maximum limit of 10,000 ppm. Linearity within any of its eight operating
ranges is given as + 1%. A TECO Model 300 Molybedenum NO Converter was
used for the N02 determinations. Sample was delivered to this analyzer at
atmospheric pressure by a metal bellows pumps (Metal Bellows MB-118). The
sample line was 12 ft of treated teflon line (Technical Heaters, Inc.). The
back pressure of the probe was continuously monitored using a Matheson test
gauge (0-760 torr, absolute).
II.E Probes
As outlined in TASK II Report (Colket et al, 1979), a probe must be
designed for the combustion system being investigated. As a result, the probes
11-13
-------
R80-994150-3
used for the flat flame burner measurements were significantly different from
those used for the large scale combustor measurements. The two most important
criteria for designing probes can be summarized by the following. First, the
presence of the probe should introduce a minimal perturbation to the tempera-
ture of the sampled media. In the post flame or exhaust gases, larger perturba-
tions can be tolerated than in the flame front gases. Second, the quenching of
the reactions in the sampled gases by static temperature and pressure reduction
must be rapid. The minimum quenching required is determined from kinetic
considerat ions.
II.E.I Flat Flame Burner
The four probes used for the flat flame burner measurements were all
expansion-type and classified in TASK II Report (Colket et al, 1979) as mini-
probes. The major distinctions between a miniprobe and the classical microprobe
(Fristrom and Westberg, 1965) are the orifice dimension and the area ratio,
i.e., the miniprobe has a larger orifice and a smaller area ratio than those of
the microprobe. In either type, however, the principal mechanism for quenching
was convective cooling and not aerodynamic cooling. Four types of miniprobes
were used, each of which had an orifice dimension of 0.025 inches (635 microns).
The first of these was entirely stainless steel with a water-cooling channel.
A schematic and photograph are shown in Figures II-6 and II-7, respectively.
The second water-cooled probe was identical to the first with the exception
that its tip was copper. The purpose for the copper tip was to decrease the
time spent by the sampled gases in contact with high temperature walls. The
third probe was water-cooled quartz similar to that used in TASK I (Dodge et
al, 1979)', however, its orifice was enlarged to the above dimension. The
fourth probe was uncooled stainless-steel. The tip and internal geometry were
identical to the metallic water-cooled probes; however, the external diameter
was 0.635 cm versus 0.95 cm because the cooling passages were not present.
II.E.2 Large Scale Combustors
Two water-cooled probes were designed to make measurements on the IFRF and
FT12 combustors. These probes have been defined as the reference probe and the
EPA probe. The geometries of these probes are depicted in Fig. II-8. The
important distinction between these probes is that the reference probe is cap-
able of being operated in the aerodynamic quench mode. The EPA probe can achieve
quenching only via the convective process. It has been defined as the EPA
probe, because it conforms to the present requirements for a probe which are
given in the Federal Register (1972, 1976). The reference probe can also be
operated in the convective quenching mode. When operated in this mode, it also
satisfies the Federal Register requirements. Figure II-9 shows the tip of the
reference probe. Figure 11-10 shows the complete reference probe assembly.
11-14
-------
DRAWING OF MINIPROBE
TIP
X X
/ / / /
/// ///////
0.254cm
X///XX
0.95cm
(D
I
o
00
O1
T]
P
CD
-------
STAINLESS STEEL TIPPED MINIPROBE
i
u
31
CD
-------
DRAWINGS OF MACROPROBES
REFERENCE PROBE
0.20cm
0.20cm
M
HO out
m 2
P
OD
-------
TIP OF REFERENCE PROBE
FIG. H-9
79-10-85-2
-------
REFERENCE PROBE
ID
I
O
oo
GAS SAMPLE
OUT
Cr-AI THERMOCOUPLE WIRES
WATER COOLING FOR
PROBE
0 5 10
CENTIMETERS
CD
o
-------
R80-994150-3
II.F Optical Apparatus
The ultraviolet optical instrumentation used for the in situ NO
determinations was chosen based on ambient conditions. Since the fiat flame
burner was operated in a laboratory where vibrations were minimal and temper-
ature was held at a near constant value, high resolution measurements were
possible. However, vibrations and large ambient temperature excursions in
large scale combustor facilities permitted only low resolution measurements
on the IFRF and FT12 combustors.
II.F.I Flat Flame Burner
The apparatus used for the flat flame burner measurements was similar to
that employed in TASK I Report (Dodge et al, 1979). Two distinct light sources
were used. The first was a hollow cathode lamp which produced emission lines
mainly from NO, N2 molecules and ions, and Ar. The spectral lines of interest
were the NOTT(0,0), 1 (1,1), f (2, 2), and ^(3,4). For reference, a succinct dis-
cussion of the spectroscopy of NO is included in TASK I Report (Dodge et al,
1979). This lamp is shown in Fig. 11-11. Its design was based on that of Meinel
(1975). Typical discharge conditions were 25 ma at 2 torr in flowing air. It
should be noted that there are some spectral lines due to species other than NO
in the T(0,0) region. The effect of these lines is discussed in TASK I Report
(Dodge et al, 1979). The second lamp used was a 1000 W high pressure Xe arc
lamp (Conrad-Hanovia 976C-0010) mounted in an Oriel housing. The center of the
optical beam was located 2.0 cm above the top of the burner.
A 1.5-m focal length J-Y spectrometer in a temperature controlled box with
a 2400 g/mm holographic grating (110 x 110 mm), aperture of f/12, and Fastie
curved slits was employed for all flat flame measurements. Typical slit
function, full width at half maximum (FWHM), was observed to be 0.0018 nm with
7 urn slit settings for the 226 nm NO lines observed in the 2nd order of the
grating. Most of the spectra were recorded with a Hamamatsu Rl66 solar blined
(Cs-Te photocathode) photomultiplier tube cooled to -30 °C in a Products for
Research TE-177 thermoelectrically cooled housing.
The signal from the photomultiplier was amplified with an Analog Devices
AD310K used in the electrometer mode with feedback components of Rf = 100 M and
Cf = 5000 pf. The scan rate was 3.95 x 10~ nm/sec. The resulting spectra
were recorded with a Hewlett-Packard 7100B strip chart recorder. In the case
of the continuum lamp, some of the spectra were corrected for lamp drift by a
ratiometric technique. This involved a reference measurement of the source
lamp prior to any absorption, and was accomplished by placing a flat mirror
slightly off the edge of beam directed through the calibration apparatus which
reflected light through a 226 nm filter and onto an EMI 9601B photomultiplier
11-20
-------
WATER COOLED HOLLOW CATHODE LAMP
-------
R80-994150-3
tube. The signal from the spectrometer was divided by this reference signal in
an Ithaco model 3512 ratiometer and this resultant ratio was recorded on the
strip chart recorder. This ratiometric technique reduced but did not eliminate
baseline drift in the recorded spectra while using the continuum lamp.
The ultraviolet radiation from the source lamp was collimated and directed
through the 12.7 mm diameter apertures, across the flat flame burner, and then
imaged on the spectrometer slit using fused silica lenses.
The spectrometer was operated in high resolution and low resolution. The
slits were set at about 5 to 10 pm for the high resolution work, corresponding
to slit functions with FWHM of about 0.0015 nm to 0.0025 nm. The slits were
set at 1380 \tm for the low resolution studies, with a FWHM value of 0.146 nm.
II.F.2 Large Scale Combustors
For the measurements on the IFRF and FT12 combustors, only the hollow
cathode lamp was employed. The radiation from this lamp was collimated into a
38 mm diameter beam by a quartz lens. The optical path through the expansion
chamber was a nominal 70 cm. Since windowless ports were used on the expansion
chamber, the actual optical path containing significant quantities of NO was
dependent on operating conditions. The beam was then focused into a 0.5 m
Czerny-Turner spectrometer manufactured by SPEX. The spectrometer was equipped
with a 1200 g/mm grating which was used in second order. The slit function was
0.146 nm full width at half height. A solar blind detector (Hamamatsu R166)
was cooled to -30 C. The grating control circuitry was modified to perform
precise repetitive scans over a selected region. This modification allowed
signal averaging to improve the signal-to-noise ratio. The output of the
detection electronics, which were operated in a dc mode, was recorded and
summed in a Northern Scientific NS575 signal averager with a NS580 module. The
contents of the NS575 memory were then recorded on 7 track digital tape by a
NS408F/Wang Mod 7 tape system.
11-22
-------
R80-994150-3
III RESULTS
III.A. General
In order to reduce the optical data and to compare optical and probe
results, complete profiles of temperature and NO concentration are required.
For brevity, only selected profiles obtained on the various combustors will be
presented here. Additional detailed profiles are given in Appendix A which
contains the results of the infrared measurements. The temperature profiles in
the appendix are the same as those which existed when the ultraviolet measure-
ments were made; however, the centerline concentrations of NO were considerably
higher than those of the ultraviolet measurements. The normalized profiles
are, on the other hand, quite similar.
The optical data were reduced using a first principles computer model
which is described in TASK I Report (Dodge et al, 1979). To compare NO mea-
surements determined optically with those determined by probe/chemiluminescent
analysis, it is important to recognize that the optical method determines the
number of molecules per unit volume for an optical path under isothermal and
isobaric conditions. The probe method, on the other hand, determines its
result in mole fraction (ppmv) irrespective of the temperature and pressure
at the probe orifice. If the temperature and pressure are known along the
optical path, it is straightforward to effect a comparison. In combustion
systems, however, gradients in temperature and pressure are encountered; thus
more effort is required to perform the comparison. The approach developed by
Gryvnak and Burch (1976a, b) for their infrared measurements and subsequently
adopted by Few et al (1976) for their ultraviolet measurements is the correct
approach. With this approach, the optical path is divided into isothermal
regions. The mean value of the NO number density is computed from the probe
determined mole fraction, temperature, and static pressure for each of the
isothermal zones. This information is then used to compute the optical trans-
mission for each region. The total transmission is determined by multiply-
ing the zonal transmissions together. (in this study, six or more zones were
employed.) This procedure is based on a Beer's Law relationship between number
density and optical thickness and, thus, it is assumed that "line-center
burnout" (see TASK I Report I, Dodge et al, 1979) is not present. For all the
results, which will be presented below, this procedure was used and the absence
of "line-center burnout" is an excellent assumption. The probe calculated
transmission will be called T . This calculated transmission will be compared
with the optically measured transmission Tm.
In order to determine T , it was necessary to account for intensity
changes due to beam-steering, scattering by particulates, continuum-type absorp-
tion by other molecules and drifts in lamp intensity and electronics. This was
accomplished by monitoring "reference" bands emitted by the hollow-cathode
III-l
-------
R80-994150-3
lamp. Specifically, these bands were the NO T(3,4) andlf(2,2) bands. No
appreciable absorption by NO occurs in these bands because these states are not
significantly populated at temperatures up to 2000K.
Finally, the quantitative comparison between the probe and optical measurements
is defined for the hollow cathode (narrow-line) lamp as
lnTc (III-D
and for the continuum lamp
IHTC (III-2)
[N0]c
l
where [NO] represents the NO concentration, and subscripts (superscripts) p, nl,
and cl represent probe, narrow-line, and continuum lamp. Ratios greater than 1
indicate that the probe determined NO concentrations are greater than the optically
determined NO concentrations. Ratios less than 1 indicate that the optically deter-
mined NO concentrations are greater than the probe determined NO concentrations.
III.B. Flat Flame Burner
Two separate types of ultraviolet measurements were made on the flat flame
burner. The first was made with the hollow cathode (narrow-line) lamp; the
Second was made with the continuum lamp. The results of both these measurements
are compared with the probe measurements.
III. B.I. Probe Measurements
As outlined in Section II. E, four probes were employed in making measurements.
For the three water-cooled probes, the NO concentrations determined were the
same within the experimental precision (^10%). In order to insure unambiguous
optical measurements, i.e., absorptions greater than 10 percent, the flames
were seeded with NO.
Three flame stoich iome t r ies , $ = 0.8, 1.0, and 1.2, were examined and the
specifics of these run conditions are listed in Table II-A. With the nitrogen
III-Z
-------
R80-994150-3
purge passing through the optical ports, vertical and horizontal temperature
profiles were obtained. A typical horizontal profile (for 4> = 0.8) is shown in
Fig. III-l. These measurements are corrected for radiation losses as outlined
in Task I Report by Dodge, et al. (1979) and were obtained along the optical
axis. The burner surface was located 2 centimeters below this axis while the
visible flame sheet was a few millimeters above the burner surface; hence,
these were exhaust stream measurements. Estimates of uncertainties in the
radiation corrections and individual and repeated measurements are indicated in
the error bars. Vertical profiles of uncorrected thermocouple temperatures for
the three flames are shown in Fig. III-2. Since the optical beam is less than
a centimeter in diameter and centered at 2 centimeters above the burner, the
beam encompasses a region for which deviations (due to height) are less than
+ 15K. As may be observed by comparing these two figures, radiation
corrections at the centerline are on the order of 140 K for these flames.
Measurements of stable species using the Scott Instrument package and
the quartz, water-cooled probe (all water-cooled probes produced the same
results within 10 percent) are reproduced in Table III-A. Equilibrium data at
the adiabatic flame temperature (Gordon and McBride, 1971) for the flat flames
are also presented in this table for comparison. It may be noted that reasonable
agreement is obtained between the measured and equilibrium values. Noticeable
differences are observed for the CO and COo concentrations. Although these
differences may be due to interconversion within the probe, it is also possible
to attribute these to differences in actual and adiabatic flame temperatures
and to incomplete combustion of carbon monoxide. Only in the case of the
stoichiometric case ( * = 1.0) is the measured total of the CO and C02 concen-
tration significantly different from the equilibrium calculations ( ^ 8%). (Data
on unburned hydrocarbons are not reported since their concentration even in the
fuel-rich flame were less than 1000 ppm.)
Measured concentrations of nitric oxide were on the order of 5, 30, and 30
ppm for the three flames, respectively. These values at flame temperatures and
for the given optical path length are much smaller than that necessary to produce
a reasonable signal-to-noise ratio for the optical measurements described here.
For the path length and temperatures encountered, concentrations of 700-1500
ppm were required for the unambiguous UV resonant lamp measurements and even
higher NO densities were required for the infrared gas correlation technique.
Consequently, all subsequent studies were made using nitric oxide premixed with
the inlet gases.
Using the stainless steel tipped, water-cooled probe and the TECO CLA,
nitric oxide horizontal profiles were obtained for a given seed level. Profiles,
normalized to the input seed level for the flames * = 0.8 and 4> = 1.2 are shown
in Fig. III-3. Data for the = 1 .0 flame is nearly identical to the data for
the 4> = 0.8 flame except the centerline fraction is slightly higher (^0.88)
for an NO seed level of 840 and 980 ppm calculated on a wet and dry basis,
respectively- For the lean flame, NO values were typically 5 to 7 percent
higher than the NO and, for the stoichiometrie and rich flames, they were about
III-3
-------
HORIZONTAL TEMPERATURE PROFILE OVER C»AIO^N2 FLAT FLAME
= 08
O THERMOCOUPLE TEMPERATURE
CORRECTED FOR RADIATION
-200O
J L
J L
1800;
J L
UU
cr
1600
1400
< 1200
tr
LU
5 1000
LU
800
600
400
J-
O
I
O
I
-11 -10 -9 -8 -7 -6 -5 -4-3-2-101 23
POSITION FROM CENTERLINE (CM)
J L
J L
10 11
-------
FIG. m-2
VERTICAL TEMPERATURE PROFILE OVER CH4/02/N2 FLAT FLAME
O 4> = 08
A = 1.0
D <4 = 1 2
1700
1600
DC
=>
DC
LLJ
CL
1500
1400
UNCORRECTED FOR RADIATION
1 2
HEIGHT ABOVE BURNER (CM)
79-10-85-14
III-5
-------
R80-994150-3
TABLE III-A
MOLE PERCENT OF STABLE SPECIES FOR
THE FLAT FLAME BURNER
(Wet Basis)
Experimental
*
0.8
1.0
1.2
°21
3.2
0.24
-
CO1
.01374
.064
4.1
C021
6.6
6.55
4.8
H202
12.6
14.1
17.8
N23
77.6
78.7
73.3
Temp. (K)
1740
1815
1800
Equilibrium
02 CO C02 H20 N2 Temp. (K)
0.8
1.0
1.2
3.
0.
0.
15
13
7ppm
0
0
3
.0051
.109
.60
6.
7.
5.
43
09
50
12.
14.
15.
9
3
7
77
78
72
.4
.1
.6
1765
1905
1904
1. Measured values but corrected for the presence of water vapor.
2. Water estimated from known input conditions.
3. Nitrogen calculated by difference.
4. Error + 40% of value.
5. Based on equilibrium flame temperature.
Except where noted, the uncertainty of the experimental concentrations is
approximately + 5% of reported (experimental) value.
III-6
-------
NORMALIZED NITRIC OXIDE PROFILES OVER CH4/O2/N2/NO FLAT FLAME
2-28-79
O 3-1-79
= 0 8 AND 0=12
NO SEED LEVEL
tf> 'WET' 'DRY'
08 850 971 PPM
1.2 828 1011 PPM
-1.0
-11 -10
-------
R80-994150-3
3 percent higher than measured NO. The excellent repeatability of the burner
and sampling conditions is indicated by the double set of points on the right-
hand side of this figure.
Vertical profiles for the three flames and the three water-cooled
probes are reproduced in Fig. III-4. Agreement between these profiles is
generally quite good (within 6%) except for relatively low values obtained by
the stainless steel tipped probe when sampling the rich flame. Since the front
part of this tip (/" 1 cm) becomes very hot (with a red-orange glow), it is
believed that catalytic reactions take place similar to that occurring in an
N02 to NO converter- This conclusion is consistent with the computed results
from TCAL (see TASK II, Colket et al, 1979) indicating that the stainless steel
tip is insufficiently cooled. Although residence times in this portion of the
probe are very short (« 1 msec), the wall temperatures very near the orifice
are significantly hotter than in a stainless steel converter (1100 to 1200 K
vs. 1000 K). The profile may be associated with the presence of hydrogen that
would be expected to decrease with height above the flame. Although this
mechanism was not verified, it seems highly likely considering the strong NOX
reducing effect that hydrogen has in hot stainless steel tubes (Benson and
Samuelsen, 1976, 1977). The relatively low values obtained in the 4> = 0.8
flame for the copper-tipped probe are unexplained. Although this difference of
7 percent may be due to a catalytic effect of a copper surface, it is unclear
why good agreement is found for the other flames. In any case, this difference
is considered to be small.
From the above results, it is seen that the recovery of the nitric oxide
needed into the flame is not complete. At the seed concentrations, approxi-
mately 15, 12, and 38 percent of the initial NO was lost for the 4> = 0.8, 1.0,
and 1.2 flames, respectively. Attention was directed at determining whether
the loss occurred in the inlet gas lines (for the unburned/premixed gas), in
the flame itself, or the probe/sampling system. Losses in the post-flame zone
were believed to be unlikely since essentially flat vertical profiles were
obtained (Fig. III-4).
These loss figures can be slightly adjusted to account for phenomena
associated with the flame and experimental apparatus. First of all, some N0~
was present as indicated by NO readings, and, consequently, the percent losses
can be decreased by 3 to 5 percent. Although it is not possible to ascribe
the presence of N02 to the flame or probe, the fraction of NOo was not
large enough relative to experimental uncertainties to warrant a detailed
investigation. Alternatively, if one assumes that the NO formed in the flame
without seed NO is also formed when NO is added, then the losses in the stoi-
chiometric and rich cases can be increased by approximately 3 percent (about 30
ppm in 1000). The estimated losses at centerline of NO may be decreased by
about 3 to 5 percent due to dilution from the nitrogen purge in the optical
ports (see Dodge, et. al., 1979). Uncertainties also include the inaccuracies
III-8
-------
FIG. IE-4
VERTICAL PROFILES OF NITRIC OXIDE OVER FLAT FLAME BURNER
O s.s. TIPPED)
A Cu TIPPED > WATER COOLED PROBES
D QUARTZ \
= 0.8 <£= 1.0
Qnn SEED 971 PPM SEED 980 PPM
yuu
LU
CL
tx
~T 800 1
C/J *
2 S
0
^
cc
2
LU
£ 700
O
0
o
2
D
LU
DC
w 600
LU
r g B o B
A A
A A
1 1
I A A A A
g § a 8 a
r
p
I I
1 23123
HEIGHT ABOVE BURNER (CM)
#=1.2
900
LU
5
Q-
Q_
w 800
O
cc
LU
O
-2L 700
O
O |
O
Q
LU
LT
£ 600.
SEED 1011 PPM
) B g 8 B
ft o 8
Cf ^\
80 °
0
^
^ B
I 1 1
2 3
HEIGHT ABOVE BURNER (CM)
79-10-85-11
III-9
-------
R80-994150-3
in blending from the mixing apparatus and in the calibration and analysis. It
is estimated that the sum of these uncertainties is on the order of 3 percent
since measured NO concentrations generally agreed to within 3 percent of the
calculated values when NO was blended only with nitrogen, and the gas sample
was extracted within 1 mm of the burner surface with no flame present and with
the nitrogen purge off.
With all of the adjustments and uncertainties mentioned above, the percent
N0x lost for these flames becomes 9, 8 and 34 percent respectively with an
uncertainty of about ± 5 percent in each number, i.e., for the lean flame, the
estimated real loss can range from 4 to 14 percent. If the natural NO formed
in the flame is not included, then these numbers become 9, 5, and 31 percent
for the * = 0.8, 1.0, and 1.2 flames, respect ively -
An uncooled stainless probe geometrically similar to the other metallic
probes was also used. This probe, as expected, glowed red when placed in the
exhaust of the flame. Using this probe, NO measurements were similar (within
10%) to measurements obtained when using the cooled probes for the lean flames
although the results were somewhat dependent on the residence time of the
uncooled probe in the flame. Data are reported in Table III-B and times
between scans are typically 5-10 minutes. For the stoichiometric flame, the
observed NO was approximately 25-30 percent less, and for the rich flame values
ranged from the same as that measured using cooled probes to only 20 percent of
that value depending on probe history and probe back pressure, i.e., residence
time. For example, at 220 torr back pressure and when the flame is quickly
changed from the lean to rich flame (^15-30 seconds), cooled and uncooled
probes behave similarly but in less than a minute the indicated NO begins to
fall and after 10 to 15 minutes a stable, but lower value (by a factor 0.67)
is obtained. Then by increasing the back pressure to 430 torr which correspond-
ingly increases the residence time substantially, the NO drops further to only
20 percent of the initial value.
The behavior of the uncooled probe is not unexpected since similar results
have been obtained by England, et. al., (1973) and since similar effects are
common for a stainless steel N02~NO converter when sampling rich flame gases.
III.B.2 Optical Measurements
1 1 1 . B . 2 . a N^£J £w-_l_ine^ Lamp_Me_asur erne nt s^
For these measurements, the temperature profiles were divided into three
zones on each side of the centerline of the burner. Broadening parameters a1
for each zone were computed using the broadening coefficients (K) obtained by
Dodge et al (1979) and the equilibrium mole fractions for each of the stoichi-
metries considered. For these atmospheric pressure flames, a1 was typically
0.50 in the highest temperature zones (/'1830K) and 1.50 in the low temperature
zones (/<75UK). A summary of these measurements is presented in Table III-C
111-10
-------
R80-994150-3
TABLE III-B
MEASURED CONCENTRATION OF NO (PPM) USING
UNCOOLED, STAINLESS STEEL PROBE OVER FLAT FLAME BURNER5
0.8J
0.8'
1.0J
1.2J
1.2'
1.2-
1.2"
height 1.5
above 2.0
burner 2.5
(cm) 3.0
Back pressure
(torr)
Direction of
Scan
Seed level
(ppm)
772
762
755
752
225
down
971
717
712
710
702
213
down
971
655
630
545
500
219
down
980
242
237
232
230
218
down
1011
227
222
220
215
218
down
1011
225
217
215
215
218
up
1011
147
142
137
132
435
down
1011
1. First scan
2. Second scan
3. Third scan
4. Fourth scan
5. These data may be compared directly to data for cooled probes presented in
Figure III-4.
III-ll
-------
R80-994150-3
TABLE III-C
0.8
COMPARISON OF NITRIC OXIDE RESULTS OBTAINED WITH WATER-COOLED
PROBES AND NARROW-LINE ULTRAVIOLET ABSORPTION: METHANE FLAT FLAMES
[N0]p
Centerline (wet)
(ppmV)
1997
a 1st
(Centerline) Bandhead
m
0.60
0.772
0.787
1st 2nd
Bandhead Bandhead
Tc Tro
0.780 0.713
0.727
2nd [NO]
Bandhead tN°]ni
TC (AVE.)
(± lo)
0.698 1.05±0.07
1.0
1.2
1862
1673
0.51
0.53
0.821
0.817
0.824
0.843
0.853
0.794
0.807
0.758
0.755
0.760
0.787
0.782
0.721 1.16±0.03
0.736 1.27±0.04
111-12
-------
R80-994150-3
As shown in this table, the agreement between the probe and optical results
are in reasonable agreement with the estimated accuracy (+ 20%) anticipated
from the results of the calibration phase of this study. The uncertainties
listed for the ratios of probe to optical results indicate only a one standard
deviation associated with the optical measurements and not those associated
with temperature and concentration uncertainties and other sources of error.
The results for the rich flame ( = 1.2) establish that the seeded-NO is being
destroyed in the flame (see TASK II, Section IV, Colket et al, 1979). Moreover,
the uncooled probe results are in good agreement with the optical results for
the lean flame ($=0.8).
III.B.2.b. Continuum Lamp Measurements
In the analysis of the data obtained with the narrow-line lamp, the results
are dependent on the temperature of the emitting molecules which for the above
measurements was approximately 600K. This temperature determines the width of
the emission lines which must be considered in relation to the absorbing lines.
An alternate emission source which provides a definable, continuum-type intensity
distribution across the Y(0,0) band of NO is a high pressure Xe lamp. The use
of this lamp provided an independent verification of the optical results because
with a high resolution spectrometer it offered single line intensity measurements
and also direct line-broadening information. Its use, however, was not practical
for the large combustor measurements because the high resolution spectrometer
could not be exposed to the harsh environment of a test cell. This method was
described in TASK I (Dodge et al, 1979) and was also employed to measure NO in
these methane flames. The lines used are given in Table III-D below.
TABLE III-D
SPECTRAL LINES USED IN NO MEASUREMENTS IN
METHANE FLAT FLAMES
Group
Assignmment
Line P22(15.5) Q22(8.5) P22(16.5) Q22(9.5) P22(17.5) Q22(10.5)
Identification Q12(15.5) R12(8.5) Q]2(16.5) R]2(9.5) Q22(17.5) R]2(10.5)
P12(26.5)
111-13
-------
R80-994150-3
The results of these measurements are given in Table III-E. As in the case
of the hollow cathode results, the deviations in the averages reflect principally
the precision of the optical data. The centerline temperatures are the same as
those reported for the flame stoichiometries given in Table III-C. Again,
within the estimated accuracy, the results between the water-cooled probe and
optical method are in good agreement. Also, good agreement was obtained with
the uncooled probe for the lean flame.
III.C IFRF Burner
III.C.I Probe Measurements
Initially, temperature profiles were measured and their dependency on
burner operating conditions (i.e., swirl number, position of fuel nozzle, and
design of fuel nozzle) and location within the combustor was examined. The
primary objectives of these tests were to (1) find stable and repeatable
operating conditions and (2) obtain reasonably flat temperature profiles in
order to simplify the reduction of the optical data. The selected burner
conditions are described in Section II-C. Probe locations as far downstream as
practical were selected to insure that only combustion products and not un-
burned or partially burned gases were sampled and that the temperature profiles
were relatively flat. Six operating conditions were chosen and these are
listed in Table II-B. Two swirl levels were examined and at each swirl number,
three stoichiometries were tested. Although flames at lower swirl numbers were
tested, these flame conditions were relatively unstable and therefore unsuitable
for these experiments.
A typical temperature profile (corrected for radiation and conduction) for
the run condition $ = 0.8, swirl = 1.25, are shown in Fig. III-5. These data
were taken using the aspirated thermocouple described in Section II. The
dotted lines represent estimates based on measurements in the wings. The
change in swirl produced no measurable difference for any of the stoichiometries.
The shape of the temperature profiles for the rich and stoichiometric flames
are similar to the lean flame with the centerline temperature varying according
to stoichiometry (see Table III-F). In the wings, temperature measurements
(uncorrected for radiation or conduction) were made using a chrome1-alume1
thermocouple (0.010" wire diameter) inserted through the open optical ports.
The measured temperatures are much lower than are expected for adiabatic
temperatures of a C-jHg/air flame. The low temperatures observed are due to
cooling from the water-cooled walls of the expansion diameter.
Stable species were measured using the SCOTT Instrument package with both
the "EPA" and reference probes. No differences were observed between these
probes and measured concentrations were independent of back pressure. Experi-
mental data are listed in Table III-F and equilibrium calculations based upon
-------
R80-994150-3
TABLE III-E
COMPARISON OF NITRIC OXIDE RESULTS OBTAINED WITH WATER-COOLED
PROBES AND CONTINUUM ULTRAVIOLET ABSORPTION: METHANE FLAT FLAMES
= 0.8
Group No.
m
[NO]p/[NO]op
1 2
0.744 0.748
0.764 0.760
1.10 1.05
[NO] =1923 ppm
Centerline (Wet)
0.745 0.754 0.747 0.739
0.741 0.757 0.739 0.722
0.98 1.01 0.97 0.93
[NO]p/[NO]
(AVE.)
(± lo)
1.01+0.06
= 1.0
[NO] =1830 ppm
Centerline (Wet)
Group No.
1
m
[NO]p/[NO]op
0.768 0.773 0.769 0.777 0.771 0.764
0.800 0.804 0.785 0.813 0.802 0.766
1.18 1.18
1.18 1.22 1.18 1.01
1.14+0.08
= 1.2
[NO] =1184 ppm
Centerline (Wet)
Group No.
m
[NO]p/[NO]op
0.839 0.838 0.839 0.842 0.834
0.875 0.840 0.867 0.840 0.864
1.32
1.01 1.23 0.99 1.25
1.16+0.15
111-15
-------
TEMPERATURE PROFILE ACROSS IFRF COMBUSTOR
4> = OR SWIRL = 1 L'fi
O PT/PT - 13% Rh ASPIRATED THERMOCOUPLE PROBE
( ORRECTF.D FOR RADIATION AND CONDUCTION
O 0010 IN C''AI THERMOCOUPLE
1400
O
-40
-30
-20 -10 0 10
POSITION FROM CENTERLINE (CM)
20
30
40
P
in
u»
-------
R80-994150-3
TABLE III-F
MOLE PERCENT OF STABLE SPECIES
FOR IFRF BURNER1
(Wet Basis)
Experimental
rn2 ro 2 H n3
\s\j \s\j o n.o*-'
Temp. (K)
0.8 4.2
1.0
1.2
9ppm5
0.0635
3.0
8.8
10.6
9.0
11.7
15.6
17.3
75.3
73.8
70.7
1200
1280
1220
Equilibrium
0-
CO
CO,
H20
Temp. (K)
0.8
1.0
1.2
3.92
<1 ppm
<1 ppm
<1 ppm
0.021
3.65
9.45
11.6
9.56
12.6
15.5
13.9
73.1
71.9
68.3
1200
1280
1220
1. Although two flames were examined (two different swirls) at each
stoichiometry, measured values of these stable species were essentially
the same.
2. Measured values but corrected for the presence of water vapor.
3. Water estimated from known input conditions.
4. Nitrogen calculated by difference.
5. Error + 40% of value.
6. Based on measured temperatures.
Except where noted, the uncertainty in the experiment concentrations is approxi-
mately + 5% of the reported value.
111-17
-------
R80-994150-3
the measured (not the adiabatic) temperature are also given. Data for only
one swirl level is given here since the data for the other swirl numbers is
essentially identical. In general, agreement between equilibrium and experi-
mental values are reasonable except for the C02 (and to some extent CO)
values for which the measured values are about 9% low. It is believed that
this difference is due to uncertainties in the fuel flow rate and/or the C02
calibration curve. The high estimated water value for the rich flame is due
to the presence of about 3.5% molecular hydrogen (equilibrium value) and the
equilibrium value of water is realistic. The presence of H2 was not accoun-
ted for when estimating the concentration of water.
Concentrations of nitric oxide were measured to be approximately 48, 40
and 25 ppm for the 4> = 0.8, 1.0 and 1.2 flames respectively. N0x was typi-
cally, 4 to 5% higher than these numbers for the * = 0.8 and 1.0 flames and was
not measured for the rich flame. Since these levels were too low (even with
the relatively long path length) to provide adequate signal-to-noise ratios in
the optical measurements, nitric oxide was blended with the inlet air.
Typical profiles of nitric oxide across the optical axis and normalized
to the seed concentration of NO are shown in Fig. III-6. The profile data
were obtained using the 'EPA' probe and did not vary over the back pressure
range examined (100-350 torr). The dotted lines are estimated extrapolations
based on other similar flame measurements. Data for the other flames are quite
similar. Also included on these profiles are experimental data obtained using
the reference probe at two back pressures. At these conditions both the theo-
retical model and experimental pressure profiles inside the probe (see Task II,
Colket et al, 1979) indicate that the flow in the probe is subsonic except
for possibly a small region in the tip. Thus, the flow is convectively cooled.
No differences between NO measurements using the reference probe and the EPA
probe are observed when operating both in the convectively cooled mode. For
all presssures examined and for both probes NO measurements were typically
within 2 or 3 percent of the NO measurement. For Fig. III-6, the NO seed
values for the $ = 0.8, 1.0 and 1.2 flames were 184, 189 and 182 ppm dry and
162, 160, and 150 ppm wet, respectively. In these calculations the 'dry1
concentrations were estimated assuming the vapor pressure of water at 3 torr
remained in the sample gas with a total pressure of approximately 500 torr-
Measurements were also made when supersonic flow (verified by pressure pro-
files) extended into the first constant area section of the reference probe.
The data are reproduced in Table III-G and are compared with measurements made
using the same probe but at higher back pressures, i.e., when the gases were
convectively cooled. Although these data are within about 10%, there appears
to be some difference between the NO measured at a low back pressure (90 torr)
versus that measured at higher back pressure. In addition, the NO /NO .
' meas seed
ratios arc- smaller than those obtained at lower seed concentrations and reported
in Fi^-. III-6. This latter result, in fact, is not surprising since the results
from the flat flame burner also show a concentration dependence. The former
IIT-18
-------
NORMALIZED NITRIC OXIDE PROFILES ACROSS IFRF COMBUSTOR
O "EPA' PROBt
D 1/16 IN OD SS TUBE. UNCOOLED
REFERENCE PROBE AT 180 TORR
A REFERENCE PROBE AT 400 TORR
O O O O O
r
J o *> ^ o o
;
' ° 2 o o 0
I
I
I I I
0 = 08. SWIRL = 1 25
Q 0 = 1.0. SWIRL = 1 25 1
0 o M
00° ,'
0=12. SWIRL = 1 25 II
O I
0 0 »|
i
II1
-30
-20
-10 0 10
POSITION FROM CENTERLINE (CM)
20
30
40
H
cr>
-------
R80-994150-3
TABLE III-G
COMPARISON OF NITRIC OXIDE
MEASUREMENTS USING THE REFERENCE PROBE
IFRF BURNER
NO (ppm)
N0y (ppm)
NO (ppm)
NO (ppm)
NO (ppm)
X
* = 0.8
Swirl = 1.25
Seed = 960 ppm
895 + 40
880
830
820
* = 1.2
Swirl = 0.63
Seed = 470 ppm
240 ± 10
246
220
Back Pressure
= 190 torr
(0.25 atm)
Back Pressure
= 380 torr
(0.5 atm)
Back Pressure
= 90 torr
(0.12 atm)
1. Supersonic flow extends into first constant area section of reference
probe.
111-20
-------
R80-994150-3
results apparently indicate a small difference between a probe that convec-
tively cools and one that aerodynamically cools; however, it is more likely
that the observed differences are associated with the very low operating pres-
sure of the sampling system. For example, due to the very low pressures, the
pumps could deliver only half (1 cfh) the normal flow (2 cfh) to the CLA. In
either case, most of the gas was extracted with a 17.5 cfm vacuum pump immed-
iately at the exit of the probe. Although the CLA was recalibrated to the
lower flow rate, a small leak of only 2 to 3% would be difficult to detect
under normal flow conditions yet would amount to a 4-6% dilution when only half
the flow passed through the sample line. In addition, less water would be
extracted at the refrigerator since the total pressure is lower. The resultant
increase in water concentration will not only act to dilute the sample on a
relative basis, but also will provide more efficient quenching of the chemilumi-
nescent reaction and consequently decrease the response of the CLA. It is
estimated that an increase in the water concentration from 1% to 3% will
decrease the CLA response (due to both chemiluminescence quenching and sample
dilution effects) by 4 to 5%. Consequently, it is believed that the differences
observed in Table III-G are not due to differences in quenching rates of the gas
sample but rather due to a decrease in sample line pressure and associated
phenomena.
111. C. 2 £p_t_i£_a_l_ Me_as ur emerits
This combustor provided the higher temperature of the two large scale
combustors used. Table III-H gives the optical results and compares them with
those of the probes for varying stoichiometries and swirls. For the lean and
stoichiometrie conditions, the agreement is excellent. Again, the precision is
that primarily of the optical measurement alone. The two values of "*m for
each stoichiometry represent an optical measurement at the specified combustor
condition referenced to spectra obtained immediately before and after the NO
seeded flame. The average signal loss on the f (3,4) and Y(2,2) reference bands
was 8 percent. For the conditions $=1.2, S=1.25, X(NO)=103 ppm, the agreement
between probe predicted transmission and the measured transmission is only
superficially good because it represents, in reality^ a s 40% discrepancy,
This is an indication of the limitation of the optical method at low concentra-
tions and high temperatures.
III.D. FT12 Combustor
III.D.I. Probe Measurements
Three flight conditions, idle, cruise, and maximum continuous were simu-
lated for this series of tests. The corresponding operating conditions are
111-21
-------
R8 0-994150-3
TABLE III-H
COMPARISON OF NITRIC OXIDE RESULTS OBTAINED WITH WATER-COOLED PROBES
AND NARROW-LINE ULTRAVIOLET ABS6RPTION: IFRF COMBUSTOR
* Swirl
T [N0]p
(centerlir
(K) ppmv
0.8 0.63 1200 192
1.0 0.63 1280 152
1.2 0.63 1220 103
0.8 1.25 1200 212
1.0 1.25 1280 156
1.2 1.25 1220 103
1.2 1.25 1220 135
3t
1st 2nd
2nd
Jandhead Bandhead Bandhead Bandhead
.j.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
m
827
813
897
866
924
924
802
808
847
855
925
932
882
861
T T
c ' m
T
C
0.816 0.772 0.749
0.
0.868 0.
0.
0.903 0.
0.
0.804 0.
0.
0.867 0.
0.
0.901 0.
0.
0.872 0.
0.
768
845 0.817
823
894 0.864
900
757 0.734
752
824 0.815
823
897 0.861
902
845 0.822
819
[NO]
[N0]nl
Ave.
1.07+0
1.13+0
1.32+0
1.05+0
0.97+0
1.41+0
1.04+0
.06
.15
.05
.06
.10
.06
.11
111-22
-------
R80-994150-3
given in Table II-C. Temperature profiles across the optical axis (same path
as for the IFRF measurements) are shown in Fig. III-7 for idle and cruise
conditions. These data were obtained using the Pt/Pt-13% Rh, aspirated thermo-
couple. The profile for maximum continuous is very similar in shape and
magnitude to that for cruise. Also shown in the figure are data from a vertical
profile which indicate no difference between the different quadrants. In
addition to these measurements, centerline temperature measurements using
coherent anti-stokes Raman spectroscopy (CARS) were made (Eckbreth, et. al,
1979). For the CARS measurements, the temperatures were 580K, 875K and 875K
for the idle, cruise, and maximum continuous conditions respectively. These
data agree quite well with the centerline thermocouple data obtained at the
same position i.e., 590, 900 and 920K.
Measurements of CO, C02, and 02 using the SCOTT instrument package
and the EPA probe are listed in Table III-I. For comparison, equilibrium data
based on the input conditions and measured gas temperature are also presented.
Good agreement is observed between the experimental and equilibrium data except
for carbon monoxide and an unexplained, high experimental value for carbon
dioxide at maximum continuous. The high concentrations of CO measured behind
the FT12 combustors are due to a quenching of the reaction from air dilution
within the combustor. With the reference probe, the C02 and 02 concentra-
tions were not measured. Carbon monoxide concentrations were the same as with
the EPA probe when the reference probe was operated both in the convective
cooling mode and with supersonic flow extending into the first constant area
section of the probe.
Without seed, concentrations of nitric oxide (total nitrogen oxides) on
centerline were on the order of 3(15), 5(28), and 6(30) ppra for the simulated
flight condition idle, cruise, and maximum continuous, respectively. These
values varied as much as 20-30% from day to day for any given probe but specific
variations due to probe type or back pressure were not observed. The cause of
the uncertainty may be variations in input conditions for the combustor or
calibration of the CLA at these low NO levels. Careful attention to obtaining
accurate base line values was not given since this program focused on NO seed
levels much higher than 25 ppm. In any case, it is interesting to note that
the N02/N0 ratios were typically quite high, on the order of five. The
source of the N02 is not due to the reaction in the sample line.
NO + NO + 02 ~* 2 N02
since the rate of this reaction is strongly dependent on the NO concentration
and sample line pressure. Experiments with high seed values of NO (s 800 ppm)
in air at much higher sample line pressure (750 vs 180 torr) indicated only 3%
conversion to N02- Instead, it is more likely that N02 is formed from NO in the
combustor during the addition of relatively cold air, in the post flame region
downstream of the combustor, or in the probe from the reaction with H0~ (see
TASK II Report, Section III.A.I, Colket et al, 1979). Insufficient information
111-23
-------
TEMPERATURE PROFILE DOWNSTREAM OF FT12 COMBUSTOR
CLOSED SYM IDLE
OPLNSYM CRUISE
O HORIZONTAL PROFILE
D VERTICAL PROFILE
(TOP QUADRANT)
0 A HORIZONTAL PROFILE
(Cr/AI THERMOCOUPLE)
1000
800 -
LU
CC
D
tr
UJ
a.
600 -
400 -
40
30
20
-J
-------
R8 0-994150-3
TABLE III-I
MOLE PERCENT OF STABLE SPECIES
FOR FT12 COMBUSTOR
(Wet Basis)
Experimental
Idle
Cruise
Max . Cont .
4
0.
0.
0.
t>
14
19
20
0^
19.0
16.8
16.5
CO1
0.
0.
0.
25
20
17
CO 2
1
2
3
.7
.8
.3
H202
1.9
2.6
2.7
77
77
77
N23
.15
.60
.33
Temp. (K
580
870
900
Equilibrium
CO
CO,
Temp. (K)
Idle
Cruise
Max. Cont.
0.14
0.19
0.20
17.9
16.8
16.6m
<1 ppb
<1 ppb
<1 ppb
1.94
2.60
2.77
1.94
2.58
2.74
77.3
77.0
77.0
580
870
900
1. Measured values but corrected for the presence of water vapor.
2. Water estimated from known input conditions.
3. Nitrogen calculated by difference.
4. Based on measured temperatures
The uncertainties in the experimental concentrations are approximately + 5%
of reported (experimental) value.
111-25
-------
R80-994150-3
is available to determine conclusively which is the primary mechanism; however,
it appears unlikely that probe reactions are responsible due to the relatively
low temperature of the gas and the necessarily low radical concentrations.
Profiles of nitric oxide were obtained with seed levels of NO at 327, 326,
and 326 ppm for the idle, cruise, and maximum continuous flames. Normalized
profiles of nitric oxide for the idle and cruise conditions are plotted in Fig.
III-8. These data were obtained using the EPA probe. Also shown are profiles
of total nitrogen oxides. For maximum continuous, the centerline fraction of
NO (N0x) recovered relative to the seed value was 0.89 (1.08). In these
gas samples, it is clear that there are relatively large fractions of N02-
For example, idle conditions convert more than 40% of the total N0x to N02. For
the same reasons discussed in the previous paragraph, it is belieyed that the N02
is probably formed in the combustor or post flame zone rather than the probe or
sampling line. Greater losses of NO are observed at idle in spite of the rela-
tively lean stoichometry because at this level mixing is less intense and local
variations in st oichiome try may be larger and may last longer than those at the
other power levels. In the very fuel rich eddies, losses similar to those in
the flat flame burner undoubtedly take place.
Also shown in Fig. III-8 are experimental measurements of nitric oxide
using the reference probe. For most of these data the back pressure was
approximately 300 torr. Although good agreement is obtained between measurements
with this probe and the EPA probe, some differences are noted for one set of
NOV measurements at cruise and idle. The FT12 assembly had been removed from
J\
the test assembly and reinstalled before this second set of NO and NO
X
measurements were made. Small shifts in alignment of the fuel nozzle or
variations in input conditions may be responsible for the changes in NO
recovery although no corresponding change in the gas temperature was observed.
The reference probe was also used to sample flame gases at reduced pressure
(^95 torr) where supersonic flow conditions extended into the first constant
area section of this probe. In Table III-J these values are compared to
measurements taken at high back pressure with the same probe. The agreement is
excel lent .
1 1 1 . D . 2 Opial Meas remen ts
These measurements were of particular interest in that a liquid fuel
(Jet-A) was used. The agreement between the probe calculated transmission and
the measured optical transmission given in Table III-K is within the expected
accuracy. The precision indicated is, as previously stated, primarily that of
the optical measurement. It should be mentioned that a strong continuum absorp-
tion was observed during these measurements under idle conditions. The absorp-
tion on the Y(2,2) and >(3,4) reference bands was about 4 percent for the maxi-
mum continuous condition, about 14 percent for cruise, and 72 percent for idle.
At the idle condition, significant quantities of hydrocarbons are present some
of which absorb in this spectral region. Without the use of the signal averag-
ing data acquisition system, the interpretation of these spectra would have
been extronu'lv difficult.
111-26
-------
NORMALIZED NITRIC OXIDE PROFILES ACROSS OPTICAL AXIS FOR FT12 COMBUSTOR
i
NJ
O
A,
Ol
Q
LU
U-1
CO
O
CO
<
LU
2
O
-
1.0 -
O.P
0.6
0.4
o.;
o'o-O-
O
-40
-30
A
A NO EPA PROBE
IDLE
EPA PROBE
CRUISE
1/16 IN O.D. TUBE
UNCOOLED
CRUISE
O
_L
-20
-10 0 10
POSITION FROM CENTERLINE (CM)
20
30
40
oo
-------
R80-994150-3
TABLE III-J
COHPARISON OF NITRIC OXIDE MEASUREMENTS USING
THE REFERENCE PROBE - FT12 COMBUSTOR
Idle
Back Pressure
+ 205 torr
(0.27 atra)
Back Pressure
+ 95 torr
(0.13 atm)
NO
N0v
X
NO
NO
395
480
385
478
Maximum Continuous
740
800
740
790
* Supersonic flow extends into 1st constant area section of reference probe
111-26
-------
R80-994150-3
TABLE III-K
COMPARISON OF NITRIC OXIDE RESULTS OBTAINED WITH WATER-COOLED PROBES
AND NARROW-LINE ULTRAVIOLET ABSORPTION: FT12 COMBUSTOR
Condition
Idle 1
Idle 2
Cruise 1
Cruise 2
Max.
Continuous 1
Max
Continuous 2
T [NO]
(Centerline)
(K)
580
580
870
870
900
900
ppmv
120
175
240
378
285
445
1st
Bandhead
Tin
0.
0.
0.
0.
0.
0.
789
621
750
661
747
635
1st
Bandhead
T
0.
0
0.
0.
0.
0.
c
792
711
755
641
709
606
2nd
Bandhead
*
0.
0
0.
0.
0.
0.
m
690
595
697
568
669
553
2nd
Bandhead
0.
0.
0.
0.
0.
0.
*c
725
625
SET
680
545
SET
623
502
[NO]
(AVE)
0.93*0.0;
0.82*0.1
0.87*0.1
1.03*0.0'
1.07*0.01
1.05*0.0
1.18*0.0i
1.13*0.0'
SET 1.16*0.0'
111-29
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IV. DISCUSSION
IV.A. Introduction
As noted in the introduction to this report, the discrepancies between
optical and probe measurements, reported by W. K. McGregor, J. D. Few, M. G.
Davis, and their colleagues between 1973 and 1976, ranged from factors of 1.5
to 6.0. It was these large discrepancies that stimulated this study; therefore,
it is important to consider the results of the present study in context with
their original work. As this study was being performed, two other separate
investigations of this problem were being conducted by independent research
groups. The results of this study will also be considered relative to those
two investigations.
IV.B. Comparison of Optical and Probe Results (TASK III)
It is possible to summarize the results of this task in the following manner.
For the exhaust gas measurements made by UTRC, deviations between optical and
probe results were generally less than 25%. Frequently, the probe measured NO
values were greater than those measured optically- Measurements were made in
turbulent and non-turbulent media and at temperatures up to>^1900K. The
combustion systems were fired with both gaseous and liquid fuels. Based on the
observations of the calibration phase of this study (TASK I), it had been
estimated that an accuracy of -20% could be anticipated. If it is assumed
that precision is related to accuracy, then the agreement between the optical
and probe measurements of NO in TASK III is within that projected 20% accuracy.
The accuracy is estimated from the accumulation of uncertainties associated
with: (1) the resetability of the combustors; (2) temperature measurements and
corrections; (3) spatial distribution of temperature and pressure along the
optical path; (4) continuum type absorption due to particulates and molecular
species other than NO; (5) lamp drift; (6) beam steering; (7) perturbations in
temperature and flow by probes; (8) sample quenching; (9) sample transfer; (10)
calibration standards; and (11) the chemiluminescent analysis method. Moreover,
the results of the infrared measurements given in Appendix A, within the
scatter of that instrument's output, are in good agreement with the results of
the probe measurements. Hence, large discrepancies between optical and probe
results like those noted earlier have not been observed. Although the bulk of
the measurements were made with metallic water-cooled probes, the measurements
made with an uncooled metallic probe on the flat flame burner were also in good
agreement with the optical measurements when oxygen was present, i.e., in an
overall lean condition.
As shown in TASK I Report (Dodge et al, 1979). the characteristics of the
capillary discharge lamp used in the original work are similar to the hollow
IV-1
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cathode lamp used in this study. Also noted in the above report was the fact
that the model used to reduce the original data was in serious error. That
model (ARO) has been subsequently corrected and has been briefly described
by Few et al (1979). The new ARO model is similar to that used by UTRC to
reduce its data; however, deviation at elevated temperatures is expected
because the UTRC model uses Weisskopf broadening theory while that of ARO uses
Lorentz theory. Nevertheless, preliminary data reduction of the ARO optical
data indicated an agreement of 30% between optical and probe results (J. Few,
private communication). It is expected that these results will be published
separately.
IV.C. Recent Related Studies
The paper published by Meinel and Krause (1978) duely noted that a major
discrepancy had been observed between ultraviolet and probe measurements of
NO by ARO personnel. Also noted was the fact that the infrared gas correla-
tion measurements of Gryvnak and Burch (1976a, b) indicated discrepancies of «^
versus factors of 1.5 to 5. In their study, Meinel and Krauss used a differen-
tial resonant line (narrow-line) absorption technique in the ultraviolet to
monitor NO in hydrogen-air and propane-air flames. The temperatures of these
flames covered the range from 1700K to 2500K. The differential measurement
technique was employed to compensate for the continuum absorption due to 02
and COj' The probe used was water-cooled quartz. For both flame systems,
the agreement between probe and optical measurements was within 20-30%. The
agreement was best for the lean conditions up to $=0.9. The deviations were
the greatest at stoichiometric conditions, i.e., $=1.0. The excellent agreement
reported under lean conditions is consistent with the results given in Section
III of this report. Where the deviations were greatest, it was the optical
method which yielded the lower NO concentrations. Nevertheless, no major
discrepancies comparable to the original ARO work were observed.
A more recent study by Falcone, Hanson, and Kruger (1979) used an infra-
red tunable diode laser to measure NO (5.2ym) in the postflame gases of a
flat flame burner. Methane/air flames seeded with NO were probed with an
uncooled quartz probe. The seed levels ranged from
-------
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and TASK III. Finally, their measurements were consistent with those reported
by Gryvnak and Burch (1976a, b), the results of this (UTRC) study, and do not show
major discrepancies.
IV.D. Original Studies: Comments
The demonstration that in situ measurements were feasible in the hostile
environments of jet combustor and engines was a significant achievement.
Moreover, the development of a first principles model to interpret optical data
in inhomogeneous media such as jet exhausts was an excellent approach to a
difficult problem. The first reported work was obtained during CIAP by McGregor
et al (1972) and was compared with probe data obtained by Neely and Davidson
(1972) and Grissom (1972). However, this work cannot be used to establish that
there is a fundamental problem with properly made probe measurements of NO.
The principal reason for this is that those optical data were not reduced with
a first principles model but with a room temperature calibration curve.
Moreover, no attempt was made to use a zonal treatment of the inhomogeneities
in temperature, pressure, and concentration. Other difficulties include the
misconception that collisional broadening is much less than Doppler broadening,
a major underestimation of the influence of the inhomogenities on the accuracy
of the optical method, the possibility of a stagnation zone in front of the
probe, and the wrong probe design for sampling the fuel laden exhaust in the
maximum afterburning conditions.
The first report describing the first principles model was that of
McGregor et al (1973). Unfortunately, this report and as well as other reports
on model verification (e.g. Davis et al, 1975) contain serious spectroscopic
problems. These problems are listed in detail in TASK I Report and are
sumarized in Section V of this report. Because it was stated in these reports
that good agreement existed between the predictions of a faulty model and
experimental data, there is evidence to suggest that the experimental data had
serious errors. An example of this is contained in Table IV-A where ARO
calibration data obtained under ideal conditions are compared with old and new
model predictions. Since the transmissions predicted by new ARO and UTRC
models are in agreement and have been verified, then a problem exists in the
measurement of transmission or in the measurement of mole fraction or pressure.
Possible sources of error could be nonlinear optical and electronic detection,
faulty gas mixing procedures, and inexact chemiluminescent calibration.
The combustor work which followed the CIAP measurements was that involving
the AVCO-Lycoming research combustor. These measurements were made on a super-
sonic exhaust stream and, hence, can only be related to the results of Section
III in an indirect way. Nevertheless, there are some points which should be
considered. Few et al (1975) indicated that discrepancies between optical and
probe NO concentrations with the optical values higher by factors of 3.5 to
IV-3
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TABLE IV-A
A COMPARISON OF CORRECTED MODEL RESULTS WITH ORIGINAL
MODEL AND VERIFYING EXPERIMENTAL RESULTS: AN EXAMPLE
(Data From AEDC-TR-76-12, Davis et al (1976), Fig. 9)
Temperature = 422K
n[NO] = 1.31 x 1015/cm3
Pathlength = 91.4 cm
2nd Bandhead Transmission
Curve
No.
1
3
5
P
(atm)
1.36
0.71
0. 19
[NO]
(opm)
55
106
395
Me as.
0.
0.
0.
820
710
467
Orig
Model
0.
0.
0.
. ARO
(6/78)
824
737
549
New
Model
0
0
0
ARO
(6/79)
.690
.598
.414
UTRC
Model (6/79)
0
0
0
.690
.598
.429
Discrepancy*
(ARO Orig. to
1.92
1.68
1.47
Discrepancy =
0r ig
IV-4
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R80-994150-3
6.0. As evidence indicating that NO was being destroyed in the probe, results
of optical measurements made in the sample line were presented which indicated
agreement between the chemiluminescent analyzer and the ultraviolet technique.
This agreement, however, is inconsistent with the fact that the model that
was used to process the optical data was in error. This again suggests experi-
mental difficulties similar to those discussed above and indicated in Table IV-A.
(Falcone et al (1979) discuss some problems encountered in making chemilumi-
nescent analyses of wet samples and comparing them with infrared results.) In
the reduction of their data, Few et al (1975) did not employ a zonal treatment
of the NO and temperature profiles. From the data presented, the probe measure-
ments were sparse. In fact, neither experimental NO concentration data were
obtained in the region beyond the width of the nozzle nor were temperature
measurements made. Static temperature, static pressure, and optical path were
predicted rather than actually measured. However, the placement of a probe in
a supersonic flow 0.5 inches downstream of an exhaust nozzle can cause a major
perturbation to the flow and temperature. Also, as noted in TASK II Report
(Colket et al, 1979), a stagnation zone in front of their turbular inlet probe
could perturb the gas samples. For air at a Mach number of 1.15, a 25% rise in
temperature can be produced. For this type of probe, the gas must decelerate
to a low Mach number at the entrance, and consequently stagnation temperatures
will be approached even if an external stagnation zone does not exist. This
evidence indicates that not only were there difficulties with the optical
measurements, but most likely proper probe technique was not employed, i.e.,
50% pressure drop occur ing at the probe orifice as required by the Federal
Register. Consequently, these measurements cannot be used to establish a
fundamental problem with the probe technique either in subsonic or supersonic
flows.
Following the AVCO-Lycoming measurements, ultraviolet and infrared measure-
ments were made on the T-56 combustor exhaust by Few et al (1976) and Grvynak
and Burch (1976a, b), respectively. As mentioned earlier, the infrared measure-
ments show discrepancies of 20-30% with the probe measurements. This was the
first time that a proper comparison of probe and optical data was performed,
i.e., a zonal treatment accounting for temperature and concentration nonuniform-
ities along the optical path. The ultraviolet data processed in the same manner
indicated discrepancies of 1.5 to 1.9 with the probe data. However, these data
were processed with a faulty model. Table IV-B gives the results reprocessed
with a correct model. The discrepancies are 30% or less and the average error
is less than 20% with the optical method measuring more NO. With the uncertain-
ties .in these measurements, this can be considered good agreement, hence, a
fundamental problem with the probe method has not been established by these
measurement s.
IV-5
-------
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TABLE IV-B
T-56 MEASUREMENTS BY ARO REEXAMINED WITH
CORRECTED SPECTRAL MODEL
(From Table 3, AIAA Paper 76-109)
2nd Bandhead Transmission
[NO] *
Run Location Pyridine Calculated from Meas. -£
Number Downstream Added
la 3
lb 3 x
lc 3 x
ld 3 x
2 18
obe Values
Tc
0.909
0.895
0.882
0.875
0.881
Tra
0.884
0.875
0.850
0.830
0.874
[NOJnl
0.77
0.83
0.78
0.72
0.95
IV-6
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V. SUMMARY AND CONCLUSION
Since this is the last in this series of reports on the measurement of NO
by optical and probe methods, it is appropriate to include the conclusions of
the first two parts of the study along with those of this the third part so
that the conclusions for the complete study can be viewed in their entirety.
V.A Optical Calibration (TASK I)
In the first part of the study on optical calibration (Dodge et al, 1979),
it was concluded that known amounts of NO can be provided for calibration
purposes at temperatures ranging from 300 K to 2000 K if certain procedures are
used. For temperatures up to 850 K, NO diluted in N2 and Ar will not signi-
ficantly (< 10%) decompose when flowed through a quartz-bed heat exchanger.
Although it was not experimentally verified, a kinetic analysis indicated that
substantial decomposition would not occur in this exchanger up to 1000 K. For
temperatures of 1000 K to 2000 K, NO seeded into a lean H2/02/Ar flat flame is
recovered in the post flame region. Detailed temperature and concentration
distributions along the optical path were obtained with thermocouples and probes.
For the highest temperatures, the thermocouple data were corrected for radia-
tion losses. At the low temperatures (< 850), the concentration measurements
were made with both uncooled quartz and metallic probes. The concentration
measurements downstream of the flat flame burner were obtained with water-cooled
quartz probes. The NO analysis was performed on-line by chemiluminescence and
mass spectroscopy.
At the beginning of this study, a detailed spectroscopic computer model
was provided by ARO, Inc. This model had been used by several authors at ARO
(McGregor et al, 1973; Few et al, 1975; Davis et al, 1976) who pointed out
serious discrepancies between probe and optical NO concentrations measured
under similar conditions. A detailed review of the spectroscopic theory upon
which the model was based indicated several significant errors. A complete
description of these errors, along with where these errors exist in previously
published reports and literature, is given in Appendix B of TASK I Report (Dodge
et al, 1979). However, these errors can be summarized by the following.
First, the equation relating the oscillator strength for an individual line to
band oscillator strength was in error by a factor of 4. Second, the equation
relating the number density of an individual state to the total number density
was in error by a factor of 2. Third, originally no distinction in population
22
was made between the "i/o anc^ ^3/2 states- This was partially corrected in
the later work, but without correct normalization. Fourth, an error in the
Honl-London factor for the Qjj lines was present in the program supplied at the
beginning of this study. Fifth, the equation which relates broadening parameter
V-l
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R80-994150-3
to collision cross section was in error by an order of magnitude. Other minor
errors and suggested improvements are also given in the above appendix.
Because of these errors, the results of the optical measurements were not
reliable and, hence, cannot be used to establish a discrepancy between NO
concentrations determined with probe and optical methods.
The spectral theory was corrected and incorporated into a new computer
model. This model was used to process both high resolution, single line data
obtained with a continuum lamp and low-resolution data obtained with a narrow-
line' lamp. Since the results from these two different optical methods were
self-consistent, the validity of the model was established.
Two of the required inputs for the model are broadening parameter and
oscillator strength. Broadening parameters for NO in Ar, N2» CX^, and CH^
were measured by the direct observation of isolated absorption lines. For the
majority of the data, the resolution was sufficiently high (full width at half
maxima < 0.0020 nm) that the contribution of the slit function to the total
line shape was minimal. The broadening of NO in ^0 at elevated temperatures
was inferred from H2/02/Ar/NO flame measurements. The temperature dependence
of the broadening parameters did not appear to follow the Lorentz broadening
theory at elevated temperature but that of Weiskopf. Oscillator strengths were
also determined from these same high resolution spectra. The broadening results
are unique; the oscillator strengths are in excellent agreement with the latest
recommended value. Moreover, oscillator strengths were determined from low
resolution using the broadening parameters determined in high resolution. With
proper accounting for emission lines present in the lamp output but not due to
NO, these strengths were in good agreement with recommended values.
Sufficient measurements were conducted and compared with model predictions
of absorption to conclude that the ultraviolet optical system based on the
hollow cathode lamp is calibrated to measure NO. In addition, similar measure-
ments were made with the capillary discharge lamp. Those measurements are
reported in TMR-79-P7 (Few et al, 1979) and TR-79-65 (Few et al, 1979).
Finally, an empirical calibration of the infrared gas correlation
spectrometer was performed (Appendix A). Because this instrument was origin-
ally designed for stack monitoring, i.e., low temperatures and high densities,
it was not well-suited for the measurements of interest here. The low temper-
ature data indicated that the instrument was 20 percent more sensitive relative
to the calibration previously used in jet combustor measurements. This varia-
tion is attributed to changes in grating alignment. A dependence of the cali-
bration on broadening gas was observed and determined. For temperatures up
to 900 K, the calibration, within the scatter of the instrument output, remained
constant. Above 900 K, a significant decrease in sensitivity was observed.
This dependence is most likely due to significant changes in the populations of
V-2
-------
R80-994150-3
the lines selected by the grating assembly. However, sufficient data were
obtained to allow measurements to be made at high temperatures if high NO
seeding of the media is used.
V.B Probe Method (TASK II)
The major conclusions of TASK II are the following. First, water-cooled
quartz, stainless steel, and copper-tipped miniprobes yield the same NO concen-
trations when sampling products from methane/oxygen/ nitrogen flames with
seeded NO at temperatures up to 2000 K and irrespective of stoichiometry. This
similarity in behavior occurs over a wide range of probe back pressures; hence,
no advantage is gained from back pressures less than 0.5 atm when sampling
atmospheric pressure flames.
Second, uncooled stainless steel probes give NO concentrations somewhat
lower (10-15%) than the cooled probes mentioned above for lean methane/oxygen/
nitrogen flames. For stoichiometrie and rich flames, the NO concentrations are
significantly less and for rich flames, the amount of loss is dependent on
probe back pressure. The destruction of NO in this uncooled probe is similar
to that encountered in NO/N02 converters operated in the absence of oxygen.
Hence, uncooled stainless steel probes are only suitable for sampling NO in
the presence of oxygen.
Third, in general, for miniprobes and microprobes, aerodynamic quenching
is not possible because of fluid mechanical and geometric constraints. However,
rapid-cooling of the sample gases (within a few milliseconds) can be achieved
by convective heat transfer to the probe walls.
Fourth, for microprobes, mass flow measurements indicate that in the
sampling of high temperature gases choked flow does not occur at the classical
pressure ratio. This result was predicted by the probe model and suggests that
quenching processes may be less efficient than those estimated in previous
studies. A kinetic analysis indicates that quenching rates are still suffic-
iently rapid for sampling NO in exhaust gases; however, the impact of slower
quenching rates on gases sampled from reactive flame zones may have to be
examined.
Fifth, unlike the small scale probes, it is possible to construct a large
scale water-cooled probe that can produce aerodynamic quenching of the sample;
however, measurements made on both gaseous and liquid fueled combustion systems
yielded essentially the same results regardless of the quenching mode, i.e.,
aerodynamic or convective. Given this fact plus the complexity of probe
construction and the difficulties in achieving the low probe back pressures
required of the aerodynamic mode, there is no advantage to aerodynamic quenching
in the measurement of NO.
V-3
-------
R80-994150-3
Sixth, the model predictions of pressure distribution and mass flow within
the large scale probe agreed well with the experimental data. In addition, the
model accurately predicted that the microprobe would not choke at the classical
pressure ratio when sampling at high temperatures. Based on these results, it
can be stated that the fluid dynamic and heat transfer processes have been
adequately described in the model for the case of fluid mechanical choking at
the probe orifice.
Seventh, a kinetics analysis of gas phase reactions known to destroy NO
indicated that no significant loss of NO would occur during the sampling pro-
cess if the sample temperature was reduced to 1000 K in approximately 1-2
milliseconds. The results of this study are consistent with this analysis.
Eighth, a review of the literature indicated no definitive study where
large differences (> 20%) between measurements of nitrogen oxides from differ-
ent probes were observed when properly designed probes and sampling lines were
used and correct calibration of the chemiluminescent analyzer was performed. A
properly designed probe is one that does not perturb the flame environment,
does not stagnate the flow, is water-cooled, operates at a back pressure to
external static pressure ratio low enough to aid in quenching of reactions, and
finally has hot walls (> 600 K) which are limited only to the front portion of
the tip such that the local gas residence time is on the order of 10 micro-
seconds or less. Proper sampling lines are those in which the residence times
are short relative to the time required for the conversion of NO to N02 and
the loss of NO in water traps and particulate filters. Correct calibration
of the chemiluminescent analyzer consists of accounting for the influence of
gases other than N2 on the introduction of NO into the chemiluminescent
reaction chamber and the collisional deactivation of excited N0.
V.C Comparison of Probe and Optical Methods (TASK III)
From the third part of this study, the following conclusions can be drawn.
First, NO concentrations determined in subsonic exhaust streams by narrow-
line ultraviolet spectroscopy are in good agreement (+ 20% or better) with
those determined with water-cooled probes. This agreement was observed for
a wide range of conditions when the optical data were processed correctly and
the probe sampling was conducted properly. These conditions included tempera-
tures from 293 K to 2000 K, and both turbulent and nonturbulent flow. Proper
processing of the optical data entails a detailed knowledge of temperature
and pressure along the optical path, adequate characterization of the lamp,
and a correct spectral model. Proper probe sampling consists of rapidly
quenching the gas sample by sudden pressure reduction and convective cooling,
rapid sample transfer, especially in the presence of oxygen, and a calibra-
tion procedure for the chemilurainescent analyzer that includes viscous and
-------
R80-994150-3
collisional deactivation effects. Moreover, this agreement was seen irrespec-
tive of probe material (metallic or quartz) and fuel type, i.e., gaseous or
liquid.
Second, good agreement between optical results and uncooled probes was
observed with measurements made in exhaust streams where oxygen is present,
i.e., overall lean systems. However, in rich stoichiometric and systems,
uncooled metallic probes gave NO concentrations which were in substantial error
(> 100%) and, hence, cannot be employed for measurements except in overall lean
systems.
Third, the infrared correlation spectroscopic measurements can be
considered, within the scatter, in good agreement with the water-cooled probe
measurement s.
Fourth, recent studies involving the measurement of NO in flat flame
exhausts are in good agreement with the results of this study. These studies
were made by a narrow-line ultraviolet method (Meinel and Krauss, 1978) and by
an infrared laser technique (Falcone et al, 1979).
Fifth, to reiterate the conclusion of Section V.B, there is no advantage
gained in operating a probe in an aerodynamic quench mode while measuring
NO.
Sixth, in the measurement of NO in exhaust streams, the optical methods,
although nonperturbing, offer no major advantage over probe methods. The
nonperturbing aspect is offset by the facts that: (1) the optical path in an
unconfined exhaust stream is most easily defined by a probe method; and (2)
static temperature and pressure distributions are necessary to reduce the
optical data, yet presently, have to be determined by probe methods. Moreover,
to improve the sensitivity of the optical absorption method at high temperatures
(> 1000 K), low pressures « 0.2 atm) and short pathlengths, multiple pass
optical systems are required.
Finally, the previously published ARO ultraviolet measurements cannot be
used to deduce that major fundamental discrepancy (50%) exists between probe
and optical results in subsonic flows. Serious problems were identified
in the spectroscopic model. Subsonic data when reprocessed did not indicate
a major discrepancy. These same problems were present when the optical data
obtained on supersonic flow were processed and, hence, no conclusion can be
drawn for the supersonic flow. Moreover, there is evidence to suggest that
probe measurements made in the supersonic flows are questionable along with the
method used to compare the optical and probe results.
V-5
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Glawe, G. E., F. S. Simmons, and T. M. Stickney: NACA TN 3766 (1956).
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Gryvnak, D. A., and D. E. Burch: AFAPL-TR-75-101, (1976a).
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Johnston, H. S: Science, 173, 517.
Land, T. and R. Barber: Transacting of the Society of Instrument Technology, 6,
112 (1954). ~~
McCullough, R. W., C. H. Kruger and R. K. Hanson: Comb. Sci. Tech., 15, 213-223
(1977).
McGregor, W. K., J. D. Few and C. D. Litton: Arnold Engineering Development
Center Report AEDC-TR-73-182, AD-771 642 (1973).
McGregor, W. K., B. L. Seiber and J. D. Few: Proc. Second Conf. Climatic
Impact Assessment Program, p. 214, Cambridge, Mass. (November 1972).
Meinel, H.: Z. Naturforsch., 30a, 323 (1975).
Meinel, H. and L. Krauss: Combustion and Flame, 33, 69 (1978).
NAS (National Academy of Science), "Environmental Impact of Stratospheric
Flight", Climatic Impact Committee (1975).
Neely, J. and D. L. Davidson: Proc. Second Conf. Climatic Impact Assessment
Program, p. 180, Cambridge, Mass., (November 1972).
Oliver, R. C., E. Baver and WasyIkiwskyj: DOT-FAA Rpt. FAA-AEE-78-24.
Oliver, R. C., E. Baver, H. Hidalgo, K. A. Gardner and Wasylkiwskyj:
DOT-FAA Rpt. FAA-EQ-77-3 (1977).
Seery, D. J. and M. F. Zabielski: unpublished.
Vranos, A., B. A. Knight, J. J. Sangiovanni, L. R. Boedeker, and D. J. Seery:
Feasibility Testing of Micronized Coal-Oil (MICO) Fuel in a Model Gas Turbine
Combust or, UTRC R79-954451-1, May 1979.
R-3
-------
Appendix A
Measuring NO In Aircraft Jet
Exhausts By Gas-Filter Correlation
Techniques, Task III
David A. Gryvnak
Ford Aerospace and Communications Corp.
Aeronutronic Division
Ford Road
Newport Beach, California 92663
September 1979
United Technologies Research Center P. 0. 82126
FINAL REPORT TASK III
-------
INTRODUCTION AND SUMMARY
Tests were conducted using the smokestack instrument described in the
Task I report to measure the amount of NO under four controlled test condi-
tions. The first were a series of tests performed, both at Ford Aerospace
and Communications Corp (FACC) and at United Technologies Research Center
(UTRC) using static cells of 10 cm and 20 cm long respectively with the NO
samples at room temperature. A second set of tests at UTRC were performed
using a Flat Flame Burner at approximately 1850 K with a path length of
17.5 cm. A third set of tests were performed using an IFRF burner, the
sample being at approximately 1300 K with a pathlength of 67.3 cm. The
fourth set of tests were performed using an FT12 burner can, here three
different power conditions were used so that the sample temperature varied
from 600 to 900 K. The pathlength was 67.3 cm. Three different stoichio-
metric conditions were used for the IFRF and FT12 burner tests, 4> = 0.8,
1.0 and 1.2, lean to rich. In addition, during the IFRF tests the exhaust
had a tangential velocity imparted to it by vanes that were inside the burner
assembly. These vanes were changed so that two different tangential velocity
conditions were tested, swirl = 0.63 and 1.25. The amounts of NO determined
using the smokestack instrument were compared to the amounts determined
using the probe instrument.
The results of Task I predicted that the values obtained by the
smokestack instrument would be higher than the probe results for temperatures
below 900 K and lower for temperatures above 900 K. The results of the tests
in Task III are in good agreement with the results of Task I. Also theo-
retical calculations were made with the use of a computer, simulating the
response of the smokestack instrument and the results are in agreement with
the values obtained by the smokestack instrument. These calculations indi-
cate that the smokestack instrument is correctly responding to the amount of
NO in the different burners at the higher temperatures and that the probe
results are quite good.
A-l
-------
DATA REDUCTION
The probe data and the data from the smokestack instrument were reduced
in a manner as described in the Task I report. For a sample at constant
temperature and concentration, the absorber thickness u is related to the
temperature, 6, pathlength L and pressure, p, of a sample in the following
manne r .
. 7. p(atm) L(cm) 21
u(molecules/cm2) = - r-; - 7 . 34 x 10 .
For a sample that has temperature and concentration gradients over a path-
length L, the absorber thickness can be found from the integrated values.
u = 7.34 x 1015 CALZ _ , (2)
where
I
AL = incremental pathlength, . AL = L,
C = centerline concentration (ppm) ,
M. = molar concentration for i increment,
6. = temperature (K) of i increment.
AL =0.5 was used for the Flat Flame Burner results, and
iL = 1.0 was used for the IFRF and FT12 Burner results.
The temperature profiles and molar concentration profiles that were supplied
by UTRC for the different burners and their associated stoichiometric and
swirl conditions are shown in Figs. 1 through 8. These are the profiles used
to determine the absorber thickness for the probe results, denoted as uc.
The values determined by the smokestack instrument, denoted as urn,
were determined by comparing the instrument response to the calibration
curve shown in Fig. 9. This is the same calibration curve used in Task I
and was originally to be used only for sample temperatures up to 900 K.
During Task I the instrument was calibrated for the elevated temperatures
used for Task III except that the carrier gas was argon. Methane modified
air was used in Task III and because no calibration curve exists for NO in
N-, at elevated temperatures, the original calibration curve was used and the
results compared with the probe values and theoretical results.
A-2
-------
41
C
0>
4-1
C
T3
HI
01
g
01
)-i
3
1.0
0.5
'T0
Flat Flame Burner
Mole Fraction Profile
'/> = 1.0
= 0.8
1.2
-20 -10 0 10 20
Distance from centerline (cm)
Figure 1. Mole Fraction Profile for the Flat Flame Burner for three conditions of stoichiometry
-------
2000
1000
01
§
(U
F--
300
1.0
0.8
Flat Flame Burner
''emperature Profile
^-0 - i.:
-20
10 0
Distance from centerline (cm)
10
20
Figure 2. Temperature Profile for the Flat Flame Burner for three conditions of stolchlometry
-------
01
c
0)
4-1
c
0)
u
-o
0)
a
O)
D
in
g
1.0
0.5 -
-40
Mole Fraction Profile
IFPF Burner
swirl = 2
-30
!
-20
T - -
=' 0.8
1.0
1.2
1
0
1
NO
-10 0 10
Distance from centerline (cm)
20
30
Figure 3. Mole Fraction Profile
Stolcliiometrv.
for the IFRF Burner with a swirl of 2 for three conditions of
-------
isoo
T"
1
NO
% = 1.0
innn
HI
u
3
(-1
O)
D-
r-
5001
300'
/ ' =1.2
/ .'""
: = o.R
-30
Tomprrature Profilr
TFFF Ki
swirl = ?
-70
I
-10 0 10
Distmce from centerline (cm)
Temper.iturp Profile for the IFRF Burner with a swirl of 2 for three conditions of
s t o i ch 1 omc t r ,'
-------
OJ
u
c
-------
1000
I
HI
00 Q.
o
500
300
-40
- 1.0
NO
-30
-20
Temperature Profile
IFRF Burner
Swirl = 4
-10 0 10
Distance from Centerllne (c
20
30
40
TemperHfire I'roMle for the IFRF Burner with a swirl of 4 for three conditions of
stoicM ometr .
-------
0)
H
,4
Lj
1)
LJ
U
LJ
r3
^3
Hi
* 0. =i
CM
> -C
6-
( MO/No > measured /(NO,
o
-4
111 ' ' ' NO
hi;iximum Continuous
^
/ \
/ \
, ("ruise \
~^\ N
' / \ N
1 / \ \
' i \ :
; ' \\ -
"~ ' / \ \
i / Idl^ - 1 I
' / /^ ^\ ! '
' / / Mole Traction Profile \ \ '
' . / '-T12 Burner Can \ > .
' i V 'x
' / V \
' / / V N
' ' / \\ v
/ / / V N
' / \Xv
£/ III III ^^.
o -jn -?n -10 o 10 ?o 30 u,
Figure 7.
"istance from Centerline (cm)
Mole Fr;ic( ion Profile Tor the FT12 Burner Can for three power conditions.
-------
innn
>
>
o
01
p
3
u
nt
M
«
I"
0)
H
M/iximum Continuous
300
-40
-30
-20
-10 0 10
Distance from Centerline (cnT>
Figure 8. 'I'emperature profile Tor the FT12 Burner Can for three power conditions.
-------
0.1
0.01 _
0.001 -
0.0001
-f 296K
o 581K
o 873K
88 OK
10
19
Absorber Thickness (moleculee/cnr)
Figure 9.
Calibration curve for NO used at Wright Patterson
Air Force Rase, Instrument response V* vs absorber
thickness ti.
-------
In order to better understand the effects on the instrument of having
the sample at elevated temperatures, calculations were made simulating the
instrument response and plotted against the sample temperature. These
results are shown as the solid curves in Fig. 10. The values for the 600 K
calculations were so close to the 300 K values that a single curve was used
for both. The values represented by + were obtained from the original cali-
bration curve and fall on the 300-600 K curve. This indicates the calcula-
tions represent the response of the instrument very well for samples at room
temperature and supports the validity for the curves for the higher tempera-
ture samples. As can be seen in Fig. 10, as the temperature increases the
response of the instrument decreases. This temperature dependence was found
to be true in Task I and the results of Task III verifies it.
RESULTS
The results of all the tests are tabulated and presented in Tables 1
through 4. The first column lists the test identification number, the
second column lists urn the absorber thickness of the sample as measured by
the smokestack instrument and the third column lists uc, the absorber thick-
ness as calculated from the probe temperature and mole fraction profiles.
The fourth column lists the ratio um/uc. The fifth column for the static
cell tests, list the temperature of the sample, for the other tests where
temperature gradients occur, the centerline temperature of the sample is
listed. The stoichiometric conditions were changed for the IFRF and FT12
burner tests and are listed in the sixth column in Tables 2 through A.
CONCLUSIONS
The values of um/uc are plotted against temperature as dots in Fig. 11.
The values represented by the squares were obtained from the curves in Fig. 10.
The results are similar to those obtained in Task I when argon was used as a
carrier gas. The smokestack results tend to be higher, up to 20 percent for
temperature below 900 K and tend to be lower, down to 50 percent, for
temperatures above 1100 K. The calculated results, represented by the
squares, show the same tendency. These calculated values were obtained by
determining the ratio of u(296)/u(6) for a constant V. They are within
20 percent of the results determined by the smokestack and probe instruments
even at the temperature as high as 1800 to 1900 K. The fact that the ratio,
at the two temperatures, of the calculated instrument response closely fits
the ratio of the measured to probe results indicates than an instrument using
xas correlation techniques, if calibrated for these temperatures could easily
predict the amount of NO that was being emitted by a jet engine. Also it
verifies that thu- probe instruments are reasonably accurate even at the
higher ter; <. raturi. , certainly not in error by factors of as great as six.
A-12
-------
0.1
1 1
NO Calculated Tnst rument Response
calculated i ;.str"inert response,
+ experimental ivstrume"f response
1
300,600K
900K
1500K
1900K
0.01
M
U)
V
0.001
0,0001
1016
u
loTT
Absorber Thickness (molecules/<
Figtire 10. Calculated Instrtiment response. The solid curves represent the calculated
Instrumer, t response for five different temperatures. The plotted points,
+, are values determined from the calibration curve shown in Figure 9.
-------
TABLE 1
STATIC CELL TEST RESULTS
urn uc um/uc
Multiply values of u by 10^
(a)(///cm2) (///cm2) (K)
UTRC TESTS
52.5
52.5
50.5
50.5
49.5
49.5
49.5
49.5
1.06
1.06
1.02
1.08
296
296
296
296
FORD TEST
52.5 49.5 1.06 296
49.8 49.5 1.01 296
(a)
The units of u are molecules/cm2, abbreviated here by
(///cm2).
A-14
-------
TABLE 2
FT12 BURNER CAN TEST RESULTS
(a)
mn uc
Multiply values of u by
(c)(#/cm2)
FAI-1
FAI-2
FAI-3
FAC-1
FAC-2
FAM-1
FAM-2
FAH-1
45.7
53.5
34. A
29.6
21.3
31.2
22.9
54.6
46.
45.
28.
31.
23.
39.
28.
50.2
um/uc
0.983
1.17
1.21
0.948
0.910
0.789
0.802
1.09
(a) Noise Equivalent u = 1 x 10^° molecules/cm
(b)
Centerline
(K)
590
590
590
900
900
935
935
500
Comments
Idle
Idle
Idle
Cruise
Cruise
Max
Max
Air Onlv
(b) Three power conditions were tested, engine at idle, cruise and maximum
continuous. In addition hot air without the engine running was seeded
for test FAH-1.
(c) The units of u are molecules/cm2, abbreviated here by (///cm2)
A-15
-------
TABLE 3
IFRF BURNER TEST RESULTS
urn . uc utn/uc 6
Multiply values of u by 10^6 Centerline
(c)(///cm2) (///en,2) (K)
Swirl = 0.63
FA-1-1 11.3 18.5 0.611 1230 0.8
FA-2-1 9.7 12.8 0.756 1330 1.0
FA-3-1 5.3 7.7 0.689 1240 1.2
FA-3-2 6.6 13.7 0.486 1240 1.2
Swirl =1.25
FA-4-1 21.5 34.7 0.620 1220 0.8
FA-5-1 10.0 22.5 0.443 1300 1.0
FA-5-2 U.3 33.8 0.626 1300 1.0
FA-6-1 8.0 13.9 0.578 1235 1.2
FA-6-2 9.7 15.4 0.630 1235 1.2
(a) Noise Equivalent u = 1.5 x 1016 molecules/cm2
(b) Three stoichiometric conditions were tested;
Lean, * =0.8, normal, i = 1.0 and rich, s* = 1.2
(c) The units of u are molecules/cm2, abbreviated here by (///cm2)
A-16
-------
TABLE A
FLAT FLAME BURNER TEST RESULTS
(a)
urn uc um/uc 6
Multiply values of u by 10^-^ Centerline
(///cm2) (///cm2) (K)
FAB 1-1
FAB1-2
FAB2-1
FAB 301
FAB 3- 2
7. A
11.3
9.1
A. 7
6.9
13.2
26.9
23.6
7.3
13.6
0.562
O.A20
0.388
0.6A1
0.503
17AO
1830
1830
1800
1800
0.8
0.8
1.0
1.2
1.2
(a) Noise Equivalent u = 2 x 10 molecules/cm2
(b) Three stoichiometric conditions were tested; lean, = 0.8,
normal, = 1.0 and rich, = 1.2
r\
(c) The units of u are molecules/cm, abbreviated here by (///cm )
A-17
-------
2.0
1 1 1 1
1 r
NO
um
uc
vs
experimental results
0 calculated results
1.0
um
uc
0
a
i
i
1000
Temperature (K)
2000
Figure 11.
Plot of um/uc versus temperature. The points
are from the results tabulated in tables 1 thru U.
The values represented by the squares,0 , are
from the calculated ratio u(296)/u(P) for a
constant V.
A-18
-------
REFERENCES
1. Burch E. E. and Gryvnak D. A.: "Infrared Gas Filter Correlation
Instrument for In Situ Measurement of Gaseous Pollutants" prepared
by Ford Aerospace and Communications Corp. for the EPA under Contract
No. 68-02-0575, EPA Report No. 65012-24-094, December 1974.
* u.S.G.P.O. 725-403/1302-1112
A-19
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