EPA/AA/TDG/92-06
Technical Report
Conversion of Methanol-Fueled 16-Valve,
4-Cylinder Engine To Operation On Gaseous
2H2/CO Fuel - Interim Report IV
by
Ronald M. Schaefer
Fakhri J. Hamady
James C. Martin
September 1992
NOTICE
Technical Reports do not necessarily represent final EPA
decisions or positions. They are intended to present technical
analysis of issues using data which are currently available. The
purpose in the release of such reports is to facilitate the
exchange of technical information and to inform the public of
technical developments which may form the basis for a final EPA
decision, position or regulatory action.
U. S. Environmental Protection Agency
Office of Air and Radiation
Office of Mobile Sources
Regulatory Programs and Technology Division
Technology Development Group
2565 Plymouth Road
Ann Arbor, MI 48105
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
ANN ARBOR. MICHIGAN 48105
JAN 8 1993
OFFICE OF
AIR AND RADIATION
MEMORANDUM
SUBJECT: Exemption From Peer and Administrative Review
FROM:
Karl H. Hellman, Chief
Technology Development Group
TO:
Charles L. Gray, Jr., Director
Regulatory Programs and Technology Division
The attached report entitled "Conversion of Methanol-Fueled
16-Valve, 4-Cylinder Engine To Operation On Gaseous 2H2/CO Fuel -
Interim Report IV," (EPA/AA/TDG/92-06) describes progress to date
on a project to convert a Nissan CA18DE engine previously modified
for operation on M100 neat methanol to operation on dissociated
methanol (2H2/CO) gaseous fuel. This engine was operated on both
M100 and simulated dissociated methanol (67 percent hydrogen and 33
percent carbon monoxide) fuels. This report describes recent
modifications made to the engine and fuel delivery system and
summarizes the results from recent testing.
Since this report is concerned only with the presentation of
data and its analysis, and does not involve matters of policy or
regulations, your concurrence is requested to waive administrative
review according to the policy outlined in your directive of April
22, 1982.
Concurrence:
larles L. Gray,/Jr/, Director, RPT
cc: E. Burger, RPT
Date:
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Table of Contents
Page
Number
I. Summary ..... 1
II. Introduction 2
III. Description of Test Engine 2
IV. Recent Fuel System Modifications 4
V. Exhaust Measurement Procedure 5
VI. Discussion of Test Results 6
A. simulated Carbureted Operation 6
B. Simulated Direct Injection Operation 8
C. Emissions and Combustion Analysis 11
VII. Summary and Conclusions .20
VIII.Future Efforts 20
IX. Acknowledgments 21
X. References 21
APPENDIX A - Test Engine Specifications A-l
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I .
A 16-valve, 4-cylinder light-duty automotive engine has been
converted to operation on a mixture of hydrogen (H2) and carbon
monoxide (CO) gaseous fuel in a 2:1 molar ratio of H2 and CO. This
engine has been used to investigate the difference in emission
levels and power output between two different fuels: M100 neat
methanol and simulated dissociated methanol gaseous fuel (2H2/CO) .
This report contains test results of power output from several
engine/ fuel system modifications. These modifications were made in
an attempt to increase the brake specific power output of the test
engine when operated on 2H2/CO fuel in reference to M100 levels.
With the gaseous fuel, several intake port/ fuel system
configurations and fuel injection nozzle designs were evaluated.
These modifications were evaluated to determine the effects of fuel
pressure, injection location, and fuel delivery methods on engine
performance .
Gaseous fuel was delivered to the engine by two different
methods, premixed air /fuel mixture in the intake manifold from
continuous port injectors (simulated carbureted operation) and
simulated direct injection. The simulated direct injection
operation was achieved by inserting blockages in four of the intake
runners where the M100 fuel injectors were located. As a result,
gaseous fuel was supplied through one intake valve and air through
the second intake valve.
The largest torque achieved in this evaluation with 2H2/CO
fuel was 80 ft-lbs, approximately 80 percent of the maximum torque
levels obtained with M100 fuel at the same WOT, 2,000 rpm operating
conditions. This torque was obtained in the simulated direct
injection configuration. When operating with the premixed mixture,
output torque reached approximately 60 ft-lbs with frequent
abnormal combustion occurrences, most notably preignition in the
intake manifold. Preignition of a hydrogen containing fuel is not
an unusual occurrence. [1-5]
Brake-specific emission levels with gaseous fuel testing
conducted in this most recent evaluation were significantly lower
than levels obtained previously. However, engine-out CO levels
were approximately double the level obtained with M100 fuel. HC
levels with 2H2/CO fuel operation were very low.
Proposed future efforts will utilize a mixture of M100 and
2H2/CO fuel for engine operation. Emissions, fuel consumption, and
engine performance will continue to be monitored for operation on
this mixed fuel.
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II. Introduction
With recent advances in internal combustion engines and
emission control development, new technologies are being directed
toward improving combustion efficiency, multi-fuel capability, and
reduced emissions. Recent developments in engine technology' have
enhanced stable burn and reduced emission levels. The use of
various alternative fuels is also being addressed to satisfy clean
air legislation for the 1990's.
One alternative fuel candidate is the concept of using exhaust
waste heat to provide the energy necessary for the dissociation of
methanol (CH3OH) to hydrogen and carbon monoxide. Methanol may be
catalytically decomposed to H2 and CO gases according to the
reaction:
CH3OH(l) 2H2(g) + C0
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two intake and two exhaust valves per cylinder. The valves are
operated by dual-overhead camshafts, one each for the intake and
exhaust sides.
The test engine was initially modified by Nissan to better
utilize the qualities of M100 neat methanol over unleaded gasoline.
These modifications were discussed in detail in an earlier
paper.[6] A summary of the test engine specifications when fueled
with M100 neat methanol is included in this report as Appendix A.
EPA then modified this engine for use with
simulated
33 volume
dissociated methanol fuel (67 volume percent H, and
percent CO) . The first modification was the installation, at
Nissan's request, of a thicker head gasket. This thicker gasket
raised the clearance between the valve face and the piston crown;
this modification was made to improve the durability of the engine.
This thicker gasket lowered the compression ratio from 11.0 to
10.5.
With M100 fuel, the engine utilized a 4-valve per cylinder
valvetrain configuration (two intake and two exhaust valves per
cylinder). This arrangement was modified to allow for admission of
air to the cylinder through one intake valve only; the second
intake valve supplied the 2H2/CO fuel. The exhaust side valve
scheme was not altered (Figure 1). This configuration is hereafter
referred to as simulated direct injection operation.
Figure 1
Simulated Direct Injection Operation
Valve Scheme For 2H-»/CO Fuel Use
This valve scheme allowed for the admission of gaseous fuel
only through one of the intake valves. An intake air control
assembly encloses the swirl control valves and is situated between
the intake manifold and the combustion chambers on the MIOO-fueled
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engine. This assembly controls the air flow so that it is through
one intake runner and/or through both intake runners as necessary.
This is to control in-cylinder charge motion on the liquid-fueled
engine.
When the engine was converted by EPA to operation on 2H2/CO
fuel, the control valve slide and actuator were disassembled and
the swirl control valves removed. The runners through the valve
assembly that contained holes for the fuel injectors were welded
shut approximately 1/2-inch upstream from the holes. These seals
prevented the admission of air to the ports through which the
gaseous fuel passes. The holes in the assembly left by the power
valve slide were sealed to prevent leakage of fuel and air between
runners.
Fuel injectors were not used to deliver the 2H2/CO fuel. The
rail and the individual injectors were removed and 3/8-inch inside
diameter stainless steel pipe fittings were used in their place.
The stainless steel fittings were threaded and the insides of the
aluminum injector holes were then threaded to adopt to these
fittings.
IV. Recent Fuel System Modifications
A fuel supply cylinder outside the test cell was used with 22
feet of 1/4-inch stainless steel tubing leading from the pressure
regulator on the cylinder to the solenoid valve inside the test
cell. After the solenoid valve, the fuel delivery system was
completely altered. The fuel line leading from the solenoid valve
to a Tylan mass flow controller was 3/8-inch in diameter and
measured approximately 27 feet in length. There were only slight
bends and no turns in this fuel line so fewer pressure drops in the
fuel delivery system would occur.
Approximately 12 inches downstream of the Tylan mass flow
controller was a pressure gauge that would measure fuel pressure to
the intake manifold. Ten feet downstream of the pressure gauge was
another solenoid valve followed by a 2-stage hydrogen flame
arrester.
The cylindrical plenum used previously to distribute fuel flow
to each cylinder was replaced with a 1/4-inch diameter fuel rail.
The fuel rail would distribute the incoming fuel to each of four
flexible fuel lines 3 inches in length leading to the fuel injector
ports. The total length from the intake valves to the flame
arrestor was approximately 11 inches.
The four fuel lines are connected to the same threaded
fittings which are screwed into the fuel injection ports in the
valve control assembly. The inside diameter of these fittings
(previously 1/4-inch) were replaced with different nozzle designs
in an attempt to increase fuel pressure and enhance the fuel
distribution. Nozzle openings from 1/2 to 3 millimeters were
evaluated to determine the best operating condition. The gaseous
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fuel is supplied to the combustion chambers by the opening of the
fuel valves when the blockages in the intake air control assembly
were present. With these blockages, fuel flow to the engine
occurred through one intake valve and air through the other. In
the remainder of this report, operation in this configuration is
called simulated direct injection.
Some testing was also conducted with these blockages removed
while still using the same fuel delivery fittings in the fuel
injector location. Because the fuel and air were premixed in the
intake manifold when operated in this configuration, this operation
was called simulated carbureted operation. Different nozzle
designs and fuel delivery locations within the intake manifold were
also evaluated in this premixed method.
V. Exhaust Measurement ProGed"****
Both dilute and cylinder-out emission samples were taken
during this latest phase of testing. Cylinder-out samples were raw
emission levels (not diluted) and were taken for each cylinder from
the runner of the exhaust manifold leading from the exhaust valves
to the exhaust pipe. Dilute emission samples were engine-out
levels and taken downstream of the exhaust manifold.
Dilute engine-out samples were taken as engine exhaust passes
from the exhaust pipe to a 2-1/2 inch diameter flexible metal tube.
This tube passes the exhaust overhead to a 6-inch rigid tube
supported from the test cell ceiling. The rigid tube delivers the
exhaust to a Philco Ford 350 cfm constant volume sampler (CVS).
Total length of the flexible and rigid tube sections is
approximately 40 feet.
A gaseous sample line has been extended through the cell
ceiling and connect the mechanical CVS with an electronic display
panel in the cell control room. A fitting in the sample line at
the control room enables bag sampling at this point. Analysis of
bag samples was accomplished at a bank of analyzers located in
another test cell. Hydrocarbon (HC) emissions were measured with
a Beckman Model 400 flame ionization detector (FID). NOx level
determination was conducted on a Beckman model 951 chemiluminescent
NOx analyzer. Carbon oxides (CO,CO2) were measured by infrared
technique using a Horiba Model A1A23 infrared analyzer.
Cylinder-out emission samples were taken for each individual
cylinder from four different taps in the exhaust manifold. The
sampling lines led to a Hankison Model E-4GSS compressed air dryer
that cooled the emission sample through an R-12 refrigerant at a
rate of 1,215 Btu/hr. The suction pressure of this unit was 33
psig. The emission sample was then collected in a bag. The total
length of the sampling line from the exhaust manifold to the
collection bag was approximately 8 feet.
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The bag samples were then taken to another location which
contained a Nicolet Rega 7000 FTIR system. This system allowed for
the raw emission sample to be diluted to 10 percent with balance of
nitrogen. Because the specific volume of emission sample taken was
not known, brake-specific emissions could not be calculated for
individual cylinders.
VI. Discussion of Test Results
A. Simulated Carbureted Operation
Simulated carbureted operation was obtained by mixing the
gaseous fuel and air in the intake manifold. This premixed charge
resulted from removing the blockages that were previously located
in one of the intake runners for each cylinder. All of the test
results presented here were obtained at steady speed (2,000 rpm)
with bottled 2H2/CO fuel.
The first phase of testing described here evaluated the effect
of three different nozzle size openings in the stainless steel pipe
fittings used to deliver the gaseous fuel. These pipe fittings,
again, were located in the fuel injector holes in the intake
manifold. Different nozzle designs were fitted in the pipe
fittings in an attempt to increase the fuel pressure and fuel
distribution in the intake system to improve torque, combustion
stability, and emissions.
The first nozzle evaluated was I/2-millimeter in diameter.
The maximum fuel flow rate these nozzles would allow was
approximately 6.7 cfm. At wide open throttle (WOT) conditions,
operation here resulted in an air/fuel ratio (A/F) of 15.4. The
engine would not run at this lean condition.
The second nozzle opening utilized was 1-millimeter in
diameter. The maximum fuel flow rate with these nozzles was 10.6
cfm, resulting in an A/F of 9.7 at WOT, 2,000 rpm operating
conditions. The maximum torque obtained during this testing was 37
ft-lbs. After approximately 1-2 minutes of engine operation, the
premixed charge would begin to ignite in the intake manifold and
substantially decrease output torque. This happened every time the
engine was operated. The engine ran smooth until engine oil
temperature reached approximately 140°F. This preignition
condition at hotter engine temperatures is quite common when a
premixed hydrogen containing fuel is used.[1-5]
The next nozzle investigated here utilized a 1.5-millimeter
diameter opening with a diffuser. Figure 2 shows a schematic of
two different nozzle designs using this size opening. With these
nozzles, the engine was severely hindered by preignition in the
intake manifold. This preignition occurred after approximately 1-2
minutes of operation once the engine has warmed. Also, the engine
could not be operated at WOT conditions during any testing here.
As the throttle was being slowly opened, there was a certain
maximum airflow that would allow for smooth engine operation. When
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—7—
the throttle was opened above this point (increasing airflow), the
engine would experience frequent preignition. The fuel delivery
pressure was approximately 60 psig during this testing.
Figure 2
Simulated Carbureted Operation
Nozzle Openings With Diffusers
1 mm
Flow
1.5 mm
(a) Single-Hole Nozzle
(b) 4-Hole Nozzle
Table l below is a summary of test results obtained with the
single-hole 1.5-millimeter nozzle openings at 2,000 rpm. Spark
timing for this testing was set at 10°BTDC.
Table 1
Simulated carbureted operation
2H2/CO Fuel Operation, 2,000 RPM Conditions
Air Flow
(ofm)
38
25
20
25
32
35
15
Fuel Flow
(cf»)
13.9
11.7
10.3
10.3
10.3
10.3
13.9
A/F
Ratio
7.4
5.8
5.3
6.6
8.4
9.2
2.9
Torque
(ft-lbs)
60
25
41
44
45
45
52
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The maximum torque obtained during this testing was 60 ft-lbs,
approximately 60 percent of the level obtained with M100 fuel at
2,000 rpm, WOT operating conditions. The engine was also severely
hindered by preignition in the intake manifold during every test
conducted in this premixed combustion method and could not be
operated at WOT.
The next phase of testing utilized a different location for
the fuel delivery pipe fittings in the intake manifold. The
gaseous fuel was now introduced in the intake manifold before the
partition of the intake runners. Four holes were drilled in the
intake manifold before the partition that led to each intake valve.
Therefore, a premixed air/fuel mixture was delivered to each intake
valve. Different nozzle sizes were also used during this testing
including the use of the 4-hole nozzle. However, testing in this
configuration did not increase output torque and also resulted in
severe preignition in the intake manifold. Again, this preignition
occurred after 1-2 minutes of operation.
B. Simulated Direct Injection Operation
Because of the severe limitations on engine performance due to
preignition in the premixed combustion method, the passageway
leading to the fuel intake valve was again blocked off. The fuel
delivery pipe fittings with the single-hole nozzles were then
mounted in the fuel injector holes where the M100 fuel injectors
would normally be located. This configuration allowed for mixing
of the air and fuel only in the combustion chamber; therefore,
simulating direct injection fuel delivery.
The original pipe fitting with a nozzle opening equal to the
fitting inside diameter (1/4-inch) resulted in smooth engine
operation with a maximum torque of 58 ft-lbs at an A/F ratio of
8.3. The fuel delivery pressure measured here was 52 psi.
The first phase of testing conducted here utilized nozzles
from the previous subsection. The maximum fuel flow attainable
with these nozzles varied substantially. The largest fuel flow
obtained was 9.9 cfm, resulting in an A/F ratio of 11.0 at WOT,
2,000 rpm operating conditions. The highest torque achieved during
this testing was 66 ft-lbs. However, the engine was still affected
by a slight preignition in the intake manifold.
The nozzle opening offering the best results here was a 3-
millimeter diameter opening with no diffuser. This fuel delivery
configuration resulted in very smooth engine operation and the
highest output torque obtained to date with this engine is 80 ft-
lbs at 2,000 rpm, WOT operating conditions. Although this is still
80 percent of the output torque obtained when using M100 fuel at
the same conditions, several literature sources suggest that this
may in fact be the output limit when using dissociated methanol
fuel.[14,15] These literature sources quantify the maximum
obtainable torque when operating on dissociated methanol as 55
percent of the M100 level. The 80 ft-lbs obtained with this engine
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in this configuration may be close to the maximum attainable output
torque at these operating conditions with the gaseous fuel. The
engine also ran very smooth, and operation at WOT was not hindered
by preignition during any test conducted during this phase of
testing.
Several other operating conditions were also evaluated,
including fuel delivery pressure measured after the Tylan mass flow
controller and before the hydrogen flame arrester. Another
operating condition that was varied was spark timing. Figure 3
below presents a curve fit for the maximum torque obtained at
several different ignition timings. All torque valves presented
here were maximum values and obtained at 2,000 rpm, WOT conditions.
Fuel delivery pressure here was held relatively constant at about
60 psig. The largest torque at these conditions seemed to occur
with a spark timing of 5 degrees before-top-dead-center (5°BTDC).
Figure 3
CA18DE Engine, 2H2/CO Fuel
Simulated Direct Injection Operation
70
60
50
40
Torque (ft-lbs)
1 5
Spark Timing (degrees BTDC)
2,000 rpm, WOT, 60 psig fuel pressure.
15
The next variable operating condition investigated was fuel
delivery pressure. This fuel pressure was measured in the fuel
delivery system after the Tylan mass flow controller and before the
hydrogen flame arrester. Spark timing was set at 5«BTDC.
The fuel pressure measured here was increased by increasing
the regulator pressure at the gas bottle. Figure 4 below presents
the results obtained at 2,000 rpm and WOT conditions.
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Figure 4
CA18DE Engine, 2H2/CO Fuel
Simulated Direct Injection Operation
Torque (ft-lbs)
80
60
40
39
58
75
95
60 65 70
Fuel Pressure (psig)
2,000 rpm, WOT, 5BTDC spark timing.
The maximum torque obtained during this testing was achieved
with a fuel pressure of 75 psig. When the pressure was increased
above 75 psig, output torque seemed to taper off. For example, at
a fuel pressure of 95 psig, output torque reduced to 72 ft-lbs.
Table 2 below presents all the results obtained from this
testing in the simulated direct injection configuration. All
torque values presented were maximum. The nozzles used had the
single-hole, 3-millimeter diameter openings without a diffuser, and
all results were obtained at 2,000 rpm, WOT operating conditions.
Table 2
Simulated Direct Injection Operation
CA18DB Engine, 2,000 RPM/WOT Conditions
Spark
Timing
(BTDC)
1
5
5
5
5
5
5
15
Fuel
Pressure
(psig)
58
39
58
60
65
70
75
60
Air
FlOV
(cfm)
33
30
37
37
39
37
37
37
Fuel
Plow
(cfm)
15.5
14.1
16.7
19.2
20.9
24.0
22.5
16.6
A/P
Ratio
5.8
5.8
6.0
5.2
5.1
4.2
4.5
6.0
Torque
(ft-lbs)
60
53
69
75
78
78
80
64
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Engine operation was kept near to stoichiometric (A/F ratio of
6.5) for most of this testing. Several literature sources again
suggest best engine performance occurs at or slightly rich of
stoichiometric when operating on hydrogen fuel.[1-5]
The largest torque obtained during the previous testing with
2H2/CO fuel was 80 ft-lbs (80 percent of the M100 fuel output) . As
a result, emissions and combustion analysis were performed at
similar operating conditions (A/F ratio of 4.5, 2,000 rpm, WOT, and
a fuel pressure of 75 psig). The A/F ratio of 4.5 utilized with
the gaseous fuel was similar to the closed-loop controlled M100 A/F
ratio of 4.7 at the same 2,000 rpm, WOT conditions. Table 3 below
details the operating conditions used for both fuels when emissions
samples were collected and combustion analysis was performed.
Table 3
Engine Operating Conditions: CA18DE Engine
Fuel
M100
2H2/CO
Speed
(rp«)
2,000
2,000
Throttle
Position
WOT
WOT
A/F
Ratio
4.7
4.5
Fuel
Pressure
(p»ig)
45
75
Air
Plow
(of*)
39
37
Torque
(ft-lbs)
100
80
Cylinder-out emission samples were taken for each of the four
cylinders. Two samples for each cylinder were taken when operating
on each fuel. These were raw (not diluted) emission samples and
were analyzed using an FTIR system. Each sample taken was collected
over approximately 4 minutes.
Figure 5 below presents cylinder-out carbon monoxide (CO)
concentrations when using either fuel. The top bar represents the
CO emission concentration leaving cylinder #1 when operated on M100
fuel. Similarly, the bar underneath that represents the CO
concentration leaving cylinder #1 when operating on 2H2/CO fuel.
These results are the average of two test runs and are presented in
parts per million (ppm). Again, these are raw emission levels and
not diluted.
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Figure 5
Cylinder-Out Carbon Monoxide Levels
Cylinder Number
Cylinder #1
Cylinder #2
Cylinder #3
Cylinder #4
'/////////////////////I,
0 5 10 15 20 25
Carbon Monoxide (ppm) (Thousands)
2,000 rpm, WOT conditions.
Concentrations of CO when using the gaseous 2H2/CO fuel were
much lower than when utilizing M100 fuel. These low CO
concentrations, ranging between 590 ppm for cylinder #3 and 1/750
ppm for cylinder #4, seem to indicate that most of the 2H2/CO fuel
is combusting and that very little unburned fuel is resulting.
This was not the case in previous testing with 2H2/CO fuel when
large amounts of unburned fuel were present in the exhaust.[6,13]
From this figure, combustion stability from cylinder-to-
cylinder may also be investigated. With M100 fuel, each cylinder
is producing approximately equal amounts of CO. The largest
variance in cylinder-out CO levels occurs between cylinders #1 and
#2, where a 20 percent variance occurs. However, when 2H2/CO fuel
is used, cylinder /3 produces a much lower amount of CO than the
three other cylinders. For instance, cylinders #3 and /4 differ by
66 percent in CO emission levels.
Figure 6 presents results from methanol emission sampling for
the same testing described in Figure 5.
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Figure 6
Cylinder-Out Methanol Emission Levels
Cylinder Number
Cylinder #1
Cylinder #2
Cylinder #3
Cylinder #4
01234
Methanol (ppm) (Thousands)
2,000 rpm, WOT conditions.
When operating on the gaseous 2H2/CO fuel, large
concentrations of methanol emissions were produced in each
individual cylinder. Also, in cylinder #2, levels of methanol
emission concentrations when operating on this fuel were higher
than MIOO-fueled levels.
When operating on M100, combustion stability with regard to
unburned fuel in each cylinder was again very good. The largest
variance in unburned fuel occurred between cylinders #2 and #3,
where a 26 percent difference in methanol emissions occurred. When
operating on the 2H2/CO fuel, cylinder #3 levels again varied from
the other three cylinders by a substantial margin. However, the
largest variance between cylinders when excluding cylinder #3 is
only 17 percent.
Table 4 below presents several other emission levels measured
during this same testing. All levels are presented in ppm's except
for water vapor (H20) and carbon dioxide (C02), which are presented
in a percentage.
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Table 4
2,000 RPM/WOT Conditions, Simulated Direct Injection Operation
Cylinder-Out Emission Levels
Cylinder
Number
#1
#2
#3
#4
Average
Fuel
M100
2H2/CO
M100
2H2/CO
M100
2H2/CO
M100
2H2/CO
M100
2H2/CO
H20
<%)
12
17
11
14
10
11
11
13
11
14
CO
(ppm)
23,650
1,200
18,930
1,620
20,000
590
23,595
1,750
21,544
5,160
CO,
(%)
1.0
0.9
1.0
0.9
0.7
0.5
1.0
0.8
0.9
0.8
NOX
(ppm)
825
1,800
1,100
1,475
520
N/A
925
1,540
842
1,605
CH3OH
(ppm)
3,400
2,935
2,715
2,785
3,655
1,815
3,210
2,425
3,245
2,490
ECHO
(ppm)
60
7
45
5
45
4
40
5
48
5
N/A = Not available
Formaldehyde (HCHO) emission levels are much lower when
operating on the gaseous 2H2/CO fuel for each cylinder.
Formaldehyde levels when the 2H2/CO fuel was used were, on the
average, 90 percent below corresponding M100 levels for each
cylinder. However, emissions of nitrogen oxides (NOx) were
substantially larger when the 2H2/CO fuel was used. On the
average, NOx levels approximately doubled from M100 levels when the
gaseous fuel was used.
Two overall dilute emission samples with each fuel were also
taken. The operating conditions were again similar to those
described in Table 3 for this testing. These diluted samples were
analyzed at a different site using different analyzers. Table 5
below presents the average of two emission samples when operated on
each fuel. Brake-specific emissions are presented here
(grams/brake horsepower-hour). Methanol and formaldehyde levels
were not measured during this testing, and only a total hydrocarbon
(HC) value is presented here.
Table 5
2,000 RPM/WOT Conditions, simulated Direct Injection Operation
Brake-Specific Emission Levels
Fuel
M100
2H2/CO
BhP
38.1
30.5
A/F
Ratio
4.7
4.5
HC
(g/BhP-hr)
1.37
0.03
CO
(g/BhP-hr)
24.7
49.0
NOX
(g/Bhp-hr)
2.0
8.0
C02
(g/BhP-nr)
205
450
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HC levels when using the gaseous fuel were substantially lower
than MlOO levels on a brake specific basis. However, brake-
specific CO levels approximately doubled from MlOO levels with the
2H2/CO fuel. This level of CO is substantially lower, however,
than levels obtained in a previous report [6] and is also
accompanied with a higher torque of 80 ft-lbs. Although NOx levels
with 2H2/CO fuel were much higher, these levels are similar to
previous NOx emissions.[6]
The second phase of testing in this subsection consisted of
investigating the in-cylinder combustion process when utilizing
each fuel. This investigation was conducted using a Kistler
pressure sensor and the test cell data acquisition system. This
investigation was performed using a pressure versus crank angle
(CA) approach. The computer software program then computes eight
other outputs based on the experimental pressure/CA diagram, engine
geometry, and operating conditions entered at the beginning of each
test. There are four basic categories of functions which result
from the further analysis of the pressure/CA data. These include
dynamic cylinder pressure and temperature data needed for a thermal
stress analysis, heat release rate and cumulative heat release,
cycle performance and losses from the indicator diagram, and cycle
thermodynamic data.[9] This report will only investigate pressure
and heat release data.
When operating on each fuel, pressure data was gathered from
each cylinder individually. However, data from each cylinder was
very similar; therefore, only one set of data for operation on each
fuel will be presented in this report. When MlOO fuel was used, 25
consecutive cycles were monitored and averaged by the computer.
With 2H2/CO fuel, fifty consecutive cycles were averaged. The same
operating conditions for each fuel, presented in Table 3, were
again used in this phase of testing. The maximum torque obtained
at 2,000 rpm, WOT conditions with MlOO fuel was 100 ft-lbs, with
2H2/CO, it was 80 ft-lbs.
Figure 7 below presents in-cylinder pressure versus crank
angle data when using MlOO fuel. The maximum pressure obtained
with MlOO fuel reached 808 psi. This maximum pressure occurred at
approximately 7 degrees after top-dead-center (ATDC). Spark timing
with MlOO fuel was 22 degrees BTDC. The indicated mean effective
pressure (imep) was calculated by the software to be 119.6 psi for
this fuel. The standard deviation in maximum pressure values for
25 consecutive cycles was found to be 28 psi.
-------
-16-
Figure 7
Pressure Trace With M100 Fuel
ECA
901
ENGINE CYCLE ANALYSIS
FILE
637,MT
B= 3.2 S: 3.2 I- 5.2 Ctel8.5
SUN=25 T«st Oat«:86-88-92/14:17:11
R!*=1999.i INEP: 119.6
Print Date:86-«8-92
-880
PS 14
-488
P - 9
ENGINE ID:
CA18DC
PMJC= 886 at 6.99CA
*
; \
-288 / \ '
-
-— —
-9
-98 TDC 98
': '• i 1 1 1 i i i 1
A similar trace was obtained when the 2H2/CO fuel was used.
(Figure 8) Maximum pressure levels reached with this fuel were
slightly lower than M100 fuel, at 754 psi. This maximum pressure
was achieved at 14 degrees ATDC. Spark timing with this fuel was
set at 5 degrees BTDC. Although the maximum output torque achieved
with 2H2/CO fuel is approximately 20 percent lower than M100
levels, the calculated imep when using the gaseous fuel is about 20
percent higher. The imep again is a calculated quantity derived
from pressure, engine geometry, and operating conditions data. The
higher imep values with gaseous fuel operation may be attributed to
the following. First, the number of cycles used for M100 operation
was different from that of 2H2/CO operation, which may alter the
software averaging process. Also, prior to 2H2/CO fuel operation,
the optical encoder was removed then remounted on the engine. This
may significantly change encoder position and consequently imep
measurement. The standard deviation in maximum cylinder pressure
with 2H2/CO fuel was 14 psi, denoting less fluctuation and more
stable operation than with M100 fuel.
-------
-17-
Figure 8
Pressure Trace For 2H->tCO Fuel
5£? i ENGINE CYCLE ANALYSIS j
; 901 ;j ,
B= 3.2 S: 3.2 i- 5.2 Ctelfl.S RP»fe2Wl,9
SU*=5« Test »at«: 98-31-92/13:22: 51 Print Da
|P - 9 j ENGINE If. PMX= 754 at 13.99O)
OU80E
-8M
psi* ft.
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/ \
\
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/ \
*400 ' \
\
/ \
/ \
/ \
V
-4
-99 TK >
ill i i I i i
MTU FILE :
331921. MT :;
IHE7= 144.2
t«:M-31-92 :
i
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1
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One possible way of investigating flame speed/ combust ion rate
is by investigating the heat release rate. Recent literature
suggests that this quantity is proportionally related to mass
burned rate (energy release) , with only a slight difference
involved, resulting from neglecting the heat release through the
cylinder walls and blowby. [10,11,12] The software uses this
quantity because it is much faster to calculate a rate of heat
release than a rate of combustion. [9]
Heat release rate, denoted dX/d6 is calculated from cylinder
pressure/volume and crank degrees data by using the following
formula [9]:
dX/d9 = [l/(92 -e,)][l/(n-l)][P2V2 -
+ (1/2) (P, - P2)(V2 - V,)
Where:
dX/d0
P
V
n
Heat release rate between two crank angles
(Btu/degree)
Cylinder pressure (psi)
Cylinder volume (cubic inches)
Polytropic index.
-------
-18-
The maximum heat release rate (related to mass burned rate)
obtained with M100 fuel was 0.035 Btu/CA. Similarly, the maximum
heat release rate with the 2H2/CO fuel was 0.050 Btu/CA.
From the heat release rate values, it is possible to
investigate a combustion duration. This duration period can be
calculated from the cumulative heat release (cumulative energy
release) versus crank angle data. This quantity is proportional to
the amount of chemical energy which must be released as thermal
energy by combustion to match the measured pressure data.
Figure 9 below presents the trace of cumulative heat release
(denoted X) versus crank angle when M100 fuel was used. The y-axis
here represents the fraction of the total heat released during an
average of 25 combustion cycles. For instance, at TDC,
approximately 30 percent of the total heat release when combusting
this fuel has occurred. The start of combustion has been selected
as X=0.05, or when 5 percent of the total heat release has
occurred. Similarly, the end of combustion has been selected as
X=0.95, or when 95 percent of the total heat release has occurred.
These values were chosen based upon the recommendation of the
software developers.[9]
Figure 9
Cumulative Heat Release With M100 Fuel
ECA
9 a i
ENGINE CYCLE ANALYSIS j[
;i MT« FILE
632. MT
! B= 3.2 S: 3.2 L: 5.2 CJfclg.3
SUN=23 Test D»tt:86-93-92/09:42:37
Wit 2982.3
Print 9»t«:96-9?-«2
IX -
-.7
-.«
-.5
-.4
-.3
-.2
-.1
ENGINE i»:
CA199C
.95
i ! •
1
31 M |
; i i i i i i i 1
-------
-19-
The total heat release duration (related to combustion
duration) was 85 crank degrees for M100 fuel. Previously, this
duration was calculated to be approximately 60 crank degrees for
M100 fuel. However, with the shorter combustion duration, measured
output torque was much higher (128 ft-lbs) than the level measured
during this testing (100 ft-lbs). It was not determined why output
torque dropped off from levels obtained during previous testing
with M100 fuel.[13] The heat release trace here reveals a fast-
burn rate until approximately 70 percent of the total heat release
has occurred. After this point, the heat release rate appears to
be very slow and prolonged.
Figure 10 below presents a similar trace for 2H2/CO fuel
operation. The total heat release duration with this fuel was
approximately 63 crank degrees, substantially faster than the M100
results. A faster burn rate would be expected with a hydrogen-
containing fuel. At 20 crank degrees after spark, (15°ATDC)
approximately 80 percent of the combustion has occurred. Eighty
percent of the total combustion was not reached until 60 crank
degrees after spark with M100 fuel. The total amount of heat
released during one combustion event with the 2H2/CO fuel was 0.84
Btu. The corresponding value with M100 fuel was 0.63 Btu,
approximately 25 percent lower.
Figure 10
Cumulative Heat Release With 2 Ho/CO Fuel
CCA
90J.
ENGINE CYCLE ANALYSIS
9ATA FILE :
831922. MT
B= 3.2 S= 3.2 L= 5.2 Cfcli.5
StHtSB Test Bate:88-31-92/13:23:16
RPIt28tt.3
Print Date:88-31-92
X - *
ENGINE ID:
CA18K
X(1MK>= .84 BTU
-1
-.9
-8
-.7
-.4
-.3
-.4
-.3
-.2
J
1
4
J
4
.85
TDC
38
i
M
i
-------
-20-
VII. sunnnaT-v and Conclusions
This engine conversion project was started to develop a
suitable test bed for a practical on-board methanol dissociator.
From the engine performance, the following main results can be
summarized:
1. The engine currently operates smoothly on dissociated
methanol fuel at approximately 80 percent of the M100 output power
level. This power output is considerably higher than the maximum
power levels reported in another literature source [14], when the
engine operated on 100 percent dissociated methanol.
2. In premixed combustion, the engine must run on a lean
mixture. Abnormal combustion is likely to occur when the engine
warms up. This is considered to be a restriction on the range of
dissociated methanol operation.
3. The standard deviation in maximum cylinder pressure with
the 2H2/CO fuel is less than M100 fuel deviation. This indicates
less fluctuation and more stable engine operation with the gaseous
fuel.
4. Dissociated methanol burned much faster than methanol
probably resulting from the hydrogen content in the fuel, which has
a flame speed over five times that of methanol (see Figures 9 and
10) .
5. The lower efficiency with dissociated methanol (as is the
case with any gaseous fuels) could be attributed to the increase in
heat transfer resulting from higher gas temperatures and the
increase of compression work. Gas temperature and compression
pressure increases can be explained based on the thermodynamic
analysis of the pressure-volume equation of an ideal gas.
6. Emission results were obtained for both fuels, however,
definitive conclusions can not be drawn at this stage.
VIII. Future Efforts
A 100 percent efficient methanol dissociator is currently not
available. Presently, the best direction for this project may be
to evaluate what the (2H2/CO)/CH3OH) ratio is for best emissions.
Running the engine on a mix of dissociated methanol and M100 may
yield more power and decrease the uncontrollable combustion and
flashback at high loads experienced with 2H2/CO operation. Also,
an optimized mixture of vaporized and dissociated methanol may lead
to satisfactory cold start performance, enhance stability during
idling, and reduce exhaust emissions.
Development and fabrication of a dissociated methanol-assisted
injector adaptor is complete. In this case, resistors can be added
to the adapters at a small cost to enhance cold start operation if
it is needed.
-------
-21-
IX. Acknowledgments
The CA18DE engine described in this report was modified for
use with M100 neat methanol and loaned to EPA by the Nissan Motor
Corporation as support for an effort to investigate the potential
of neat methanol as an alternative motor vehicle fuel.
The authors appreciate the efforts of Marc Haubenstricker of
the Fuels and Chemical Analysis Branch for FTIR analysis support.
The authors also appreciate the efforts of Jennifer Criss and Mae
Gillespie of the Technology Development Group for typing and
editing support.
X. References
1. "Hydrogen As A Fuel And The Feasibility Of A Hydrogen-Oxygen
Engine," Karim, G. and M. Taylor, SAE Paper 730089, January 1973.
2. "State of the Art And Future Trend Of Hydrogen-Fueled
Engines," Furuham, S., JSAE Review, March 1981.
3. "Ignitability Of Hydrogen-Air Mixture By Hot Surfaces And Hot
Gases In Hydrogen-Fueled Engines," Enomoto, K. and S. Furuham, JSAE
Review, July 1981.
4. "Hydrogen-Powered Vehicle With Metal Hydride Storage And
D.I.S. Engine System," Kama, J. and Y. Uchiyama, SAE Paper 880036,
February 1988.
5. "Combustion Characteristics In A Hydrogen-Fueled Rotary
Engine," Morimoto, K., et al., SAE Paper 920302, February 1992.
6. "Conversion Of Methanol-Fueled 16-Valve, 4-Cylinder Engine To
Operation On Gaseous 2H2/CO Fuel-Interim Report III," Schaefer, R.
M., et al., EPA/AA/CTAB/91-01, April 1991.
7. "Conversion Of Methanol-Fueled 16-Valve, 4-Cylinder Engine To
Operation On Gaseous 2H2/CO Fuel-Interim Report II," Piotrowski, G.
K. and J. Martin, EPA/AA/CTAB/89-02, March 1989.
8. "Resistively Heated Methanol Dissociater For Engine Cold Start
Assist-lnterim Report," Piotroski, G. K., EPA/AA/CTAB/88-02, March
1988.
9. Operation Manual For Engine Cycle Analysis Program, Power and
Energy International Inc., 1988.
10. "Heat Release Analysis Of Engine Pressure Data," Gatowski, J.
A., et al., SAE Paper 841359, Massachusetts Institute of
Technology, October 1984.
11. "Factors Limiting The Improvement In Thermal Efficiency Of
S.I. Engine At Higher Compression Ratio," Muranaka, S., et al.,
SAE Paper 870548, February 1987.
-------
-22-
12. "Basic Findings Obtained From Measurement Of The Combustion
Process," Holenberg, G. and I. Killman, SAE Paper 820126, 1982.
13. "Progress Report On In-House Dissociated Methanol Project,"
Note, from G. K. Piotrowski and R. M. Schaefer to Charles L..Gray,
Jr., September 1991.
14. "Study of the Methanol-Reformed Gas Engine," Hirota, T.,
JSAE Review, March 1981.
15. "Engine Operation on Partially Dissociated Methanol," Konig,
A., et al., SAE Paper 850523, February 1985.
-------
A-l
APPENDIX A
TEST ENGINE SPECIFICATIONS, M100 FUEL OPERATION
CONDITION AS LOANED BJLHISSJ
Manufacturer
Basic engine designator
Displacement
Cylinder arrangement
Valvetrain
Combustion chamber
Bore X Stroke
Compression ratio
Compression pressure
Fuel control system
EGR
Valve clearance
Idle speed
Engine oil
Fuel
Air/fuel control
Spark advance control
Nissan Motor Co., LTD
CA18DE
1809 CC
4-cylinder, in-line
Dual-overhead camshaft
Pentrpof design
83 mm x 83.6 mm
10.5
16.5 kg/square cm (350 rpm, 80°C)
Electronically controlled
fuel injection
EGR not used
0 mm (automatically adjusting)
750 rpm
Special formulation supplied by
Nissan for methanol
engine operation
Ml00 neat methanol
Excess air ratio may be varied from
0.5 to 2.0 by means of
an external control
Ignition timing can be varied
from OOBTDC to 54«BTDC by means
of an external control
------- |