EPA/AA/CTAB-91-01
Technical Report
Conversion of Methanol-Fueled 16-Valve,
4-Cylinder Engine to Operation On Gaseous
2H2/CO Fuel - Interim Report III
by
Ronald M. Schaefer
Gregory K. Piotrowski
James C. Martin
April 1991
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
Emission Control Technology Division
Control Technology and Applications Branch
2565 Plymouth Road
Ann Arbor, Michigan 48105
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
ANN ARBOR. MICHIGAN 48105
OFFICE OF
AIR AND RADIATION
MEMORANDUM .
SUBJECT: Exemption From Peer and Administrative Review
FROM:
TO:
Karl H. Hellman, Chief
Control Technology and Applications Branch
Charles L. Gray, Jr., Director
Emission Control Technology Division
The attached report entitled, "Conversion of Methanol-
Fueled 16-Valve, 4-Cylinder Engine to Operation On Gaseous
2H2/CO Fuel - Interim Report III," (EPA/AA/CTAB/91-01)
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 has been operated on both MlOO and
simulated dissociated methanol (hydrogen and carbon monoxide)
gaseous fuels. This report describes modifications made to the
engine and summarizes the results of recent testing. Further
work on this project will be described in a future technical
report.
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:
Date
ECTD
Nonconcurrence:
Date:
Charles L. Gray, Jr., Dir., ECTD
cc: E. Burger, ECTD
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Table of Contents
Page
Number
I. Summary 1
II. Introduction 2
III. Description of Test Engine 3
IV. Exhaust Analysis 3
V. Recent Engine/Fuel System Modifications 4
VI. Discussion of Test Results 6
VII. Highlights From Current Testing 9
x
VIII.Future Effort 10
IX. Acknowledgments 11
X. References 12
APPENDIX A - Test Engine Specifications - A-i
2H2/CO Fuel Operation
APPENDIX B - Previous Engine/Fuel System B-l
Modifications For 2H2/CO Fuel Operation
APPENDIX C - Air/Fuel Ratio Calculation C-l
For 2H2/CO Fuel Operation
APPENDIX D - Exhaust Mass Emission Calculation D-l
For 2H2/CO Fuel Operation
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I. Summary
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
to CO. This engine has been used to investigate the difference
in emission levels and lean limit operation between two
different fuels: M100 neat methanol and simulated dissociated
methanol gaseous fuel (2H2/CO).
The work described in this report contains results of
recent emission testing begun in July 1990 with the engine
equipped with stock and modified intake camshafts. These
results are compared to results obtained during previous
testing with the modified camshaft. This previous work was
completed in March 1989 and is described in EPA/AA/CTAB-89-02.
[1] The present report also contains a summary of fuel
system/engine experiments conducted to more accurately measure
gaseous fuel flow to the test engine and increase the power
output of the engine.
Table 1 is a summary of our test results. The first entry
refers to testing conducted in March 1989. Previously, the
test engine was operated at lean conditions with the 2H2/CO
fuel. Under load, the maximum output torque achieved using the
gaseous fuel was 26.6 ft-lbs at 2,000 rpm and an A/F ratio of
11.9:1. (The stoichiometric A/F ratio for operation on the
gaseous fuel is the same as it is for M100 operation, 6.4:1.)
Recent testing consisted of the engine operating under
load at wide-open throttle (WOT), fueled with gaseous 2H2/CO,
and with a spark timing of 0° before top dead center (BTDC) .
Spark timing was limited to near BTDC because severe engine
backfire or knock resulted when spark timing was advanced.
Separate tests were performed with the engine equipped with
both modified and stock intake camshafts. Fuel flowrate here
was calculated from the change in weight of the gas bottle
during each test, the density of the fuel, and the time
duration of each test. A meter which measured the remainder of
the gas bottle contents in standard cubic feet was also used.
During testing with the modified camshaft, an output
torque of 60 ft-lbs at an A/F of 7.89:1, under 2,000 rpm, WOT
conditions was measured. This^ torque was more than twice the
highest value measured during the previous testing performed
under both WOT/throttled and lean operating conditions.
Output torque increased during engine warmup. When the
engine was cold started, the output torque was usually 15
ft-lbs below the maximum value recorded later. The torque
reached its maximum value after approximately 5 minutes into
each test. It remained constant at that value for the
remainder of the test until the engine was shut off.
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Table l
Summary of Test Results
Nissan CA18DE Engine, 2H2/CO Fuel
Test
Number
1
2
3
4
5
6
7
8
Date
03/01/89
10/30/90
12/04/90
01/28/91
01/30/91
02/20/91
02/21/91
02/25/91
Camshaft
Modified
Modified
Modified
Stock
Stock
Stock
Stock
Stock
RPM
2,
2,
2,
2,
2,
1,
1,
2,
000
000
000
000
000
750
750
000
Torque
ft-lbs BHP
27
55
60
65
65
67
66
70
10
20
22
24
24
22
21
26
.30
.94
.85
.75
.75
.32
.99
.28
Air/Fuel
11.90
8.33
7.89
N/A
N/A
6.07
7.36
N/A
N/A Not available.
Note: All tests at WOT; torque values are maximum.
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Approximately 13 percent of the fuel was unburned and
passed through the exhaust with the modified camshaft. The
stock intake camshaft was then placed in the test engine to
enhance mixing of the air/fuel charge in the chamber prior to
combustion. The result was the highest torque measured on a
single test (70 ft-lbs) under the same 2,000 rpm, WOT operating
conditions. The engine ran much smoother with the stock
camshaft at these same conditions, with no fluctuation in
torque during each entire test. Higher amounts of unburned
fuel at 1,750 rpm (41.7 percent was not burned) under richer
conditions were noted.
The 70 ft-lbs torque value obtained here is approximately
38 percent below the maximum value (110 ft-lbs) obtained by
Nissan with an MIOO-fueled, 12.0 compression ratio CA18DE
engine. However, with recent engine/fuel system modifications,
the power output has been increased 160 percent when compared
to results obtained from previous testing with 2H2/CO fuel.[l]
A direct comparison of emissions test results from the
engine when it is alternately fueled with M100 and 2H2/CO
fuels is not possible at this time. The previous testing with
the M100 fuel utilized a catalytic converter in the exhaust
stream while 2H2/CO fuel results are engine-out emissions.
Also, the limited amount of gaseous fuel in the T-cylinder
storage bottles did not permit starting and warming to true
steady-state conditions prior to emission testing.
Higher emissions of CO and NOx were measured during this
testing. High CO emissions may result from the substantial
amount of unburned fuel passing out of the exhaust. H2 in
the exhaust was also measured and was consistently twice the CO
levels, this proportion being the same as that of the
components in the gaseous fuel.
Future efforts will utilize a recently acquired mass flow
controller to accurately control and measure fuel flow. The
large amounts of unburned fuel in the exhaust will be
investigated. An in-cylinder pressure sensor will also be used
to investigate the combustion event.
II. Introduction
Methanol may be catalytically decomposed to H2 and CO
gases according to the reaction:
CH3OH(1) 2H2(g) + C0(g)
The decomposition of methanol to this gaseous fuel mixture
has been postulated as a more efficient method of using
methanol as a light-duty motor vehicle fuel. The major
attraction of methanol decomposition is that the resulting
gases have a higher heating value per pound than the original
liquid methanol. A discussion of the application of
dissociated methanol as a light-duty automotive fuel was
presented in previous papers.[1,2]
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In order to evaluate this concept, EPA modified a Nissan
CA18DE multi-valve engine to better utilize the combustion
characteristics of dissociated methanol fuel. This engine, a
stock model modified by Nissan Motor Corporation for use with
liquid methanol, was loaned to EPA by Nissan for use in
alternative fuels research. This report summarizes the most
recent EPA efforts to investigate dissociated methanol as an
automotive fuel with this engine.
Ill. Description of Test Engine
The base engine used for this project was a Nissan CA18DE
engine. The stock engine is an in-line, 4-cylinder, 1.8-liter
capacity powerplant. The valve arrangement is a 4-valve per
cylinder configuration, consisting of two intake and two
exhaust valves per cylinder. The valves are operated by two
overhead camshafts, one each for the intake and exhaust sides.
The test engine was 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. [1] A summary of them is included in this report in
Appendix A.
EPA also modified the engine to use simulated dissociated
methanol fuel (66 volume percent H2 and 33 volume percent
CO). The most significant modification made here was the
replacement of the intake camshaft with a specialty camshaft.
The specialty cam admits air only through one intake valve and
gaseous fuel only through the second valve. These EPA
modifications were also discussed in a previous report [1] and
are detailed here in Appendix B.
EPA installed, at Nissan's request, a thicker head gasket
for the testing mentioned in this report. This thicker head
gasket raised the clearance between the valve face and the
piston crown; this modification was made to improve the
durability of the engine. The effect of this modification was
to lower the compression ratio from 11.0 to 10.5. The current
testing referred to in this report made use of this
modification.
IV. Exhaust Analysis
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 hung from ceiling
supports. 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 40 feet.
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A gaseous sample line and electronic ties have 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 is
accomplished at a bank of analyzers located in another test
cell. Emissions measured as hydrocarbons (HC) are measured on
Beckman model 400 flame ionization detector (FID). NOx level
determination is conducted on a Beckman model 951
chemiluminescent NO/NOx analyzer. CO is measured by infrared
technique using a Horiba model A1A23 infrared analyzer.
Hydrogen gas in the exhaust was measured using a Gow-Mac model
550 gas chromatograph calibrated with a 40 percent hydrogen
span gas.
V. Recent Engine/Fuel System Modifications
A significant period of time, in excess of one year, had
elapsed from the date of the last report [1] to the start of
the testing commented on here. It was necessary, therefore, to
first perform leak checks on the entire fuel system and a
leakdown check on the engine cylinders to determine their
integrity. No leaks were detected when the fuel system was
pressurized, and the greatest loss of pressure in a cylinder
was only 2 percent, indicating that the compression had not
significantly deteriorated.
Next, the fuel valve lifters were removed and the fuel
system was pressurized to 60 psi using bottled nitrogen. The
engine was then motored by the dynamometer. No flow in the
flowmeter was observed, indicating no leakage in the fuel
delivery system.
When the modified intake camshaft was installed, gaps were
noted in the gasket that mates the swirl control valve housing
to the engine head. These gaps made possible the transfer of
fuel and air between the separated fuel and air intakes in each
runner. These gaps were plugged to limit inaccuracies in
air/fuel flowrate measurement.
Air flowrates through the engine at WOT conditions over a
range of engine speeds were determined and are plotted in
Figure 1. Air flowrates over the same conditions with the
engine as modified by Nissan for M85 liquid fuel use are also
plotted for comparison. (The air intake passages were
significantly modified when the special intake cam was added to
restrict air flow to one of the intake valves in each
cylinder.) The objective of these measurements was to
determine the effect of the restriction on air flow.
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Figure 1
Air Flow Rate
4000
Air Flow (liter/min.)
CA18DE (M85) WOT
3000 -
2000
1000 -
CA18DE (H2/CO) WOT
TWO RUNS
0 800 1600 2400 3200 4000 4800 5600
Engine Speed (rpm)
The two sets of data follow a roughly similar trace until
approximately 3,000 rpm, where restriction of air flow to only
one runner may have significantly affected the volumetric
efficiency. However, for the engine speed range 800-2,500 rpm
the air flowrates are similar. In this range, volumetric
efficiency values are approximately 80 percent.
The Dwyer 10 cfm rotameter used during the previous
testing may have provided inaccurate fuel flowrate measurements
as it was not calibrated for the gaseous fuel. With varying
engine speeds at constant air flowrates, the rotameter
indicated only slight differences in fuel flowrates. During
one test, an audible leak of the gaseous fuel through the
rotameter control valve was detected. A less-audible leak may
not have been detected as the result of background noise from
the ventilation system in the test cell.
Other fuel flowrate measurement devices were tried,
however, none of these methods provided consistently accurate
measurements. To date, three different fuel measurement
devices have been used when operating the engine on the gaseous
fuel (rotameter, electronic/calibrated orifice metering system,
and a dry gas meter). Each should have been capable of
measuring fuel flow into the engine. However, in each case the
methods provided conflicting flowrate information when the
engine was operated under steady-state conditions.
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One indirect check of fuel consumption for this gaseous
fuel system is to use the change in mass of the cylindrical
fuel tank as a measure of fuel flowrate. The fuel tank was
weighed immediately prior to and following an engine test; the
change in fuel tank mass indicates fuel consumed. The engine
was brought to test conditions immediately after start, and
these conditions remain unchanged during testing. This is not
quite steady-state testing due to the warmup of the engine that
occurs after start. The time duration of the test was
recorded, and the mass of fuel consumed was converted to
standard cubic feet of gas. This method, used in the testing
discussed below, provide accurate, consistent measurements of
gaseous fuel flowrate.
A scaled pressure gauge which correlates bottle pressure
with standard cubic feet of gas present in the cylinder was
also used as a check on the weighing method referred to above.
Finally, it was necessary to vent the crankcase to the
test cell ventilation system. This action was taken as the
result of a severe oil leak at the oil filter caused by
overpressure in the crankcase. This situation was alleviated
by this rerouting of the PCV system.
VI. Discussion of Test Results
All of the testing described here was performed using
2H2/CO bottled gas, simulating dissociated methanol fuel.
Table 2 is a summary of the emission results. Test numbers
here correspond to the same test numbers in Table 1. In test
numbers 5 and 7, two bag samples were taken during one test
run, hence the a and b distinctions.
The first entry in Table 2 refers to testing conducted
during March 1989. Air/fuel ratios at that time were
calculated to be 11.9:1, very lean of stoichiometric. This
value may be high; subsequent experiments at similar conditions
have suggested that the rotameter supplied fuel flowrates were
too low. Only 27 ft-lbs of brake torque were generated under
these conditions.
The remainder of the tests described in Table 2 were
conducted as part of the recently completed testing. The head
gasket, which reduced the compression ratio to 10.5, from 11,0
previously, was in place for this testing. The rotameter which
previously measured fuel flowrate was also removed from the
fuel circuit; any backpressure therefore caused by the meter
was removed. Test numbers 2 and 3 were conducted with the
modified intake camshaft in place, as in test number l. At WOT
conditions, torque increased to 55 ft-lbs, a considerable gain
over the value noted previously. Fuel flowrate was calculated
by running at a single set of conditions and noting the change
in the mass of the fuel bottle and the duration of the
experiment. H2 and CO emission concentrations were
measured. Because intake and dilution air was also metered,
the rate of unburned fuel could be calculated. The rate of
unburned fuel was calculated to be approximately 13 percent.
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-8-
Table 2
Emission Test Results
Nissan CA18DE Engine, 2H2/CO Fuel
Test
Number
1
2
3
4
5a
5b
6
7a
7b
8
Torque
(ft-lbs)
27
55
60
65
65
65
67
66
66
70
UBF
(%)
N/A
13.4
13.8
N/A
N/A
N/A
24.8
41.7
41.7
N/A
Brake
A/F
11.90
8.33
7.89
N/A
N/A
N/A
6.07
7.36
7.36
N/A
0
0
0
0
0
0
0
0
0
0
HC
.130
.011
.008
.004
.007
.006
.004
.006
.005
.015
Specific Emissions
(q/BHP-hr)
CO
2.
29
33
79
57
78
76
125
119
11
27
.23
.62
.66
.25
.09
.37
.40
.20
1.90
C02
426
349
349
455
376
355
261
256
239
452
NOx
8.
0.
6.
10.
9.
6.
4 .
2.
2.
7.
57
79
69
87
33
96
09
35
24
64
N/A Not available.
a,b Two bag samples for one test run.
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_g
Several other experiments were conducted in order to
accurately determine the fuel flowrate. Only H2 and CO
emissions were measured during these experiments; the values
measured during that work were similar to those given to the
second and third tests in Table 2.
Spark ignition was timed at 0 degrees before top dead
center (BTDC). Advancing the spark even slightly caused an
audible knocking condition. At 2,000 rpm, part throttle also
caused an audible knock. It was not possible to vary fuel
flowrate with a high degree of accuracy using the current fuel
system.
The modified intake cam was then replaced with the stock
camshaft and hydraulic lifter system. This camshaft would
enable fuel and air to mix in the cylinder earlier, as the
stock camshaft permits the introduction of fuel earlier in the
combustion cycle. The stock control slide housing, however,
did not replace the housing modified to separate the valves
into fuel and air admission passages. Fuel continued to be
admitted through a single valve while air only was admitted
through the other valve.
Tests 4 through 5b in Table 2 were conducted at 2,000 rpm,
WOT conditions with the stock intake camshaft. The admission
of fuel was accomplished in the same manner as in previous
experiments, and was not closely controlled.
The higher cam profile and extended valve open period
caused a richer mixture, richer than stoichiometric. Torque
increased to 65-70 ft-lbs at the richer condition. This
maximum value was still below the value of 110 ft-lbs
experienced by Nissan with an MIOO-fueled, 12.0 compression
ratio CA18DE engine. No backfire was experienced at WOT. The
amount of fuel unburned was unknown because of a calibration
problem with the engine air sensor.
NOx emission levels were similar in magnitude between the
testing conducted with the modified camshaft and the stock
camshaft. CO emissions, a component of unburned fuel, more
than doubled to approximately 75 g/BHP-hr, with the stock
camshaft.
Engine speed was then reduced to 1,750 rpm at WOT
conditions. Brake torque was measured at approximately 67
ft-lbs, similar to the values recorded at 2,000 rpm. Air/fuel
ratio went slightly lean during this testing to approximately
7.3:1. Fuel efficiency decreased significantly, however, as
unburned fuel rose sharply to a calculated value of 40
percent. CO levels, representing unburned fuel, rose sharply
as engine speed was reduced. H2 was measured at roughly
twice the volumetric concentration of CO during this testing.
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A pressure sensor was installed in the spark plug well of
the number 1 cylinder in the test engine. An attempt was made
to monitor cylinder pressure during the combustion event and
use this in an attempt to relate the pressure pattern to the
onset of lean misfire. It was hoped that the shape of the
pressure versus crank angle curve would provide information
concerning abnormal combustion occurrences. The pressure
sensor ultimately failed, however, due to pressure wave
resonation in the cavity which housed the sensor.
It is not yet possible to determine to what extent
air/fuel mixing within the cylinder is a problem and whether
the lower torque values are associated with mixing. At WOT, in
all cases, when fuel flowrate was reduced, output torque at
constant engine speed was also reduced. For air/fuel ratios in
excess of 6.4:1, enough air should have been present to
complete the combustion of the fuel present.
VII. Highlights From Current Testing
1. Restricting the air flow to the engine to one of the
two intake valves per cylinder did not appreciably affect the
maximum air flowrate possible in the engine speed range
800-2,500 rpm at WOT conditions.
2. The rotameter used to measure fuel flowrate was
eliminated from the fuel system, and the compression ratio was
reduced to 10.5 through the installation of a new head gasket.
At 2,000 rpm engine speed, WOT conditions brake torque was
measured at 55-60 ft-lbs. This was a considerable increase
above the levels measured previously at these conditions.
3. The testing mentioned in 2. above, was conducted at
an air/fuel ratio of approximately 8.0:1 (lean of
stoichiometric). Thirteen percent of the gaseous 2H2/CO fuel
was passed through the exhaust as unburned fuel during this
testing. CO emissions, an indicator of unburned fuel,
increased sharply during this testing, to approximately 30
g/BHP-hr.
4. Testing was also conducted with the stock intake
camshaft in place of the specialty camshaft. At 2,000 rpm, WOT
conditions, brake torque increased slightly to 65 ft-lbs. The
amount of CO in the exhaust more than doubled, from levels
measured with the specialty camshaft.
When the engine speed was reduced and held constant at
1,750 rpm the percentage of unburned fuel rose sharply to about
40 percent. Brake torque rose only slightly to 67 ft-lbs. CO
(unburned fuel) increased to levels exceeding 100 g/BHP-hr.
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VI11.Future Efforts
This engine conversion project was begun to develop a
suitable test bed for a practical, onboard methanol
dissociation system. Further development of this engine
concept will be structured to accommodate this goal. Immediate
plans concern development of two measures of engine performance:
1. Emissions/fuel economy; and
2. Engine performance at lean operating conditions.
Further emissions testing at various engine speed/load
operating conditions will be conducted to characterize the
emissions profile of this engine when operated on both M100 and
dissociated methanol. A/F ratio at these various test points
will also be determined. A/F ratios will now be controlled by
varying fuel flowrate to the engine with the use of a Tylan
General Corporation mass flow controller. This equipment will
enable accurate metering and control of the gaseous fuel.
Previous testing with M100 liquid methanol was conducted
with a catalytic converter in the exhaust stream. Testing will
be conducted with the catalytic converter removed in order to
provide engine-out emissions data with M100 fuel.
Spark timing was limited to near TDC in these tests by
knock. Spark timing will continue to be adjusted ""as air/fuel
conditions are changed with the new fuel controller in order to
better utilize this operating parameter.
One way to determine the proximity to the lean misfire
limit at various engine operating conditions is to obtain a
quantifiable measure of increasing engine roughness as the
air/fuel mixture is leaned out. A measure of proximity to lean
misfire limit may be obtained directly, through measurement of
changes in cylinder pressure during the combustion effort. An
indirect method might involve the measurement of the
variability in successive crank rotation times as leanness
increases. The test engine is not equipped with a knock
sensor; it should therefore be possible to obtain a
quantifiable measure of engine performance as the lean misfire
limit is approached when the engine is fueled with the gaseous
2H2/CO blend.
EPA has obtained a cylinder pressure transducer less
susceptible to the resonation problem experienced with the
earlier generation sensor used in the present work. This
sensor will be used in an effort to optimize the combustion
event.
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IX. Acknowledgments
The CA18DE test 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
Jennifer A. Criss and Leslie A. Cribbins of CTAB/ECTD for
typing, formatting, and editing this report.
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X.References
1. "Conversion of Methanol-Fueled 16-Valve, 4-Cylinder
Engine to Operation on Gaseous 2H2/CO Fuel - Interim Report
II," Piotrowski, Gregory K., James Martin, EPA/AA/CTAB-89-02,
March 1989.
2. "Resistively Heated Methanol Dissociator for Engine
Cold Start Assist - Interim Report," Piotrowski, Gregory K. ,
EPA/AA/CTAB/88-02, March 1988.
3. "Internal Combustion Engines and Air Pollution,"
Obert, E. F., Harper and Row, New York, NY, 1973.
4. "Standards for Emissions From Methanol-Fueled Motor
Vehicles and Motor Vehicle Engines: Final Rule," Federal
Register, U.S. Environmental Protection Agency, April 11, 1989.
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A-l
APPENDIX A
TEST ENGINE SPECIFICATIONS, M100 FUEL OPERATION
CONDITION AS LOANED BY NISSAN TO EPA
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
Pentroof design
83 mm x 83.6 mm
11.0, 10.5*
16.5 kg/square cm (350 rpm,
80 degrees Celsius)
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 0 degrees BTDC to 54
degrees BTDC by means of an
external control
Reduced to 10.5 for testing referred to in this paper.
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B-l
APPENDIX B
PREVIOUS ENGINE/FUEL SYSTEM MODIFICATIONS
FOR 2H2/CO FUEL OPERATION
The simulated dissociated methanol product gas used in
this work is a mixture of H2 and CO gases in the molar ratio
2H2/CO. EPA did not possess a methanol dissociation system
capable of generating the necessary quantities of gaseous fuel
at the time work on this project was started; the engine was
therefore tested on a bottled gas mixture of 2H2/CO.
The Nissan CA18DE engine utilizes a 4-valve per cylinder
valvetrain configuration; both the stock gasoline and M100
methanol modified versions utilize 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 gaseous fuel. The
exhaust-side valve scheme was not modified (Figure 1).
Figure 1
Valve Scheme
2H2/CO Fuel Conversion
Nissan CA18DE Engine
AIR EXH. \
FUEL. , EXH. i
VALVE SCHEME
2H2/CO FUEL CONVERSION
NISSAN CA18DE ENGINE
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B-2
APPENDIX B (CONT'D)
PREVIOUS ENGINE/FUEL SYSTEM MODIFICATIONS
FOR 2H2/CO FUEL OPERATION
The advantages of structuring the intake process this way
are threefold. First, air flow into the engine may be less
restricted if the fuel, already in the gaseous state, is
introduced into only one of the intake runners. Second, there
may be less chance of flashback and a resulting manifold
ignition if fuel exclusively, and not a combustible fuel/air
mixture, is introduced at an intake valve. Finally, fuel may
enter the combustion chamber at the designer's discretion,
rather than at the same time the air needed for combustion is
admitted.
It was necessary to alter the fuel and air intake system
in order to allow 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
liquid-fueled 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. The control valve slide
and actuator were disassembled and the swirl control valves
removed. The runners through the valve assembly that contained
wells for fuel injectors were welded shut approximately
1/2-inch upstream from the well holes. These seals prevent the
admission of air to the ports through which the gaseous fuel
passes.
The hole in the assembly left by the power valve slide was
sealed to prevent leakage of fuel and air between runners. A
metal impregnation technique was used to seal the holes. The
sealed holes were then coated with a layer of epoxy.
Fuel injectors are not used to feed the gaseous state
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 wells were
then threaded to accept the fittings.
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B-3
APPENDIX B (CONT'D)
PREVIOUS ENGINE/FUEL SYSTEM MODIFICATIONS
FOR 2H2/CO FUEL OPERATION
The 2H2/CO fuel is a gaseous blend with a composition of
67 and 33 volume percent H2 and CO respectively. This fuel
is stored in compressed gas cylinders (T-sized) at 2,000 psig.
A fuel supply cylinder is located outside the test cell,
approximately 5 feet from the cell wall during testing. The
bottle, fitted with a regulator and pressure gauge, is opened
by a hand valve prior to testing. The fuel line from the
bottle is 1/4-inch stainless steel tubing, approximately 22
feet in length from bottle to cell wall.
The stainless steel fuel line enters the cell through a
hole drilled through the concrete wall. A Gould electrically
controlled solenoid valve is located in the line immediately
after the wall. An electrical signal from the control room
controls the opening of the valve.
The fuel line from the cell wall to a fuel flow regulator
measures approximately 54-1/2 feet. This regulator is a Twin
Bay Model TB-100. Gas flow through this regulator is
controlled by a flexible diaphragm. The diaphragm is opened
proportionally to the pressure exerted by a stream of air
provided by a tank of compressed air; the pressure exerted by
this airstream is controlled by a valve located in the cell
control room.
The final stage of the fuel system supplies the gaseous
fuel to the combustion chamber ports. The fuel passes to a
cylindrical plenum, this plenum serving as a header to four
flexible fuel lines. Inserted in each of the four fuel lines
approximately 17 inches from each cylinder is a 2-stage H2
flame arrester. The fuel lines are connected to threaded
fittings which are screwed into the fuel injection ports in the
valve control assembly. The 2H2/CO fuel is supplied to the
combustion chambers by the opening of the fuel valves.
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C-l
APPENDIX C
AIR/FUEL RATIO CALCULATION
WITH 2H2/CO FUEL
Given:
Air flowrate, 29 standard cubic feet/minute (scfm)
Change in weight of gas bottle, 4.5 Ibs
Density of fuel, 0.02969 Ibs/cubic feet
Time of test, 10.0 minutes (min)
Fuel flowrate = (4.5 lbs)/(0.02969 Ibs/cubic feet)(10.0 min)
Fuel flowrate = 15.16 scfm
Air/fuel ratio is defined [3] as:
Mass flowrate of air, dimensionless (1)
Mass flowrate of fuel
Molecular weight of air, 28.89, approximately
Calculate molecular weight of fuel, 2H2/CO:
2/3 (molecular weight of H2, 2) = 1.333
1/3 (molecular weight of CO, 28) = 9.333
Molecular weight of fuel, approx. 10.666
At standard conditions for gases:
PV = nRT (2)
Where:
P = pressure (atmosphere)
V = volume (cubic feet)
n = pound moles
R = gas constant (0.7302 atm-cubic feet/lb mol-degrees R)
T = Temperature (degrees R)
At standard conditions:
T = 492 degrees R
P = 1 atmosphere
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C-2
APPENDIX C (CONT'D)
AIR/FUEL RATIO CALCULATION
WITH 2H2/CO FUEL
Mass flowrate may then be defined as:
(PVt/RT)(molecular weight) = nt(molecular weight) (3)
Where:
vt = cubic feet/minute
nt = Ib moles/minute
Calculate A/F ratio:
Mass flowrate of air from (3)
(1 atm)(29 scfm)(28.89 Ib/lb mol)/(0.7302)(492 degrees R)
= 2.332 Ib/minute of air
Mass flowrate of fuel using (3)
(1 atm)(15.16 scfm)(10.67 Ib/lb mol)/(0.7302)(492 degrees
R)
= 0.4501 Ib/minute of fuel
From (1):
A/F = (2.332 Ib/minute air)/(0.4501 Ib/minute fuel)
A/F =5.18
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APPENDIX D
EXHAUST MASS EMISSION CALCULATION
WITH 2H2/CO FUEL
The procedure for calculating mass emissions for
methanol-fueled light-duty engines is defined in the Federal
Register,[4] and that same method was utilized in this report.
From exhaust gas bag analysis, you are given the following
dilute concentrations: HCe, COe, C02e, and NOxe. It is now
necessary to correct for background concentrations. All
concentrations are in parts per million (ppm) except for C02
concentrations which are in a percentage (percent). This is
done with the use of the following formula,
Yconc = Yex - Yb(l - 1/DF) (4)
Where:
Yconc = emission concentrations corrected for background
Yex = dilute concentrations measured in bag samples
Yb = background concentrations
DF = dilution factor.
The values used for the background concentrations of each
emission were:
HCb = 1.0 ppm
COb = 0.0 ppm
C02b = 0.04 percent
NOxb = 0.0 ppm
The dilution factor is calculated by:
DF = 100[x+y/2+3.76(x+y/4-z/2]/C02ex+(HCex+COex)0.0001
(5)
This formula is provided for methanol-fueled vehicles where
fuel composition is CxHyOz. Therefore, for our fuel (2H2/CO),
x=l, y=4, z=l.
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D-2
APPENDIX D (CONT'D)
EXHAUST MASS EMISSION CALCULATION
WITH 2HZ/CO FUEL
Once each emission is corrected for background
concentrations, it is now possible to calculate the mass of
each emission contained in the bag sample with the following
formula:
Ymass = Vmix x Dy x (Yconc/1,000,000) (6)
Where:
Ymass = mass value of each emission, grams
Vmix = total dilute exhaust volume, cubic feet
Dy = density of each emission, grams/cubic feet
Yconc = corrected concentration of each emission, ppm.
The densities of each emission are also listed in the
Federal Register. When finding the correct mass of NOx, there
is an additional NOx factor (Kh) that must also be applied to
equation 6. This value was calculated as follows:
Kh = 1/[1 - 0.0047(H - 75)] (7)
Where:
Kh = NOx factor
H = Absolute humidity, grams of water per kilogram
of dry air.
The NOx factor used for all calculations was 0.9.
Once the mass of each emission in the bag sample is known,
it is now possible to calculate a brake specific emission value
so that direct comparisons of different tests could be made.
First the brake horsepower needs to be calculated by:
BhP = Tn/5252.1 (8)
Where:
BhP = brake horsepower
T = engine output torque, ft-lbs
n = engine speed, rpm.
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D-3
APPENDIX D (CONT'D)
EXHAUST MASS EMISSION CALCULATION
WITH 2H2/CO FUEL
By knowing the time of each bag sample, brake specific
emission values can be found by:
BSY = Ymass/(BhP)(t) (9)
Where:
BSY = brake specific emissions, grams/BhP-hour
Ymass = mass value of each emission, grams
BhP = brake horsepower
t = time of emission bag sample, hours.
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