72-2
A Report on the Emission Performance of the
Ford Stratified Charge Engine Using the
1975 Test Procedure
August 1971
John C. Thomson
Office of Air Programs
ENVIRONMENTAL PROTECTION AGENCY
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Vehicle Tested
The vehicle tested during this evaluation was an Army
M-151 1/4 ton truck. This was the same vehicle tested in
May 1970 and April 1971, with only minor modifications to
the emission control system. The M-151 is a general purpose
vehicle used throughout the world by the U.S. Army. It is
equipped with a four wheel drive system with the front wheel
drive portion controlled by the driver. It is also equipped
with a four speed transmission. This transmission has a
very low first gear and for normal driving it is not used.
For all of the emission tests, the transmission was used
only in second, third, and fourth. A modified shift pattern
was suggested by Ford due to the unusual weight to horsepower
ratio of this vehicle. The Army M-151 was tested with an
inertia weight of 2,750 pounds for this series of tests based
on shipping weight. This vehicle is supplied with a seventy
horsepower engine, and when the friction losses of the drive
train are taken into account, can only meet the required
accelerations with difficulty. In addition, the independent
rear suspension system will not tolerate the vibration from
the four cylinder engine at low speed, necessitating more
gear changes than normally required. As a result, it is
difficult to achieve the best possible emission results from
this engine as installed in the Army vehicle.
The engine used in these tests, a 141 CID four cylinder with
3" bore and 3 7/8" stroke, was developed by the Ford Motor
Company through joint U.S. Army - EPA funding. This engine
is the "low emission" version of their stratified charge
combustion system and is called the Proco conversion.
The basic stratified charge system used by Ford uses an un-
throttled air intake with fuel injected directly into the
cylinder. This engine uses a low pressure (600 p.s.i.)
mechanical fuel injection pump that is integrated with the
ignition distributor. The injected fuel mixes with a portion
of the air in the vicinity of the spark plug, where it is
ignited. The combustion system is shown in Figure 1. The
extended tip spark plug places the spark near the center of
the cup combustion chamber.
In order to provide low emissions from this engine, several
modifications were made in the control systems. Extensive
dynamometer tests indicated that a very close control over
fuel air ratio was required in order to achieve the emission
values needed to meet 1976 standards.-;) For this reason an air
throttle system was developed to provide a 17:1 air-fuel
ratio. In addition exhaust gas recirculation was added to
reduce the amount of oxides of nitrogen. Due to the direct
cylinder injection this exhaust gas recirculation seems to
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have no effect on driveability, even at 11% recycle used
during the first three minutes of test. During the re-
mainder of the test, about 9-10% recycle was used.
This engine was provided with a thermal reactor. However,
the contribution of the reactor to emission reduction was
minimal according to Ford data. In addition, an Engelhard
off-the-shelf catalytic reactor was used to reduce the peak
on hydrocarbons and to encourage a reaction between the CO
and NO in the exhaust. A lead sterile fuel was used to be
compatible with this reactor.
The air-fuel ratio control was an experimental unit and did
not contain an ambient pressure compensator. The lack
of pressure compensation made the system dependent on atmos-
pheric pressure and explains some of the variation in test
data. A special spark plug that is similar to a production
plug was also used.
As this vehicle does not need enrichment during start or
warm-up, there is little change between cold and hot start
data other than that found due to the cold catalyst. For
this reason repetitive hot start tests were not made.
Data from this vehicle was reported in report number 70-4
"Exhaust Emissions from a Stratified Charge Ford Combustion
Process (FCP) Engine". In addition, data on another stan-
dard M-151 is in report number 70-2 "Emissions from a Standard
M-151 Jeep".
Tests Used
In order to evaluate the emission performance of the vehicles
tested, the 1975 LA4-S4 test cycle was used for all tests.
This is the test cycle that will be used for certifying all
new light duty motor vehicles beginning in 1975. The emis-
sion standards for 1975 and 1976 are shown below, with the
1976 standards also shown with the emissions data in Table 1.
HC CO NO7
1975 0.41 3.4 3.0
1976 0.41 3.4 0.4
Throughout the report, HC will be used to abbreviate unburned
hydrocarbons, CO will be used for carbon monoxide and NOx
for oxides of nitrogen.
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For these tests results are reported with HC measured using a
flame ionization detector, CO and CC>2 using a non-dispersive
infrared analyzer and oxides of nitrogen using the chem-
iluminescent technique.
Emission Results
The results of our tests are reported in Table 1. In this
table a comparison is made between the projected standards,
the vehicle as tested, and the standard M-151. On two new
standard M-151's a single number has been obtained by averaging
three tests. It appears that the vehicle approaches the
standards for 1976. The emission reduction over the standard
vehicle is very significant. Emission results using the 1972
test procedure are available in report number 71-23 from the
Test and Evaluation Branch.
Conclusions
The Ford stratified charge system has the potential of meeting
the 1976 emission standards while still maintaining the
driveability and fuel economy of the uncontrolled vehicle.
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Table 1
1975 LA4-S4 Emission Test Comparison
All Results in Grams Per Mile
HC CO NOx
FID IR_ CI
PROCO (FCP) Test #1 0.32 0.36 0.56
Test #2 0.34 0.73 0.53
Federal Standards (1976) 0.41 3.4 0.4
Standard M-151 5.4 17,2 2.0
(1 of 2 vehicles, 6 tests)
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