EVALUATION OF A GM 1976 PROTOTYPE
VEHICLE - A CATALYTIC EXHAUST
MANIFOLD SYSTEM
June 1972
Henry L. Gompf
Test and Evaluation Branch
Environmental Protection Agency
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Background
As part of the Office of Air Programs continuing effort to
keep abreast of potential 1975-76 control technology, a test
sequence was conducted on a General Motors prototype utilizing
•a catalytic exhaust manifold system concept. Data compiled at
General Motors Corporation on the test 'vehicle indicated low
mileage average emission data as follows:
i
Hydrocarbon .25 grams per mile
Carbon Monoxide 2.4 grams per mile
Oxides of Nitrogen .34 grams per mile
Due to the consistent success displayed by' 'this system in
meeting the required 1976 emission level in the General Motors
laboratory, an evaluation program was initiated by EPA. At
the time of the evaluation in the Ann Arbor laboratory, GM
had not yet subjected this candidate system to durability
evaluation.
System Description
The prototype system under evaluation was supplied to EPA
installed on a 1972 Chevrolet Belair equipped with an automatic
transmission and a 350 cubic inch displacement California engine
Beyond necessary engine modifications, the vehicle was equipped
with four major emission controls.
1. A uuick heat intake manifold ,&&£, was incorporated to
assist in cold start fuel evaporation. Exhaust from both
exhaust manifolds was piped transversely through a single
plane hot plate in the intake manifold resulting in dual
cross flow for warm-up.
2. A Grace noble metal catalyst was employed for oxidation
of hydrocarbon and carbon monoxide. The catalyst had a
monolith structure.
3. A Gulf noble metal catalyst was employed for reduction
of oxides of nitrogen. This catalyst had a .monolith .structure
4. An air pump and associated valving was used to supply
air for exhaust port oxidation and oxidizing air to the
Grace catalyst bed.
The sequence of operation during EPA's evaluation was
largely manual. For cold start purposes the choke was manually
released within three seconds of vehicle start-up. Initially
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air injection was directed manually to the exhaust ports during
catalyst bed warm-up. After reaching necessary catalyst temp-
erature (approximately 60 seconds) the major portion of the air
injection was manually diverted to the oxidizing catalyst for
the duration of the testing cycle. Simultaneously the exhaust
to the EFE manifold was shut-off. The manual controls utilized
could feasibly be replaced with temperature actuated valves after
further optimization studies.
Both catalyst beds were neatly packaged together at the
rear of each exhaust manifold. Special note should be made of
the fact that this system does not employ any exhaust gas
recirculation for the control of oxides of nitrogen other than
that obtained from valve overlap with the 1972 California
camshaft.
A schematic view of the overall engine system is presented
in Figure 1 of this report. Figure 2 schematically shows
typical valving and a cross section of the catalyst beds. (Note
that this figure shows pellatized beds whereas the one tested
was monolithic in structure) .
Test Procedure
The GM prototype system was tested three times from a cold
start using the 1975 Federal emission test procedure. Full
details of this procedure are found in the July 2, 1971, Federal
T3^rr-ic?-f1'£iT» ir/"\1iTm£a "Z. f\ Mi iTr»V\^»-v- TOO T5oT»4- TT
All three tests were conducted using the General Motors
recommended dynamometer inertia loading of 5000 pounds. Test
fuel was Indolene Clear (an available lead free standard fuel) .
In addition, one hot start 1972 split-bag procedure was
conducted at an inertia weight of 4000 pounds to indicate,
if possible, major effects of vehicle size on emissions with
this type of system.
Emission Test Results
Table 1 shows the results of the three individual cold
start tests. As can be seen the hydrocarbon and carbon monoxide
levels were lower than those" reported by GM in their previous
testing. The oxides of nitrogen levels measured in the EPA
evaluation were higher than GM's figures. In the General Motor's
testing the vehicle consistently met 1976 required levels, while
the EPA testing showed that the oxides of nitrogen exceeded
allowable levels. The vehicle did consistently meet maximum
allowable emission levels for 1975 vehicles.
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Table 2 compares the hot start 1972 procedure emissions
of the 5000 pound test weight with the 4000 pound results.
Significant in this table is the 12% reduction in oxides of
nitrogen at the 4000 pound weight.
Fuel consumption during the three cold start tests was
analytically calculated. An average fuel consumption of 9.9
miles per gallon was reported during EPA tests compared to 9.4
miles per gallon reported by GM.
While no quantitative analysis of the vehicle driveability
was made, a report from the test driver and that from another
EPA evaluator both reported excellent driveability.
Conclusions
Based on discussions with General Motors engineers differ-
ences between EPA emission results and those previously reported
by GM were probably due to an interceding vehicle tear-down and
build-up immediately prior to delivery to the EPA laboratory.
While the prototype vehicle tested showed excellent potential
of meeting Federal required levels for 1975-76 a vehicle with
minimal deterioration of driveability and fuel economy, it is
impossible to assess the full potential of the system without the
input of durability mileage data. It appears, however, that this
prototype system is an excellent candidate for extended mileage
lu?. t ion ;
Due to the characteristics of catalytic-based systems
parallel analyses for ammonia, aldehyde and particulate content
of the exhaust are desirable to assure 'overall compliance with
light duty motor vehicle goals.
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Table 1
1975 FTP Emission Results
(All results in grams per mile at 5000 pounds)
Date HC CO C02 NOx
High Range/Low Range
*6-5-72
6-6-72
6-7-72
0.26
0.21
0.16
1.4
1.8
1.1
1.6
1.8
891.8
891.8
895.7
0.47
0.45
0.49
EPA Average
0.21 1.4 1.7 893.1 0.47
**GM Average
0.25 --- 2.4 --- 0.34
***GM Average
0.20 --- 1.1 835.9 0.44
*Note: After the test on 6-5-72 an orifice change controlling
secondary air was performed. No obviously apparent
effect «resuired.
**GM data collected prior to engine tear-down, rebuild, and
subsequent delivery to EPA.
***GM data collected in one test immediately prior to delivery
to EPA and immediately following the return of the vehicle
to GM.
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Table 2
Hot Start 1972 FTP Emission Results
(All results in grams per mile)
Test
Inertia Weight Date HC_ CO C0_2 NOx
5000 # 6-5-72 0.11 0.5 869.6 0.31
5000 # 6-6-72 0.13 1.'3 874.4 0.34
5000 # :6-7-72 0.09 0.5 877.1 0.35
Average at
5000 # 0.11 0.8 873.7 0.33
4000--# 6-7-72 0.18 0.6 800.9 0.29
% Change from
5000 # 641* 25%** 8%** 12%**
* increase
•* decrease
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*
AIR PUMP
AIR CONTROL
VALVE
IMPROVED CARBIIRETIOM
AKD CHOKE
QUICK KEAT MAJHFOLD
DUAL CROSS FLOW'
FOR WARM-UP
REACTOR CONTROL
WARM-UP CONTROL '
p?
t'.
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PORT AIR
(COORDINATED
VALVES SHOWN IN
MOx
REDUCING
IN CENTEJ
SECTION
EXHAUST GAS FROM
QUICK HEAT MANIFOLD
CATALYTIC EXHAUST MANIFOL
HC/CO OXIDIZING
IN PERIPHERAL SECTION
CONVERTER AIR
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