74-13 DWP
An Evaluation of a 350 CID
Compound Vortex Controlled
Combustion (CVCC) Powered
Chevrolet Impala
October 1973
Emission Control Technology Division
Office of Air and Water Programs
Environmental Protection Agency
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74-13A
NOTE REGARDING HONDA ACTION FOLLOWING CVCC IMPALA TEST
Honda R&D Co. Ltd. has informed EPA that the hot start
emission problem encountered in the EPA test program has
been investigated with the following results.
1. The hot start (Bag 3) tests were influenced
by flooding of the auxiliary pre-chamber
carburetor. The flooding was caused by a
sticking float valve.
2. Honda has taken corrective action by
redesigning the float valve system to
prevent side forces on the valve body
and changing the tip material to provide
a more positive seal.
Although no further tests have been made by EPA on the
redesigned system, it is acknowledged that the corrective
action described by Honda reflects the type of "further
engineering effort" anticipated in the attached EPA report
in paragraph 2 of the Test Results section.
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Background
In the fall of 1971 Honda Motor Company of Japan announced
publicly that they had developed an engine featuring Compound
Vortex Controlled Combustion (CVCC) which would meet the
Federal emission requirements for model year 1975 without
after-treatment devices such as thermal reactors or catalysts.
To confirm what appeared to be a substantial breakthrough
in emission control technology, EPA conducted confirmatory
tests during December of 1972 on three Civic vehicles powered
by 119 CID versions of this concept. The following 1975 FTP
emissions values are the overall average values for the tests
performed on those cars at the EPA laboratory:
Hydrocarbons (HC) 0.21 gm/mi
Carbon Monoxide (CO) 1.96 gm/mi
Oxides of Nitrogen (NOx) 0.81 gm/mi
After their earlier work on four cylinder engines and sub-
compact cars Honda adapted the CVCC process to a larger
engine and vehicle combination to demonstrate that the
CVCC concept would successfully reduce emissions on full-size
American cars. A 350 CID Chevrolet V-8 engine was modified
and installed in a Chevrolet Impala. After Honda reported
achievement of the 1976 Interim Standards, a confirmatory
test program was scheduled by EPA.
Vehicle Tested
A 1973 Chevrolet Impala powered by a Honda Compound Vortex
Controlled Combustion (CVCC) engine was tested by EPA. This
CVCC engine was a modification of a stock 350 CID Chevrolet
engine. The heads and intake manifold were replaced with
the prechamber and dual carburetion systems which form the
CVCC concept. Rated maximum horsepower was 160 hp at 4000
rpm for the CVCC engine as opposed to 160 hp at 3700 rpm for
the stock 350 CID engine as measured by Honda.
The CVCC engine burns a heterogeneous air-fuel mixture. In
concept it is similar in some respects to the stratified charge
engines of Ford (PROCO) and Texaco (TCCS). While the Ford and
Texaco engines use direct cylinder fuel injection to obtain
charge stratification, the Honda CVCC engine obtains stratifi-
cation with the use of a separately carbureted prechamber.
Two separate intake valves are used on each cylinder of the
CVCC engine. One valve is located in the prechamber and the
other in the main chamber. A small one-barrel carburetor is
used on the 350 CID engine to supply a rich mixture to each
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prechamber. A four-barrel carburetor is used to supply the
engine's main chamber with a very lean mixture. Combustion
is initiated in the prechamber with a conventional ignition
system and spark plugs (one plug per prechamber). As the
burning gases .expand from the prechamber, they ignite and
burn the lean mixture present in the main chamber. A schematic
of the combustion system appears in Figure 1.
The overall air-fuel ratio of the CVCC engine is significantly
leaner than stoichiometric. Conventional engines cannot be
operated as lean because of the difficulty in igniting
homogeneous mixtures leaner than about 18:1 A/F. Ignition is
easily achieved in the CVCC engine by locating the spark plug
in the fuel rich prechamber. This very lean overall operation
is conducive to low CO emissions because the high availability
of oxygen facilitates the conversion of CO to C02. The combin-
ation of adequate oxygen and temperature in the main chamber is
the essential factor in controlling HC emissions.
NOx formation is a function of air (N2+02) availability and
temperature. A significant portion of the combustion in the
engine occurs in the very rich region of the prechamber where
the air availability is low. By the time the combustion has
progressed to the main chamber, where there is high air avail-
ability, the temperature has dropped because of expansion.
The Impala had accumulated 3000 miles with the CVCC engine at
the time of the EPA testing. The vehicle was equipped with a
three-speed automatic transmission, air conditioning, power
steering and power brakes. No "add-on" type emission control
systems such as catalysts, thermal reactors, air injection, or
exhaust gas recirculation (EGR) were used.
Test Program
The following test work was conducted on the subject vehicle:
1. Four cold start 1975 Federal Test Procedures at 5000
pounds simulated vehicle inertia.
2. Steady state gaseous emission testing at idle, 15 mph,
30 mph, 45 mph, 60 mph.
3. One hot start split bag 1972 Federal Test Procedure
at 5000 pounds simulated vehicle inertia and light
duty rear wheel power setting.
4. One hot start split bag 1972 Federal Test Procedure
at 5500 pounds simulated vehicle inertia and medium
duty rear wheel power setting.
5. One Clayton Key-Mode test.
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In addition to analysis for typical gaseous emissions the
samples were analyzed for aldehydes using an MBTH (3-methyl,
2-benzothiazolinone hydrozone) method. Fuel consumptions were
also calculated using a carbon balance technique. Because of
Honda's scheduling commitments for the test car, there was
not sufficient time to obtain particulate or sulfate emissions
data.
Test Results
Test results are summarized in Tables I, II, III, IV, V and
VI attached.
Table I presents the results of the 1975 Federal Test Procedure
emission measurements. Tests 1 and 4 demonstrate that levels of
CO and HC below the statutory 1975/76 levels can be achieved
with this vehicle, and that oxides of nitrogen levels are con-
sistantly below the 1976 interim standard of 2.0 grams per mile.
During tests 2 and 3, problems associated with the hot soak
period resulted in high levels of CO and HC during the bag 3
portion of the tests. The high CO level in bag 3 of test 2
appeared to be associated with flooding of the prechamber car-
buretor. This was corrected by Honda technicians prior to test
3. The high hydrocarbon level in bag 3 of test 3 was apparently
caused by a false hot start which resulted in excessive cranking
by the EPA driver. Another false start occurred on test 4, but
the more experienced Honda driver was able to recover with less
hydrocarbon penalty. It is believed that the hot start problems
experienced on the prototype vehicle can be corrected with
further engineering effort.
The consistently low cold start (bag 1) hydrocarbon and CO
levels during all of the tests should be emphasized. An average
value for bag 1 of 0.38 gm/mi HC and 3.51 gm/mi CO was observed.
Good control of oxides of nitrogen was also demonstrated with
this vehicle. An average value equal to 1.72 gm/mi was obtained
for the 1975 FTP testing.
Table II gives 1972 FTP hot start results for both a light duty
loading and a medium duty loading. This testing was conducted
by running bag 1 and bag 2 sections of the 1975 FTP from a hot
start (1972 FTP hot start split bag). The bag 1 and 2 data was
then combined to give a 1972 FTP hot start result. Some problem
relative to hot starting may be reflected in the medium duty
results. Test number 2-H was run after readjusting the dynamometer
load for a medium duty horsepower with the subject vehicle. Thus,
prior to the hot soak the vehicle was subject to higher than
normal loads. However, the bag 2 results show promise for the
CVCC approach in medium duty vehicle application.
Table III gives steady state emissions and fuel economy test
results. Table V gives results of Clayton Key-Mode testing.
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Aldehyde levels as measured by the EPA MBTH method are given
in Table IV. An average level of approximately .03 gm/mi
was observed during this testing. In comparison with other
late model cars, the CVCC engine appears to yield low aldehyde
emissions.
t
Comparison of the subject vehicle's fuel economy with cert-
ification results for 1973 vehicles of similar weight and
engine displacement is given in Table VI. It is apparent
that the CVCC-powered Impala had comparable or slightly better
fuel economy than these vehicles.
Conclusions
1. Although the results of this testing were not consistent
as a result of hot starting problems, the ability of the CVCC
engine concept to meet statutory 1975/76 hydrocarbon and
carbon monoxide standards when applied to a full-sized vehicle
application was confirmed.
2. Low cold start hydrocarbon and carbon monoxide levels were
repeatedly demonstrated during this testing.
3. Although the statutory 1976 NOx standard was not achieved,
good NOx control was demonstrated even without the use of EGR.
4. Fuel economy of this vehicle was comparable or slightly
better than 1973 vehicles having similar weight and engine
displacement.
5. Aldehyde emissions from the CVCC engine were found to be
lower than from present production cars.
6. The CVCC engine achieved low emission levels without the
use of "add-on" type devices or exhaust after-treatment. -
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HOHDA CVCC ENGINE
spark plug
prechamber inlet valve
prcchamber
Figure 1
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Table I
1975 FTP Results on 350 CID CVCC Powered
Chevrolet Impala
Testl
Hydrocarbon(gm/ni)
(gm/mi)
Cal. Fuel Consumption
1
2
3
4
Bag 1
0.45
0.35
0.40
0.33
Bag 2
0,14
0. OS
0.13
0.12
Bag 3
0.39
0.50
2.38
0.71
Composite
0.27
0.23
0.80
0.32
Bagl
4.A2
1.77
4.34
3.32
Bag 2
2.53
2.45
1.96
2.71
Bag 3
2.22
12.35
2.67
2.54
Composite Bag 1 Bag 2 Bag 3 • Composite Bag 1 Bag 2
2.88 2.57 1.17 2.14 1.72 864.97876.26
5.01 2.58 1.42 2.47 1.95 789.60 787.56
2.64 2.11 1.00 2.02 1.S1 849.57 858.94
2.79 2.30 1.29 1.97 1.68 892.07 9.2.17
Bag 3
770.13
765.76
738.10
796.68
Composite
844.98
787.05
824.04
876.52
MFC
10.5
11.2
10.8
10.2
Note: Above tests run at 5000 Ibs. inertia
and 14.7 rear wheel hp at 50 mph
(hp includes lot ffcr air conditioning)
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Test *
1 H
2 H
TABLE II
Comparison of Light Duty vs. Medium Duty
Loading on 350 CID CVCC Impala
1972 FTP (Hot Start, Split Bag) Results
Hydrocarbon (gm/mi) j_ Carbon Monoxide (Rm/mi) Oxides" of Nitrogen(gm/ni) Carbon Dioxide(gm/mi) Cal. Fuel Consump. Comment
Bag 1 Bag 2 Composite' Bag 1 Bag 2 Composite Bag 1 Rag 2 Composite Bag 1 Bag 2 Composite MPG
0.34
2.83
0.04
O.OS
0.18
1.38
2.46
2.91
2.19
2.23
2.34
2.56
2.23
2.77
1.54
1.55
1.R7
2.13
737.23 790.70
834.R5 853.55
765.11
844.45
11.5 Inertia-5000 Ibs
hp-14.7 6 SO mph
10.4 Inertia-SSno Ibs
hp-22.7 8 50 moti
(Med. Duty LD.)
NOTE: Because of an apparent hot start problem on test 2H,
the bag 1 data are questionable. However, the bag 2
data illustrate that there was very little increase
in emissions when the vehicle was tested using
medium duty loading.
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TABLE III
Comparison Steady State Emissions
350 CID CVCC Impala vs. A Stock 1973 350 CID Impala
HC
CO
NOx
Idle (gm/5 rain)
15 mph (gm/mi)
30 mph (gm/mi)
45 mph (gm/mi)
60 mph (gm/mi)
Fuel Economy (mpg)
350
CVCC
0.50
0.16
0.00
0.00
0.01
Stock
350
N/A
0.60
1.22
0.51
0.32
350
CVCC
2.04
3.30
0.65
0.19
0.53
Stock
350
N/A
7.26
9.98
4.71
2,48
350
CVCC
0.21
0.37
0.53
1.00
3.00
Stock
350
N/A
0.52
0.37
0.93
1.78
350
CVCC
424.32
662.68
542.49
604.73
557.75
Stock
350
N/A
620.32
443.44
451.89
487.24
350
CVCC
*
13.3
16.3
14.7
15.9
Stock
350
N/A
14.0
19.2
19.3
18.0
NOTE: a) CVCC data - - rear axle ratio: 3.08
- - loading characteristic is per belt-driven Clayton
Dynamometer set at 14.7 rear wheel Hp at 50 mph
b) Stock data - - rear axle ratio: 2.73
- - loading characteristic is per belt-driven Clayton
Dynamometer set at 14.0 rear wheel Hp at 50 mph
* 350 CID CVCC Idle Fuel Consumption: 0.58 gal/hr
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Table IV
MBTH Aldehyde Results for
350 CID CVCC Powered
Chevrolet Impala
Test # Comment Composite Bag HC Ald'y % Ald'y
gm/mile gm/mi
2 Cold Start 75 FTP 0.23 0.0286 12.4
3 Cold Start 75 FTP 0.80 0.0355 4.4
4 Cold Start 75 FTP 0.32 0.0195 6.1
2 H Hot Start 72 FTP Split Bag 1.38 .0338 2.4
350 CVCC Average 0.0294 6.3
•73 Duster (225 CID eng.) 1>80 0.116 6.5
Avg. 3 tests
•73 Maverick (302 CID eng.) 2.25 0.104 4.6
Avg. 3 tests
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TABLE V
Clayton Key-Mode Results
and Comparison for 350 CID
CVCC-Powered Chevrolet Intpala
High Speed
Avg. 15 1970-71 vehicle
Catalyst-equipped Prototype
Ford Galaxie (351 CID)
350 CID CVCC Impala
Low Speed
Avg. 15 1970-71 vehicle
Catalyst-equipped Prototype
Ford Galaxie (351 CID)
350 CID CVCC Impala
Idle
Avg. 15 1970-71 vehicle
Catalyst-equipped Prototype
Ford Galaxie (351 CID)
350 CID CVCC Impala
HC
ppm-c
136
29.9
2.01
158
47.5
5.68
192
170
292
CO
PPM
4000
181
91.7
5000
52.4
206
22000
81.5
1010
NOx
PPin
3151
286
563
2013
390
236
164
54.2
97.9
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Table VI
Comparison of 350 CID CVCC Impala
Fuel Economy with Similar Homogenous
Charge Gasoline Powered 1973 Vehicles
Vehicle Eng. Displace;- Test Inertia Axle Ratio Economy
ment - CID Lbs. MPG
Pontiac Catalina 350 5000 3.23 8.1
Olds Delta 88 350 5000 3.08 9.9
Olds Cutlass Supreme
Vista Cruiser 350 5000 3.23 9.4
Buick LaSabre 350 5000 3.08 10.5
Average 9.5
CVCC Impala 350 5000 3.08 Avg. '72: 10.4
Note: 1) Comparative Data taken from 1973 Certification results
2) Avg. '72 FTP Fuel Economy Results for CVCC Iirtpala Calculated
from Bag 1 and 2 results from '75 FTP Results.
3) Data from 1973 Chevrolet Impala certification not used because
the car was certified at a lighter weight (4500 Ibs.).
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