71-17
An Evaluation of the* Exhaust Emissions From Two Vehicles
Equipped With'Compressed Natural Gas Conversion Kits
December 1970
John C. Thomson
Division of Motor Vehicle Research and Development
Air Pollution Control Office
ENVIRONMENTAL PROTECTION AGENCY
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71-17
An Evaluation of the Exhaust Emissions From Two Vehicles
Equipped With Compressed Natural Gas Conversion Kits
December 1970
John C. Thomson
Division of Motor Vehicle Research and Development
Air Pollution Control Office
ENVIRONMENTAL PROTECTION AGENCY
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Vehicle Tested
An evaluation of the emission characteristics of two vehicles
equipped with compressed natural gas conversions was made during
the month of November. The first vehicle to be evaluated was
a six cylinder Chevrolet. The second vehicle was a four door
Ford pick-up truck. Both vehicles used dual fuel conversions
with modified Impco fuel systems. Vehicles were capable of
being driven on either gasoline or compressed natural gas.
Tests Conducted
Two different driving cycles were used in the evaluation of
the compressed natural gas vehicle. In the first tests nine
cycles of the seven mode 1970 Federal emission test driving
schedule were used (9X7 CVS). For the other tests, the 1972
test procedure for certification of new vehicles was used.
This driving schedule is non repetitive and simulates typical
urban driving. During both tests exhaust was collected using
the constant volume sampling technique as described in the
November Federal Register. Oxides of nitrogen were analyzed
using both an electro chemical technique and the wet chemical
modified Saltzman method. Carbon monoxide and carbon dioxide
were measured using non-dispersive infrared while unburaed
hydrocarbons were determined using a flame ionization detec-
tor .
Emission Results
The results reported in Table 1 compare the Ford Truck, using
both gasoline and natural gas. All of the results are report-
ed in grams per mile. As this is" only a research cycle,
there are no Federal standards. In Table 2 the emissions
are reported as measured on the 1972 test procedure. The,
standards for 1972 with this cycle are hydrocarbon 3.4
grams per mile and carbon monoxide 39 grams per mile. Jill
three tests show results under these levels. The standards
for 1975 proposed in the July 1970 Federal Register are
hydrocarbons 0.5 grams per mile, carbon monoxide 11 grams
per mile and oxides of nitrogen 0.9 grams per mile. None
of these vehicles meet these standards.
Conclusions
1. The level of emission of the vehicles tested are below
1972 standards.
2. The level of emission of the vehicles tested are above
the proposed 1975 standards.
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3. The reduction shown between gasoline and CNG on the
Ford truck is less than normally expected and may be due
to the dual fuel system being used.
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TABLE 1
Constant Volume Sampling Using 1970 Driving Cycle
(9X7 CVS)
Ford Truck
Natural
Gasoline Gas
Hydrocarbons 3.9 3.1
Carbon Monoxide 23 10
Carbon Dioxide 533 448
Oxides of Nitrogen* 7.4 5.2
Oxides of Nitrogen** 5.4 4.1
Results Reported in Grams Per Mile
*NOx Box results reported as NO2
**Saltzman results reported as N02
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TABLE 2
1972 Federal Test Procedure
LA4
Chevy
6 Cylinder Ford Truck
Hydrocarbons
Carbon Monoxide
Carbon Dioxide
Oxides of Nitrogen*
Oxides of Nitrogen**
Results
Natural Gas
2.1
3.8
434
4.6
2.0
Reported in Grams
Gasoline
3.0
21
466
2.8
Per Mile
Natural Gas
3.0
25
633
4.6
*NOx Box results reported as NO2.
**Saltzman results reported as NO2-
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