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 unburned
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.  All
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
   Gasolin-e 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 N02
**Saltzman results reported as N02
. .

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TABLE 2
.1972 Federal Test Procedure
LA4
  Chevy    
  6 Cylinder Ford Truck
  Natural Gas Gasoline Natural Gas
Hydrocarbons 2.1   3.0 3.0
Carbon Monoxide 3.8   21 25
Carbon Dioxide 434   466 633
Oxides of Nitrogen* 4.6    
Oxides of Nitrogen** 2.0   2.8 4.6
 Results Reported in Grams Per Hile 
*NOx Box results reported as N020
**Saltzman results reported as N02.
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