71-11
An-Evaluation of A Variable Cam Timing Technique
As A Control Method For Oxides of Nitrogen
October 1970
John C. Thomson
Division of Motor Vehicle Research and Development
National Air Pollution Control Administration
Department of Health, Education and Welfare
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71-11
An Evaluation of A Variable Cam Timing Technique
As A Control Method For Oxides of Nitrogen
October 1970
John C. Thomson
Division of Motor Vehicle Research and Development
National Air Pollution Control Administration
Department of Health, Education and Welfare
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Device Tested
A device to allow internal exhaust gas recirculation through
variable camshaft timing was tested to determine its effects
on exhaust emissions. This device made use of a vacuum
diaphragm and associated circuits to vary the position of
the camshaft in relation to the crankshaft as a function of
engine load and speed. The purpose of thisi device is to
increase the amount of residual exhaust in the cylinder to
lower oxides -of nitrogen. Theieffect hoped for would be
similar to the external exhaust gas recirculation systems
currently under investigation. The vehicle used was a 1970
Plymouth Fury with a 383 cubic inch engine and automatic
transmission. A more complete description of the system can
be found in a Society of Automotive Engineers paper number
700673 titled "Variable Cam Timing as an Emission Control
Tool".
Test Procedure
The following tests were conducted:
1. The 1970 Federal emission test procedure as used
for certification of new motor vehicles (7-mode).
2. A closed3 constant volume sampling technique using
nine repeats of the Federal emission test cycle (9-CVS).
3. A closed, constant volume sampling technique using
the LA4-S3 driving schedule as specified for 1972 and
later testing (LA4).
The closed cycle data were taken using a constant volume
sampling technique yielding "true mass" emission results.
The bag samples were analyzed using non-dispersive infrared
analyzers for carbon monoxide and carbon dioxide with
hydrocarbons measured using a flame ionization detector.
An electrochemical technique was used for determination of
oxides of nitrogen in the CVS sample.
Emission Results
The data shown in Table I compares the results found on this
system on the three emission cycles used. These tests
cover the complete range of emission measuring techniques
and give a good insight into the effect of this device.
Table II compares the 1970 results expressed in parts per
million HC and NOX and percent CO from the variable timing
technique with some results taken on similar cars using
external exhaust gas recirculation. The exhaust recirculation
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vehicles were 1969 full sized cars and the results are an
average of four cars at a comparable mileage. From this
data, it would appear that variable cam timing has a
beneficial effect on the control of oxides of nitrogen with-
out increasing emission of hydrocarbons or carbon monoxide.
Conclusions
1. The variable cam timing device shows improvements in
oxides of nitrogen.
2. The use of this device alone would not meet 1973 emission
levels except for oxides of nitrogen.
3. This system appears to be more effective than external
exhaust gas recirculation for oxides of nitrogen control.
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Table I
Emission Results
(all numbers reported in grams per mile)
7-mode 9-CVS LA4
HC
CO
C02
NOx
1.9
18
1.7
4.5
49
735
2.2
4.3
49
810
1.9
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Table II
Emission Comparison of Internal versus External
Exhaust Recirculation Techniques
(all tests using 1970 procedure)
Variable Exhaust
Cam Timing Recirculation
HC ppm 140 ppm 320 ppm
CO % .66 % 1.4 %
NOx ppm 400 ppm 800 ppm
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