Reduction in Hydrocarbon Emissions and
Improvement of Cold-Start Driveability of a Spark-Ignition Engine by Retarding the Intake Timing, 03-9095
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Charles E. Roberts
Rudolf H. Stanglmaier
Inclusive Dates: 08/26/98 - 12/26/98
Background - The most severe operating
condition experienced by gasoline-fueled spark ignition engines involves a cold start.
During the first one or two minutes of engine operation, engine components are cool and
the conditions for vaporizing fuel within the intake manifold are unfavorable. This
failure to properly blend the fuel with the air results in large amounts of unburned and
partially burned hydrocarbon emissions and in increased driveability problems.
Approach - The goal of this project was to
quantify the improvements possible by advancing the engine intake timing during the
cold-start and warm-up periods through variable valve actuation (VVA). An engine
simulation code was used to model the thermodynamic effects of the proposed intake-phasing
scheme. These results indicated a potential for enhanced in-cylinder fuel vaporization. An
experimental approach was used to investigate the potential emission benefits that could
be achieved with the proposed method on a production engine. A complementary model to
evaluate the hydrocarbon emissions reduction potential further augmented the experimental
Accomplishments - The project results indicate
that optimized intake phasing potentially reduces hydrocarbon emissions and improves
driveability in modern production engines during the start-up cycle. The use of variable
valve timing systems on production vehicles permits the implementation of advanced fueling
and cam timing schemes that result in improved cold-start driveability and reduced
unburned hydrocarbons. This work indicates that these positive benefits can be realized
with a mechanically simple VVA system that allows for intake event phasing with an
actuation time of approximately one second.
Effects of intake cam phasing on engine out
unburned hydrocarbon emissions are illustrated.
A typical result of modified intake cam
phasing is shown in the graph.
Lubricants, and Vehicle Systems Program
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