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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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Principal Investigators
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 results.

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.

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Effects of intake cam phasing on engine out unburned hydrocarbon emissions are illustrated.

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A typical result of modified intake cam phasing is shown in the graph.

Engines, Fuels, Lubricants, and Vehicle Systems Program
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