Investigation of Intake Timing Effects on the Cold Start Behavior of a Spark Ignition Engine 1999-01-3622

Recent advances in Variable Valve Actuation (VVA) methods have led to development of optimized valve timing strategies for a broad range of engine operating conditions. This study focuses on the cold-start period, which begins at engine cranking and lasts for approximately 1 minute thereafter. Cold-start is characterized by poor mixture preparation due to low component temperatures, aggravated by fixed valve timing which has historically been compromised to give optimal warm engine operation. In this study, intake cam phasing was varied to explore the potential benefit in hydrocarbon emissions and driveability obtainable for cold-start.

A simple experimental approach was used to investigate the potential emissions benefits realizable through intake cam phasing. High speed cylinder pressure and Fast Flame Ionization Detector (FFID) engine-out hydrocarbon (HC) measurements were made to characterize instantaneous cold-start emissions and driveability. A complementary numerical model to further evaluate the HC emissions reduction potential augmented the experimental results. The results obtained indicate that optimized intake phasing provides the potential for simultaneous start-up hydrocarbon emissions reductions and driveability improvements in modern production engines. The trend toward use of variable valve timing systems on production vehicles makes it viable to implement advanced fueling and cam timing schemes for improved cold-start driveability and reduced unburned hydrocarbons.