The Formation of a Combustible Mixture During the First Cycle of Cranking and Startup in a Port-Fuel-Injected Spark-Ignition Engine

Abstract

As automotive engine emission standards continue to become more stringent, excellent cranking, and startup fuel control will become imperative in order to achieve minimum engine-out emissions. Optimized engine starting requires the generation of a strong first firing cycle. Fortunately, an engine’s first cycle event is physically less complex than future engine cycles, providing the opportunity for accurate modeling. A physically based crank mixture preparation model coupled with a multicomponent fuel model was developed to provide insights into the fuel vapor generation process during the first cycle of engine starting. Excellent agreement with experimental data is obtained over a range of operating conditions. Model results show that for increased engine temperatures, fuel distillation becomes of comparable importance to the convective mass transfer fuel vapor formation mechanism. Additionally, the modeling work suggests that fuel pooling near the intake valve is occurring at rich fueling levels. The important effect of engine speed during intake is correctly predicted by the model.