Fuel Metering Effects on Hydrocarbon Emissions and Engine Stability During Cranking and Start-up in a Port Fuel Injected Spark Ignition Engine

A cycle by cycle analysis of engine behavior during the first few cycles of cranking and start-up was performed on a production four-cylinder engine. Experiments were performed to elucidate the effects of initial engine position (rest position after last engine shut-down), first and second cycle fueling, engine temperature, and spark timing on fuel delivery to the cylinder, engine-out Hydrocarbon (EOHC) emissions, and Gross Indicated Mean Effective Pressure (IMEPg). The most important effect of the piston starting position is on the first firing cycle engine rpm, which influences the IMEPg through combustion phasing. Because of the low rpm values for the first cycle, combustion is usually too advanced with typical production engine ignition timing. For both the hot start and the ambient start, the threshold for firing is at an in-cylinder air equivalence ratio (λ) of 1.1. Open-Valve Injection is detrimental to the mixture preparation process during cranking because it causes mixture non-uniformity, directly deposits fuel in the cylinder which increases EOHC, and for the ambient start, wets the spark plug which results in misfiring.