Effects of charge motion control during cold start of SI engines

Abstract

An experimental study was conducted to investigate the effects of various intake charge motion control approaches on the cold start-up process of a port fuel injected SI engine. Engine experiments were performed to assess the effectiveness of enhanced charge motion on mixture preparation, combustion, and hydrocarbon (HC) emissions. Different charge motions were produced by three different shapes of charge motion control valves (CMCV), which block off 75% of the engine's intake ports. Cold-fluid steady state experiments were carried out with the CMCV open and closed. Increased charge motion with the CMCV closed was found to shorten the combustion duration, which caused the 50% mass fraction burned to occur up to 5⁰ CA earlier for the same spark timing. By the use of the CMCV, significant improvements in combustion stability (up to 1.5% reduction in COV) and fuel efficiency (up to 8% reduction in ISFC) were achieved with increased levels of spark timing retard due to enhanced air-fuel mixing and relatively faster burning. Engine start-up experiments were conducted with three different geometric charge motion control valves.

(cont.) The CMCV improved mixture preparation due to increased swirl and tumble intensities, which enhanced fuel distribution and evaporation. Moderate spark retard (AOp = -5⁰) was found to reduce the engine-out HC emissions during the engine start-up process. Peak engine-out HC emissions with the CMCV closed occurred in the earlier stages of engine start-up process relative to the CMCV open case. Greater fuel vaporization and faster burning rate with the CMCV closed allowed reduced fuel injection and additional spark retard, resulting in significantly reduced HC emissions. The engine-out HC emissions were reduced by 18% during the 0-3 seconds and by 7% during the 3-20 seconds.