Optimization on timings of injection and spark of a high compression-ratio stratified-charge methanol engine under ultra-lean burn

摘要

High compression-ratio and ultra-lean burn are the two most effective measures to enhance economy of spark-ignition engines. The investigations were performed on a high compression-ratio stratified-charge direct-injection spark-ignition methanol engine with an injector of non-uniform spray-line distribution. The effect of timings of injection and spark on the concentration field of the stratified-charge mixture, combustion and emissions behaviors of methanol engine under ultra-lean burn conditions was studied by simulation. Simulation results demonstrated that an ideal stratified-charge mixture was the guarantee to obtain the best performance of a high compression-ratio spark-ignition methanol engine under ultra-lean burn. The timings of injection and spark had a remarkable effects on mixture formation, combustion and emission of a methanol engine under ultra-lean burn. There existed an optimal timings of injection and spark to obtain the peak in-cylinder pressure, peak heat release rate and peak in-cylinder temperature of methanol engine under ultra-lean burn, as well as the shortest ignition delay and combustion duration. Lower CO (carbon monoxide), unburned methanol and soot emissions, and higher NO (nitric oxide) emission were acquired at optimal timings of injection and spark under high compression-ratio and ultra-lean burn. Hence, realizing an ideal stratified-charge combustion was the key to obtain the best performance of a spark-ignition methanol engine under high compression-ratio and ultra-lean burn.