Feasibility of CNG DI stratified combustion using a spark-ignited rapid compression machine

Feasibility of compression natural gas direct-injection (CNG DI) stratified combustion is investigated by using a rapid compression machine. Results show that CNG DI stratified combustion has the short initial flame development duration and main burning duration and high pressure rise due to combustion caused by the charge stratification. Stratified combust ion can extend the lean combustion limit to very lean region. CO increases steeply with the increase in equivalence ratio φ when φ is larger than 0.8 due to the excessive stratification and NO_x peak value shifts to the region of low φ due to charge stratification. Combustion efficiency maintains more than 0.92 in the range of Φ from 0.1 to 0.9 and it deteriorates at very low φ due to bulk quenching and at large φ due to excessive stratification. The combustion efficiency calculated from combustion pro ducts shows good agreement with that obtained from the heat release analysis. Thus CNG DI is considered to have much potential in a spark-ignition engine on the basis of wide operation range of φ and high energy conversion efficiency.