Study on combustion characteristics of direct injection natural gas engine by using a rapid compression machine

Investigation of combustion characteristics of direct injection natural gas engine is carried out using a rapid compression machine. Combustion characteristics of three types of injection modes are analyzed and compared with that of homogeneous combustion. The results show that direct injection natural gas combust ion has higher value of pressure rise due to combustion than that of homogeneous mixture. Short flame development and rapid burning period is found in the case of fuel injection for the wide range of equivalence ratio. No great difference in the rate of heat release and the rate of pressure rise is also found for different fuel injection modes. The heat release rate and the rate of pressure rise in the case of fuel injection combustion has the high value and finishes early compared with that of the homogeneous mixture combustion. The study found that flame development and rapid burning period would decrease with the shortening of the time interval between the fuel injection and the ignition start. Optimization of the time interval between the fuel injection and ignition start is a key important parameter for the direct injection natural gas engine. The study shows that the combustion of direct injection natural gas is the premixed controlled stratified charge combustion. The premixed controlled stratified charge combustion has the advantage of low emission and fast burning rate.