Characteristics of natural gas direct injection combustion under various fuel injection timing

Characteristics of natural gas direct-injection combustion (CNG DI) under various fuel injection timing were studied by using a rapid compression machine. Results show that CNG DI can realize much faster combustion than that of homogeneous combustion while shortening the time interval between injection timing and ignition timing can remarkably decrease the combustion duration. Unburned hydrocarbon would increase over a wide range of equivalent ratio, shortening the time interval between injection timing and ignition timing can decrease the value to that of homogeneous mixture combustion. While CO keeps low level over a wide range of equivalent ratio, N0_x is high and CO is little affected by fuel injection timing. High value of pressure rise due to combustion can be realized and it is insensitive to the variation of fuel injection timing. High combustion efficiency can be achieved and it is also independent on injection timing.