Study of cycle-by-cycle variations of natural gas direct injection combustion using a rapid compression machine

Abstract

Cycle-by-cycle variations of natural gas direct injection (CNG DI) combustion were studied by using a rapid compression machine. Results show that CNG DI combustion can realize high combustion stability with less cycle-by-cycle variation in the maximum pressure rise, the maximum rate of pressure rise and the maximum rate of heat release at the given equivalence ratios. Mixture stratification and fast flame propagation with the aid of turbulence produced by the high speed fuel jet are considered to be responsible for these behaviours. Cycle-by-cycle variations in combustion durations and combustion products present higher magnitudes than those of maximum pressure rise and maximum rate of heat release. Cycle-by-cycle variations of CO and unburned CH₄ show an interdependence with the variation of the late combustion duration, and the variation of NO _x shows an interdependence with the variation of the rapid combustion duration. Cycle-by-cycle variations are found to be insensitive to the equivalence ratios in CNG DI combustion.