Study on cycle-by-cycle variations in a direct injection natural gas engine

The cycle-by-cycle variations in a direct injection natural gas engine were investigated. The results show that there exist the misfire cycles and the partial burn cycles when operating on the small equivalence ratio conditions (φ < 0.4). Meanwhile, the indicated mean effective pressure (p_mi) gives low value while the coefficient of variation of p_mi is higher compared to that operating on the large equivalence ratio. High maximum cylinder pressure (p_max) cycles correspond to the fast burning cycles. Interdependencies exist between the maximum cylinder pressure and its corresponding crank angle, the maximum rate of pressure rise and its corresponding crank angle, the maximum cylinder pressure and the indicated mean effective pressure. Furthermore, better interdependencies also exist between the maximum cylinder pressure and the flame developing period, between the maximum cylinder pressure and the rapid burning period. High p_max corresponds to short flame developing period and short rapid burning period. The value of pp_mi is found to be related to the accumulated heat release in a cycle.