Effects of injection strategy on the knocking behavior of a pilot ignited direct injection natural gas engine

Pilot ignited direct injection natural gas engines have become a research focus due to the high thermal efficiency and low emissions. However, when stratified combustion mode is adopted, more attention should be paid to the knocking behavior. In this paper, the effects of injection strategy on the knocking behavior of a pilot ignited direct injection natural gas engine have been studied. The results indicated that the knocking intensity will be increased at advanced natural gas injection timing, delayed diesel injection timing and raised injection pressure. The three major resonance modes that dominate the pressure oscillations are the first circumferential mode, the third circumferential mode and the first radial mode. Advancing natural gas injection has negative effects on cyclic variations of indicated mean effective pressure while have negligible effects on the cyclic variations of combustion duration. After correlation analysis of parameters, it was found that knocking behavior is highly correlated with maximum heat release rate, combustion duration and maximum combustion pressure, whereas has weak correlations with combustion phasing and cyclic variations.