Extension of PREMIER combustion operation range using split micro pilot fuel injection in a dual fuel natural gas compression ignition engine: A performance-based and visual investigation

The effects of split pilot fuel injection on engine performance and PREmixed Mixture Ignition in the End Gas Region (PREMIER) combustion characteristics were investigated in a single-cylinder dual-fuel natural gas engine ignited with diesel fuel. In particular, the effect of second spray timing on combustion mode was examined. PREMIER combustion was observed in a wider range of operating conditions with split injection strategy compared to single injection strategy. We determined that it was possible to both decelerate heat release and suppress knocking to PREMIER combustion, and accelerate heat release and promote normal combustion to PREMIER combustion, with suitable second injection timing. The maximum of thermal efficiency of PREMIER combustion operation with split injection was close to the results obtained with knocking operation. In-cylinder images showed that split injection strategy advances or retards the progress of combustion by controlling the size and rate of growth of flame kernels, depending on the timing of the second injection. The combustion progress is earlier when the pilot fuel delivered during the first injection autoignites during the second injection. Kernel growth and the final size were adversely affected when the second injection was initiated after pilot fuel autoignition.