The effects of partially premixed combustion mode on the performance and emissions of a direct injection natural gas engine

Direct injection natural gas engines have been widely recognized as a promising alternative for conventional diesel or natural gas engines attributed to their advantages in both efficiency and emissions. However, with the promulgation of the more stringent emission regulations, the control of soot and CO (carbon monoxide) emissions becomes a major issue for the investigation of direct injection natural gas engines. In this paper, partially premixed combustion mode is applied to a direct injection natural gas engine based on a 3D model coupled with dual fuel chemical kinetic mechanism. The effects of the proportion of the natural gas pre-injection and the injection timing of the natural gas pre-injection are analyzed based on the combustion and emission results. In order to further optimize the partially premixed combustion mode, the combined use of partially premixed combustion mode and EGR (exhaust gas recirculation) was also assessed. The results indicate that soot and CO emissions could be substantially reduced without penalties in NOx and thermal efficiency by the coordination of PNPI (proportion of natural gas pre-injection), NPSOI (injection timing of natural gas pre-injection) and EGR.