Visualization of end-gas auto-ignition during PREMIER combustion in a dual-fuel gas engine

Abstract

The purpose of this study is to visualize PREMIER combustion phenomenon in a micro-pilot diesel fuel ignited dual-fuel engine with differentiating the causes of knocking and PREMIER combustion. The auto-ignition characteristics in the end-gas region were investigated with combustion visualization and in-cylinder pressure analysis using a compression-expansion machine (CEM) fueled with a natural gas. The micro-pilot diesel fuel injection timing used to generate PREMIER combustion occasionally induced knocking and pressure oscillations, while normal and PREMIER combustion did not cause the pressure to oscillate. The auto-ignition in the end-gas region of both knocking and PREMIER combustion was found to cause a second rise in pressure before the propagation premixed flame reached the cylinder wall. As the auto-ignition in PREMIER combustion was later than in knocking, the area and mass of the end-gas region were smaller. The KI factors, which represented the intensity of the pressure oscillations, were higher in the case of knocking than in the case of PREMIER combustion. As the knock intensity increases in CEM, the dominant frequencies of 10 kHz and 14.5 kHz are generated in addition to the dominant frequency of 6.4 kHz. The auto-ignited flame area spread faster during knocking than during PREMIER combustion. Knocking caused a sudden pressure difference and imbalance between the flame propagation and end-gas regions, followed by pressure oscillations.