Studies on temporal and spatial variation characteristics of spray boundary in diesel spray (Effects of injection pressure on spray vortex formation)

In recent years, with the depletion of fossil resources, there is a need to further improve the thermal efficiency of diesel engines. In order to improve the thermal efficiency of diesel engines, it is necessary to realize rapid combustion. The combustion process in diesel engines is greatly affected by spray characteristics and depends on air fuel mixture characteristics. Therefore, it is necessary to grasp the detailed spray characteristics in mixture formation process. In the past, many studies on the spray characteristics in mixture formation process have been reported. For example, Nishiura et al experimentally evaluated the effect of fuel injection pressure, nozzle hole diameter, and ambient density on the spray characteristics (Nishiura and Inoue ,2019). However, most of the previous reports have evaluated the spray characteristics using the total time averaged over a quasi-steady period for the physical quantity. Thus, the temporal and spatial variability of the spray and the large-scale vortical structure have not been sufficiently investigated. In this study, the turbulent intermittency phenomena in diesel sprays were investigated by using sheet scattered light imaging, focusing on the large-scale vortex structure that affects the formation mechanism of the diesel spray mixture. The intermittency of the diesel spray was investigated by applying the analysis method used for clarifying the phenomenon of turbulent intermittency in free jet flow to the analysis of the diesel spray. In this experiment, the effects of injection pressure on the intermittent behavior of the diesel spray were investigated.