Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : March 17, 2021 - March 18, 2021
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(1). However, most of the previous reports have evaluated the spray characteristics such as spray tip penetration and spray angle using the average over a period of time in a quasi-steady state. Thus, the temporal and spatial variability of the spray feature 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. Figure 1 shows the captured images of scattered light photography obtained in this experiment. In addition, Fig.2 shows the time-dependent changes in scattered light intensity when the measurement points are changed. From Fig.2, it can be confirmed that the period when the scattered light intensity is high appears intermittently near the spray boundary (measurement point B). Therefore, by analyzing the time-series changes in the obtained scattered light intensity distribution, the presence or absence of spray droplets was determined, and the intermittentness of spraying was investigated. In this experiment, the effects of injection pressure and ambient density on the intermittent behavior of the diesel spray were investigated. The main conclusions are as follows.
(1)For all injection pressure ranges, the Strouhal number St becomes approximately constant at 0.27.
(2)As the ambient density increases. the Strouhal number St increases.
