燃油液滴撞击对液膜厚度和温度影响的实验研究

During cold start of diesel engines, liquid-phase fuel quickly forms a deposited oil film after impinging on the wall. In order to analyze the coupling effect of oil film thickness and temperature and the interaction between the fuel and the deposited oil film, an optical experimental system was constructed to investigate the effects of non-dimensional oil film thickness (0.01 ≤ H^∗ ≤ 11.43) and temperature (253 K ≤ T ≤ 373 K) after fuel droplets impact. The results show that the dynamic characteristics of fuel droplets after impacting the oil film are significantly influenced by the oil film thickness, occurring annular splashing when H^∗ < 0.16, appearing finger-like splashing and delayed splashing when 0.16 ≤ H^∗ < 1, and occurring jet splashing when H^∗ ≥ 1. The splashing mode is more likely to shift from delayed splashing to annular or jet splashing along with the increase of oil film temperature, making splashing threshold reduced. The splashing mode transition is resulted mainly from the stability of the liquid crown structure enhanced with increased oil film thickness and decreased oil film temperature. Analysis of the liquid crown-pit-jet phenomenon on larger spatial and temporal scales reveal that, due to differences in energy transfer, the liquid crown height decreases with increasing oil pool depth, and significantly increases with rising oil pool temperature. The pit depth increases with both oil pool depth and temperature.