Experimental investigation on evaporation and micro-explosion characteristics of ethanol/RP-3 aviation kerosene blend droplets at elevated pressures and temperatures

Under the background of energy conservation and emission reduction in the aviation industry, blends of ethanol with aviation kerosene have been widely accepted as a potential alternative fuel. Investigating its evaporation process is essential for comprehensively understanding the mechanisms of spray combustion process, which provides significant insights for improving the utilization of aviation fuel. Therefore, in this study, the effects of initial droplet size, ambient temperature and pressure on the micro-explosion and evaporation characteristics of RP70E30 droplets (70% RP-3 aviation kerosene and 30% ethanol by mass) are experimentally investigated. The evolutions of droplet temperature and size are simultaneously obtained by a suspended thermocouple and a high-speed video camera. The results indicate that in the cases without micro-explosion, RP70E30 droplet evaporation undergoes two stages, namely: transient heating and equilibrium evaporation stages. While the evaporation process of RP70E30 droplet with micro-explosion could be separated into three stages: transient heating, fluctuation evaporation and equilibrium evaporation stages. The sequential order of fluctuation evaporation stage and equilibrium evaporation stage is determined by the occurrence time of micro-explosion. RP70E30 droplets only exhibit weak rupture phenomena: weak micro-explosion and puffing. For all test conditions, a continuous increase in droplet temperature is observed throughout the entire evaporation process, and its trend exhibits a three-stage characteristic, including a rapid rise, a slow rise and then another rapid rise stages. At 400 °C and 1 bar, increasing initial droplet diameter (from 0.746 to 1.258 mm) can promote the heating and evaporation of RP70E30 droplet. While at 1 bar and 600 °C, the droplet with an initial diameter of 1.156 mm evaporates at a slower rate than droplet with an initial diameter of 1.030 mm in the early evaporation process. This is because weak micro-explosion somewhat suppresses the evaporation of PR70E30 droplet, which is attributed to the formation of bubbles increasing the heat transfer resistance inside the droplet. The droplets having similar initial diameters (from 0.95 to 1.05 mm) were selected to investigate the effects of ambient pressure and temperature on evaporation. At all the studied temperatures (400–600 °C) and pressures (1–20 bar), increasing ambient pressure and temperature both have a promoting effect on the heating and evaporation of RP70E30 droplet. Moreover, at 1 bar, high temperature can increase the possibility of micro-explosion. At 5–20 bar, no micro-explosion occurs.