Superheat limit and micro-explosion in droplets of hydrous ethanol-diesel emulsions at atmospheric pressure and diesel-like conditions

Micro-explosion of emulsified fuels has been studied on promoting the secondary break-up and improving fuel-air mixing. However, most studies are limited to atmospheric conditions, and experimental observation of micro-explosion under diesel-like conditions is rarely reported. The predictive model for the superheat limit of hydrous ethanol-diesel emulsion needs to be re-examined. In this study, firstly, with the molecular kinetics theory a mathematical model for predicting the superheat limit of hydrous ethanol diesel emulsions are established. Then, the model is verified by the experimental results of micro-explosion in the emulsion droplets. The superheat limit is independent of volume fraction of hydrous ethanol in the emulsions. The intensity of micro-explosion obeys the parabolic rule when changing volume fraction of the hydrous ethanol. The intensity of micro-explosion with the homogeneous nucleation is higher than with the heterogeneous nucleation. The emulsions of 30% and 40% hydrous ethanol exhibit the higher probability for the homogeneous nucleation than the other emulsions. Finally, the droplet behaviors of the emulsions under the diesel-like high-pressure conditions are experimentally observed. While the micro-explosions can be clearly observed for some droplets, neither the micro-explosion nor puffing are observable for most other droplets. The mechanism behind the phenomena is discussed.