Evaporation and micro-explosion characteristics of oxymethylene dimethyl ether–diesel binary droplet

Abstract

This study investigates evaporation behavior, puffing, and micro-explosion in droplets of pure diesel, oxymethylene ether (OME1), and diesel/OME1 blends (20%–90% OME1 by volume) using high-speed backlighting imaging. While the 50% OME1 blend exhibits micro-explosions, the 60% and 70% blends show only puffing, and higher or lower OME1 fractions primarily undergo smooth evaporation. The findings indicate that increasing the OME1 concentration accelerates droplet evaporation. Moreover, the evaporation process exhibits universal behavior when droplet lifetimes are scaled by the characteristic evaporation time scale and the binary mixtures show a behavior similar to a homogenous single-component fuel. A modified D2-law has been proposed to account for binary mixture composition. Morphological observations reveal two dominant pathways: strong micro-explosions, which lead to explosive disintegration and rapid ligament growth, while weak micro-explosions involve mild puffing, and smooth ligament formation culminating in larger droplets. We further analyze this ligament evolution through a breakup regime map, constructed using non-dimensionalized ligament neck diameter, gamma distribution shape parameter, and ligament aspect ratio. Results show a strong correlation between these parameters, indicating a statistical transition in ligament-to-droplet fragmentation modes. An analysis of the dominated time scales shows that strong micro-explosions occur in an inertial-dominated regime, where the ligament stretching time is relatively much shorter than the capillary time scale, while weak micro-explosions occur at relatively higher time scale ratios, suggesting capillary-dominated breakup. The drop size distribution, driven by inertial-dominated regime, is well described by a gamma distribution. These findings enhance our understanding of multicomponent droplet atomization and its relevance to spray-driven combustion.