Characterizing bubble dynamics in combustion and atomization of alcohol/PODE4 and alcohol/n-undecane binary droplets

Abstract

This work explores bubble dynamics in the combustion and atomization of binary droplets, with special attentions on the effects of bubble dynamics on the combustion and atomization characteristics. A typical renewable synthetic fuel polyoxymethylene dimethyl ether 4 (PODE4) and a typical kerosene component n-undecane are used as the weakly volatile components, while C1-C5n-alcohols are used as the highly volatile components in order to change the boiling point difference of components in the binary droplets. Nucleation capability of alcohol/PODE4 binary droplets is found to be higher than that of alcohol/n-undecane binary droplets. Alcohol/PODE4 binary droplets with higher boiling point differences (ΔTbp s) tend to have multiple nucleation sites and undergo multiple bubble growth and coalescence, while most of the rest binary droplets tend to have limited nucleation sites and undergo single bubble growth. The bubble evolution velocity decreases with the decreasing ΔTbp, while the bubble growth in alcohol/PODE4 binary droplets are generally slower. Bubble breakup mainly results in ejection and micro-explosion in this work, which are associated with small and big bubble breakup, respectively. Five atomization modes with different bubble evolution, bubble breakup and droplet atomization processes are concluded. The combustion and atomization characteristics of most of the investigated binary droplets are remarkably influenced by the bubble dynamics. The binary droplets with higher ΔTbp s are susceptible to strong atomization modes and consequently tend to have shorter normalized droplet lifetimes and larger atomization indices. Alcohol/PODE4 binary droplets have generally greater atomization indices than alcohol/n-undecane binary droplets.