Micro-explosion characteristics and mechanism of multi-component fuel droplet with high volatility differential

Abstract

Micro-explosion is considered as one of the effective ways to improve atomization, combustion and reduce emissions. The present study examined the micro-explosion characteristics and mechanism of multi-component fuel droplets using fiber-support method and high-speed backlit imaging technique. The multi-component fuel blends consist of 2, 5-dimethylfuran (DMF) as a lower volatile component, while Jatropha oil is used as the higher volatile constituents. The results show that the micro-explosion modes are categorized as puffing, breakup + puffing, vapor jetting, jetting + puffing according to the single micro-explosion intensity and droplet breakup index. The breakup + puffing mode is the dominant mode, and the jetting + puffing mode only appears in droplets with 25/75 and 50/50 composition. The formation mode of secondary droplets includes short-wave mode and long-wave mode. Two types of bubble formed during Jatropha oil/DMF blended droplets micro-explosion: bubbles caused by DMF superheating and bubbles caused by fatty acid pyrolysis. Moreover, the diameter and the velocity of secondary droplets obey Lorentz distribution and Weibull distribution respectively. The micro-explosion of Jatropha oil droplets experienced bubbles nucleation, bubbles growth, bubbles coalescence, bubbles movement and fragmentation, which are mainly caused by the pyrolysis of fatty acids. However, the micro-explosion of Jatropha oil/DMF blended droplets presents two mechanisms according to the different DMF content. The low DMF concentration leads to formation of a layer of Jatropha oil film on the droplet surface first, and then goes through a similar process with Jatropha oil droplets. The high DMF concentration leads to formation of a layer of DMF film on the droplet surface first. Then go through the same process as high DMF concentration.