Puffing and Micro-Explosion Behavior in Combustion of Butanol/Jet A-1 and Acetone-Butanol-Ethanol (A-B-E)/Jet A-1 Fuel Droplets

Butanol is mainly produced by acetone-butanol-ethanol (A-B-E) fermentation. The higher costs associated with the separation of butanol from the A-B-E mixture has prohibited the large-scale production of butanol. The direct use of the intermediate product (A-B-E mixture) could be an economical pathway if utilized for clean combustion. The present investigation deals with the puffing and micro-explosion characteristics in the combustion of a single droplet comprising butanol/Jet A-1, A-B-E/Jet A-1 blends, and A-B-E. The complete sequence of processes leading to micro-explosion, i.e., onset of nucleation, growth of vapor bubble, and subsequent breakup of droplet, for various fuel blends has been analyzed from the high-speed images. It is witnessed that puffing plays a crucial role in enhancing the micro-explosion especially in droplets with 50/50 composition. The probability of microexplosion in droplets with A-B-E blends was found to be higher than that of butanol blends. Although the rate of bubble growth was almost similar for all butanol and A-B-E blends, the final bubble diameter before the droplet breakup was found to be higher for 50/50 blends than that of 30/70 blends. The occurrence of micro-explosion shortened the droplet lifetime, and this effect appeared to be stronger for droplets with 50/50 composition. Micro-explosion led to the ejection of both larger and smaller secondary droplets; however, puffing resulted in relatively smaller secondary droplets. Bubble growth and subsequent puffing/micro-explosion were also observed in the secondary droplets, which might play an important role in enhancing the atomization and, hence, combustion.