  The present investigation deals with the puffing and micro-explosion
characteristics in the combustion of a single droplet comprising butanol/Jet
A-1, acetone-butanol-ethanol (A-B-E)/Jet A-1 blends, and A-B-E. The onset of
nucleation, growth of vapor bubble and subsequent breakup of droplet for
various fuel blends have been analyzed from the high-speed images. Puffing was
observed to be the dominant phenomenon in 30% butanol blend, while
micro-explosion was found to be the dominant one in other fuel blends (blend
with 50% butanol or 30% A-B-E or 50% A-B-E). It was observed that puffing
always preceded the micro-explosion. The probability of micro-explosion 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 compared to micro-explosion.
Puffing/micro-explosion were also observed in the secondary droplets.
