Title: Experimental investigations on nucleation, bubble growth, and micro-explosion characteristics during the combustion of ethanol/Jet A-1 fuel droplets,
Abstract: The combustion characteristics of ethanol/Jet A-1 fuel droplets having three
different proportions of ethanol (10%, 30%, and 50% by vol.) are investigated
in the present study. The large volatility differential between ethanol and Jet
A-1 and the nominal immiscibility of the fuels seem to result in combustion
characteristics that are rather different from our previous work on butanol/Jet
A-1 droplets (miscible blends). Abrupt explosion was facilitated in fuel
droplets comprising lower proportions of ethanol (10%), possibly due to
insufficient nucleation sites inside the droplet and the partially unmixed fuel
mixture. For the fuel droplets containing higher proportions of ethanol (30%
and 50%), micro-explosion occurred through homogeneous nucleation, leading to
the ejection of secondary droplets and subsequent significant reduction in the
overall droplet lifetime. The rate of bubble growth is nearly similar in all
the blends of ethanol; however, the evolution of ethanol vapor bubble is
significantly faster than that of a vapor bubble in the blends of butanol. The
probability of disruptive behavior is considerably higher in ethanol/Jet A-1
blends than that of butanol/Jet A-1 blends. The Sauter mean diameter of the
secondary droplets produced from micro-explosion is larger for blends with a
higher proportion of ethanol. Both abrupt explosion and micro-explosion create
a large-scale distortion of the flame, which surrounds the parent droplet. The
secondary droplets generated from abrupt explosion undergo rapid evaporation
whereas the secondary droplets from micro-explosion carry their individual
flame and evaporate slowly. The growth of vapor bubble was also witnessed in
the secondary droplets, which leads to the further breakup of the droplet
(puffing/micro-explosion).