Experimental study of water-in-oil droplet micro-explosion using LIF measurements : effect of radiative heating configuration

Water-in-oil (W/O) emulsions are innovative substitutes to the classical hydrocarbon fuels, because of thereduction of pollutant emissions allowed by the presence of water and, to the micro-explosion phenomenon.The micro-explosion is the fragmentation of a mother drop in a cloud of ne child droplets, due to the suddenvaporization of the water subdroplets within the emulsion drop. This is also called "secondary-atomization"and leads to a better fuel-air mixing, which increases combustion eciency. Nevertheless, this phenomenonis stochastic, and can happen with greater or lesser eciency. When the fragmentation of the emulsion dropis only partial, the event is called "pung". The current objective of research in W/O emulsion atomizationis to understand the way to optimize the micro-explosion occurrence and its eciency. This paper presentsthe rst results of the investigation of the behavior of W/O emulsions under radiative heating. The behaviorof the dispersed water subdroplets during heating is investigated by means of Laser Induced Fluorescence(LIF) method, coupled to a fast camera. Natural convection motion of the water droplets is observed.Two emulsions of dierent mean diameter of the dispersed phase are tested which show a strong impactof coalescence on micro-explosion occurrence. Two heating schemes are presented and compared, namelyradiative heating from the top and the bottom of the droplet.