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 the reduction 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 sudden vaporization 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 phenomenon is stochastic, and can happen with greater or lesser eciency. When the fragmentation of the emulsion drop is only partial, the event is called "pung". The current objective of research in W/O emulsion atomization is to understand the way to optimize the micro-explosion occurrence and its eciency. This paper presents the rst results of the investigation of the behavior of W/O emulsions under radiative heating. The behavior of 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 impact of coalescence on micro-explosion occurrence. Two heating schemes are presented and compared, namely radiative heating from the top and the bottom of the droplet.