Characteristics of a free-falling single-droplet of water-in-oil emulsion broken up by a pulse laser

Water-emulsified oils have been used in a variety of combustion systems, and their atomization characteristics have been studied to control combustion. In particular, many studies have been conducted on micro-explosions, in which an emulsion droplet is broken up into a number of smaller fragments mainly due to phase change of dispersed micro-scale water droplets. In this study, the breakup phenomena of a free-falling single droplet of water-emulsified liquid-fuels (n-decane, n-dodecane, and n-hexadecane) were investigated experimentally. The external energy of a pulse laser was introduced into the emulsion droplet, after which the dynamic response of the emulsion droplet were examined. It was found that the breakup trends were different depending on parameters such as oil type, oil concentration, and laser energy. The dynamic behaviors were categorized into four regimes, and their criteria were related to the effective Weber number of the emulsion droplets. Their physical characteristics are discussed and some empirical relationships are suggested regarding configurational characteristics such as the swelling scale of a liquid membrane, the number of secondary droplets, and the droplet diameter.