Modes of atomization in biofuel droplets induced by a focused laser pulse

Abstract

Single droplet fragmentation of different liquids is essential for the fundamental understanding and augmenting of the atomization process involved in several industrial processes. Most importantly, there is a need to increase our understanding of the atomization of biofuels in combustion devices such as gas turbines and internal combustion engines. In this work, we describe and compare the laser-induced fragmentation of ethanol, Rapeseed Methyl Ester (RME), and their emulsions. We use a nanosecond laser pulse of various laser energies to fragment droplets. Acoustic levitation is used for non-contact manipulation of an isolated single droplet, and the fragmentation sequences are recorded using two high-speed cameras. Three breakup modes are observed: Droplet rupture and air entrapment, sheet breakup, and prompt/catastrophic fragmentation. At lower laser energy, air entrapment inside the droplet occurs. Sheet breakup and catastrophic breakup are observed for droplets of RME emulsions. The ligament-mediated atomization via Rayleigh-Plateau instability and the resulting secondary droplets are studied in detail. The breakup of RME-Ethanol emulsions results in the formation of small secondary droplets compared to pure liquid droplets.