On explosive boiling of a multicomponent Leidenfrost drop

TL;DR

This study investigates the explosive gasification of a multicomponent Leidenfrost droplet, revealing how volatile component evaporation leads to microemulsion formation and ultimately causes the droplet to explode upon contact with a superheated surface.

Contribution

It provides detailed high-speed observations of the explosive process in multicomponent droplets, highlighting the role of component evaporation and microemulsion formation in the explosion mechanism.

Findings

Ethanol evaporation triggers oil microdroplet nucleation.

Oil microdroplets coalesce into a large encapsulating droplet.

Droplet explosion occurs upon contact with the superheated surface.

Abstract

The gasification of multicomponent fuel drops is relevant in various energy-related technologies. An interesting phenomenon associated with this process is the self-induced explosion of the drop, producing a multitude of smaller secondary droplets, which promotes overall fuel atomization and, consequently, improves the combustion efficiency and reduces emissions of liquid-fueled engines. Here, we study a unique explosive gasification process of a tricomponent droplet consisting of water, ethanol, and oil ("ouzo"), by high-speed monitoring of the entire gasification event taking place in the well-controlled, levitated Leidenfrost state over a superheated plate. It is observed that the preferential evaporation of the most volatile component, ethanol, triggers nucleation of the oil microdroplets/nanodroplets in the remaining drop, which, consequently, becomes an opaque oil-in-water microemulsion. The tiny oil droplets subsequently coalesce into a large one, which, in turn, wraps around the remnant water. Because of the encapsulating oil layer, the droplet can no longer produce enough vapor for its levitation, and, thus, falls and contacts the superheated surface. The direct thermal contact leads to vapor bubble formation inside the drop and consequently drop explosion in the final stage.