Direct Puffing Simulation of Miscible and Emulsified Multicomponent Single Droplets

Abstract

The aim of the present study is to achieve direct simulation of the puffing of a multicomponent droplet using interface capturing approaches. A non-ideal multicomponent phase equilibrium model is used to determine the composition of boiled vapour. Firstly, the puffing of a two-miscible-component (ethanol:water=1:1 in wt.%) droplet in two-dimensional configuration is directly simulated. The distribution of ejected vapour is impacted by a rotating and shape oscillating satellite droplet. The ejected vapour contains much more ethanol than water, facilitating the transport of the volatile fuel component inside the droplet to the ambient air. The morphological changes to the droplet induced by puffing promote considerably the contact of the boiling surface with air, significantly increasing the scalar dissipation rate of vapour/air. The effects of the nucleation bubble location and droplet temperature on puffing were investigated. Secondly, the puffing of an emulsified three-component (ethanol/water in dodecane) droplet in two-dimensional configuration is simulated. Grid independency has been checked for both the two-miscible-component and three-component emulsified droplet cases. Depending on the water volume fraction in the sub-droplet, which varies from 10% to 70% and is the key parameter herein, both one and two breakups of the parent dodecane droplet are observed. The characteristics of the sub-droplet “invasion” towards the inside of the parent dodecane droplet are investigated, together with the puffing statistics on the puffing delay time, satellite droplet size, surface areas of both the sub- and parent droplets, and oscillation dynamics of the sub-droplet.