Polytechnic University of Valencia Congress, ILASS2017 - 28th European Conference on Liquid Atomization and Spray Systems

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Microexplosion and Puffing of an Emulsion Fuel Droplet
Jun Xia, Junji Shinjo

Last modified: 18-07-2017


Microexplosion is rapid disintegration of an emulsion droplet caused by explosive boiling of embedded liquid subdropletswith a lower boiling point. Microexplosion and puffing (partial microexplosion) are potentially beneficialto achieving enhanced secondary atomisation. These eruptive secondary atomisation mechanisms will help tomeet conflicting requirements for an atomising fuel spray with regard to penetration achieved by large droplets andevaporation/mixing achieved by small droplets.Although with great interest, our understanding of microexplosion is still limited and therefore optimising andcontrolling microexplosion is not feasible yet. This paper reviews our recent research outcome on microexplosionand puffing of an emulsion fuel droplet from high-fidelity interface-capturing simulation study, which directly resolvesthe dynamics of boiling and evaporating liquid/gas interfaces, immiscible liquid/liquid interfaces with jump conditionsfor mass, momentum and heat transfer across a resolved interface.We first unveiled microexplosion and puffing dynamics of an emulsion fuel droplet in a quiescent ambient.Since convective heating has important effects on temperature distribution inside a fuel droplet in realistic engineconditions, which determines the initial nucleation location and thus the microexplosion outcome, a model has beenproposed to approximate the temperature distribution inside a droplet, for which momentum and heat transport wasfound to be only moderately correlated under typical engine conditions. With this model in place that allows forsaving considerable computational cost on setting up initial conditions for microexplosion simulation, puffing effectson fuel/air mixing is then investigated, which can be quantified by the scalar dissipation rate (SDR) of the primaryfuel decane, the SDR of the secondary fuel ethanol and the cross SDR. We then further extended our simulationstudies towards reacting conditions and investigate puffing effects on a droplet wake flame.The series of high-fidelity simulation studies is believed to have considerably improved our understanding ofmicroexplosion dynamics and impact on local fuel/air mixing and combustion. Based on the improved knowledge,microexplosion induced secondary droplet breakup models can be developed and incorporated into hybrid highfidelitysimulation of spray atomisation and combustion enhanced by microexplosion.

DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4762

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