Modeling Temperature Distribution Inside an Emulsion Fuel Droplet Under Convective Heating: A Key to Predicting Microexplosion and Puffing

Abstract

Microexplosion/puffing is rapid disintegration of a water-in-oil emulsion droplet caused by explosive boiling of embedded superheated water sub-droplets. To predict microexplosion/puffing, modeling the temperature distribution inside an emulsion droplet under convective heating is a prerequisite, since the temperature field determines the location of nucleation (vapor bubble initiation from superheated water). In the first part of the present study, convective heating of water-in-oil emulsion droplets under typical combustor conditions is investigated using high-fidelity simulation in order to accurately model inner-droplet temperature distribution. The shear force due to the ambient air flow induces internal circulation inside a droplet. It has been found that for droplets under investigation in the present study, the liquid Peclet number PeL is in a transitional regime of 100<PeL<500. The temperature field is therefore somewhat distorted by the velocity field, but the distortion is not strong enough to form Hill's vortex for the temperature field. In the second part of the present study, a novel approach is proposed to model the temperature field distortion by introducing angular dependency of the thermal conductivity and eccentricity of the temperature field. The model can reproduce main features of the temperature field inside an emulsion droplet, and can be used to predict the nucleation location, which is a key initial condition of microexplosion/puffing.

Puffing-enhanced fuel/air mixing of an evaporating -decane/ethanol emulsion droplet and a droplet group under convective heating

“…The governing equations are the Navier-Stokes conservation equations of mass, momentum, energy and species (Shinjo & Umemura 2010Shinjo et al 2014Shinjo et al , 2016Shinjo, Xia & Umemura 2015). Four species, namely C 10 H 22 , C 2 H 5 OH, N 2 and O 2 , are considered, and chemical reactions are not included.…”

“…In Shinjo et al (2014), the droplet breakup dynamics due to puffing and microexplosion was directly simulated under quiescent ambient conditions, although the convective effect on heating and vapour mixing was not included in the first-stage work, where understanding the puffing dynamics was the research aim. In Shinjo et al (2016), convective heating of an emulsion droplet prior to puffing and microexplosion was investigated. A model was proposed to approximate the temperature distribution inside an emulsion droplet under convective heating.…”

“…It should be pointed out that the temperature distribution inside a parent droplet largely determines the bubble initiation location -an important initial condition for puffing simulation. In the present study, the simplifications made in the previous studies have been removed, and the model developed in Shinjo et al (2016) is used to initialise the inner-droplet temperature distribution. Puffing-enhanced mixing will be investigated in fully three-dimensional configurations for both a single emulsion droplet and a droplet group under convective heating.…”

Microexplosion and Puffing of an Emulsion Fuel Droplet

“…Jump conditions [9,10] are used to compute the heat, momentum and mass transfer across an interface. The details can be found in [11,12,13,14].…”

“…Therefore models developed for inner-droplet velocity distribution [16,17] cannot be borrowed to approximate temperature distribution. A new model was therefore developed [12] to approximate the inner-droplet temperature distribution and used here to save computational cost on droplet heating.…”