Effects of water subdroplet location on the start of puffing/micro-explosion in composite fuel-water droplets

Abstract

A new approach to the verification of the predictions of the earlier developed model of puffing/micro-explosion is suggested, based on the implementation in the numerical code of the analytical solution to the heat transfer equation within a composite droplet. Verification is based upon a comparison between the predictions of the numerical code with this model and those of a fully numerical solution to the equation (the heat transfer module available from COMSOL software). The agreement between the predictions of both codes supports both approaches to the problem. The model is generalised to consider the shifting of the water subdroplet away from the centre of the fuel droplet. This generalisation is based on the numerical solution to the heat transfer equation in the composite droplet taking into account this shift. The start of puffing/micro-explosion in the generalised model is related to the time instant when the temperature at the point of the water/fuel interface closest to the surface of the fuel droplet reaches the water nucleation temperature. The shift is characterised by the distance between the centres of the water subdroplet and the fuel droplet. It is shown that even if this distance is half of the maximal possible distance, the errors in times to puffing/micro-explosion obtained using the original and generalised models do not exceed 5%, which can be tolerated in most practical applications.