Puffing/micro-explosion in composite multi-component droplets

Abstract

A new simple model for the puffing and micro-explosion of composite multi-component water/liquid fuel droplets is suggested. This model is based on the assumption that a spherical water sub-droplet is located in the centre of a spherical fuel droplet. The effects of droplet thermal swelling are considered; the Abramzon and Sirignano model is applied for the analysis of droplet heating and evaporation. It is assumed that puffing/micro-explosion starts when the temperature at the water/liquid fuel interface becomes equal to the water nucleation temperature. Assuming that the species diffusion coefficient is constant at each time step, the equation for species diffusion inside the droplet is solved analytically. Raoult’s law at the surface of the droplet is used. The analytical solution to the equation for species diffusion is incorporated into the numerical code alongside the previously obtained analytical solution to the equation for heat transfer inside the droplet. Both solutions are used at each time step in the calculations. The model is used for the analysis of puffing/micro-explosion of kerosene/water droplets. The experimentally observed and predicted times to puffing/micro-explosion are shown to be reasonably close, decrease with increasing ambient gas temperatures and increase with increasing initial droplet radii. Taking into account the presence of multiple components in fuel leads to longer times to puffing/micro-explosion compared to the case when kerosene is approximated by cycloundecane (the dominant component in kerosene).