Micro-explosions in composite droplets: experimental observations and modelling

Some of the most recent experimental and modelling results concerning the puffing/microexplosion of water-fuel composite droplets are presented and discussed. The experimental results refer to images of droplets during puffing/micro-explosion, times to puffing/micro-explosion and measurements of the temperatures inside the droplets. The model for puffing and microexplosion assumes that a small spherical water sub-droplet is located in the centre of a fuel droplet. The heat conduction equation is solved analytically inside this droplet at each time step, using the Robin boundary condition at its surface and the continuity conditions at the fuel-water interface. This analytical solution and an appropriate approximation of the nucleation temperature are incorporated into a numerical code in which droplet evaporation and the variable thermophysical properties are accounted for. It is assumed that the puffing/microexplosion process starts when the temperature between water and fuel reaches the nucleation temperature of water. The model predictions are shown to be consistent with available experimental data referring to the time to puffing/micro-explosion.