Puffing/micro-explosion of two closely spaced composite droplets in tandem: Experimental results and modelling

Abstract

The results of the experimental and theoretical investigations of the mutual effect on their puffing/micro-explosion of droplets in a flow, using an example of two closely spaced droplets in tandem, are presented. It is shown that the time to puffing/micro-explosion (τp) of the lead droplet is always shorter than that of the downstream droplet, and the difference between them decreases with increasing distance between droplets divided by their initial diameters (2Rd0). It is shown that the τp of both droplets increases with increasing Rd0. The experimental results are interpreted in terms of the previously developed model for fuel/water droplet puffing/micro-explosion, based on the assumptions that the water sub-droplet is located in the centre of the fuel droplet and that this process is triggered when the temperature at the water/fuel interface reaches the water nucleation temperature. The effect of interaction between the lead and downstream droplets is taken into account via modifications to the Nusselt and Sherwood numbers for these droplets using the results of numerical calculations. Both experimentally observed and predicted values of τp are shown to increase with increasing Rd0. They are shown to be longer for the downstream droplets than for the lead droplets. The experimentally observed differences in τp for the lead and downstream droplets are close to the predicted differences.