Micro-explosion and puffing of a group of two-component droplets

Abstract The experimental findings on the movement, evaporation, boiling, and breakup of a group of heterogeneous droplets in a high-temperature gas are presented. The experiments are carried out with droplets moving in a tubular muffle furnace at a temperature of up to 1100 °C. We use emulsion droplets and immiscible droplets consisting of two components: water and Diesel fuel or rapeseed oil. The most typical conditions are singled out for the micro-explosion and puffing of a group of two-component droplets located at a variable distance relative to each other. By varying the distance between droplets (their concentration in a gas), one can control the transition between gradual evaporation without destruction, partial fragmentation throughout the heating time, also known as puffing, and total breakup into a cloud of small droplets, also referred to as micro-explosion. The video frames of the experiments show that even partial fragmentation of initial droplets intensifies the collisions of newly formed droplets with the neighboring ones moving in various echelons. Therefore, we carried out additional experiments to narrow down the necessary conditions for the fragmentation to occur in at least 75% of cases. Chain-like droplet fragmentation mechanisms are observed for droplets moving at a distance of no more than 9 typical sizes from each other. No micro-explosion is observed when the distances between droplets are smaller than that. Finally, we single out the conditions necessary for the ignition of secondary fragments after their production through micro-explosion.