Collective effects during the formation of child droplets as a result of puffing/micro-explosion of composite droplets

Abstract

Puffing and micro-explosion are among the major phenomena behind the industrial secondary atomization of composite droplets. These effects significantly reduce the average size of secondary droplets formed during the jet breakup to 5–10 times of the original droplet size in the case of puffing and to 100–200 times in the case of micro-explosion. The initial droplet sizes (radii) ranged from 0.5 to 1.5 mm. Here we present the research findings on the collective effects during the formation of child droplets as a result of puffing/micro-explosion of composite droplets. We have analyzed the characteristics of child droplets formed during the micro-explosive fragmentation of a group of three composite droplets. We used two fuel blends: 90 vol% of Diesel fuel, 10 vol% of water; 10 vol% of Diesel fuel, 90 vol% of water. Typical sizes of child droplets formed during the fragmentation of each droplet in a group were determined by shadowgraphy. The number and size of secondary fragments practically do not change when the distances between parent droplets do not exceed 8–10 radii. In these conditions, the integral fragmentation characteristics of a group of droplets are in acceptable agreement with those of isolated droplets. With shorter distances between droplets, there are considerable differences in the characteristics of secondary droplets formed during the puffing/micro-explosion of composite droplets. Conditions were recorded in which puffing or micro-explosion can occur as a result of collisions between secondary fragments and parent droplets.