Child droplets from micro-explosion of emulsion and immiscible two-component droplets

Here we present the experimental findings of the research into the integral characteristics of secondary droplets produced from the micro-explosive fragmentation of two types of initial droplets. Both types are based on water and tetradecane: an emulsion droplet and a two-component immiscible droplet with water as the core and tetradecane as the envelope. We study the threshold (critical) conditions for the micro-explosion of droplets on a substrate heated up to 550 °C. In the course of experiments, we recorded the number, sizes, velocities, temperatures, and component composition of child droplets. It is shown that the parameters of child droplets differ significantly in the case of two-component droplets and emulsion droplets. The decisive impact comes from the heating temperature. Using a combination of Schlieren Photography, Particle Tracking Velocimetry, and 2-Color Laser Induced Fluorescence, we have determined the proportions of the concentration and size of secondary water droplets and combustible component droplets in the emerging aerosol cloud. We have also calculated the kinetic energies of child droplets. When generalizing the experimental findings, we established the conditions for the generation of a high-temperature fine mist aerosol through the micro-explosive breakup of two-component droplets and recorded the typical trajectories of secondary fragments. We show that such conditions are possible for both emulsion droplets and immiscible two-component droplets with a pronounced interface. It is established that much more secondary fragments of water are produced in the second case. This result shows that water separates from the combustible component more intensely in the second case, and the micro-explosion systems relying on water and combustible liquid droplets mixing in the combustion chamber bear more promise.