Breakup characteristics of a single-droplet of water-in-oil emulsion impinging on a hot surface

Abstract Various combustion devices are employing water-emulsified fuels to control flame stability and NOx emission, and impinging of emulsion on a hot-surface has been used as one of practical atomization methods. However, reports of experimental results of emulsion breakup after impinging have not been sufficient, particularly when the surface temperature was higher than the fuel boiling temperature. In this study, a premixed flame burner having transparent quartz plates was used as a hot surface. Thus, three-dimensional breakup behaviors of water-in-oil emulsion structures of n-dodecane could be observed not only from the side, but also from the bottom. It was possible to visualize the instantaneous phenomena occurring between the liquid droplet and the hot surface. Three experimental parameters were varied: impinging momentum, surface temperature, and water concentration. The dynamic behaviors of the emulsion droplets after impinging were classified into five regimes. Representative characteristics of the secondary droplets such as number, size, and spatial distribution were quantified. Finally, the breakup mechanism of water-in-oil emulsion on a hot surface was explained and a simple empirical model that can be used in numerical simulation was proposed.