Observation of Microexplosions in Spray Flames of Light Oil-Water Emulsions (3rd Report, Influence of the Diameter of Dispersed Water Droplets on the Spray Flame Structure)

Abstract

Microexplosions of light oil-water emulsified fuel droplets were successfully documented using a high-speed video camera with laser illumination. The local frequency of explosion occurrence, temperature profile and exhaust gas emission were measured in spray flames of water-in oil type emulsion formed using an air-assist atomizer with a ring pilot burner. Those results indicate that the flame structure changes as the water droplet diameter in the emulsion fuel was varied, even if the fuel components and their fractions were same. When fuel includes water droplets, whose median diameter was around 75μm, HC and CO emissions were reduced as compared to those for the fuel of smaller water droplet content. It is probable that if the water droplet diameter is uniform, avalanching microexplosions occur at certain local region in the flame, and the water content vaporizes almost at once and extinguishes the flame. It leads to HC and CO emission increase. When the water droplet diameters are large, atomizer atomizes those; therefore, emulsion droplets include various size of water droplet in the flame. Consequently, the avalanching microexplosion occurrence is avoided, and HC and CO emissions are reduced.