高温壁面上におけるO/WおよびW/Oエマルション燃料液滴の微粒化挙動の比較

抄録

An experimental study has been performed for comparing the atomization behavior during spheroid-type evaporation on a heated surface between oil-in-water (O/W) and water-in-oil (W/O) emulsion droplets. The base fuel of the emulsions was n-dodecane, and the water content set to 20 % in volume. The effect of the initial droplet size on the atomization behavior was examined as well as that of the surface temperature. For the O/W emulsion, phase separation occurred at the early stage of evaporation and a water-based fluid was enveloped by a shell of the base fuel. Disruptive microexplosion, which corresponds to intense secondary-atomization, took place earlier due to explosive boiling of the fluid. Both the minimum waiting time and the waiting time for the disruptive microexplosion decreased with increasing the surface temperature. The waiting time was scarcely affected by the initial droplet size, while the minimum waiting time increased with increasing the size. For the W/O emulsion, intermittent puffing microexplosion and/or the disruptive microexplosion occurred. Aggregation and coalescence of water and the phase separation appeared to occur prior to the disruptive microexplosion at higher surface temperatures, while the phase separation hardly occurred and the droplet disappeared after the intermittent puffing microexplosion at lower surface temperatures. The occurrence of the disruptive microexplosion was delayed due to longer time period until the phase separation than that for the O/W emulsion. The intermittent puffing microexplosion retarded the phase separation. The waiting time was either scarcely affected by the initial droplet size, while the minimum waiting time increased with increasing the size.