Observation of micro-explosions in spray flames of light oil-water emulsions

Abstract

The micro-explosion of emulsified fuel droplets was successfully observed, and the distribution pattern of local frequency of explosion occurrence was estimated in open spray flames of water-inoil type light oil-water emulsion formed using a twin-fluid (air) atomizer with a ring pilot burner. A schlieren optical system with a deep-cut type knife-edge was adopted for back light illumination, and the process of micro-explosion of each droplet was recorded by a high-speed video camera with an image intensifier. Almost all the patterns of micro-explosion having been observed for single suspended emulsion drops were seen occurring also in the present spray flames. The frequency of micro-explosion occurrence increased as the water fraction in the emulsion was raised or agitation period was elongated. It appears that this frequency increases suddenly from 90 mm above the fuel injection nozzle. It is highly probable, however, that micro-explosion starts somewhere more upstream without being observed due to the difficulty in observation resulted from the excessive density of droplets, since the effect of water addition is most prominent in the upstream region.