A schlieren optical system with a deep-cut-type knife edge was adopted for back-light illumination, and the droplet behavior was recorded by a high-speed video camera. Microexplosion of emulsified fuel droplets was successfully documented using this method. Further, the local frequency of explosion occurrence was estimated in open spray flames of water-in-oil-type emulsions formed using an air-assist atomizer with a ring pilot burner. Almost all the patterns of micro explosion observed for single fiber-suspended emulsion droplets, usually a few millimeters or more in diameter, were also observed in the present spray flames. The frequency of microexplosion occurrence increased if the water fraction in the emulsion was raised or the emulsion-stirring period was elongated It appeared that this frequency increased suddenly from 90 mm above the fuel injection nozzle. Since, however, the effect of water addition was most prominent in the upstream region, it was highly probable that microexplosion started somewhere more upstream, though unobservable due to the experimental difficulty resulting from the excessive density of droplets there.