The characteristics of atomization in supersonic flow using water and methyl alcohol were investigated. This was visualized by a schlieren system using a 500ns duration Xenon spark light source and by direct photography Measurements were also made for each static pressure.
Two types of injector were tested. One was a flat plate injector, and the other a backward step injector. The liquids were injected vertically into the supersonic flow of Mach number 1.4 and 1.5 out of a 09mm orifice in the flat plate. The backward step was 5mm in height and the injection point was positioned just behind the step.
Finer atomization was obtained by the backward step injector. This was because the atomization occured in the complex boundary layer region behind the step. The layer was disturbed by the expansion fan generated at the corner of the backward step and the recompression Shockwave that is caused by boundary layer separation downstream of the orifice.
The effect of the injectant density, a function of its momentum which is related directly to the position of the injector and the surface tension of the injectant on the quality of the atomization was clarified.