Characteristics of Liquid Film and Spray Injected from Swirl Coaxial Injector

Abstract

The liquid film flow on the inner wall of the center post of a swirl coaxial injector was analyzed theoretically. The development of the boundary layer in the liquid-film flow and the transition from laminar to turbulencewere studied. The film thickness at the post exit was measured using a contact needle probe, and the predicted film thickness was compared with the measurements. The film thickness varies in the azimuthal direction due to the geometry of the liquid inlet. The average film thickness at the post exit increases as the post length increases. The sheet cone angle and breakup length were measured using photography and a contact mesh probe, and their empirical equations were deduced by modifying those of a simplex swirl injector, taking into account the liquid momentum loss due to a long center post. These equations predict the sheet cone angle and breakup length well, except for small liquid flow rates. The mean droplet size and droplet velocity were measured by a phase Doppler particle analyzer. The measured spray characteristics exhibited characteristics similar to those of a conventional airblast atomizer.