Prediction of Mean Droplet Size of Sprays Issued from Wall Impingement Injector

The purpose of this study is to make a numerical model that predicts the spray characteristics of a wall impingement injector. The film flow on the wall was analyzed theoretically using the laminar boundary-layer model. The biquadratic velocity profile was employed for the laminar boundary layer. The thickness of the liquid film on the wall was measured by an automatic thickness measurement system, which was newly developed for the present study and is based on the contact needle method. From the measurements, the film thickness decreased first toward the periphery, and then increased along the line that was perpendicular to the liquid injection direction. The theoretical analysis of the film thickness on the wall agreed well with the measurements. The sizes of the droplets from the newly developed wall impingement injector were predicted by using the proposed theoretical analysis of a film flow and the existing liquid-film breakup model. From the measurements from the phase Doppler particle analyzer, the mean droplet size decreased once toward the spray periphery and then increased. This trend of the droplet size was coincident to that of the liquid-film thickness at the edge of the wall. The mean droplet size decreased as the liquid injection pressure increased. The predictions of the droplet size agreed well with the measurements.