EFFECT OF RECESS ON MIXING AND ATOMIZATION CHARACTERISTICS OF LIQUID-LIQUID SWIRL COAXIAL INJECTORS

The effects of recess on the mixing and atomization characteristics of a liquid-liquid swirl coaxial injector were investigated in eight cases of recess length. The orifice recess, a geometric parameter, has a strong influence on the coaxial spray because it varies the interaction position between two liquid sheets. The concentration-sensitive mass distribution and mixing efficiency were measured by using the planar liquid laser-induced fluorescence method. It was found that the mixing efficiencies in the internal mixing injection were higher than those in the external or tip mixing injection by about 10% at axial locations of more than 3 cm. The mixing efficiency slightly decreased in the internal mixing injection as the recess number increased. This is due to the increase of the discharge coefficient and breakup length with the increase of the recess number in internal mixing injection. In addition, the mean drop sizes according to the recess number were measured using an image-processing method. The internal interaction of two propellants led to the increase of the effective film thickness at the injector exit, and thus the disintegrated drop size increased. As a result, the increase in the recess number resulted in the increase in SMD of liquid-liquid swirl coaxial injectors.