Effect of Recess on the Spray Characteristics of Liquid-Liquid Swirl Coaxial Injectors

The effects of recess in a liquid - liquid swirl coaxial injector on the spray characteristics have been investigated by measuring the spray angle and breakup length in eight cases of recess length. The orifice recess, a geometric parameter, has a strong influence on the spray and mixing characteristics by varying the interaction point between two liquid sheets. The variation of the recess length resulted in three different injection regimes: external, tip, and internal mixing injection. The coaxial spray characteristics in the external mixing injection regime are found to be mainly governed by the merging phenomenon and momentum balance between two liquid sheets. In the internal mixing injection regime, an impact wave is generated by the impingement of the inner spray on the outer liquid film inside the injector. The amplitude of the impact wave is gradually attenuated due to the fluid viscosity, flowing along the outer injector wall after impingement. This attenuation of the impact wave according to the recess length could affect the stability of a liquid sheet; therefore, the breakup length is found to increase with the increase in recess number.