Spray characteristics of an open-end swirl injector

The open-end swirl injector is unique because it has no convergent nozzle; i.e., the diameter of the swirl chamber and the nozzle is the same. Open-end swirl injectors are widely used in Russian oxidizer-rich staged combustion cycle engines, such as the preburner and main chamber injectors used in liquid-oxygen (LOX)/kerosene engines RD-120, RD-170, and RD-180. However, the guidelines for the design of open-end swirl injectors are unclear and cannot refer to the existing model for closed swirl injectors. In the present study, spray formation from open-end swirl injectors is described by experimentation in a spray test facility. The experiments were performed with injectors of different configurations to test the effect of injector geometry and flow conditions on the spray characteristics. It was found that as the geometric characteristic constant of the open-end swirl injectors increases both the mass flow rate and the discharge coefficient decrease. There are discrepancies when predicting the discharge coefficient of open-end swirl injectors with the existing models for closed swirl injectors; hence, an empirical equation for predicting the discharge coefficient of open-end swirl injectors is proposed. The spray cone angle increases as the pressure drop and geometric characteristic constant increase. The breakup length of the liquid sheet formed by the open-end swirl injector is inversely proportional to the pressure drop and geometric characteristic constant. The empirical equations for the spray cone angle and sheet breakup length of the open-end swirl injectors were fitted from the experimental results, respectively, which included both the effect of the injector geometry and flow conditions in the injector.