The bi-swirl injector, which consists of two single swirl injectors, is used to discharge the propellants into a combustion chamber in a liquid rocket engine. Since the combustion efficiency and stability of the engine are influenced by the spray characteristics and spray conditions the injector, the spray characteristics of the swirl injector is required to design the optimized combustion engine and injector. In this study, the research on the spray characteristics of bi-swirl injectors by different recess length, mass flow rate, and swirl direction was conducted with three different study objectives in cold-flow test. The first objective of this study was to investigate the spray characteristics by the recess length and mass flow rate. From the test results, the change of the spray characteristics such as the discharge coefficient and spray angle were studied by the mixing characteristics by the recess length. The second objective was to investigate the change of the spray characteristics by the swirl direction using co-swirl injector, in which two single swirl injectors rotate the same swirl directions, and counter-swirl injector, in which two single swirl injectors rotate the opposite swirl directions. The last study objective was to investigate the change of spray characteristics by the injector geometries and the ratio of mass flow rate by comparing the study of bi-swirl injectors for thrust chamber, in which the injector discharge the mass flow rate of oxidizer larger than that of fuel, and for gas generator, in which the injector discharge the mass flow rate of the fuel large than that of oxidizer.
The experiment was conducted by two step, single injection and bi-injection, to investigate the change of spray characteristics. In single injection, two single swirl injectors in the bi-swirl injector discharge the fluids individually. After that, both injectors discharge the fluids at the same time in bi-injection.
From the experimental results of discharge coefficient, It was found that the discharge coefficient was independent of the mass flow rate and the recess length in single injection. However, the discharge coefficient of outer injector in bi-swirl injector was decreased in tip mixing and internal mixing modes in bi-injection. Therefore, it was concluded that the collision and mixing of two fluids caused the discharge coefficient to decrease.
From the results of spray angle, It was found that the change of mixing characteristics by the recess length and the change of spray patterns. In single injection, the spray angle was independent of the mass flow rate, but it was decreased as the ratio of mass flow rate was increased in bi-injection. Also, the measured spray angle was compared to the theoretically estimated spray angle.
From the result of the swirl direction, the spray angle was greatly affected. Especially some cases showed that the swirl direction of mixed spray was changed in counter-swirl injector. Also, the discharge coefficient of co-swirl injector and counter-swirl injector was decreased if there was the collision inside the injector but the amount of decrement was slightly different by the swirl direction.