Experimental Study on the Dynamic Characteristics of Open Type Swirl Injector with Varying Geometry

Abstract

Combustion instability can break out any kind of engine that uses combustion process to get power. Liquid Rocket Engine (LRE), especially, operates in extremely high temperature and high pressure condition, combustion instability directly leads to failure of the engine. Combustion instability occurs when heat release from the combustion chamber and acoustic wave interact, acoustic wave from the process causes pressure fluctuation to the fuel or oxidizer flowing into the injector. Additional devices like baffle or acoustic cavity were attached to LREs to suppress combustion instability, necessarily, bringing weight increment of the engine and finally reducing efficiency. If the injector, which is in the middle of the whole combustion process, could act like a damper itself, the engine would stay stable for the outer disturbance. Then it will be possible to manufacture highly efficient, high performance LRE with low cost. This is the reason injector dynamics should be investigated. Hydrodynamic mechanical pulsator was produced to generate pressure oscillation, electrical conductance was made and installed at the end of the orifice to measure film thickness. Total 7 different open type injector, varying either length or diameter of the swirl chamber, was produced to figure out the effect of geometrical variation. Experiment for static characteristics was preceded, the behavior of mass flow rate and liquid film thickness along the manifold pressure was measured. Measured liquid film thickness was compared to the empirical equations of previous studies, analyzed the reason for not matching each other. For the dynamic study, by generating pressure fluctuation to the liquid flowing into the open type swirl injector, we measured the following response characteristics. Liquid film thickness and pressure at the end of the orifice was chosen as output parameters. Effect of swirl chamber length and diameter was also observed on the dynamic characteristics of the injector.