A Study on Dynamic Characteristics of Gas Centered Swirl Coaxial Injector with Acoustic Excitation

Abstract

Combustion instability is critical problem in developing liquid rocket engine which is the phenomenon occurred by the combination of combustion in its chamber and the flow of propellants supply system. The combustion instability phenomenon basically aggravates the combustion efficiency and control system, and moreover it can triggers the destruction of engines in severe cases. The several methods like baffle and cavity have been used for suppression of combustion instability. In this study, the method as part of these efforts to suppress combustion instability was sought through the injector. One cause of the combustion instability is the disturbance of feeding propellants and such disturbance can be generated for various reasons. Because the disturbance can be amplified which is propagated to the combustion chamber and its effect undergoes feedback process returned to the supply system, the design of the injector in the middle of such a chain process is very important. If the injector can suppress the disturbance coming from the supply line as a kind of buffer it will serve to reduce combustion instability. However, previous research was mainly only about the response of disturbance in a single swirl injector with liquid pulsation. The research about the response of disturbance in gas-liquid injector with acoustic excitation has not been conducted much. In this study, the response characteristic was observe by acoustic excitation of speaker to simulate the phenomenon that gas propellant is supplied with disturbance in gas centered swirl coaxial injector. The film thickness at injector exit which affects various spray characteristics such as spray angle, break up length, SMD was measured by using a liquid film electrode. Also the response of spray to the disturbance was observed by high-speed photography. The recess ratio, the gap thickness, the gas-liquid momentum flux ratio, the frequency of feeding gas was changed to investigate the effect of these experimental parameters.