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

Abstract

It is important to study on the combustion instability to develop liquid rocket engines for preventing lower combustion efficiency and destruction of the combustion chamber. Various methods such as a baffle and cavity are used to prevent the combustion instability. It is important to suppress the combustion instability by designing an injector because it is in the middle of the process of the disturbance propagating in a rocket engine. Most of studies on the injector focuses on the simplex injector with liquid pulsation. In real rocket engine system, however, coaxial injectors are primarily used. In previous studies on a gas-centered swirl-coaxial injector, the dynamics characteristics and the spray pattern was analyzed on the condition of gas excitation. Therefore, research on coaxial injector with liquid pulsation is essential. In this study, instability of liquid fuel flow with perturbation of liquid propellant flow in a gas-cantered swirl- coaxial injector was investigated using air and water. The liquid perturbation was generated by a mechanical pulsator, and film thickness variation at the end of the injector which affects spray characteristics such as spray angle, break up length, and Sauter mean diameter(SMD) was measured using electrodes. The spray image which shows the evidence of the flow fluctuation such as a monolayer and spray width changes was achieved using DSLR camera and high speed camera. The dynamic characteristics of the gas-centered swirl-coaxial injector was studied varying tangential inlet diameter and gap thickness without gas flow. In addition, the response characteristics of the injector was investigated varying the momentum flux ratio while the gas and liquid were simultaneously injected.