Stability Characteristics of Bi-swirl Coaxial Injectors in Fuel-rich Combustion

Combustion stability characteristics in a small-scale combustor with seven liquid-liquid bi-swirl coaxial injectors were studied experimentally. Liquid oxygen and kerosene (Jet A-1) were burned in a fuel-rich combustor simulating a liquid rocket engine gas generator. While changing mixture ratios between 0.286 and 0.370, static pressure, temperature, and dynamic pressure data in the propellant manifolds and combustion chamber were acquired. In addition, chamber pressures were varied between 47.9 bar and 69.0 bar, which covered the sub- and supercritical pressures of oxygen. When the chamber pressure was above the critical pressure of oxygen, dominant pressure waves were not encountered. However, when the chamber pressure was below the critical pressure of oxygen, low-frequency pressure oscillations were found to develop in the manifolds and combustion chamber. Additionally, the amplitude of such low-frequency pressure oscillations increased as the pressure drop across the fuel-side injector was reduced. Accordingly, the effects of chamber pressure and pressure drop across the injectors must be carefully considered when designing a swirl coaxial injector operating in fuel-rich conditions.