Combustion Dynamics and Stability of a Fuel-Rich Gas Generator

The dynamic characteristics of fuel-rich combustion have been studied using an experimental combustor simulating a gas generator for a liquid rocket engine. The combustor bums liquid oxygen and fuel (Jet A-1) at a mixture ratio of about 0.32 and a chamber pressure ranging from 4.10 to 7.24 MPa, which co rers subc ritical to supercritical pressures of oxygen. For the investigation of combustion dynamics, pressure fluctuat on measurements using piezoelectric sensors have been a major probe throughout the present study. Two different types of injector heads equipped with biliquid swirl coaxial injectors and either a short nozzle or a turbine manifold nozzle have been used in the study. Fuel-rich combustion of both injector heads with the short nozzle revealed pressure pulsation at frequencies of about 128 Hz, which attenuates along with an increase of a chamber pressure. Combustion tests with the turbine manifold nozzle conducted at.chamber pressures lower than the oxygen critical pressure showed combustion instabilities at a frequency of 330 Hz, which has been identified as a longitudinal re sonant mode by a linear acoustic analysis. The combustion instabilities seem to be induced by inherent pressure fluctuations from the biliquid swirl coaxial injector when the chamber pressure is below the oxygen critical pressure.