Propellant Injector Influence on Liquid-Propellant Rocket Engine Instability

Abstract

The avoidance of acoustic instabilities, which may cause catastrophic failure, is demanded for liquid-propellant rocket engines. This occurs when the energy released by combustion amplifies acoustic disturbances; it is therefore essential to avoid such positive feedback. Although the energy addition mechanism operates in the combustion chamber, the propellant injector system may also have considerable influence on the stability characteristics of the overall system, with pressure disturbances in the combustion chamber propagating back and forth in the propellant injector channels. The introduced time delay may affect stability, depending on the ratio of the wave propagation time through the injector to the period of the combustion chambers acoustic modes. This study focuses on transverse-wave liquid-propellant rocket engine instabilities using a two-dimensional polar coordinate solver (with averaging in the axial direction) coupled to one-dimensional solutions in each of the coaxial oxygen–methane injectors. A blockage in one (or more) of the injectors is analyzed as a stochastic event that may cause an instability. A properly designed temporary blockage of one or more injectors can also be used for control of an oscillation introduced by any physical event. The stochastic and design variables parameter space is explored with the polynomial chaos expansion method.