A Short Note On Rocket Engine Combustion Instability

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Rocket Engine Combustion Instability
Naveen Penmetsa
University of Colorado, Boulder, CO, 80309

C ombustion instability has long been an area of research in the design of both aircraft and rocket engines. Specifically in terms of rocket engines, combustion instabilities occur in every type of engine including solid rocket motors, cryogenic engines, hyperbolic engines, and hydrocarbon engines. Although combustion oscillations tends to exist in almost every engine, the goal is to minimize these variations in combustion such that any pressure oscillations are below the ambient noise of the engine itself. In order to reduce the linear and nonlinear coupling that causes these instabilities, it is important to identify not only the types of oscillations that occur but also the causes for each of these oscillations.
In liquid engines there are three main types of instabilities. These are chugging oscillations which are low frequency, buzzing oscillations which are of an intermediate frequency, and screeching which is a high frequency oscillation. Additionally, instabilities can oscillate in three different direction, due to the three dimensional nature of combustion. These directions are longitudinally, radially, and transversely.

Flow States’ Effect on Liquid Engine Combustion Instability
The various forms of combustion instability in liquid rocket engines are directly and indirectly affected by the state of the flow from the inlet of the injector to the throat of

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