Cryogenic oxygen/hydrogen flame response to acoustic excitation in a rectangular rocket combustor

Abstract

The interaction of cryogenic oxygen and hydrogen flames with an externally forced acoustic field has been investigated. Tests have been conducted with an injection configuration and combustor operating conditions which are representative of real rocket engines. For the first time, such tests with LOx/H2 propellants and acoustic forcing have been conducted at combustion chamber pressures above 10 bar, the reported results herein from a test at 43.5 bar. Optical access to the combustor allowed the simultaneous high speed recording of hydroxyl radical (OH*) chemiluminescence and backlit shadowgraph images of the flame during periods of forced excitation of acoustic resonance modes of the combustion chamber. Significant changes in the structure of the flame were observed during periods of acoustic resonance; primarily in the length of the flame and distribution of heat release. These observations are discussed with respect to feedback mechanisms in naturally occurring combustion instability.