Experimental Investigation of Self-Excited Combustion Instabilities in a LOX/LNG Rocket Combustor

Kurzfassung

Two types of combustion instabilities were observed in a multi-injector research combustor with liquid oxygen and liquefied natural gas (LOX/LNG) propellants operating at conditions similar to an upper stage rocket engine. The first was identified as an excited tangential acoustic mode of the combustion chamber and can be explained by coupling with the LOX injectors, similar to the mechanism previously observed in tests with LOX/H2 propellants. The other type is characterized by longitudinal acoustic oscillations with peak-to-peak amplitudes of at least 40% of the mean chamber pressure. Analysis of the test data suggests that sudden upstream displacement of a lifted flame may be the trigger mechanism for the second type of instabilities.