Flame response to acoustic excitation in a rectangular rocket combustor with LOx/H2 propellants

Abstract

Research efforts are currently underway at the German Aerospace Center (DLR) Lampoldshausen, which aim to understand the mechanisms by which self-sustaining oscillations in combustion chamber pressure, known as high frequency combustion instabilities, are driven. Testing has been conducted in the rectangular combustor ‘BKH’, running cryogenic oxygen and hydrogen propellants under pressure and injection conditions which are representative of real rocket engines and with acoustic forcing. 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 42 bar. Optical access to the combustor allowed the application of high speed hydroxyl radical (OH*) chemiluminescence imaging of the flame during periods of forced excitation of acoustic resonance modes of the combustion chamber. This paper reports the investigation of flame response to acoustic excitation. Both fluctuation in OH* emission intensity and deflection of the flame at frequencies corresponding to the excitation frequency have been observed. These responses are then discussed as potential indicators of driving mechanisms for combustion instabilities.