Abstract
Self-excited combustion oscillations in a model rocket combustor is investigated experimentally. A unique dump combustor, CVRC (Continuously Variable Resonance Combustor), is employed to realize a well-controlled self-excitation. The combustor has a coaxial injector whose oxidizer post has a choked inlet that is variable in length allowing for a desired response for the self-excitation. Gaseous methane and decomposed hydrogen peroxide are supplied and burnt in an optically transparent combustor. The flame inside the combustor during hard oscillation is observed by high-speed (20 kfps) CH*-band emission imaging. Together with the images, pressure fluctuations near the dump wall are recorded. As a result, the existence of a nonlinear acoustic wave (N-wave) is suggested when the amplitude of the pressure oscillation exceeds roughly one tenth of the mean pressure. The relation between the occurrence of N-wave and the CH*-band emission oscillation is investigated by applying snapshot POD (Proper Orthogonal Decomposition). Particular spatial modes of the flame emission oscillation are found to appear in accordance with the occurrence of the N-wave.
