Self-Excited Non-Linear Acoustic Wave in a Single-Element Model Rocket Combustor and Its Influence on Flame

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.

Study on Nonlinear Dynamics Using the State Space of Combustion Oscillation in a Rocket Combustor

“…From these results, the three characteristic Modes (i.e., Modes 1, 2, 3) that dominate energy supply to the combustion oscillation are identified. In particular, the pumping near the recirculation zone for Modes 1 and 2 corresponds to the luminous zone experimentally observed by Tanabe et al 3) at the side wall of the CVRC. In other words, Modes 1 and 2 are thought to be related to the energy being supplied to the nonlinear pressure wave.…”

“…Tanabe et al showed that nonlinearity arises in pressure wave generated in the CVRC when amplified. 3) It was also shown that the non-linear pressure oscillation was enhanced at the time of heat release near the dump plane in the combustor. Kanda et al focused on impingement jet injectors, coaxial and concentric injectors, which were generally utilized in liquid rocket engines.…”