Prediction of combustion instability is essential in reducing development costs of large scale rocket engines. Recently, high fidelity CFD models have shown some ability to represent the stability characteristics of sub-scale experimental combustors. A challenge remains in acquiring experimental measurements of critical combusting flow properties, especially measurements of the unsteady heat addition field, for comparison to models. Previous studies have shown that OH* and CH* emission intensity is a function of pressure, strain rate, equivalence ratio, and turbulence level. Since these flame properties have large variations at all times in an unstable rocket combustor it is difficult to decouple the chemiluminescent emission from all variables except heat release. Emission due to chemiluminescence can, however, be isolated from other flame property variables in a computational model. A detailed chemical kinetics model is used to investigate the relationship between chemiluminescent species and heat release rate of the flame. This predicted relationship is then compared to experimental spectral measurements captured with a fiber optic probe both to check the validity of the model and to provide insight on the ability of the chemiluminescent light emission to indicate heat release in the unstable CVRC flame.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.