Chamber Length Limits of a Continuously Variable Geometry Rotating Detonation Combustor

The sensitivity of rotating detonation combustor operation and performance to the length of the combustion chamber was characterized using continuous variation of the chamber length during operation. As the chamber length was both increased and decreased, the sensitivity of the combustion process to varying reactant residence times was characterized using high-speed aft-end imaging of the chamber annulus. The propulsive performance of the combustor was evaluated using thrust and equivalent available pressure, relating them back to reactant supply pressures for the assessment of combustor pressure gain. The specific impulse of the combustor remained relatively constant as the chamber length was decreased from its maximum values up to a limiting length for each operating condition, beyond which combustion was no longer supported within the chamber and significant performance degradation was observed. Modeling of the detonation fill height revealed that relatively low specific impulse measurements could be attributed to unburned reactants exiting the chamber, and a more efficient use of reactants was potentially the cause for improved performance at higher mass flow rates as the detonation wave number increased, fill height decreased, and reactant residence time decreased.