Visualization of the Detonation Wave Structure in a Small-Scale Hydrogen–Oxygen Rotating Detonation Combustor

This study presents the high-speed visualization of the detonation wave structure in a small-scale hydrogen–oxygen rotating detonation combustor. A 68 mm Rotating Detonation Combustor was modified with a quartz-glass ring, such that radial optical access into the annular detonation chamber was realized. The optical access window covers approximately the first 22 mm of the detonation chamber. The modified experiment was hot-fire tested with the propellant combination gaseous hydrogen–oxygen. Simultaneous high-speed imaging from the back-end of the chamber and normal to the chamber axis allows a thorough investigation of the detonation wave characteristics. Both high-speed cameras were operated at 180,000 frames per second in order to resolve and capture the detonation waves. The downstream camera was used in order to investigate the number of waves and the spinning direction. A stable regime of three co-rotating waves was observed. The wave speed achieved 71% of the theoretical CJ-velocity. The second camera recorded the passing detonation waves through a quartz ring via OH* emissions. From the post-processed OH* images, a better understanding of the detonation wave structure, including the filling height of the fresh gas mixture as well as the approximate angles of the detonation and the shock wave, could be gained. The obtained height of the detonation wave is about 11–12 mm or 6–7 detonation cell sizes for the given setup and experimental conditions.