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

Abstract

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 that has already been tested extensively at DLR Lampoldshausen was modified with a quartz-glass ring, such that radial optical access into the annular detonation chamber was realized. The optical access windows covers approximately the first 22 mm of the detonation chamber. The modified experiment was hot-fire tested at the test bench M3.1 with the propellant combination gaseous hydrogen-oxygen. Simultaneous high-speed imaging from the back-end of the chamber and from the side allows a thorough investigation of the detonation wave characteristics. Both high-speed cameras were operated with 180,000 frames per second in order to resolve and capture the detonation waves. The down-stream camera was used in order to investigate the number of waves inside the annular chamber and the spinning direction. For the investigated operating condition 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 wave through a quartz-ring via OH* emissions. The post-processed images show the structure and position of the detonation waves inside the annular combustion chamber. From the 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 mm or 8-9 detonation cell sizes for the given setup and experimental conditions.