Experimental Analysis of Detonation Wave Modes in a Disk-Shaped Rotating Detonation Rocket Engine Using Liquid Propane and Nitrous Oxide

This study experimentally investigates the detonation propagation behavior of a disk-shaped rotating detonation rocket engine (Disk-RDRE) operating with self-pressurizing liquid N2O and C3H8. Ignition was achieved using a gaseous H2/O2 pre-detonator, and the detonation development inside the combustor was characterized exclusively through high-speed optical diagnostics. High-speed imaging was used to construct spatio-temporal contours, perform spectral (FFT/STFT) analysis, and conduct modal decomposition using proper orthogonal decomposition (POD). Following ignition, a single rotating detonation wave was established within approximately 2 ms and remained stable throughout the analysis window. High-speed imaging confirmed continuous azimuthal propagation without observable mode transitions. Spectral analysis revealed dominant frequencies on the order of 6.7-6.8 kHz, and STFT results showed that these frequencies remained temporally stable across the measured interval. POD further indicated that the single-wave structure was consistently captured by Mode 1 and Mode 2, while weak Mode 3 activity was attributed to luminosity based noise rather than physical multi-wave behavior. These findings experimentally demonstrate the feasibility, stability, and repeatability of liquid-propellant Disk-RDRE operation, offering insight into the development of pressure gain propulsion systems using storable liquid propellants.