An experimental study on CH4/O2 continuously rotating detonation wave in a hollow combustion chamber

• The feasibility of sustaining the CRDW in a hollow combustion chamber through annular injection distribution was verified.
• The unstable and stable rotating detonations in CH4/O2 mixture were analyzed.
• The propagation characteristics of rotating detonation were studied.
• The injecting condition played a significant role in sustaining a stable CRDW.

CH4/O2 continuously rotating detonation waves (CRDWs) have been experimentally achieved in a special model with a hollow combustion chamber rather than a typical cylindrical annular chamber. Experiments were conducted at atmospheric backpressure and under various injection conditions (different mass flow rates of CH4/O2 gaseous mixture). The injection conditions, together with the time domain and frequency domain characteristics of the high frequency pressure, have been analyzed. A high speed camera was employed to roughly record the reaction zone structure. Results show that for the given test mode working with lower mass flow rates – 38 g s−1 CH4 and 131.7 g s−1 O2 (leading to an equivalence ratio of 1.154), CRDWs occurred but were not stably propagating. In contrast, stably propagated CRDWs were observed in a four-wave mode when mass flow rates were increased to 36.1 g s−1 CH4 and 217.2 g s−1 O2 (leading to an equivalence ratio of 0.665). The corresponding average frequency and average velocity of the CRDWs were 19.251 kHz and 1512 m s−1, respectively. FFT and STFT discussions on the high-frequency pressure history of CRDWs validated the stability of rotating detonation waves in the hollow chamber. This study further verified the feasibility of triggering the CRDW in a unique hollow combustion chamber through annular injection distribution. Injecting enough combustible mixture is the essential condition for sustaining a stable CRDW.