Due to the low chemical activity and large detonation cell size, methane-air continuous rotating detonation (CRD) is hard to be realized in a traditional small annular chamber without extra additives. In order to investigate the characteristics of methane-air CRD wave in a small chamber, three hollow chambers with Laval nozzles are adopted in this research. The methane-air CRD can be realized in a quite small chamber (diameter of 80 mm) under very particular condition. The operating range enlarges with the increase of chamber diameter. The CRD wave propagation frequencies vary apparently with chamber diameter while the propagation velocities stay in a quite narrow range of 1744–1812 m/s, and the relative deviation is within 4%. The CRD wave propagation process is very stable, and the propagation velocity accounts for 99% of the theoretical C-J velocity in the chosen test. Optical observation results illustrate that the reduction in chamber diameter or increase in nozzle contraction ratio will lead to CRD deterioration. By comparing the frequencies of high-frequency pressure and optical observations, the coupling of inducing shock wave and combustion flame is proved quantitatively.
