The competitive relationship between detonation and deflagration in the inner cylinder-variable continuous rotating detonation combustor

To investigate the impact of the competitive relationship between detonation and deflagration on continuous rotating detonation, a series of ethylene-air and hydrogen-air rotating detonation tests are conducted by varying the inner cylinder length. In the experiments, ethylene-air detonation wave self-sustains in the hollow chamber part closely following the terminal of inner cylinder, instead of in the 5 mm-wide annulus. The deflagration in the upstream annulus combined with the deflagration prior to continuous rotating detonation wave in the hollow chamber part is supposed to be parasitic combustion, which destroys the accumulation of combustible mixture. The increase of intensity and longitudinal range of parasitic combustion makes the operating range, propagation frequency, and stability decrease. In contrast, hydrogen-air detonation wave can self-sustain in the 5 mm-wide annulus. However, the short annulus cannot hold the integrated detonation wave, and the separated structures of detonation wave make the ratio of commensal combustion increase. It is suggested that continuous rotating detonation should be quickly initiated within the short distance to reduce the impact of parasitic combustion, and the structural integrity of detonation wave should be maintained to reduce the ratio of commensal combustion. Besides, longitudinal pulsed deflagration mode is discovered and analyzed.