Propagation characteristics of stable detonation waves in curved channels with the lateral expansion effect

When a stable detonation wave propagates in a curved channel, it will be influenced by the curvature of the channel, which has been investigated in previous studies. Actually, propagation of a stable detonation wave in a curved channel becomes more unstable if the lateral expansion effect is introduced. However, this is an objective phenomenon in practical rotating detonation chambers. In order to clarify the impacts of the channel curvature and the lateral expansion on the propagation of stable detonation waves, this study has been carried out using a mixture of ethylene, oxygen, and nitrogen. The effects of the channel curvature, the detonable mixture height, and the equivalence ratio on the propagation characteristics in both confined and semi-confined curved channels have been focused in this experimental work. The propagation process was recorded by high-speed photography, and the cell width was obtained using the smoke visualization method, while the peak pressures near the outer wall were also measured. The results imply that the deficits of wave velocity and peak pressure are magnified when introducing the lateral expansion phenomenon, especially under fuel-lean and fuel-rich conditions. Meanwhile, the channel curvature and the mixture height also have a great impact on the detonation propagation. Five propagation modes have been observed after the stable detonation waves enter the curved channels with a semi-confined configuration, i.e., a stable mode, a critical mode, a weakly unstable mode, a highly unstable mode, and a deflagration mode. In addition, for the two observed unstable modes, decoupling occurs periodically near the inner wall. Finally, the critical conditions of the stable detonation mode in the semi-confined channel have been clarified. The critical inner radius should be 13.10–15.24 times of the average cell width, and meanwhile, the minimum detonable mixture height is equivalent to 7.03–8.12 times of the average cell width.