An experimental study of the propagation characteristics for a detonation wave of ethylene/oxygen in narrow gaps

Abstract

To investigate the propagation characteristics of a detonation wave in a narrow gap, the detonation processes of a stoichiometric ethylene-oxygen mixture were studied at different initial pressures in narrow gaps ranging 1.0–4.0mm in height. Flame propagation through the narrow gap was observed with a high-speed camera, and the trajectories of triple points on the detonation waves were obtained using a soot-deposition plate. The results showed that both higher initial pressure p0 and lower narrow gap height h could accelerate the deflagration-to-detonation transition process and determine how the detonation wave propagates, e.g., galloping detonation, stuttering detonation, and stable detonation. To attain unstable detonation propagation, the corresponding range of initial pressures increased with decreasing height of the narrow gap. A smaller height of the narrow gap led to a higher initial pressure threshold corresponding to the detonability limit. This could be determined by the range of h/λ; the onset of galloping detonation occurred when 0.17<h/λ<0.27. Since the effect of the boundary layer on detonation propagation could not be neglected in narrow gaps, the velocity deficits were relatively large compared with those from a large scale channel. It was found that the velocity deficits were inversely proportional to the narrow gap height and initial pressure, and the relation between them was obtained by fitting the experimental data, i.e., ΔD=0.65h-0.8p0-0.5.