Effect of obstacle thickness on the propagation mechanisms of a detonation wave

Effects of obstacle thickness on the mechanism of detonation propagation in 2H2–O2 mixture are investigated experimentally in a square channel with a cross-section of 300 × 300 mm and 6 m long. Two typical obstacles with the thicknesses of 20, 60 and 80 mm are considered, i.e., a square orifice and a perforated plate. Eight equally spaced pressure transducers are used to record the time-of-arrival of the combustion wave, from which the average velocity can be determined. The smoked foil is employed to record the detonation cellular structures. Three various propagation regimes are seen: (1) below the critical pressure, a steady detonation wave is not formed before the obstacles, and then the detonation wave is produced by the mechanism of DDT; (2) near the critical condition, the steady detonation wave is decayed firstly across the obstacles, afterwards, the re-initiation mechanism is observed by the shock-wall interaction; (3) well within the limits, the perturbations induced by the obstacles nearly have no effect on the detonation propagation. Moreover, two different ignition mechanisms are observed after the obstacles, i.e., symmetric and asymmetric ignition. The critical condition of detonation propagation can be quantified as DH/λ > 1 where DH is the hydraulic diameter and λ is the cell size.