An experimental study on the onset of detonation downstream of a perforated plate with staggered orifices

Abstract

The present study investigated the onset of detonation (OD) process which takes place downstream of a 0.9-mm-thick perforated plate. The orifice diameter of the plate is 1.6 mm with a blockage of 59%, and it was placed perpendicular to the axial direction of a smooth detonation tube. ‘Stable’ mixture C2H2 + 2.5O2 + 70%Ar and ‘unstable’ mixture C2H2 + 5N2O were tested, respectively. Ionization probes and smoked foils were used to record detonation velocities and corresponding cellular patterns. Excellent agreement of the velocity trends and smoked foil results shows that a critical pressure range exists to identify ‘go’ and ‘no go’ of OD downstream of the perforated plate. However, the OD mechanisms for these two gaseous mixtures are distinct: for the ‘stable’ mixture, OD occurs in the downstream near field (6 tube diameters in this study), whereas, OD in the ‘unstable’ mixture could also observed in the far field via the transition of deflagration to detonation after a long duration of quasi-steady regime. This distance reaches up to tens of tube diameters when close to the critical pressure.