Experimental study of acetylene/air detonation waves in partially confined channels

The propagation of detonation waves in partially confined channels is a critical issue in combustion research and has garnered significant attention in detonation propulsion applications. This study experimentally investigates the propagation characteristics of acetylene/air detonation waves in a unilaterally open channel. A geometric parameter termed the "open area ratio" is defined to quantify the relative size of the open area. The cellular structure and the transient evolution of the shock wave-flame interaction are captured using soot foil and high-speed shadow photography. The experiments reveal three distinct detonation propagation states, which depend on various factors such as the equivalence ratio of the mixture, channel height, and open area ratio: detonation extinction, re-initiation of detonation after extinction, and sustained detonation. An empirical relationship is established regarding the ability of detonation waves to propagate through partially confined channels, which is related to the dimensionless channel height and open area ratio. The re-initiation of detonation is induced by local explosions resulting from direct Mach reflections occurring at the partially confined boundaries. The Quasi-One-Dimensional model for predicting weakly confined detonation wave velocities incorporates the influence of the open area ratio. It is found that the velocity deficit is approximately proportional to the open area ratio and inversely proportional to both the channel height and reactant sensitivity. The velocity deficits calculated by the Quasi-One-Dimensional model not only agree well with experimental measurements but also accurately predict whether detonation waves can propagate through partially confined channels.