No abstract

A combined experimental and theoretical study of deflagration-to-detonation transition (DDT) in smooth narrow channels is presented. Some of the distinguishing features characterizing the late stages of DDT are shown to be qualitatively captured by a simple one-dimensional scalar equation. Inspection of the structure and stability of the traveling wave solutions found in the model, and comparison with experimental observations, suggest a possible mechanism responsible for front acceleration and transition to detonation.

Flame propagation experiments in stoichiometric H 2 -air are conducted in a smooth 482-mm long, 10-mm × 10-mm square cross section channel, closed at the ignition end and open at the opposite end. Direct observation is used to track the flame acceleration dynamics. The effect of facility specific parameters (i.e. ignition energy, boundary conditions near the ignition end, window material and settling time between filling and ignition) on flame propagation and acceleration is assessed. The absolute mean deviation is used as a metric to determine the effect of the aforementioned parameters on the collected front position data, and Response Surface Methods for experimental design is applied to examine inter-parameter interactions. Results show that the boundary conditions near the ignition end (i.e. large/small ignition offset) have the largest influence on the recorded front position with the remaining parameters playing a less important role. The early stages of flame propagation is compared against theoretical predictions to understand the discrepancies observed in the data; a simple acoustic model was found sufficient to explain the increased acceleration rates observed for the large ignition offset cases. Finally, a link between the observed front oscillations during flame acceleration and the flow rate dynamics at the channel's open end is highlighted.