Non-dimensionalized distances and limits for the transition of deflagration to detonation

Abstract

This experimental work investigates the possibility to non-dimensionalize the limits and the distances of the Deflagration-to-Detonation-Transition process (DDT). The deflagration was ignited using jets of hot gases generated by the impact of a Chapman-Jouguet detonation on a multi-perforated plate. Small holes were uniformly distributed on the plate, over the whole tube section. The tube was 1-m long with square cross-section 40 × 40 mm 2 . The reactive mixtures were the stoichiometric compositions of hydrogen, methane and oxygen (1-x )H 2 + x CH 4 + 1 2 (1 + 3 x )O 2 with the composition parameter x ranging from 0 to 1. The initial pressure p 0 was varied from 12 to 35 kPa, and the initial temperature was 294 K. The re-ignition conditions and distances were obtained as functions of x, p 0 and the plate properties. The mean widths of the detonation cells measured at the wall were used to nondimensionalize the DDT distances, the surface of the perforations and the surface of the walls of the plate holes. This non-dimensional DDT distance thus appears to be a concave increasing function of the non-dimensional perforated surface independent of the regularity of the cellular structure. DDT processes are very dependent on the system configuration and the ignition conditions but our analysis suggests that the proper selection of non-dimensional numbers built from the system characteristics can help in anticipating the corresponding DDT limits and distances to a reasonable approximation.