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This study addressed a deflagration–to–detonation transition (DDT) process after interaction of the convex flame with a planar shock wave. High–speed video cameras and schlieren optical technique were utilized to observe the DDT as well as shock–flame interaction processes. A double–diaphragm shock tube was used to produce the shock wave, while the flame was produced by igniting a premixed gas of stoichiometric methane–oxygen at the observation section. Experiments were conducted by changing Mach number of the incident shock wave, M s and a distance of flame front from the end wall, x0. As a result of schlieren photographs, flame propagation behaviors at initial stage were classified into four patterns, named as (a) coupling, (b) concave, (c) partial coupling and (d) convex type. The propagation patterns of flame were highly dependent on the initial position of flame front, x 0. Under the experimental conditions, DDT was not observed when the flame had been propagated revealing (a) coupling (observed with the conditions of x 0 > 110 mm) and (d) convex type (x0 < 50 mm). However, the DDT was observed following that the flame had been propagated revealing (b) concave or (c) partial coupling (50 < x0 < 110 mm). Furthermore, it was elucidated that DDT was typically caused through the following processes. (i) When the convex flame interacted with planar shock, the unburned gas was penetrated into burned gas inducing Richtmyer–Meshkov instability. (ii) The flame was highly accelerated at boundary layers behind the reflected shock. (iii) After accelerated flame propagated through the unburned shocked region, local explosion was occurred on the wall followed by detonation onset.

Detonation transition process caused by interaction of convex flame with planar shock wave