Physics of the transition to detonation of gaseous flames

The deflagration-to-detonation transition of a self-accelerating flame brush in a closed channel is produced by the local explosion of a tiny kernel of unburned gas on a laminar element of the flame front. This unexplained explosion was analyzed recently by a series of asymptotic analyses. Originally identified on the tip of a laminar elongated flame in tubes of small radius, the explosion mechanism is extended here to self-turbulent flames, to hot spots in the boundary layers and also on cellular flames expanding in free space. The mechanism is presented here to physics-oriented readers, skipping technical details of the theoretical developments. The runaway of the local temperature and pressure is due to the coupling of the inner flame structure with the acceleration-induced downstream-running pressure waves in the external flows. This leads to a dynamical saddle-node bifurcation whose critical condition is in good agreement with experiments.