Experimental characterization of flame acceleration and deflagration-to-detonation transition in meso-scale tubes

Reaction propagation of ethylene/oxygen and methane/oxygen mixtures in capillary tubes of 1 and 2 mm in diameters were experimentally studied. Deflagrative flame was initiated in middle of the small tube, and the reaction fronts accelerated as it propagated downstream towards the exits. Lengths of the tubes investigated ranged from 0.4 to 1 m (one side), and deflagration-to-detonation transitions were observed for all equivalence ratios with successful initiations. The visible reaction front propagates at speeds slightly below Chapman-Jouguet speed for ethylene/oxygen mixture in the 1 mm and 2 mm tubes as well as methane/oxygen mixture in the 2 mm tube after deflgration-to-detonation transition was reached. An overshoot in propagation velocity was found during transition process. However, low speed detonation and galloping detonation modes were the typical propagation modes for methane/oxygen mixtures in the 1 mm tube. Run-up distances were found to be invariant to the length of the tube.