An experimental study on the deflagration-to-detonation transition in millimeter scale tubes

The deflagration-to-detonation transition of ethylene-oxygen mixture was studied in thin tubes with inner diameters of 2, 4 and 8 mm. To better make the experiment comparable to the previous simulation configuration, the flames were ignited from stationary state which conforms to the precondition of closed-end ignition. Flame speeds and other parameters were measured using high speed camera. The characteristics of pre-detonation acceleration were analyzed both qualitatively and quantitatively. It is concluded that, unlike the results that the numerical researches have found, there are four distinctive acceleration stages during the DDT process. In thinner tubes, flames propagate faster, while the characteristic acceleration time is shorter in larger tubes. The sound speed of the burned and unburned gas is considered to be the critical velocity, beyond which the flame may be boosted more quickly to detonation. When the saturation speed in the third acceleration stage becomes supersonic in larger tubes, the DDT distance may be shortened.