Investigation on the mechanism of wave and flame in the deflagration to detonation transition process

A series of single-shot detonation experiments was performed to characterize the deflagration to detonation transition(DDT) process for H2/Air mixtures in a 60 mm square tube that was 2 m in length.High-speed digital imaging was used to track flame propagation beginning from the ignition,and simultaneous seven high-speed pressure transducers,mounted along the tube wall between 850～1200 mm,were used to record progress of the compression and shock wave.According to high-speed images,it is found that DDT process has five phase:① Normal combustion is initiated by an electric spark and its velocity is only 0～15 m/s;② Flame acceleration and deflagration formation which propagates with 500～1000 m/s;③Hot spots appear along the tube wall;④ formation of explosion center which creates blast wave;⑤ formation of strong detonation wave which propagates with 1800～2000 m/s.In the zone from 850 to 1 200 mm,which pressure transducers were mounted,the maximum pressure value firstly rises from 1.5 MPa to 7 MPa,then down to 2～3 MPa,and the detonation wave velocity is about 2000～2100 m/s,which is suit with the result achieved from the high-speed digital imaging.