The characteristics of the propagation of a detonation from a cylindrical tube of constant cross section into a diverging cone were experimentally investigated using the smoked-foil technique for three explosive gas mixtures: C2H2+2.5O2, 2H2+O2+4.5Ar, and C2H4+3O2+0.44N2. The initial pressure and the cone enlargement angle were varied as governing parameters. The results were summarized in terms of the ratio between the inner diameter of the cylindrical tube through which a detonation initially propagated and the detonation cell width d and of the cone enlargement half angle . Four patterns of detonation propagation were observed in the diverging cone: continuous propagation, re-initiation on the cone wall, re-initiation apart from the cone wall, and failure. The obtained results were qualitatively consistent with past experimental results reported by other researchers. However, quantitatively, the obtained results were dependent on the explosive gas mixtures, particularly on the so-called critical tube diameter. Actually, when the critical values of d against detonation failure were normalized by that corresponding to 90 ,° a single curve unifying all data to some degree was obtained. In addition, some characteristics of the detonation behavior in the diverging cone were explained by simple models.

We experimentally investigated the promotion of deflagration-to-detonation transition (DDT) in hydrogen-air mixtures contained in a tube in which straight-shaped rods were installed as obstacles. In the experiments, the number of obstacle rods, their spacing, their blockage ratio, and the equivalence ratio of the hydrogen-air mixture were varied as the governing parameters. The obstacle rods had a spacing of 10 or 20 mm and a blockage ratio of 0.32, 0.41, or 0.51. As a result of an optimization of the obstacle-rod conditions, when fourteen rods, whose blockage ratio was 0.32, were installed in a tube with a spacing of 20 mm and with a hydrogen-air mixture with equivalence ratios from 0.8 to 1.2, the run-up distance to the DDT was shortened to approximately 20 times the tube diameter.

No abstract