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We experimentally investigated the influences of a small obstacle on the sidewall upon a detonation cellular structure using the smoked-foil technique for a stoichiometric hydrogen–oxygen mixture diluted with argon at pressures ranging from 15 to 60 kPa. The obstacles were of four types: forward-facing steps and slopes and backward-facing steps and slopes. The step height was varied and set to 1, 2, or 5 mm, but the slope height was fixed at 5 mm. The forward-facing slope angle was set to 40° or 75°, and the backward-facing slope angle was set to 20° or 40°. Under all conditions, for the forward-facing steps and slopes, the detonation cellular structure was negligibly affected, except for the region around the tip of the step and slope. However, for the backward-facing step, the detonation re-activation phenomenon occurred downstream of the obstacle. In addition, the enlarged cellular pattern due to the rarefaction wave and the trajectory of the re-activated strong transverse wave were observed downstream of the obstacle. Furthermore, a finer cellular pattern was observed downstream of the re-activation phenomenon. The distance between the backward-facing step and the re-activation position zra was fitted well by a power-law relation of the step height |h| and the cell width of the steadily propagating detonation λCJ as zra/λCJ = 2.7(|h|/λCJ)0.80. When the obstacle was the backward-facing slope, the smoked-foil records could be classified into two types based on whether the signatures of the detonation re-activation phenomena were clearly observed or not. Finally, when the finer cellular pattern was observed, the behavior of the cell-width enlargement subsequent to the re-activation phenomenon was similar in all cases, and the characteristic length required for the finer cellular pattern to relax to the steady-state pattern was approximately 10 times zra.

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.

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/λ and of the cone enlargement half angle θ. 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/λ against detonation failure were normalized by that corresponding to θ = 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.

In this study, experiments on a pulse detonation turbine engine (PDTE) were conducted. The final goal of this work is the self-sustained operation of a PDTE system in which all of the air used for its operation is supplied by a turbine-compressor driven by pulsed detonations in the system itself. Currently, air used for PDTE operation is supplied by using an external device because the air flow rate for PDTE operation is too high. That is, air is used not only for combustion but also for purge of the residual hot burned gas in a pulse-detonation combustor (PDC), and sometimes for the control of the turbine-inlet temperature by blowing secondary air into a PDTE system downstream of the PDC. In this work, for reducing the air flow rate for PDTE operation, the water-droplet-injection technique was introduced in two ways. First, water droplets were injected into the PDC for purging the residual hot burned gas. Second, water droplets were injected into the PDTE system downstream of the PDC for controlling the turbine-inlet temperature. In particular, the effect of the latter was analyzed by using simple model calculations. As a result, the turbine-inlet temperature was precisely controlled by the water-droplet injection, and the air flow rate for PDTE operation was drastically reduced.