In this study, an ignition method called flame jet ignition (FJI) is applied to pulse detonation engine (PDE) for shortening DDT (deflagration to detonation transition) time and increasing specific impulse while keeping lean burn. FJI, where ignition is initiated in a cavity, is known to have effects on increasing combustion speed and combustion efficiency in internal combustion engines. For the single-cycle experiment where a premixed gas is used, DDT time is reduced in a stoichiometric mixture from 3.2ms to 1.2ms by using FJI comparing with CSI. Specific impulse is increased by 15% in lean mixtures as FJI is used. Multi-cycle tests are performed at the operational frequency less than 16Hz to find that FJI has an effect on reducing DDT time on multi-cycle operation.

When detonation propagates in a tube with obstacles or with variable sections, it is fundamentally an important issue to elucidate how detonation fails and re-initiates in such a tube. In the present study experiments and numerical simulation are performed to investigate mechanisms of failure and re-initiation of detonation propagation in obstacled tubes. First of all, numerical simulation is validated by comparing data with experiments to analyze propagation mechanism of detonation in obstacled tubes. Two different obstacle configurations, staggered and symmetrical array, are used to see detonation failure and re-initiations. As the result, it is found that detonation failure occurs when it collides with obstacles to become expansion waves and re-initiations behind combustion wave fronts for both staggered and symmetrical cases. Jet ignition promotes fast deflagration transition to detonation in the symmetrical obstacle configurations.

Behavior of pressure waves generated due to a laser ablation of a metal plate in water has been investigated with shadowgraph technique and measurement of their pressure histories. A second harmonic radiation of a Q-switched Nd:YAG laser (wavelength; 532 nm, pulse duration (FWHM); 7 ns) was focused onto a water-immersed plate made of type 304 stainless steel (SUS304). The plate thickness was 0.1 mm, 1 mm and 10 mm, and the laser energy was varied from 49 to 470 mJ. High-pressure ablation plasma was generated on the plate surface by the laser irradiation, and three types of pressure waves, i.e., blast wave, transmitted wave and leaky wave, were visualized. The blast wave, which was directly driven in water by expansion of the high-pressure plasma, propagated as an-almost-hemispherical wave without being influenced by the plate thickness. Behavior of other waves was influenced by the thickness. In case of 1-mm and 10-mm-thick plates, the transmitted waves were emitted as a result of transmission of pressure waves repeatedly propagating between the plate surfaces. Their frequency was consistent with a round travel period through the plate thickness. For the thick plate, the leaky waves, which were caused by longitudinal and Rayleigh or transversal waves propagating along the plate surface, were observed. Especially, leaky wave produced by Rayleigh or transversal wave had a width approximately the same as a spot diameter of the laser irradiation. For the sufficiently thin plate, the leaky waves produced by lamb waves propagating along the plate surface were observed.

Gas generation behavior of gas generating agents have been examined for mixtures using of 5-amino-1H-tetrazole (5-ATZ) as a fuel component together with various types of oxidizers (lithium perchlorate LiClO₄ (LP), potassium perchlorate KClO₄ (KP), sodium nitrate NaNO₃ (SN), potassium nitrate KNO₃ (KN), strontium nitrate Sr (NO₃)₂ (SrN), and copper(II) oxide (CuO) ), through deflagration test inside a closed 4 liter vessel. As a result, the degree of pressure gradients were in the order of LP > KP > SN > KN > SrN > CuO. Meanwhile, temperature gradients inside the vessel were in the same order. It was found that 5-ATZ/SN and 5-ATZ/KN mixtures’ pressure gradients were larger and their generated gas temperature were lower than those of 5-ATZ/SrN mixture.

Fundamental jet performance tests of linear shaped charges (LSC) were conducted to evaluate their jet penetration behavior. The criteria used for these tests were based on penetration tests for conical shaped charges (CSC). Photos of the aluminum-sheathed LSC jet taken by using flash X-ray confirmed the jet velocities to be about 2,400m・s^-1. The steel plate penetration tests uses steel plates, insulated sheets, a pulse generator and a digital oscilloscope. The penetration velocities of aluminum- and lead-sheathed LSC against steel plates were calculated to be less than 1,000 m・s^-1 at a maximum region. These proposed testing methods are very useful for improving the performance of LSC.

In order to establish safe, inexpensive, and effective laboratory experimental technique for simulating the behavior of shock waves generated by large-scale explosion, an experimental investigation of shock waves propagation created by the explosion of a micro-charge, Silver-azide with 10-mg of mass, inside the 50th-scaled model with complicated closed-cell structure is reported. Comparing the relationship between overpressure and scaled-distance by the micro-charge with by TNT, we have evaluated that the scaled-law is also established for the micro-charge explosion as same as for large-scale explosion. The TNT equivalence ratio for the micro-charge has been estimated to be 0.31. Visualization of shock waves propagation inside the model have been carried out using double-exposure holographic interferometry equipped with a pair of 1-m-diameter parabolic mirror. Both overpressure measurements over walls inside the model and visualization results indicate that overpressure inside closed-space values more than 10 times as large as at open-space. The fact that muti-refrection of shock waves inside the model gives high-frequent overload to the structure has been shown.