The performance of an idealized pulse detonation turbine engine (PDTE) was thermodynamically analyzed. In the analysis, both of detonable and inert gases were dealt with as the working media taking account of the differentiae of a PDTE against a conventional gas turbine engine utilizing isobaric combustion. Further, the thermodynamic states of the working media at the inlet of the turbine were estimated. As an example, the performance of a hydrogen-fueled PDTE was calculated. By comparing the performances of internal combustion engines utilizing detonation, isochoric combustion, and isobaric combustion, it was shown that a PDTE has a potential for being a higher-performance engine than a conventional gas turbine engine utilizing isobaric combustion.

Analogy between wedge-induced steady oblique detonation and one-dimensional unsteady piston-supported detonation is investigated based on a series of simulation results. The simulations are carried out by one and two-dimensional Euler Equations. Four types of wave structure of the wedge-induced oblique detonation appear in the simulation results. Those structures are basically the same as those of the piston-supported detonation, except for the type having the triple point on the oblique detonation wave. The reactant mass fraction history on the piston surface agrees well with that on the wedge wall in all types. A series of simulations of the one-dimensional piston-supported detonations varying activation energy, heat release, and piston speed are carried out in an attempt to understand a dominant parameter determining of the wave structure. We focus on reaction intensity as the dominant parameter. The reaction intensity, which is newly proposed as the ratio of the induction to total reaction time, represents the characteristic of the wave structure of the detonation. The reactant mass fraction history on the piston surface of the piston-supported unsteady detonation gives the induction and total reaction time. The reaction intensity of the piston-supported detonation classifies the wave structures in one-dimensional piston-supported detonation, and agrees well with that of the wedge-induced detonation.

It is essential to understand gas leakage/combustion phenomena precisely in order to find out the rational security measures of LP gas. These phenomena can not be clarified for all conditions by experimental approach, because the phenomena are complicated and depend on various physical and chemical factors. Thereupon, the practical total evaluation system was developed, in which the series of phenomena including leakage, dispersion, combustion, structure strength and fragment scattering of real scale were analyzed on the basis of recent development of the computer and computational science. The appropriateness of the analyzing method was examined by comparing the results of the simulation with those of the real scale experiments.

Pulse detonation engine (PDE) holds promise to increase performance of air breathing propulsion systems by taking advantage of high cycle efficiency due to constant volume heat addition characteristics of detonative combustion. Currently, PDE is an active research topic with experimental developments reported by many researchers. Several of these investigations attempted multiple cycle experiments, however, it is uncertain as to whether detonations were produced on a regular basis in these tests. The experimental results for development of hydrogen-fueled pulse detonation engine are discussed in this paper. Although characteristics of premixed detonation of hydrogen-air mixture are well investigated, characteristic of detonation in non-premixed or partially premixed gases has not been studied yet. As the first step, a single cycle test was conducted to research of deflagration to detonation transition (DDT) of hydrogen / air directly injected to combustion chamber. As the second step, a multiple cycle test up to 10 Hz was conducted to demonstrate the feasibility of multiple cycle operation of PDE. Thrust wall pressure, tube wall pressure along the tube, and ionization current were measured. Sharp pressure spike was observed. It shows that the overdriven detonation wave was formed at thrust wall. The injection systems were also studied for single injection and double injection. It should be noted that, although the detonation waves could not be initiated instantaneously at the igniter, the resulted impulse on thrust wall could be improved by double injection system as compared with single injection system.

Numerical simulations of one-dimensional and two-dimensional detonations have been performed with two-step chemical reaction mechanisms for a stoichiometric hydrogen-air mixture at initial conditions of 42.7 kPa and 293 K. One-dimensional overdriven detonations are initiated by solutions of steady ZND detonations for degree of overdrive 1.1-2.0, and by shock compression with a piston for degree of overdrive 1.2. Shock pressure histories developing from steady detonations indicate high frequency oscillations for degree of overdrive 1.6-2.0 and low frequency oscillations for 1.1-1.5. In the piston initiation case, post-shock pressure is temporally led in a highly overdriven condition by penetration of an interior detonation and is gradually attenuated by incident rarefaction waves. In this decaying process of the overdriven detonation, both high frequency and low frequency oscillations are observed for the fixed degree of overdrive 1.2. The relation between the shock pressure and the oscillation characteristics such as period and pressure amplitude agrees with results of steady detonation initiations. An initiation process of a two-dimensional detonation from high pressure and temperature conditions is also numerically investigated. Oscillation characteristics on the center line of the cell in two-dimensional detonation indicate a similar transition to one-dimensional detonations in the decay process of initial overdriven conditions but do not depend on the shock pressure very much.

The behaviors of deflagrations initiated near the center of 1.5 m3 hydrogen-air clouds were observed in a field experiment. The equivalence ratio of gas mixtures was varied in the range from 0.5 to 4.0. The corresponding changes of flame spread size, flame propagation velocity, and sound noise level were measured. In fuel lean cases, spherical flames were observed, while in fuel rich cases, the spherical flame propagation was followed by a rapid flame spread near the ground surface and a fireball at the top part of the cloud. The high-speed photographs and the records of ion probes show that the flame spread size and the flame acceleration increase with increasing the hydrogen concentration. The propagation velocity of spherical flames are one order of magnitude faster than the laminar burning velocity, and both quantities have a common dependency on the mixture equivalence ratio. The flame velocity reaches the maximum value of about 40 ms-1 near the equivalence ratio of 2.0. The flame velocity in the fireballs reaches 180 ms-1 at the maximum. The sound noise level increases with increasing equivalence ratio.