Teruo Yoshihashi

Diffusion flame stabilized on a porous plate in a parallel airstream

Effects of an obstacle on the structure and stability of a laminar diffusion e ame established on a porous plate in a parallel airstream have been investigated experimentally. The obstacle, a backward-facing step or a rectangular cylinder, is located upstream of the porous plate through which gaseous methane is injected uniformly. Structures of the e ame are elucidated by the direct and schlieren photography. Flame shapes are described and stability diagrams are plotted for the freestream velocity and the fuel injection velocity, which are discussed with e ow structures.

A high-speed photographic study of the transition from deflagration to detonation wave

Experiments were conducted to investigate the DDT process of the oxyhydrogen gas in the rectangular detonation tube of 3 m long. The repeated obstacle was installed near the ignition plug and the effects of the obstacle on the DDT process were investigated. The behaviour of the combustion and detonation wave were visualized utilizing Imacon high-speed camera with the aid of Schlieren optics.As a result, DDT process was visualized, i.e. (i) multiple shock waves were induced by the expanding combustion wave, because the combustion flame played a role as a piston and compressed the unburned gases. (ii) The acceleration of the combustion wave was occurred and the distance between the shock wave and the combustion flame became shorter. (iii) Eventually, the local explosion was occurred and cause overdriven detonation wave to propagate at the velocity of about 3 kms−1.

A study on DDT processes in a narrow channel

One of the fundamental problems to be studied on a Pulse Detonation Engine (PDE) is the deflagration to detonation transition (DDT). For the development of the PDE, it is essential to shorten a distance of detonation transition that is called a detonation induction distance (DID). We carried out an experimental study of DDT in a narrow channel with height of 1-5mm by using pressure and soot track records in oxyhydrogen mixtures. Detonation limits was discussed according to height of tube and equivalence ratio. According to pressure history and soot track record, detonation velocity, DDT process and DID was discussed. Over driven detonation and attenuated detonation was observed in the narrow channel. DID that measured by soot track record applied to experimental formula for oxygen and hydrogen system.

A Study of the Initiation Process of Dust Layer Detonation

Detonations of dust-oxidizer gas systems have recently attracted considerable attentions because of their possible role in explosion hazards of combustible dusts such as corn starch, wheat, aluminum, coal and so on. In these detonations in a heterogeneous system, the structure of the reaction zone behind the shock front may be very complex because physical processes such as momentum, heat and mass exchanges between particles and the gas phase are coupled with chemical processes. The present study aims to elucidate the initiation process of dust layer detonation using corn starch in a horizontal tube. Experimentally, the behaviour of shock waves and reaction waves are elucidated in the initiation process of dust layer detonation.

Instabilities of Flame Front Propagating in a Constant-Volume Chamber. Effects of Dilution by Inert Gases.

The present work is a continuation of our previous study to obtain a fundamental understanding of instabilities of a flame front propagating in a constant-volume combustion chamber. In this report, attention was focused on effects of dilute gases on this phenomenon. Experiments were conducted in a disk-shaped constant-volume chamber of 100 mm diameter and 30 mm height with a window. The flames were visualized by instantaneous schlieren photography. It was found that the instabilities arise for lean hydrogen/oxygen mixtures diluted with argon as well as helium, wich can be explained as thermodiffusive effects. For methane or propane/oxygen mixtures, the diluent plays an important role. Using argon as a diluent renders the flame unstable in accord with the thermodiffusive theory, while using helium renders it stable which cannot be explained by this theory. For these mixtures diluted by helium, initial disturbances might be suppressed by viscosity.

The initiation process of heterogeneous detonation waves (Kerosene spray and film)

Experiments were performed on the initiation of a heterogeneous detonation wave propagating through mixtures of liquid fuel and a gaseous oxydizer. The liquid fuel tested was kerosene in the forms of a spray and a film attached on tube walls. The ignition was performed by oxyhydrogen detonation. The effects of the content of oxygen in the oxydizer were investigated. It was found that for pure oxygen as an oxydizer, detonation waves were established by the combustion of kerosene, but for an oxydizer with a small amount of oxygen, only low Mach number shock waves with combustion waves following after were formed. For the former case, the ignition was initiated by the strong shock wave front, but for the latter case, the liquid phase seemed to be ignited by the combustion products of the initiator gas.