Since the detonation wave propagates at high speed (up to 2,000 m/s), the reactant can be converted into a product in a short time. In this article, I show that the detonation combustor has sufficient thrust performance as a rocket engine, and that it has the same thrust performance whether it is an annular shape or a single cylinder shape. It is also shown that the integration of the detonation combustor into the system enables the demonstration test of the sliding system and the propulsion test of the space flight system. Finally, I introduce the use of liquid propellant and the cooling method and clustering of single cylinder detonation combustor as important technical issues for practical use.
Japan Aerospace Exploration Agency has now been working to understand detailed morphologies of detonation wave encountered in Rotating Detonation Rocket Engine (RDRE), which is one of the most potential engine concepts for light-weight and compact rocket system, and to investigate how they influence thrust performance and operational stability of the engine. Combustion experiments of an annular RDRE propelled by gaseous methane and oxygen were conducted to measure thrust performance and to visualize detonation propagation and CH*/OH* chemiluminescence, from which specific thrust was revealed close to the theoretical value with stable propagation modes, and without throat contraction. CH* chemiluminescence also indicated deflagrative combustion anchoring at the injection plane, which could partly explain the performance degradation in a configuration with throat. Experimentally observed detonation velocity ranged 45-75 % of Chapman-Jouguet (C-J) velocity, which was partly confirmed to be induced by incomplete mixing from the results of two/three-dimensional simulation employing detailed chemical kinetics. However, numerically predicted velocity was higher by several tens of percentage, indicating potential influence of thermal/viscous loss to the confinement. Overall, physical insight was achieved into non-ideal behavior of detonation including strongly curved wave front induced by incomplete mixing and our findings emphasizes a need for better mixing techniques to achieve more ideal characteristics of detonation.
In this article, thermal spray is explained first. The fundamental processes included in thermal spray and the classification of thermal-spray methods are described. Next, the detonation mode of combustion, the pulse-detonation technology, and the properties of the pulse-detonation thermal spray are explained. Also, some detonation guns for thermal spray developed in the past are introduced. After that, thermal-spray experiments carried out on a daily basis in Hiroshima University are introduced. Additionally, new technologies developed for the pulse-detonation guns for thermal spray in Hiroshima University are described. Finally, the past development and present status of the pulse-detonation technology are briefly discussed by using the Hype Cycle.
Underwater shock wave, generated by the imploding detonation of propane-oxygen mixture, was applied for sterilization and extinction processing of microorganisms. We filled the water containing microorganisms into a stainless steel pipes having inner diameter of 10.9 mm, 49 mm and 60 mm, and transmitted the underwater shock waves which have the maximum pressure of about 100MPa. As microorganisms of the treatment experiments, Coliform group, Microcystis species, Artemia salina and Heterosigma akashiwo were used. We found that the case of 2 shots of the underwater shock wave for Coliform group can sterilize about two digits compared with initial counts and the case of 6 shots of the underwater shock wave can sterilize completely. We found that the mortality rate of Microcystis species increases gradually with the increase in the number of times of shock processing. Although the maximum mortality rate of Microcystis species was 99.9% in one day after processing, it turned out that it becomes 100% in one week after processing. The mortality rate became small when the value of the consistency of Microcystis species was large. We found that we can completely kill Artemia salina by 5 shots and Heterosigma akashiwo by 1 shot of the underwater shock wave.
Experiments were performed to investigate the deflagration-to-detonation transition (DDT) process in the channel equipped with repeated obstacles. A premixed gas of hydrogen-oxygen was ignited and the DDT process was visualized by using a high-speed video camera with an aid of schlieren optical method. A configuration of the repeated obstacle such as a separation distance, d and a height, h were varied to investigate effects of these parameters on the detonation induction distance (DID) as well as DDT process. Furthermore, the flow-field was visualized by changing the directions of obstacle installation, such as vertical installation and transverse one. The DDT process could be clarified in detail, because the transverse installation of obstacle could acquire the flow-field in depth direction of the obstacle. As a result, it was clarified that the DDT was occurred by highly accelerated flame caused by the interaction between deflagration wave and the vortex-ring behind obstacle. Thus, the vortex-ring generated by the diffraction of compression waves was interacted with the deflagration wave, and this behavior produced a high-velocity deflagration wave through the unburned gas pocket behind obstacle. This high-velocity deflagration wave propagated in the depth direction could be a trigger of DDT onset via local-explosion. The detonation induction distance was also determined by observing a fish-scale pattern on the soot which was typical of the detonation propagation, and the relationship between DID and the configurations of repeated obstacle was also obtained.
Planar laser induced fluorescence (PLIF) is a powerful tool to probe two-dimensional species and temperature distribution in combustion fields. In this paper, the basic principle of laser induced fluorescence (LIF), two-photon absorption LIF (TALIF) for species measurements and 2 line LIF for temperature measurements has been reviewed. Emphasis has been put on technical details in the application of these techniques in two-dimensional flame diagnostics. PLIF measurements of HCHO and OH in cool and hot flames were performed, which provides important information for the study of low-temperature and high-temperature oxidation reactions. Recent progress on extending TALIF to two-dimensional measurements of hydrogen atom was introduced. Conditional 2 line OH-PLIF measurement of temperature distribution was proposed and used in the study of an oscillating flame in micro channel.
Planar laser induced fluorescence (PLIF) is useful tool to investigate flame structure, and a lot of attempts have been made to clarify characteristics of turbulent flames by introducing high repetition rate, multi-species or three dimensional measurements. In this manuscript, evaluations of flame displacement speed by using high speed PLIF, flame front curvature by using multi plane PLIF and chemical species distributions in thin reaction zones by using OH and formaldehyde PLIF are introduced. Experimental techniques have been assessed by using data of direct numerical simulation of turbulent premixed flames. Also a part of recent progresses in the techniques of PLIF for above topics are briefly introduced and discussed.
Effects of the ambient temperature on oxidatively degraded methyl oleate (OME) droplet combustion were studied by conducting droplet combustion experiments at high temperature (750 ℃) and room temperature. Degraded OME was prepared with the Rancimat method, where a fuel sample was kept at 100 ℃ for 24 hours. Droplet combustion experiments were conducted at atmospheric pressure in air or CO2 rich condition under microgravity. At both high and room temperature, puffing was observed during the droplet combustion for degraded OME, which may be due to the difference of volatilities between oxidation products. At high temperature, after a bubble was formed inside the droplet, it expanded abruptly, resulting in a droplet disruption. Although the droplet disruption accompanied mass loss of the droplet, a part of the fuel was remained on the suspender and continued burning. The remained fuel also showed bubble formation and disruption periodically until the end of the droplet lifetime. On the other hand, at room temperature, ejections of fuel vapor and tiny droplets were observed intermittently. This indicates that puffing occurred on the droplet surface because the surface was heated by a Fe-Cr wire to ignite the droplet. In addition, at room temperature, puffing stopped and the droplet began to burn quiescently at the latter stage of burning, which is probably because only high-volatile components were injected by puffing and a large amount of low-volatile ones were remained in the droplet. Furthermore, effects of CO2. on puffing were studied at room temperature. However, no effects on similarity and the beginning time of puffing were observed. This indicates that droplet was heated approximately to the limit of superheat by a Fe-Cr wire, and effects of flame temperature were negligible
Generally in industrial gas fired boilers, maximum supply pressure of gas fuel at the nozzle is set from 70 to 130 kPa(G), because undesirable behaviors such as combustion noise, oscillation or flame instability occur in boilers under operation at high supply pressure conditions. These facts are widely known as a kind of ‘common sense’ among boiler engineers. However, if the pressure of gas fuel can be increased, many merits are acquired from a view point of industrial design. For example, gas fuel flow control system can be simplified, and smaller size gas pipes for high pressure gas fuel are effective for cost reduction. In the present study, influence of gas supply pressure at the burner on flame stability are evaluated by combustion experiments, and then discussed on the basis of numerical simulation. Furthermore, effects of the developed gas nozzle on low oscillation are disclosed. Center firing gas burners equipped with the developed nozzle under operation at high pressure of 410 kPa(G) were applied to the actual industrial boiler whose steam production capability was 90 ton/h. As the results of wide-range operation tests, high combustion efficiency and stable boiler performance were verified.