Takuma Endo

• Hiroshima University

In fast ignition laser fusion, electron beam guiding with a kilo-tesla magnetic field has been proposed to avoid divergence of the beam, which significantly enhances the core heating efficiency. In addition to beam guiding, magnetic fields affect electron heat conduction and alpha particle energy transport. The objective of this study is to estimat...

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...

The effects of different mole fractions of hydrogen and carbon dioxide on the combustion characteristics of a premixed methane–air mixture are experimentally and numerically investigated. The laminar burning velocity of hydrogen-methane-carbon dioxide-air mixture was measured using the spherically expanding flame method at the initial temperature a...

Ignition delay times (IDTs) and laminar flame speeds (SL) of C9H20 (nonane) isomers are systematically investigated. IDTs of normal nonane (n-C9), 2-methyloctane (2mC8), 2,4-dimethylheptane (24mC7), and 2,2,4,4-tetramethylpentane (2244mC5) are experimetally obtained by a shock tube facility and numerically simulated by a chemkin 0-D reactor model....

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 effect of laser ignition on the deflagration-to-detonation transition (DDT) was experimentally investigated. Explosive gas, which was 0.87[(1/4)C2H4+(3/4)O2]+0.13N2 contained in a smooth-wall tube at 100 kPa and approximately 20 °C, was ignited by a 1064-nm 12-ns laser at either 8 or 88.8 mm from the closed tube end connected to the gas-feeding...

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...

The self-similar propagation of expanding spherical flames in lean hydrogen–air mixtures at elevated pressure was experimentally investigated using a dual-chamber apparatus with the quartz windows that enabled observing a flame radius of up to 110 mm. The flame images of the fully developed cellular structure were recorded, and the largest values o...

The kilo-tesla-class converging magnetic field effects on the core heating properties and the energy and duration of relativistic electron beam (REB) required for ignition in fast ignition laser fusion has been evaluated by parametric 2D hybrid simulations where a uniformly compressed DT core with ρ = 300 g/cm³ is heated by REB with TREB = 3 MeV, I...

The minimum explosible concentration (MEC) and flame propagation behaviors of propane/L-leucine powder hybrid mixtures were experimentally investigated. The results of the experiment demonstrated that the MEC values decreased as the propane concentration increased. Additionally, the findings of the analysis proved that the flame propagation limitat...

We present a systematic approach how to characterize the dynamics of a laser-produced Au plasma, generated with a commercial Joule-class laser system. By means of our diagnostic methods, we identify the dominant ionic species within the water-window spectral region, as well as the radiated energy, the x-ray emission duration and the total dimension...

Herein, the ignition characteristics, including the minimum ignition energy (MIE) and minimum explosible concentration (MEC), of amino acid powders (L-leucine, L-valine, L-threonine, L-alanine, and L-serine) were experimentally investigated. The MIE and MEC values of branched-chain amino acid (BCAA) powders were much lower than those of the other p...

A high operating frequency of a pulse detonation engine is required to increase the thrust-to-engine weight ratio or thrust density. The semi-valveless pulse detonation cycle (PDC) proposed by Matsuoka et al. (2017) can achieve a high operating frequency exceeding several kilohertz. For achieving a higher operating frequency close to the upper limi...

In this study, two critical Péclet numbers, Pe c , for the onset of cracks on the flame surface, and, Pe cl , for the onset of fully developed cellular flame leading to flame acceleration, of hydrogen–air flames were experimentally evaluated. The dependency of Pe cl on Ma b , the Markstein number for flame speed, and Ka cl , the critical Karlovitz...

To generate bright water-window (WW) soft x rays (2.3–4.4 nm), gold slab targets were irradiated with laser pulses (1064 nm, 7 ns, 1 J). Emission spectroscopy showed that the introduction of low-pressure nitrogen enhanced the soft x-ray yield emitted from the laser-produced Au plasma. The intensity of the WW x-ray transported in a 400-Pa N 2 atmosp...

In this study, Minimum Ignition Energy (MIE) and Minimum Explosible Concentration (MEC) of L-isoleucine and glycine powder with two different particle size distributions were experimentally investigated. The experimental results showed that the values of MIE and MEC of L-isoleucine powder were lower than those of glycine powder. The pyrolysis and t...

The purge layer of a semi-valveless pulse detonation cycle (PDC) needs to be minimized for operating at a gas-dynamic upper frequency limit. Therefore, it is essential to better understand the process of burned gas backflow for minimizing the purge layer thickness. The flow field of the semi-valveless PDC was visualized to illustrate the movement o...

To develop laser-ignition technology, transparent glass plates were artificially sooted and irradiated repetitively by laser from the front (sooted) and back sides separately. Generally, the back-side irradiation was more effective at soot removal. However, the cleaning effect was saturated after thousands of laser shots. Although the saturated soo...

We develop two cascade arc plasma sources for application to plasma windows for virtual vacuum interfaces. For windowless vacuum-atmosphere separation, a compact arc discharge source having a channel diameter of 3 mm is fabricated, and an atmospheric Ar thermal plasma is generated. For an alternative differential pumping system, separating low- and...

In accidental gas explosions, flame acceleration owing to cellular instabilities such as diffusional–thermal instability and Darrieus–Landau instability can cause considerable damages, for example, the formation of a strong blast wave. In particular, as the flame scale increases, Darrieus–Landau instability, caused by a density jump, progressively...

The development of cellularity for expanding spherical hydrogen-air flames at elevated pressure, owing to hydrodynamic and diffusional-thermal instabilities was experimentally investigated using high-speed schlieren images. The critical flame radii and critical Peclet numbers at which cracks begin to propagate and for the onset of flame acceleratio...

A compact apparatus to produce arcjet plasma was fabricated to investigate supersonic flow dynamics. Periodic bright–dark emission structures were formed in the arcjets, depending on the plasma source and ambient gas pressures in the vacuum chamber. A directional Langmuir probe (DLP) and emission spectroscopy were employed to characterize plasma pa...

Laser ignition and spark-plug ignition were experimentally compared in high-speed ethylene-oxygen mixture flows of up to approximately 100 m/s. Nd:YAG laser of 12-ns pulse duration and a semi-surface discharge-type spark plug of 1.8-ms discharge duration were used to conduct the experiments with deposited energy of approximately 24 mJ in both cases...

To realize kilohertz and higher frequency of a pulse detonation cycle (PDC), enhancement of deflagration-to-detonation transition (DDT) is necessary. A novel semi-valveless PDC method, in which the inner diameter of the oxidizer feed line is equal to that of the combustor, can increase the pressure of detonable mixture by increasing total pressure...

For examining the ability of laser ignition, a quiescent lean-fuel propane?air mixture was ignited in a constant-volume chamber by a spark induced by a pair of electrodes and an automotive spark driver, a spark induced by focused high-power laser, or a spark induced by focused high-power laser between a pair of dummy electrodes, where the deposited...

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 b...

The motion of a fluid in a valveless pulse detonation combustor (PDC) at an operating frequency of 500. Hz was investigated using a novel PDC, in which the inner diameter of the oxidizer feed line was equal to that of the combustor (inner diameter = 10. mm). Gaseous oxygen was supplied to the PDC in a valveless mode. In contrast, supercritical ethy...

To realize a novel vacuum-atmosphere interface that does not require a large differential pumping system, a robust cascade arc discharge source called a plasma window is constructed and tested for long-term operation. By modifying a test plasma with a direct current discharge, a vacuum interface with a high gas pressure ratio of 1/407 between the d...

A novel method for the operation of a pulse detonation combustor is proposed and demonstrated for realizing high frequencies without using a purging material. In the developed operation method, oxygen is supplied to the pulse detonation combustor in the valveless mode. Fuel, which is supercritical ethylene, is injected into the pulse detonation com...

For improving the laser absorption efficiency in laser ignition, the transmitted laser light was returned to the laser-produced plasma by using a corner cube. In the experiments, the transmitted light was reinjected into the plasma at different times. The laser absorption efficiency was found to be substantially improved when the transmitted light...

Experiments on thermal spray by pulsed detonations at 150 Hz were conducted. Two types of pulse detonation combustors were used, one operated in the inert gas purge (GAP) mode and the other in the liquid-purge (LIP) mode. In both modes, all gases were supplied in the valveless mode. The GAP mode is free of moving components, although the explosive...

For the improvement of the laser-absorption efficiency in laser-induced gaseous breakdown, a corner cube was used to return the transmitted light to the laser-produced plasma. We demonstrated that the laser-absorption efficiency was considerably improved.

A novel method for purging the residual hot burned gas in the cyclic operation of a pulse detonation combustor (PDC) was developed. With this new method, called the liquid-purge (LIP) method, residual hot burned gas is purged by injecting liquid droplets into the PDC. The injected liquid droplets are rapidly vaporized after the combustion of the de...

We developed an arcjet plasma device having a converging and diverging supersonic conical nozzle. Bright and dark emission structures were formed, depending on the gas pressure in the expansion section. In order to understand the mechanism for the formation of the structures, we evaluated the plasma parameters (electron density and temperature) by...

An arcjet plasma generator with a converging and diverging slit nozzle was constructed. This plasma source allowed us to directly observe the arc plasma in the discharge section, which provided useful information about a transition from ionizing thermal plasma to recombining phase. Spatial distributions of the electron temperature and density in th...

A diamond-shaped shock wave was created in a helium arcjet plasma. Visible/ultraviolet emission spectroscopy was used to investigate the condition for the formation of stable shocks and to determine characteristics of the plasma. Dependence of the position of the shock front on the gas pressure in the expansion region was investigated. It was found...

A water-cooled single-tube pulse detonation turbine engine (PDTE) system was constructed using a turbocharger designed for automobiles, where the output of the system was the compression work done by the turbocharger. The PDTE system was operated for more than 10 minutes at the frequencies of 10 and 60 Hz using hydrogen as the fuel and air as the o...

To directly observe an arcjet inside the plasma discharge section, we developed an arcjet plasma device having a converging and diverging slit nozzle. Spectroscopic observations in the directions parallel and perpendicular to the plasma expansion axis were made to examine the characteristics of the arcjet plasma inside the nozzle. Intense continuum...

Initiation and propagation characteristics of a detonation in an extremely narrow gap were experimentally studied using a soot-foil-pattern technique. In the experiments, we used stoichiometric propane-oxygen-nitrogen gas mixtures, where dilution ratio was varied as a governing parameter. A narrow gap, whose height was varied as another governing p...

Initiation and propagation characteristics of detonations in extremely thin channels were experimentally studied using a soot-foil-pattern technique. In the experiments, we used stoichiometric propane-oxygen-nitrogen and hydrogen-oxygennitrogen gas mixtures, where dilution ratio was varied as a governing parameter. A thin channel, whose height was...

Endo et al (2004) applied thermodynamic analysis to a simplified Pulse Detonation Turbine Engine (PDTE) system to estimate ideal performance the theoretical thermal efficiency of a non-compressor type PDTE system is assumed to be 20% to 30% with an ethylene-oxygen mixture Several experimental studies were conducted using a test apparatus composed o...

In the present research, we experimentally verified the partial-fill effect in a multicycle pulse detonation rocket engine. The intermittent thrust of a pulse detonation rocket engine was measured by using a spring-damper mechanism that smoothed this intermittent thrust in the time direction. The intermittent mass flow rates were assessed by gas cy...

An arcjet discharge device with a rectangular converging and diverging nozzle was developed, which allowed us to optically observe high-density plasma inside the anode nozzle Spectroscopic observation along the plasma expansion axis was carried out to examine the characteristics of the arc plasma inside the nozzle Analyzing intense continuum and li...

Multi-cycle experiments on a multi-tube pulse detonation engine (PDE) were carried out. The PDE consisted of four detonation tubes. They were ignited sequentially with the operation frequency of 120-200 Hz (30-50 Hz/tube). The exhaust gas flows from the detonation tubes were combined in a cone-shaped collecting duct, to the exit of which a straight...

The effects of the initiator conditions to the detonation initiation and the impulse of the pulse detonation engine were investigated. White-gasoline-air mixture in the main combustor was detonated by the initiator filled with white-gasoline-oxygen mixture. It was found that a predominant parameter to initiate the detonation of white-gasoline-air m...

A model for estimating the propulsive performance of a partially fueled simplified pulse detonation engine is proposed. The model has two significant advantages: no empirical parameter is required, and the model enables estimation of both the impulse and the duration during which the pressure at the thrust wall remains higher than its initial value...

Performance analyses of pulse detonation rocket engines (PDREs) were numerically studied, focusing on partial-fill effects at ground tests. The initial detonable mixture, inert gas, fuel-fill fraction, equivalence ratio, and initial temperature of inert gas were changed as governing parameters. The simulation results were compared against those of...

The cycle of an ideal pulse detonation engine (PDE) was theoretically analyzed. A PDE was modeled as a straight tube, one end of which was closed and the other end open. A detonation wave was ignited at the closed end and simultaneously started to propagate toward the open end. When the detonation wave broke out from the open end, a rarefaction wav...

The performance of pulse detonation engines was analytically estimated by using a simple model. A pulse detonation engine was modeled as a straight tube. One end of the tube was closed and the other was open, and a detonation wave was ignited at the closed end. One cycle of the pulse-detonation-engine operation was divided into three phases: combus...

Detonation initiation in a liquid-fuel pulse detonation engine (PDE) was experimentally investigated. The PDE at Hiroshima University consisted of an initiator and a main combustor. The initiator was filled with liquid-fuel-oxygen mixture, and the main combustor was filled with liquid-fuel-air mixture. The experiments were carried out with varying...

Solid-state electrochemical reduction was applied for yttria partially stabilized zirconia. The reduction was done by applying a DC voltage to the sample in a vacuum furnace at a temperature range from 400 to 700°C. The sample was reduced since oxygen is released at anode but oxygen is not supplied at cathode in vacuum. The reduced yttria partially...

Described were the overview of the performance-estimation models for a propulsive pulse detonation engine (PDE), and the performance of the actual flight model of a pulse detonation rocket engine (PDRE-FM). As the performance-estimation models, the wave-dynamics model and the thermodynamics model were touched on. Furthermore, the homogeneous-diluti...

The pulse detonation engine (PDE) has recently become recognized as a possible new aerospace propulsion system. The PDE system has high thermal efficiency because of its constant-volume combustion and its simple tube structure. We are now constructing a simple PDE system, an ethylene-oxygen single-tube pulse detonation rocket (PDR), in order to ver...

Performance analysis of the Pulse Detonation Rocket Engine (PDRE) is numerically conducted focusing on partially filled system. Initial explosives, inert gas species, tube fill fraction, and equivalence ratio are chosen as parameters to clarify their effects on the performance of PDRE. The simulation results are compared with previous studies that...

Gas dynamics in a simplified pulse detonation engine (PDE) was theoretically analyzed. A PDE was simplified as a straight tube with a Axed cross section. One end of the tube was closed, namely, this end was the thrust wall, and the other end was open. A detonation wave was initiated at the closed end and simultaneously started to propagate toward t...

Pulse Detonation Engine at Hiroshima University was designed to use the liquid-fuel-air mixture. This PDE consists of the main combustor filled with liquid-fuel-air mixture and the initiator that uses liquid-fuel-oxygen mixture. In the present paper, the effects of the conditions of liquid-fuel-oxygen initiator on the detonation initiation of liqui...

Performance analysis of the Pulse Detonation Rocket Engine (PDRE) is numerically conducted focusing on partially filled system. Initial explosives, inexplosive gas species, tube fill fraction, and equivalence ratio are chosen as parameters to clarify their effects on the performance of PDRE. The simulation results are compared with previous studies...

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...

One-dimensional numerical analyses of pulse detonation engine (PDE) have been performed by numerous workers. In one-dimensional codes, however, it is basically difficult to set adequate boundary conditions at exit plane, although PDE performance depends strongly on the boundary conditions. To evaluate the influence of boundary conditions, we perfor...

How to generate a steady-state detonation around a hypersonic projectile in stoichiometric hydrogen-oxygen premixed gases is studied. The speed of the hypersonic projectiles was beyond the Chapman-Jouguet (C-J) detonation speed. The flowfield around the projectile was visualized by using a gate intensified charge-coupled device camera (single-frame...

Hypersonic projectiles whose speed was beyond the Chapman-Jouguet (C-J) detonation speed, were fired into stoichiometric hydrogen-oxygen premixed gases. The flowfield around the projectile was visualized using a gated CCD camera. A steady-state detonation wave was generated around the projectile. With respect to the flow Mach number behind the wave...

Projectiles were fired at hypersonic speeds into stoichiometric H2-Air and H2-O2 premixed mixtures. The flowfield around the projectiles was visualized using a shadowgraph and a Schlieren technique with a gated CCD camera and a multi-frame camera. We made a comprehensive study of shock-induced combustion and detonation waves around hypersonic proje...

Hypersonic projectiles, whose speed was beyond the Chapman-Jouguet (C-J) detonation speed, were fired into stoichiometric hydrogen-oxygen premixed gases. The flowfield around the projectile was visualized using a gated CCD camera. Around the projectile, a steady-state detonation wave was generated. With respect to the flow Mach number behind the wa...

Hypersonic projectiles were fired into CO-O2 and CO-O2-H2 gas mixtures. For observation of combustion phenomena around the projectiles, we employed a high-speed framing schlieren technique. When we used CO-O2 mixtures as combustible gases, no shock-induced combustion was observed. However, addition of a small amount of H2 into the CO-O2 mixtures en...

We studied the oblique detonation waves around hypersonic projectiles. Projectiles (10 mm diameter, conical nose shape) were fired at hypersonic speeds (2.8 ± 0.1 km/s) into stoichiometric hydrogen-oxygen mixtures (pressure between 10 kPa and 50kPa, at room temperature T = 300.2 ± 1.4 K). The flowfields around the projectiles were visualized using...

Hypersonic projectiles were fired into CO-O2 and CO-O2-H2 gas mixtures. For observation of combustion phenomena around the projectiles, we employed a highspeed framing schlieren technique. When we used CO-O2 mixtures as combustible gases, no shock-induced combustion was observed. However, addition of a small amount of H2 into the CO-O2 mixtures ena...

Projectiles were fired at hypersonic speeds into stoichiometric H2-air mixtures. The flowfields around the projectiles were visualized using a high-speed framing schlieren technique. We comprehensively studied oblique detonation and oscillating combustion phenomena around the hypersonic projectiles, where the varied parameters were the projectile v...

Projectiles were fired at hypersonic speeds into stoichiometric H2-air mixtures. The flow fields around the projectiles were visualized using a multiframe schlieren technique. We made a comprehensive study of oscillating combustion phenomena around hypersonic projectiles with the following variable parameters: projectile nose shape, velocity, and d...

We report the generation of long-life plasmas confined by the heavy shell surrounding a plasma produced by lasers. We also demonstrate the neutron production from shell-confined carbon-deuterium plasmas using a GEKKO XII glass laser system at 1.05 mum and 0.53 mum wavelengths. A maximum neutron yield of more than 108 per shot without an implosion w...

We are devoting ourselves to development of pulse detonation turbine engines system as high-efficiency power generators. This system consists mainly of Pulse Detonation Engine, Shock diffuser and Turbocharger for the vehicle. And since it has water cooling device, this system may operate for a long time. In this present report, the details about th...

As is well known, hydrodynamic instabilities play an important role in inertial-confinement-fusion implosions. Target surface perturbations are imposed, in addition to the original surface roughness, by imprint of laser irradiation nonuniformity. These perturbations may be amplified by rippled shock propagation before the shock transit through the...