Toshi Fujiwara

Pressure History at the Thrust Wall of a Simplified Pulse Detonation Engine

Gas dynamics in a simplified pulse detonation engine (PDE) was theoretically analyzed. A PDE was simplified as a straight tube with a fixed 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 the open end. When the detonation wave broke out from the open end, a rarefaction wave started to propagate from the open end toward the closed end. This rarefaction wave was reflected by the closed end. By considering this rarefaction wave to be self-similar in the analysis of the interference between this rarefaction wave and its reflection from the closed end, we analytically formulated the decay portion of the pressure history at the closed end (thrust wall) without any empirical parameters. By integrating the obtained pressure history at the thrust wall with respect to time, important performance parameters of a PDE were also formulated. The obtained formulas were compared with numerical and experimental results and agreed with them very well.

Flow features of shock-induced combustion around projectile traveling at hypervelocities

The shock-induced combustion with periodic unsteadiness around a projectile fired into hypersonic flows is numerically studied. The mechanism of periodic unsteadiness is clarified using an x-t diagram of the flow variable on the stagnation streamline. The frequencies of the periodic unsteadiness obtained quantitatively agree with the experimental observations. The key parameters which are responsible in triggering the instability and in determining the frequency of the periodic unsteadiness are discussed by using the time integration of the species equations. The result indicates that the key parameters are induction time, heat release, and concentration of the heat release. The induction time is a key parameter for the frequency of the unsteadiness. The concentration of heat release is important for the unsteadiness itself. Total energy creating the compression waves depends on the amount of heat release itself. All of these features are recognized in a simple zero-dimensional analysis.

Numerical investigation of oscillatory instability in shock-induced combustion around a blunt body

The basic characteristics of oscillatory instabilities of shock-induced combustion around a spherical projectile flying at hypersonic speed is investigated on the basis of numerical simulation using a two-step chemical reaction model. A series of simulations is conducted to understand the mechanism of these oscillatory instabilities. The oscillatory instabilities are clearly observed when the projectile radius is about 7.5-10 times the induction length

Chapman-Jouguet Oblique Detonation Structure Around Hypersonic Projectiles

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 e owe eld around the projectile was visualized by using a gate intensie ed charge-coupled device camera(single-frame schlieren picturesand OHradical self-emissionimages ). Threeparameters are varied:1 ) the projectile e ight length from diaphragm rupture location, 2 )the initial pressure of mixture below/above the critical pressureforsteady detonation initiation around a hypersonicprojectile, and3 )theprojectilespeed.Atthepressure condition below the criteria, the detonation structure is composed of three different shock and detonation waves, which appear just after a diaphragm rupture and evolve in time: an overdriven bow detonation wave, a strong detonation wave, and a diffracted shock wave. Their propagation after diaphragm rupture is investigated, and it is found that the C ‐J detonation wave moved away from the projectile and only a reactive bow shock wave remained around projectile far away from the diaphragm. At the pressure condition above the criteria, a steady oblique detonation wave was generated around the projectile as soon as the projectile broke the diaphragm. In this steady-state detonation-wave case, with respect to the e ow Mach number behind the wave front, the whole detonation wavewas divided into fourparts: 1 )strong overdriven detonation wave, 2 ) weak overdriven detonation wave, 3) quasi-C‐J detonation wave, and 4 ) C‐J detonation wave. It has been found that a rarefaction wave is generated at the projectile shoulder and that curvature of the wave has a signie cant effect on the structure of the detonation wave.

Diagnostics of an argon arcjet plume with a diode laser

The diode-laser absorption technique was applied for simultaneous velocity and temperature measurements of an argon plume exhausted by an arcjet. The Ar I absorption line at 811.531 nm was taken as the center absorption line. The velocity and the temperature were derived from the Doppler shift in the absorption profiles and the full width at half-maximum of the plume absorption profile, respectively. From the measured plume velocity and temperature, the total enthalpy of the exhausted plume, the thrust efficiency, and the thermal efficiency of the arcjet were derived, and the performance of the arcjet was examined. The results are demonstrated to agree with results derived by other methods, and the technique can be applied to the measurement of other arcjet systems without much modification.

Sensitivity Analysis of Rotating Detonation Engine with a Detailed Reaction Model

D compressible Euler equations are used for hydrogen/oxygen rotating detonation engine (RDE) to perform a sensitivity analysis for rotating detonation conditions. First of all the used program was compared with the experimental data obtained by Kindracki and Wolanski. The computational average pressure just after the injection of mixture is similar to that of experimental one; about 0.2 to 0.4 MPa. Sensitivity analyses show that the inlet pressure, Mach number, and temperature have a significant effect on rotating detonation device performance. The results show a narrow window of the inlet conditions for the stable operation while achieving high performance of rotating detonation engine.

Detonation Limit Thresholds in H2/O2 Rotating Detonation Engine

The rotating detonation engine (RDE) is a new engine system using detonation, which may provide a higher performance and smaller and simpler design in comparison with the pulse detonation engine (PDE) and other traditional engines. However the research on RDE stands just at the first step now. The authors perform a numerical analysis to understand about RDE in terms of features of rotating detonation and its propagation limit. The lower threshold pressure of detonation limit was 2.6 MPa and the upper threshold pressure of detonation limit was 7.1 MPa. The engine performance analysis shows that the maximum mixture based specific impulse (I spm ) was about 440 s, which is comparable with that of the present typical rocket engine.

Influence of main flow inlet configuration on mixing and flameholding in transverse injection into supersonic airstream

Abstract A numerical study on mixing and combustion of hydrogen transversely injected into a main airstream is performed, by solving two-dimensional full Navier–Stokes equations. The focus of this paper is to study the means of increasing the mixing and combustion efficiencies, and the flameholding capability for supersonic propulsion application by changing the main flow inlet configuration. Accordingly, the following three inlet configurations are considered: (1) A finite parallel flow with backward-facing step; when the main flow enters through a finite-width inlet of wall, the wall under the inlet acts as a backward-facing step. (2) A finite parallel flow without step; although the inlet configuration is identical to Case 1, there is no step under the inlet. (3) The infinite parallel flow; the main flow enters throughout the left boundary. As combustion modeling we have used full chemistry between hydrogen and air consisting of eight species (H 2 , O 2 , H, O, OH, H 2 O, HO 2 , H 2 O 2 ) and 19 reactions shown in Table 1 . The effects of inlet configurations are evaluated by calculating mixing and combustion efficiencies. The results show that a finite parallel flow with backward-facing step (Case 1) causes the highest penetration and mixing of hydrogen and provides the best flameholding region between the downstream injecting slit and backward-facing step. The effects of high penetration and mixing on combustion, and characteristics of the reacting flowfields are studied. The finite parallel flow configuration (Cases 1 and 2) makes the bow shock steeper and eventually increases the diffusion of hydrogen in the downstream of injecting slit.

Numerical Analysis of First and Second Cycles of Oxyhydrogen Pulse Detonation Engine

In the present study, numerical analysis of pulse-detonation-engine (PDE) cycles such as combustion, exhaustion, and fuel-injection phases is performed. A numerical scheme that is second-order accurate in time and space, MacCormack-total-variation-diminishing scheme, was used to solve the Navier-Stokes equations, where a simplified two-step chemical reaction model is introduced. The dependence of fuel-injection time on 1) the opening width of intake port, 2) reservoir pressure, and 3) injection angle is studied. Through the numerical analysis of PDE-cycle operation, the time required for each phase is estimated for each model PDE; the dependence on PDE tube length and the time required for PDE operation are studied. The performances (such as impulse and thrust density) of four straight model PDEs that have different tube lengths are estimated and compared with the theoretical result of Endo-Fujiwara analysis. The useful formula for impulse per unit area, which is similar to the expression in the theoretical analysis, is derived from the numerical analysis.

Numerical Analysis of Threshold of Limit Detonation in Rotating Detonation Engine

Rotating Detonation Engine (RDE) is a new kind of detonation engine, which may provide a high performance with a smaller and simpler system than the traditional ones. In order to optimize RDE system, the threshold of detonation limit must be studied for its best design and its best run. In this paper, the following four aspects are discussed: (1) what will be happen to the rotating detonation li mit when the computational area is doubled; (2) what will be happen to rotating detonation when the ignition energy is increased; (3) what will be happen to specific impulse (Isp) when the ignition energy is increased. The results show that the lower detonation limit gets the computational area effct, but the upper one does not. The max specific impulse of Ispf is about 4000 s and that of Ispm is about 450 s.