Performance analysis of experimental‐scale scramjet engine driven DCW‐MHD generator

Numerical analyses of the experimental‐scale scramjet engine driven magnetohydrodynamics generator implemented in the Hypersonic Vehicle Electric Power System project have been carried out to clarify plasma behaviors and power generation characteristics. Three‐dimensional numerical analyses have been performed under the two inlet conditions: one is the uniform inlet temperature condition, and the other is the nonuniform inlet temperature condition. Under the nonuniform inlet temperature condition, the generator performance approximately agrees with the experimental result. The tendency of the voltage loss is also reconstructed near the power takeoff electrodes though the voltage loss is smaller than that observed in the experimental result. The electric power output under the nonuniform inlet temperature condition is 40% smaller than that under the uniform inlet temperature condition. This is because the ratio of the Joule dissipation to the work by the Lorentz force increases owing to the decrease of active generator region as the current concentrates in the high‐temperature region when the inlet temperature nonuniformity is considered. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Performance analysis of self‐excited pulsed MHD power systems

Performance characteristics of self‐excited pulsed MHD power systems are investigated with one‐dimensional time‐dependent calculations using a gas–liquid two‐fluid model. First, the Russian pulsed MHD power system “Pamir‐3U” is analyzed. The result of numerical simulations of hot‐fire tests shows good agreement with the experimental data, confirming the validity of the mathematical model. Performance analysis of Pamir‐3U reveals that the power output is approximately constant with the variation of load resistance, while the ballast resistor consumes a large amount of electric power. It is also shown that the system has been optimally designed to supply a large load current. Next, a new system yielding larger power output is proposed and analyzed. The obtained characteristics show that the new system can provide the maximum power output of 25 MW, which is 10 MW larger than that of Pamir‐3U. © 2000 Scripta Technica, Electr Eng Jpn, 132(3): 30–37, 2000     

Plasma behavior in a non‐equilibrium disk MHD generator with a spatially non‐uniform seed fraction

The influence of azimuthal non‐uniformity of the seed fraction on plasma structure and performance in a non‐equilibrium disk MHD generator is investigated with a two dimensional r–θ numerical simulation. It is found that a locally high seed fraction causes mainly non‐uniformity of gas‐dynamical properties, whereas a locally low seed fraction develops a non‐uniform plasma. Both locally high and low seed fractions reduce generator performance considerably. These results suggest a spatially uniform seed fraction should be required for high power generation. ©1999 Scripta Technica, Electr Eng Jpn, 126(4): 48–54, 1999     

Numerical simulation of blow‐down closed‐cycle disk MHD generator

Numerical simulations of the closed‐cycle disk MHD generation experiment with Tokyo Institute of Technology's Fuji‐1 blow‐down facility are performed. In the calculations, the r–z two‐dimensional time‐dependent simulation code developed by the authors that can take the effect of water contamination into account is used, and the experimental conditions of Run A4109 operated by Disk‐F4 generator are selected as the numerical conditions. When the water contamination is the lowest level realized in the experiments, the simulation results coincide with the experimental results reasonably well, though there exist some discrepancies caused by inaccuracy of used basic plasma parameters, limitations of the two‐dimensional approximation, and so on. The voltage–current curve is almost linear, indicating that the MHD interaction is relatively weak and the flow field is mainly determined by the back‐pressure. The increase of the water contamination level results in decreased seed ionization rate at the generator channel inlet, leading to the steep deterioration of the generator performance. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 46–54, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10335     

Three‐dimensional numerical analysis of a liquid metal MHD generator

Three‐dimensional numerical analysis of a liquid metal MHD generator has been carried out. The three‐dimensional structures of the electromagnetic field and fluid flow in the MHD generator have been clarified, and the effect of the electrode width on the performance has also been examined, taking account of the current flow in the electrode. Structures of the electromagnetic field and fluid flow are complicated owing to the three‐dimensional current flow, induced magnetic field, and Lorentz force. The highest performance is found to be obtained when the width of the electrode is equal to that of the generator. The performance predicted from three‐dimensional analysis is somewhat lower than that from two‐dimensional analysis because of the larger input power. The increase in the input power is attributed to the increase in Lorentz force caused by less reduced magnetic flux density and to the additional friction loss on the insulator walls (x?y plane). © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(3): 19–26, 2007; Published online in Wiley InterScience ( www. interscience.wiley.com ). DOI 10.1002/eej.20282     

Stabilization analysis of commercial‐scale subsonic diagonal‐type MHD generator considering loading conditions

In previous research on subsonic diagonal‐type MHD generators, the authors have proposed a conceptual design with relatively low Mach number in order to stabilize the MHD generator of commercial scale and have shown that the MHD generator works stably under constant‐current loading condition. In the present paper, effects of loading conditions on stability of the MHD generator are examined. A channel‐length scale linear stability analysis and time‐dependent calculations are carried out, where both gasdynamical boundary conditions and loading condition are taken into account. These analyses show that the MHD generator behaves stably under various loading conditions such as constant‐voltage loading condition and ohmic loading condition. Then the stability of the MHD generator connected with an ac power system is also analyzed by time‐dependent calculations. The analysis shows that the MHD generator stably provides the rated power to the ac power line. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 16–24, 1999     

Behavior of magneto‐acoustic waves in a nonequilibrium subsonic disk MHD generator

The behavior of magneto‐acoustic waves in a nonequilibrium subsonic disk MHD generator was examined. The solution of the sixth‐order dispersion relation obtained by linearizing the set of MHD equations suggested that a magneto‐acoustic wave which propagates at a velocity of u_r ? a(u_r: radial fluid velocity, a: sound velocity) should be damped in subsonic flow. From time‐dependent quasi‐one‐dimensional simulations, it was verified that the pressure disturbance in the subsonic generator was damped at approximately the same rate as the value predicted by the linear theory. From a simplified analytical model, the mechanism of magneto‐acoustic instability with fully ionized seed was discussed, and the damping criterion for the magneto‐acoustic wave was clarified. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 20–26, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10108     

Analysis of performance characteristics of pulsed MHD generator with gas–liquid two‐phase flow

A preliminary analysis of two‐phase flow in the pulsed MHD generator Pamir‐3U is carried out. The two‐fluid model for dusty gas flow is applied to treat the two‐phase working body which consists of combustion gas and liquid particles of Al₂O₃. One‐dimensional time‐dependent calculations show that the velocity lag and the thermal lag between the two phases are large when the particle diameter is 15 μm. The lags become small when the diameter is small because the decrease of the diameter increases the momentum transfer and the heat transfer between the two phases. When the large Lorentz force develops a shock wave, the interaction between the two phases relaxes the shock wave. The increase of the particle diameter decreases the channel current and the power output because the increased diameter decreases the energy conversion from the liquid phase. © 1999 Scripta Technica, Electr Eng Jpn, 127(2): 15–23, 1999     

Numerical Simulation of Power Generation Characteristics of a Disk MHD Generator with High‐Temperature Inert Gas Plasma

The power generation characteristics of a disk magnetohydrodynamics (MHD) generator with high‐temperature inert gas (argon) plasma have been examined by a time‐dependent two‐dimensional numerical simulation. The numerical simulation results based on the experimental conditions show that the enthalpy extraction ratio (= electrical output power/thermal input) can reach above 10%, which surely supports the reasonability of the experimental results. Proper selection of working conditions, especially the inlet total gas temperature, is necessary, since the gas temperature dominantly determines the electrical conductivity in the generator, unlike the conventional seeded plasma MHD generator. It is also found that the plasma is not in the recombination process but in the ionization process, where the ionization degree moderately increases along the flow. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(3): 23–30, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21237     

Numerical Study on Periodic Structure Evolution of Output Power in MHD Generator by Using Pulse‐Assisted Ionization Discharge

A pulse‐assisted ionization discharge applied to a magnetohydrodynamic (MHD) generator is proposed as a technique to increase an electrical conductivity of working fluid. In this study, a periodic structure of output power in the MHD generator by using pulse‐assisted ionization discharge was evaluated. As a result, the discharge electrode length and the velocity of working fluid affect the discharge current distribution. The periodic structure of output power was observed in the several conditions. When the velocity of working fluid is roughly same as the sound speed, the periodic structure of output power was not observed.     

Fault analysis of the interconnecting system between a commercial‐scale subsonic diagonal‐type MHD generator and an ac power system

Fault analyses are performed for the interconnecting system between a commercial‐scale subsonic diagonal‐type MHD generator and an ac power system through a line‐commutated inverter. The behavior of the interconnecting system is first examined for the case of single misfiring of one thyristor in the inverter. In this case, the load current increases because the inverter system is short‐circuited. Following the theory of inverter commutation, the load current decreases to the rated value and the MHD generator is restored to the rated condition. Next, the cases of a single‐line ground fault and of a three‐phase short circuit fault are investigated. The line voltage decreases and thus the load currents increase after the fault. This increase of load currents destroys the design‐point flow of the MHD generator. Phase‐control angle control of the inverters is required in order to restore the rated operation of the MHD generator. © 2001 Scripta Technica, Electr Eng Jpn, 136(1): 29–36, 2001     

Experimental and theoretical analyses on power generation characteristics of co-axial MHD energy conversion device

Experiments on power generation were conducted under the open-circuit condition to validate theoretical analyses on the power generation characteristics of a co-axial MHD energy conversion device. Considering distribution of externally applied magnetic field and the electromotive force induced by the rotation of the conductive inner cylinder, the results show that the experimental open-circuit voltage was lower than the theoretical one for the wide channel width, whereas the experimental open-circuit voltage was higher than the theoretical one for the narrow channel width. The inclination of the inner cylinder might cause the decrease in effective radial ratio.     

Plasma Fluid Flow Behavior and Power Generation Characteristics in a High‐Temperature Inert Gas Plasma Faraday MHD Generator

The plasma fluid flow behavior and power generation characteristics in a Faraday magnetohydrodynamic (MHD) generator using a high‐temperature inert gas (argon) plasma have been examined in a time‐dependent two‐dimensional numerical simulation. The inhomogeneous and unstable plasma at an inlet total temperature of 7000 K results in reductions and fluctuations in the output power. The plasma becomes homogeneous and stable as the inlet total temperature increases to 9000 K. One of the reasons for the suppression of ionization instability may be weakness of the dependency of the electrical conductivity on the electron number density, because the Coulomb collision of electrons becomes dominant during deviation from Saha equilibrium.     

Two‐dimensional numerical simulation on performance of liquid metal MHD generator

The performance of a liquid metal MHD generator is investigated with a two‐dimensional numerical simulation. The effects of the electrode length, the position of current lead connection, and the insertion of an insulator on the performance are examined taking account of the current flow in the electrode. There exists an optimal electrode length for a given distribution of applied magnetic flux density. For a short electrode, the efficiency decreases because the power output becomes small. For a long electrode, on the other hand, the efficiency also decreases owing to the leakage current from the upstream and downstream edges of the electrode. An optimal current lead position was revealed. This fact is ascribed to the distributions of induced magnetic field and the current flow in the electrode. It was found that insertion of the insulator is effective for improving the performance, by which the eddy current can be reduced. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(1): 25–32, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.20165     

Transient response of closed‐loop MHD experimental facility

Transient responses of a closed‐loop MHD experimental facility from nonpower generation to power generation have been investigated by means of time‐dependent quasi‐one‐dimensional numerical simulations. For the long‐time continuous power generation experiment, the time required to obtain the steady state for the power generation is estimated to be approximately 20 hours. By increasing the electrical input power to the heater as an exponential function of time, the temperature increment of ceramics can be moderated. When the duration of the experiment is around 10 minutes, argon gas temperature at the exit of the heater hardly changes because of the large heat capacity of structure materials. It is found that the fluid disturbances are induced at the instant of the power generation and they propagate as they repeatedly reflect at the sudden change of duct shape. Since all of the induced disturbances attenuate approximately 0.4 second after the power generation, the time scale that the disturbances exist in the facility is estimated to be 1 second at most. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(1): 46–52, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20237     

The effect of an externally applied radio‐frequency electromagnetic field on the performance of a disk MHD generator

The effects of an externally applied radio‐frequency (rf) electromagnetic field on the nonequilibrium performance of a disk MHD generator were examined experimentally. As a preliminary experiment, plasma production by the applied rf electromagnetic field was attempted in the disk generator (Disk‐PIA), in which rf induction coils were embedded in the one‐side disk wall, under the conditions of no seeding, no flow, and no magnetic field. From the results of the preliminary experiment, it was confirmed that the argon plasma (～110 Torr) was produced uniformly in the azimuthal direction by the rf electromagnetic field even in the presence of exposed anodes in the faced disk wall and metallic support at the disk center. In MHD power generation experiments with the Disk‐PIA installed in the shock‐tube facility, the increase in the electrical output and more indiscrete discharge attributed to the rf electromagnetic field were verified with good reproducibility for the first time. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(4): 46–53, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10009     

New Dynamic Self‐Consistent Mathematical Model and Torque Characteristics of Permanent‐Magnet Synchronous Motors with Magnetic Cross‐Coupling

This paper proposes a new dynamic mathematical model of permanent‐magnet synchronous motors (PMSMs) with magnetic cross‐coupling and presents a new analysis of the torque characteristics of the motors. Generally speaking, dynamic mathematical models used for the design and analysis of PMSM control systems must consist of three basic equations that describe the main motor characteristics as an electrical circuit, torque generator, and electromechanical energy converter. In order to obtain reasonably compact models, some characteristics have to be approximated. However, in the case where the approximations used in the three basic equations are different from each other, the dynamic mathematical model often loses self‐consistency and becomes self‐contradictory. The proposed model, which takes the magnetic cross‐coupling into account, is self‐consistent and compact, and its effectiveness is validated by experimental data. Using the self‐consistency and compactness, this study presents a new analysis of the torque characteristics of PMSMs, focusing on efficient torque generation. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(1): 42–55, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22382     

Fundamental experiments of radio‐frequency preionized inert gas plasma MHD electrical power generation

A seed‐free radio‐frequency (RF) preionized inert gas plasma MHD electrical power generation has been first demonstrated in fundamental experiments with a shock‐tunnel facility. An enthalpy extraction ratio of 2.6% was successfully obtained even under an inlet total temperature of 2200 K at which the power generation can be operated continuously. Since the RF input power required for the preionization tends to be increased for lower inlet total temperature, the reduction of the RF input power is needed for further improvement in the total performance.     

Development of Cockcroft–Walton‐type high‐voltage DC generator with RF air‐core transformer

A new Cockcroft–Walton (CW)‐type high‐voltage DC generator with RF air‐core transformer used as a step‐up transformer has been developed. The design concept of the air‐core transformer is shown, which is operated on the resonance condition between the inductance of the secondary coil and the stray capacitance of CW circuit with the conical‐type coil structure. Adapting the RF air‐core transformer to CW circuit with DC‐300 kV 100 mA, excellent performances have been demonstrated. In the new CW circuit, it results in downsizing of capacitors to operate at higher frequency than conventional ones, and reduction of the volume by approximately 40% has been shown in the typical DC generator with 1 MV 100 mA. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 18–26, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20500