The possibility of the improvement in performance of a nonequilibrium disk magnetohydrodynamics (MHD) generator by externally applying a radio frequency (RF) electromagnetic field (RF preionization) was examined experimentally. The MHD power generation experiments were carried out using a shock-tube driven disk MHD generator with the RF induction coils for the two inlet stagnation temperatures of 2275(/spl plusmn/75) K and 2650(/spl plusmn/50) K. As a result, under the conditions of both high and low stagnation temperatures, the output power was increased by the RF preionization. The increase was markedly observed for the low inlet stagnation temperature, where the plasma could not be produced only by the Joule heating attributed to a self-excited electromotive force. For the high inlet stagnation temperature, the plasma state in the MHD channel was improved by the RF preionization, leading to the increase in the output power. For the low inlet stagnation temperature, the marked increase in the output power by the preionization was not only because applying the RF electromagnetic field triggered the plasma production by the Joule heating attributed to a self-excited electromotive force but also because the plasma with the high electrical conductivity was produced in the more upstream region of MHD channel by the Joule heating attributed to the RF electromagnetic field.

Experimental studies on performance of a nonequilibrium disk MHD generator with radio-frequency preionization

The present paper describes the performance of a radio-frequency (rf) electromagnetic-field-assisted magnetohydrodynamics (MHD) electrical power generator and compares it to a multiple-load MHD generator. rf heating which is superimposed on self-excited Joule heating preionizes cesium-seeded helium gas independent of the in situ loading conditions, whereby Hall potential profile is improved and electron temperature is increased. Furthermore, the dynamic stabilization effect cancels ionization instability and homogenizes plasma structure, which is the most important superiority of the rf-power assistance over a conventional plasma actuation by loading-rate control. The power-generating performance is significantly improved with the aid of the rf power under wide seeding and loading conditions, where the electrical load-matching characteristic is slightly changed.

Performance of rf-assisted magnetohydrodynamics power generator

We describe seed-free pure-argon-plasma magnetohydrodynamic (MHD) power generation assisted by an external radio-frequency electromagnetic field to enhance the nonequilibrium plasma excitation process. The rf heating induces nonequilibrium ionization under a low total argon-gas temperature at which thermal ionization is insufficient. The rf-assisted plasma, the behavior of which is rather stable, contributes to continuous MHD energy conversion.

Rf-assisted magnetohydrodynamic power generation in a pure-argon plasma

We describe a radio-frequency (rf) electromagnetic-field-assisted magnetohydrodynamic power generation experiment, where an inductively coupled rf field (13.56MHz, 5.2kW) is continuously supplied to the disk generator. The rf power assists the precise plasma ignition, by which the otherwise irregular plasma behavior was stabilized. The rf heating suppresses the ionization instability in the plasma behavior and homogenizes the nonuniformity of the plasma structures. The power-generating performance is significantly improved with the aid of the rf power under wide seeding conditions: insufficient, optimum, and excessive seed fractions. The increment of the enthalpy extraction ratio of around 2% is significantly greater than the fraction of the net rf power, that is, 0.16%, to the thermal input.

Radio-frequency power-assisted performance improvement of a magnetohydrodynamic power generator

We describe the suppression of ionization instability and the control of a magnetohydrodynamic electrical power-generating plasma by coupling with a radio-frequency (rf) electromagnetic field. The rf heating stabilizes the unstable plasma behavior and homogenizes the nonuniform plasma structure, whereby the power-generating performance is significantly improved.

Suppression of ionization instability in a magnetohydrodynamic plasma by coupling with a radio-frequency electromagnetic field

Performance of Disk MHD Generator with One-sided Anode

Experiments of Non-equilibrium MHD Power Generation with Radio-Frequency Pre-Ionization

The production of nonequilibrium plasma and the fluid flow with the MHD interaction are examined experimentally with a shock-tube driven disk channel with no loading electrodes. For low magnetic flux density and low seed fraction, where nonuniform and unsteady plasma is generated, the static pressure decreases monotonically in the radial direction, although the pressure increases in the entire region of the channel in comparison with the value under no MHD interaction. For magnetic flux density and seed fraction above some critical values, a fairly uniform plasma is produced. The static pressure, however, is found to increase abruptly in the channel and the total pressure is considerably reduced at the location, where the abrupt pressure increase occurs. These facts imply that steady and uniform plasma should be produced without locally constricted strong Lorentz force to improve the adiabatic efficiency of a disk MHD generator. © 2002 Scripta Technica, Electr Eng Jpn, 138(4): 42–49, 2002; DOI 10.1002/eej.1137

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/eej.1137

Production of nonequilibrium plasma and MHD interaction in disk MHD channel

Power generation experiments have been conducted with a shock-tube driven disk-shape Hall-type MHD generator using cesium seeded helium gas. The generator performance relies heavily on a seed fraction rather than channel load resistance; suggesting that a plasma condition in a supersonic nozzle is quite responsible for the performance. It is inferred from characterizing the fluid-dynamical behavior by static pressure increase that keeping a higher total pressure ratio under the condition of the relatively lower seed fraction enable us to achieve the higher isentropic efficiency as long as appropriate electrical conductivity is obtained. Attempts to clarify the time- and spatial-variations of electron temperature and electron number density are indicative that the plasma behavior in an MHD channel has considerable effects on the generator performance as well as an inlet plasma condition does. One of the most revealing finding is the fact that the excessive nozzle resistance has been one of the performance-limiting parameters. The employment of the high seed fraction under the high nozzle loading condition results in large pressure loss and deterioration of the performance.

Takayasu Fujino

Papers

Experimental studies on performance of a nonequilibrium disk MHD generator with radio-frequency preionization

Performance of Disk MHD Generator with One-sided Anode

Experiments of Non-equilibrium MHD Power Generation with Radio-Frequency Pre-Ionization

Production of nonequilibrium plasma and MHD interaction in disk MHD channel

Experiments on the Performance of a Nonequilibrium Disk MHD Generator with Helium