The MARK V 32 MW Self Excited Rocket Driven MHD Generator

摘要

The Mark V self excited rocket engine driven MHD generator (RMHD) program was initiated at the Avco Everett Research Laboratory (AERL) in 1962 to demonstrate a solution for the then perceived need for a simple, low cost source of extremely high power for limited duty cycle applications. At the time the Mark V program was initiated, the maximum power which had been achieved by an MHD generator was several hundred kilowatts for a few seconds. The Mark V was the first MHD generator to achieve more than 1.5 W output, the first to be self excited, the first to deal with engineering a high power water cooled MHD channel with literally thousands of electrically isolated elements, and the first to experience the potentially catastrophic consequences of improper management of the electric fields and interelectrode potentials in a high power MHD generator. The program objectives and specifications and design of the overall experiment, fluid mechanics of the MHD interaction, the heat sink self excited magnet, combustion chamber, water cooled MHD channels, load bank and initial checkout are outlined. Two channels were employed. The first channel included an upstream continuous electrode Faraday (CEF) section for magnet excitation followed by a segmented electrode Faraday (SEF) section for net power output. The second channel was CEF design with the load switched in series with the magnet following excitation. Both channels were water cooled. Fifty six power generation runs were carried out with the first channel, and twelve with the second CEF channel. The Paper focuses on the first channel. Initial effort with the first channel focused on self excitation which was readily achieved, but not without some breakdown issues. Effort then concentrated on ramping up the net power output and was confronted immediately with the issue of controlling the voltage potential between adjacent channel electrodes in such a way as to avoid catastrophic breakdown between elements. The tedious attention which was required to control these interelement potentials is described . An important factor uncovered during testing of the first channel was the performance improvement and reduction in magnet excitation power when the generator was operated in the supersonic mixed impulse-reaction mode at lower magnetic field rather than with the design reaction mode. A straight pipe supersonic diffuser was added to facilitate operation in this mode. The need to adjust channel loading to avoid damaging interelectrode breakdown prevented a systemic mapping of generator performance over a wide range of operating conditions, including those which would clearly have led to improved performance. Optimum results were a net power output of 23.6 MW with magnet dissipation of 8 MW. The maximum net output for the second CEF channel was 14 MW. The lessons learned from the Mark V program were: 1: The need in a high power MHD generator to limit interelement potentials to avoid catastrophic electrical breakdown between the elements, 2: The engineering difficulties in the design of a high power water cooled MHD channel with literally thousands of electrically isolated elements, 3: The practical necessity for reducing the number of individual power outputs in order to enable a tractable power conditioning solution. These lessons were invaluable for the design of later high power MHD generators.