Magnetohydrodynamic power generation using externally ionized, cold, supersonic air as working fluid

Magnetohydrodynamic (MHD) power extraction from cold air has been demonstrated using short-duration, high-repetition rate, high-voltage pulses (2 ns, 100 kHz, 5 kV/cm) to ionize a Mach 3 (600 m/s), 0.04 kg/m³ flow. Because the power used to ionize the flow using such a method was less than 1 % of the total flow enthalpy, the flow was not heated significantly. A few tens of milliwatts were extracted from the 3-cm cube region of ionization, which scales to hundreds of kilowatts of power in higher velocity, larger-scale devices that would be appropriate for flight applications. Peak electron number densities between 5 × 10¹¹ and 10¹² cm^-3 are reported from complementary measurements using microwave absorption in a variable magnetic field. The Hall parameter was estimated from the electrical properties of the MHD channel. Modeling predictions were found to be in agreement with experimentally extracted Faraday current measured between the high-voltage pulses. Modeling also confirmed that the electrons have low energy between the pulses and that the resultant cathode and anode voltage falls are quite low, on the order of 1 V.