Preliminary study of a fuel cell powered magnetoplasma engine with e-beam ionization

A fuel-cell powered magnetoplasma jet engine (magjet) using electron-beam ionizers is here proposed for airbreathing flight in the supersonic/hypersonic regime. The engine consists of a fuel-cell duct containing the power source and of a high-speed duct producing most of the thrust through a magnetoplasmadynamic (MPD) accelerator. To reduce the shocks and heat loads in the fuel cells, the enthalpy of the air is extracted beforehand through a MPD generator. The power produced by the latter and by the fuel cells is then split optimally between the MPD accelerator located in the high-speed duct and one located downstream of the fuel cells. The performance is assessed through exact solutions of a quasione- dimensional model which includes the effect of ion slip, Joule heating, and heat dissipated through electron-beam ionization. The magnetic field strength as well as the mass flow rate ratio between the high-speed and fuel cell ducts are seen to affect the thrust considerably at lower Mach number, but to have a smaller impact at hypervelocities. Flight beyond Mach 6 would necessitate substantial cooling of the fuel cells due to the ion slip effect preventing sufficient enthalpy extraction, independently of the magnetic field strength. For a fuel cell efficiency of 0.6 and a mass flow rate ratio of 5, the magjet delivers a specific impulse within 15% of the one of the turbojet in the Mach number range 1-3 given a magnetic field of 8 Teslas. From Mach 3 to 5, a magnetic field strength varying between 2 and 4 Teslas is seen to be sufficient to match the performance of conventional engines.