A magnetohydrodynamic drive or MHD accelerator is a method for propelling vehicles using only electric and magnetic fields with no moving parts, accelerating an electrically conductive propellant (liquid or gas) with magnetohydrodynamics. The fluid is directed to the rear and as a reaction, the vehicle accelerates forward.[1][2]
The first studies examining MHD in the field of marine propulsion date back to the early 1960s.[3][4][5][6][7][8][9][10][11][12]
Few large-scale working prototypes have been built, as marine MHD propulsion remains impractical due to its low efficiency, limited by the low electrical conductivity of seawater. Increasing current density is limited by Joule heating and water electrolysis in the vicinity of electrodes, and increasing the magnetic field strength is limited by the cost, size and weight (as well as technological limitations) of electromagnets and the power available to feed them.[13][14]
Stronger technical limitations apply to air-breathing MHD propulsion (where ambient air is ionized) that is still limited to theoretical concepts and early experiments.[15][16][17]
Plasma propulsion engines using magnetohydrodynamics for space exploration have also been actively studied as such electromagnetic propulsionoffers high thrust and high specific impulse at the same time, and the propellant would last much longer than chemical rockets.[18]
https://en.wikipedia.org/wiki/Magnetohydrodynamic_drive
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