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Electrothermal Propulsion Electro-thermal propulsion systems are those systems in which electrical energy is used to heat propellants, thus producing thrust. Principle Electro-thermal systems heat propellants, which produce gases. The gases are then sent through a supersonic nozzle to produce thrust (see principle of propulsion). Working
Arcjets can be used to heat the propellants. In an arcjet, the propellant is heated by an electrical arc discharge. The arcjet consists of a cathode and an anode, a constriction channel, nozzle and propellant injector. The arc in the arcjet is nothing but a beam of electrons that is emitted from the tip of the cathode and collected at the positively biased nozzle (anode). Between the cathode and anode there is a narrow passageway called the constrictor. The electric field between the anode and the cathode causes the electrons to accelerate in the direction of anode (due to the attraction of the anode). Gas is injected near the base of the cathode through injection ports with an azimuthal swirl. Azimuthal projections are projections onto a plane that is tangential to some reference point. The swirl • Prevents the arc from bending and touching the walls. Thus constrictor is prevented from melting. • Helps circulate the gas through the arc, which can have an effective temperature in excess of 15,000° C. • Stabilizes the arc. • Cools the electrodes and chamber walls. • Brings the gas into longer and more effective contact with the arc. The arc gets superheated and the gas at the centerline of the constrictor is fully ionized. This gas heats the swirling boundary gas through radiation Thus the centerline temperature of the gas is very high. The hot propellant is then accelerated out of the thruster through the expansion nozzle. Typical propellants for arc jets include ammonia, hydrogen, and hydrazine, with the lighter propellants providing higher specific impulse and lower engine temperatures. The next electric propulsion is the Electromagnetic propulsion.
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