MIT experiments show Ionic thrust engines produce 50 times more thrust efficiency per kilowatt than jet engines and could be scaled for light aircraft

MIT researchers have run ionic thruster experiments and found they may be a far more efficient source of propulsion than conventional jet engines. In their experiments, they found that ionic wind produces 110 newtons of thrust per kilowatt, compared with a jet engine’s 2 newtons per kilowatt. Steven Barrett, an assistant professor of aeronautics and astronautics at MIT, envisions that ionic wind may be used as a propulsion system for small, lightweight aircraft. In addition to their relatively high efficiency, ionic thrusters are silent, and invisible in infrared, as they give off no heat — ideal traits, he says, for a surveillance vehicle.

There could be all kinds of military or security benefits to having a silent propulsion system with no infrared signature.

A basic ionic thruster consists of three parts: a very thin copper electrode, called an emitter; a thicker tube of aluminum, known as a collector; and the air gap in between. A lightweight frame typically supports the wires, which connect to an electrical power source. As voltage is applied, the field gradient strips away electrons from nearby air molecules. These newly ionized molecules are strongly repelled by the corona wire, and strongly attracted to the collector. As this cloud of ions moves toward the collector, it collides with surrounding neutral air molecules, pushing them along and creating a wind, or thrust.

The device was most efficient at producing lower thrust.

There is one big obstacle to ionic wind propulsion: thrust density, or the amount of thrust produced per given area. Ionic thrusters depend on the wind produced between electrodes; the larger the space between electrodes, the stronger the thrust produced. That means lifting a small aircraft and its electrical power supply would require a very large air gap. Barrett envisions that electrodynamic thrusters for aircraft — if they worked — would encompass the entire vehicle.

PNAS – On the performance of electrohydrodynamic propulsion

Another drawback is the voltage needed to get a vehicle off the ground: Small, lightweight balsa models require several kilovolts. Barrett estimates a small craft, with onboard instrumentation and a power supply, would need hundreds or thousands of kilovolts.

“The voltages could get enormous,” Barrett says. “But I think that’s a challenge that’s probably solvable.” For example, he says power might be supplied by lightweight solar panels or fuel cells. Barrett says ionic thrusters might also prove useful in quieter cooling systems for laptops.

Ned Allen, chief scientist and senior fellow at Lockheed Martin Corp., says that while ionic thrusters face serious drawbacks — particularly for aerospace applications — the technology “offers nearly miraculous potential.”

“[Electrohydrodynamic thrust] is capable of a much higher efficiency than any combustion reaction device, such as a rocket or jet thrust-production device,” Allen says. Partly for this reason, Allen says Lockheed Martin is looking into the technology as a potential means of propulsion.

ABSTRACT – Partially ionized fluids can gain net momentum under an electric field, as charged particles undergo momentum-transfer collisions with neutral molecules in a phenomenon termed an ionic wind. Electrohydrodynamic (EHD) thrusters generate thrust by using two or more electrodes to ionize the ambient fluid and create an electric field. We characterize the performance of EHD thrusters of single- (SS) and dual-stage (DS) configurations. SS thrusters refer to a geometry using one emitter electrode, an air gap and a collector electrode with large radius of curvature relative to the emitter. DS thrusters add a collinear intermediate electrode. SS thruster performance was shown to be consistent with a one-dimensional theory. Increasing the gap length requires a higher voltage for thrust onset, generates less thrust per input voltage, generates more thrust per input current and most importantly generates more thrust per input power. A thrust-to-power ratio as high as approximately 100 Newtons per kilowatt was obtained. DS thrusters were shown to be more effective than their SS counterparts at producing current, leading to a smaller total voltage necessary for producing equal thrust. However, losses involving ion collection at the intermediate electrode led to reduced thrust-per-power compared with the SS thruster of equal length.

2 pages of supplemental information

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