Could Plasma Thrusters Really Replace Jet Engines?

A new plasma thruster could scale up to compete with traditional jet engines.    

As reported by Popular Mechanics: Chinese scientists suggest they’re bringing space plasma thrusters down to Earth, with a new kind that performs as well in the atmosphere as others do in the vacuum of space.

Using just air and electricity, researchers from the Institute of Technical Sciences at Wuhan University say they’ve overcome longtime atmospheric issues like air friction and made a plasma thruster that can compete on the ground.

In a new paper in American Institute of Physics Advances, the scientists describe how they built and tested their plasma thruster.

“We demonstrated that, given the same power consumption, its propulsion pressure is comparable to that of conventional airplane jet engines using fossil fuels,” they say, which is an extraordinary claim.

The plasma thrusters used in space are specially suited to the zero-G and very thin or nonexistent air. “Even though such a plasma engine has a very small propulsion force, after months and years of constant acceleration, the spacecraft can ultimately reach a high speed,” the researchers explain. So in the absence of friction in space, a tiny amount of power can increase in a linear way without limits, like a snowball rolling downhill that can eventually crush a house.

The plasma thruster design.

Bringing plasma thrust into the atmosphere means contending with strict design limitations. The researchers cite an MIT development of an interim “Tesla type” plasma thruster that’s more powerful than ones for space, but not quite enough for typical aircraft. Instead, these researchers have supercharged the thrust using high temperatures and the application of powerful microwaves.

The homemade heat-resistant device used to measure propulsion pressure in the experiment. The device has a small hole at the top for inserting smaller steel beads in order to adjust the threshold weight, at which the ball starts to rattle due to the effect of the plasma jet.

“In this report, we consider a microwave air plasma jet thruster using high-temperature and high-pressure plasma generated by a 2.45 GHz microwave ionization chamber for injected pressurized air,” the researchers say. A microwave oscillator called a gravitron sends microwaves down a tube that terminates with an igniter that heats the plasma. The tube intensifies the microwaves and the resulting plasma is held in a cohesive shape by the flow of fresh air.

The small laboratory model scales up, the scientists say, to the equivalent of a commercial jet engine—enough to theoretically compete with the fossil fuel technologies we use today. From the study:

“[U]sing a high-power microwave source or an array of multiple microwave sources in parallel operation, with materials resistant to high temperature and pressure, it is possible to construct a high-performance microwave air plasma jet thruster in the future to avoid carbon emissions and global warming that arise due to fossil fuel combustion.”

All this sounds amazing, right? So what’s the catch?

Well, the super hot plasma is so hot that it might melt anything that could contain it. In order to scale up a small laboratory model into a full-size electric plasma thruster, future researchers will need to run tests on materials and construction as well as the best ways to combine everything into the most powerful thrusters. To even test the thrust, the scientists had to make a new heat-resistant measuring setup using quartz and steel.

So while this may be a milestone step, the realization of its white-hot potential is likely a decade or more away.