Imagine a shiny modern airliner crisscrossing the globe powered exclusively by clean electricity and fresh air. That’s the grand vision of a new generation of jet thrusters making big noise in engineering labs around the world. But is this technology the solution to runaway climate change and fossil fuel dependency or just a load of hot air?
Join me today as we take a metaphorical test flight with the electric plasma jet engine before we get stuck into the complexity of electric plasma jet engines. They truly are just as exciting as the name implies. Let’s look at how conventional jet engines actually work — jet fuel which is usually a kerosene based petroleum mixture gets mixed up with compressed air and ignited. This resulting gas heats rapidly which in turn expands with explosive force. This force is then harnessed to power fans or blasted directly out of the back engine.
Demonstrating classic jet thrust electric plasma jet engines on the other hand forego any smelly toxic hydrocarbons instead they generate that crucial propulsive expansion of gas with the help of hot plasma, plasma since you ask, is just another state of matter like solid liquid or gas. Plasma occurs under quite specific circumstances like at the burning heart of a star or in the air surrounding highly charged phenomena such as lightning bolts. If plasma can be artificially superheated the theory goes an engine powered by its expansion could generate enough thrust to fly an aircraft. This essential premise has been experimentally explored by labs in the US and Berlin but the most promising recent breakthrough happened in of all places Wuhan.
China professor Zhao Tang a polymath who has worked at Caltech and Bell labs across various fields from nanotechnology to artificial photosynthesis was investigating the use of microwaves in synthetic diamond production in a moment of inspiration. Tang wondered whether a similar technology could be used to generate thrust to this end he and his team at the institute of technological sciences at Wuhan University developed a device which ionizes compressed air by running it past electrodes then forcing it along a specially designed quartz tube. This produces for starters a low temperature plasma here comes the clever bit the tube containing this plasma intersects with a waveguide that waveguide a pipe essentially is carrying magnetron generated microwaves that pipe ingeniously gets narrower as it approaches the quartz tube so the microwaves meet the low temperature plasma at the narrowest point at their greatest intensity. When that happens the focused microwaves caused charged particles in the plasma to oscillate wildly releasing energy and a quite dazzling 1000 degrees Celsius of heat this in turn creates that all-important thrust.
Although still in its early stages of development tang is optimistic that within a couple of years his newfangled device might be ready to power drones before hopefully progressing to manned aircraft. So can we stop drilling for oil already not quite yet one fundamental drawback, Tang and his team have yet to overcome is that positively 1000 degree burn temperature which is far too hot for any aviation grade engine, housing to endure not without substantial and probably quite deadly so-called plasma erosion, there’s also the not insubstantial question of scale under laboratory conditions. Tang’s microwave-powered thruster was able to lift a rattly one kilogram steel ball over a 24 millimeter diameter tube in terms of simple force.
This could hypothetically be directly scaled up to power a usable jet engine but the airflows would need to be scaled up by a factor of about 15000. In the world of engineering what works on a small scale rarely if ever works on the grand dimensions of a commercial jet airline more intractable than any of those minor gripes however is the snag of how to electrically power the device in flight without access to the power grid. Conventional jet fuel for all its many failings carries far more energy than batteries can manage at the same weight as much as 43 times more energy indeed and weight is a huge deal when you need to get airborne. Tang’s experiment created about 28 Newton of thrust per kilowatt of power. The engines on the airbus A320 for perspective produce about 220000 Newton of thrust that means any comparably roomy aircraft powered by Tang jets would burn more energy than 700–800 kilowatts of juice.
Let’s say we’re using currently available battery technology you need some 570 Tesla power wall 2 units for just one hour’s flight which isn’t very helpful. Anyway considering an airbus A320 can only carry about a third of that many power walls as payload, Tang like other researchers in the plasma jet field is waiting on improvements in batteries or compact fusion nuclear reactors to get their brainchild onto the runway incidentally the idea of using small conventional nuclear fission reactors such as Russian KLT-40s has been mooted although the problem of how to radioactively shield passengers not to mention the catastrophic cost of any crash makes. This plan shall we say unlikely and even if enough power could be harnessed on a plane analysts reckon the cabling required to carry all that juice to the plasma engines would be prohibitively heavy using current technology.
Anyway despite lofty claims from the Wuhan team many analysts believe the technology is inherently flawed potentially even if the power issues are solved Steve Barrett an MIT professor of aerospace engineering was positively scathing when asked to comment on the research on twitter last summer. This is wrong in terms of the physics and measurements he funded after reading about the Wuhan team’s steel ball experiment what they’ve essentially done is like heating a stove top pressure cooker until the valve rattles and called the result thrust but pressure cookers don’t fly. He went on to suggest that adding heat by microwave or any other method only works if you compress the air first like a jet engine requiring mammoth amounts of power otherwise jet engines would not have compressors and you could just ignite a candle and get thrust candles don’t fly around either.
Still the technology isn’t wholly useless NASA has been using electric plasma engines for some years now in space without the friction of atmospheric pressure to overcome they work just fine energizing xenon plasma even with such little mph. thanks to months and years of constant acceleration in the gulf of space they can reach high enough speeds to complete interplanetary missions some futurologists have tantalizingly suggested we might see a coming generation of hybrid planes that use plasma jets for cruising in the high atmosphere after fossil fuels do all the heavy lifting on takeoff still suffice it to say that it’ll be a good while before this promising green technology gets off the ground what do you think can you imagine jetting on holiday on an electric plasma powered aircraft anytime soon let us know in the comments.