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 us today as we take a metaphorical test
flight with the electric plasma jet engine. Before we get stuck into the nitty gritty 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 of the
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 it’s 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 Jau 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
magnotron-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 focussed microwaves
cause charged particles in the plasma to oscillate wildly, releasing energy and
a quite dazzling 1000 degrees C of heat. This in turn creates – ta-dah!
– 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 Hadean 1,000 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 1kg steel ball over a 24mm 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 15,000. In the world
of engineering, what works on the small scale rarely if ever works on the grand
dimensions of a commercial jet airliner. 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
Newtons of thrust per kilowatt of power. The engines on the Airbus A320, for perspective,
produce about 220,000 Newtons of thrust. That means any comparably-roomy aircraft
powered by Tang Jets would burn more than 7,800 kilowatt of juice. Let’s say we’re
using currently available battery technology. You’d need some 570 Tesla Powerwall 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 Powerwall’s as payload. Tang, like other researchers in the plasma jet
field, are 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. Oh, 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 resolved. Steven Barret , 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 thundered 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 energising xenon plasma. Even with such little oomph, 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 tantalisingly 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 take off.
Still, suffice to say 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 any time
soon? Let us know in the comments, and don’t forget to subscribe for
more high-concept tech content.
I wonder when the posts here will start to be “we did it” instead of “oh man we’re gonna do it. Definitely possibly maybe, idk, in the future. But we sure are gonna do it.”
We can't even run a fusion reactor properly WITH superconductors...
I hope something interesting happens in my lifetime but I doubt it. Rich c$bst trying to escape to the moon because they fu led this planet up so badly isn’t it either.
How is fusion going to power a flying machine? Are they going to somehow skip the steam engine step?
Is this method avoiding the use of magnets and therefore superconductors then? Also the physicist mentions that the air must first be compressed but is that not what is happening when the diameter of the tube is reduced?
Congratulations, you have found a way to turn electricity into thrust. Its probably worse than the usual technique of a motor and a propeller. If you had a magical source of unlimited electricity, this would work. But given a magical source of unlimited electricity, all sorts of other tech would work. Given fusion, fusion produces heat. You don't want to turn your heat into electricity and then back into heat.