Conventional jet engines generate thrust by mixing fuel with compressed air, then igniting it. As the burning mixture rapidly expands, it gets blasted out of the back of the engine, propelling the craft forward.
On the other hand, a plasma jet engine does away with the standard air and fuel mixture. Instead, it makes use of electricity to compress and excite gas into a plasma — an extremely hot, dense ionised state comparable with the insides of a fusion reactor or a star — then generate an electromagnetic field from it.
Plasma engines have remained in experimental stages for quite some time, and their use is focused mainly on propelling satellites and other spacecraft. But researchers at the Technical University of Berlin led by Berkant Göksel intend to change that.
According to Göksel, their aim is to develop a system that can operate at over 30 kilometers up, where ‘standard engines cannot go’, and which could even bring along passengers and take them to the edge of the atmosphere and beyond. In other words, they want to use plasma engine to propel a passenger jet and enable it to fly at altitudes that are much higher than where typical jets can go, practically to the edge of space.
While plasma jet engines are typically designed to operate in a vacuum or in low pressure areas like those found high up in the atmosphere, Göksel’s team has managed to test a plasma engine that works on air at a pressure of one atmosphere. As Göksel told New Scientist: “We are the first to produce fast and powerful plasma jets at ground level. These jets of plasma can reach speeds of up to 20 kilometers a second.”
The team was able to achieve this by using a ‘rapid stream of nanosecond-long electric discharges to fire up the propulsion mixture’, a technique that’s somewhat similar to what’s used in pulse detonation combustion engines. The technique isn’t just more efficient; it can also significantly extend the range of aircraft, also lowering operational cost in the process.
As promising as the results of the team’s tests are, however, there are still several stumbling blocks that need to be overcome before their engine can be used on an actual aircraft.
For starters, the team has only been able to test mini thrusters so far. By mini, we mean 80 millimeters long. A commercial plane would need about 10,000 of them to fly, which makes the concept quite impractical based on their current design. Smaller planes would be more feasible as these would only require between 100 and 1,000 thrusters. Which is why the team is choosing to concentrate on those first.
Because a considerable amount of electricity is needed to generate and sustain plasma, the most challenging part of using a plasma engine would have to be the power source. As pointed out by Dan Lev from the Technion-Israel Institute of Technology: “An array of thrusters would require a small electrical power plant, which would be impossible to mount on an aircraft with today’s technology.” Making the thrusters bigger to reduce the number needed for an aircraft won’t be a viable solution as well because it will still require the same amount, or maybe even more power.
Göksel and his team are hoping for a way to work around this, whether through a breakthrough in compact fusion reactors, or by using alternative power sources like solar panels or maybe ‘beaming power wirelessly to the engines’. They are also exploring the possibility of creating hybrid planes which will integrate their plasma engine with a pulse detonation combustion engine or a rocket.
Details of the research have recently been published in the Journal of Physics Conference Series.