Submission + - A new type of jet engine could revive supersonic air travel (economist.com)
Both engines would be used to propel missiles, overcoming the range and speed limitations of current propulsion systems, including rockets and existing types of jet engines. However, if the companies are successful in getting them to work, RDEs might have a much broader role in aviation—including the possibility of helping revive supersonic air travel.
In a nutshell, an RDE “replaces fire with a controlled explosion”, explains Kareem Ahmed, an expert in advanced aerospace engines at the University of Central Florida. In technical terms, this is because a jet engine relies on the combustion of oxygen and fuel, which is a subsonic reaction that scientists call deflagration. Detonation, by comparison, is a high-energy explosion that takes place at supersonic speeds. As a result it is a more powerful and potentially a more efficient way of producing thrust, the force that drives an aircraft forward.
image: The Economist
A conventional jet engine uses lots of moving parts (see diagram). Rotating blades draw in air and compress it before igniting it with fuel in a combustion chamber, creating rapidly expanding hot gases that blast out of the rear. As the gases exit they drive a turbine, which keeps the whole process going. An RDE is simpler. Air entering the front is forced into a hollow space between two concentric cylinders. When fuel is pumped into this area, it mixes with the oxygen in the air and detonates, creating a rotating supersonic shock wave that spirals around the gap and out of the rear. Once it has started, the detonation is self-sustaining.
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