A rotating detonation engine (RDE) is a proposed engine using a form of pressure gain combustion, where one or more detonations continuously travel around an annular channel. Although none are in production, computational simulations and experimental results have shown that the RDE has potential, and a there is wide interest and research into the concept.
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Theoretically, detonative combustion, (i.e. that which happens at speeds above the speeds of sound), is more efficient than the conventional deflagrative combustion. If this theoretical gain in efficiency can be realized, there would be a major fuel savings benefit. Because the combustion is supersonic, it can also more efficiently provide thrust at speeds above the speed of sound.
The disadvantages of the RDE include stability and noise.
How it works
The basic concept of an RDE is a detonation wave that travels around an annulus, which is a circular channel. First, fuel and oxidizer are injected into the channel, normally through small holes or slits. Initially, a detonation must be initiated in the fuel/oxidizer mixture by use of some form of ignitor. After the engine is started, however, the detonation is self-sustaining. The passing detonation ignites the fuel/oxidizer mixture, which releases the energy necessary to sustain the detonation. The combustion products expand out of the channel and are also pushed out of the channel by the incoming fuel and oxidizer.
Although the RDE's design is similar to the pulse detonation engine (PDE), one aspect that makes the RDE superior is the fact that the waves constantly cycle around the chamber, while the PDE requires the chambers to be purged after each pulse.
An image of an RDE can be found on the American Institute of Aeronautics and Astronautics Pressure Gain Combustion Program Committee's Resources page.
Current development
Several organisations have been working on RDE design.
US Navy
The US Navy is pushing the development of this engine, but there is no known time of completion. Researchers at the Naval Research Laboratory (NRL) have been showing particular interest in detonation engines, such as the RDE, because they realize these engines have the capability to reduce the fuel consumption in their heavy vehicles. Several obstacles still remain to overcome in order to use the RDE in the field. NRL researchers are currently focusing on getting a better understanding of how the RDE works.
Aerojet Rocketdyne
Since 2010, Aerojet Rocketdyne has conducted over 520 tests of multiple configurations of a rotating detonation engine.
NASA
Researchers at NASA also play a part in the development of the RDE. Daniel Paxson, an accredited scientist at the Glenn Research Center, has used simulations in computational fluid dynamics (CFD) to assess the RDE's detonation frame of reference and compares the performance with the PDE. He found that the results from his code of the RDE were shown to be in favor of those from a more complex code; thus, stating that the RDE can perform at least on the same level. Furthermore, he found that the performance of the RDE can be directly compared to the PDE as their performance were essentially the same.
Other research
Other experiments have used numerical procedures to better understand the flow-field of the RDE.