# How the Rotating Detonation Engine Works

## Circular Logic

We tend to think of the pressures created inside an engine as being more controlled rather than disorganized "detonation" -- we want it to be predictable, not chaotic. But if an engine can control a typical cycle with enough precision to produce steady power, it can also control detonations. And the burst of pressure that a detonation produces can result in a more efficient engine, if it's harnessed correctly. Typically, an engine mixes air with fuel to prepare it for detonation, which is when the fuel releases its energy. The efficiency of the fuel's energy release, though, is highly dependent on the type of engine.

This is where the rotating detonation engine differs from more common types of gas turbine engines. The air and fuel are mixed (as usual) before they're injected into a long, circular combustion chamber, in what "Physics Today" has described as "a sequential, circular manner." The first detonation sets off a cycle in which the pressure from ignition continues around the chamber, lighting each injection in sequence. The pressure from each ignition keeps the cycle moving. The pressure then forces the exhaust gas out of the combustion chamber through an exhaust nozzle, which is actually the thrust generated by the engine, and moves on to power whatever type of vehicle the engine is installed in (in this case, typically, a ship or an airplane).

The rotating detonation engine is actually a variation of another engine design: the pulse detonation wave engine. Though pulse detonation engines provide energy savings over many other types of engines, they still have their own inefficiencies. One reason is the combustion chamber which must be purged after each pulse. The rotating detonation engine is an improvement over the pulsing design, because the detonation wave constantly cycles around the chamber, eliminating the need to waste time and energy by purging.

Because detonations create extreme pressures, a detonation engine can be designed without the additional compressor that's usually required. Not only are compressors typically complex, but their operation generally sucks up a lot of energy, too. However, adding a compressor to a detonation engine actually makes it even more efficient. This compatibility makes it easier to retrofit gas-turbine engine vehicles to be used with detonation engine technology [source: Green Car Congress].