Pulsejets (which could have been called pulse deflagration engines) rely on pulsed deflagration to generate energy and thrust. Their pulsed mode makes them hideously loud and rather inefficient, but they can be quite simple to build - they can even have no moving parts.
Pulse detonation engines work in a rather similar way, but rely on pulsed detonation instead of deflagration. It makes them much harder to build (and possibly even louder), but theoretically much more efficient.
Rotating detonation engines are a further development. The pulsed regime being source of inefficiencies, vibrations and noise (so much noise), it is replaced by continuous detonation fronts endlessly going around an annular chamber, with fuel and oxidiser injected behind each front, for the next one.
Is there such a thing as a rotating deflagration engine? Is it theoretically feasible?
The advantage appears obvious at first glance: avoid the inefficiency of pulsed mode from a pulsejet, while avoiding the complexity of using detonation for more manageable (if less efficient) deflagrations. One could also hope to keep some of the simplicity of pulsejets, with fewer moving parts and air being aspired in the chamber as part of the cycle.
However, I couldn't find any reference to such an engine, whether attempts to build it, studies, or even description of why it wouldn't actually work.
Note: this is not about turbines or rocket engines. Those are technically continuous deflagration engines, but there is continuous pumping of fuel and oxidiser (air from the compressor in the case of the turbine), and a stationary burn zone. A rotating deflagration engine would have moving deflagration fronts with fuel and oxidizer (like air) injected after a deflagration front moves away.
