A pulse detonation engine is an unsteady propulsive device in which the combustion chamber is periodically filled with a reactive gas mixture, a detonation is initiated, the detonation propagates through the chamber, and the product gases are exhausted. The high pressures and resultant momentum flux out of the chamber generate thrust.

Quasi-steady thrust levels can be achieved by repeating this cycle at relatively high frequency and/or using more than one combustion chamber operating out of phase.A pulse detonation engine has a detonation chamber with a sidewall. At least two fuel ports are located in the sidewall, spaced longitudinally apart from each other. An oxygen fuel mixture is introduced into the forward port and detonated. This creates a detonation wave which propagates with an air fuel mixture introduced into the rearward fuel port.

After the detonation, purge air passes through the chamber before the next detonation. A rotating sleeve valve mounted around the detonation opens and closes the fuel ports as well the purge ports.One of the newest and most exciting areas of pulse-jet development is the Pulse Detonation Engine (PDE). While they work on similar principles to a regular pulsejet, the PDE has one very fundamental difference -- it detonates the air/fuel mixture rather than just allowing it to simply deflagrate (burn vigorously). The exact details on many of the PDE designs currently being developed are rather sketchy -- mainly because they have the potential to be extremely valuable so most of companies researching in this field are not about to tell us what they're doing. It seems that nobody yet has the PDE developed to the point of being a practical propulsion device (or at least if they have, they're not telling anyone). From what I've been able to gather, the main focus is currently being placed on researching and improving the detonation process.

The current generation of PDEs doesn?t seem capable of continuous running for any length of time -- they're more or less just single-shot devices requiring several seconds to recharge between detonations. Many developers have high hopes that the PDE will ultimately become the most cost-effective method of propelling supersonic sub-orbital craft. The ultra-high compressions obtained by detonation offer the potential for much better fuel-efficiency than even the best turbojet, and the fact that they are an air-breathing engine reduces the fuel-load and increases safety when compared to rocket motors.