Editing Pulse detonation engine (section)

== Operation ==

The basic operation of the PDE is similar to that of the [[Pulsejet|pulse jet engine]]. In the pulse jet, air is mixed with fuel to create a flammable mixture that is then ignited in an open chamber. The resulting combustion greatly increases the pressure of the mixture to approximately 100 atmospheres (10 MPa),<ref>[http://www.publicaddress.net/default,4114.sm "Pulse Detonation Engines"], An interview with Dr John Hoke, head researcher from Innovative Scientific Solutions Incorporated PDE program under contract to the United States Air Force Research Laboratory,  broadcast on New Zealand radio, 14 April 2007</ref> which then expands through a nozzle for thrust.

To ensure that the mixture exits to the rear, thereby pushing the aircraft forward, a series of shutters are used to close off the front of the engine. Careful tuning of the inlet ensures the shutters close at the right time to force the air to travel in one direction only through the engine. Some pulse jet designs used a tuned resonant cavity to provide the valving action through the airflow in the system. These designs normally look like a U-shaped tube, open at both ends.

In either system, the pulse jet has problems during the combustion process. As the fuel burns and expands to create thrust, it is also pushing any remaining unburnt charge rearward, out of the nozzle. In many cases some of the charge is ejected before burning, which causes the famous trail of flame seen on the [[V-1 flying bomb]] and other pulse jets. Even while inside the engine, the mixture's volume is constantly changing which inefficiently converts fuel into usable energy.

All regular jet engines and most rocket engines operate on the ''[[deflagration]]'' of fuel, that is, the rapid but [[Speed of sound|subsonic]] [[combustion]] of [[fuel]]. The pulse detonation engine is a concept currently{{When|date=May 2023}} in active development to create a jet engine that operates on the supersonic ''[[detonation]]'' of fuel. Because the combustion takes place so rapidly, the charge (fuel/air mix) does not have time to expand during this process, so it takes place under almost [[Isochoric process|constant volume]]. Constant volume combustion is more efficient than open-cycle designs like [[gas turbine]]s, which leads to greater [[fuel efficiency]].

As the combustion process is so rapid, mechanical shutters are difficult to arrange with the required performance. Instead, PDEs generally use a series of valves to time the process carefully.{{Cn|date=May 2023}}

Most PDE research is military in nature, as the engine could be used to develop a new generation of high-speed, long-range [[reconnaissance aircraft]] that would fly high enough to be out of range of any current anti-aircraft defenses, while offering range considerably greater than the [[SR-71]], which required a massive tanker support fleet.{{Cn|date=May 2023}}

Key difficulties in pulse detonation engines are achieving DDT without requiring a tube long enough to make it impractical and drag-imposing on the aircraft (adding a U-bend into the tube extinguishes the detonation wave); reducing the noise (often described as sounding like a jackhammer); and damping the severe vibration caused by the operation of the engine.{{Cn|date=May 2023}}