A pulse detonation engine (PDE) is a type of engine operating as a propulsion system in a craft that can operate theoretically from subsonic up to hypersonic speeds. Theoretically, a pulse detonation engine can have a burn efficiency higher than that of other types of engine designs, such as turbojet engines, turbofan engines, and pulse jet engines, and will have fewer moving parts than other types of engine designs.
Common jet engines and many rocket engines operate on the deflagration of fuel, the rapid but subsonic combustion of fuel, because when using typical hydrocarbon based fuels, combustion velocity rates are in the range of about 25 feet per second to about 125 feet per second. While the combustion velocity of the -subsonic deflagration of fuel is slow in a typical jet engine, the fuel is burned completely within the engine so long an after burner is not used on the engine. A pulse detonation engine differs from the prior art jet engines and pulse jet engines because the pulse detonation engine operates on the supersonic detonation of fuel, rather than the subsonic burning of the fuel. In a pulse jet engine, fuel is mixed with air to create a mixture that is ignited with the resulting detonation of the fuel-air mixture increasing detonation velocity to supersonic velocities and the pressure of the combustion gases to high pressure levels. The combustion gases are then expanded through a nozzle for thrust pushing the vehicle forward.
A pulse detonation engine differs from a pulse jet engine in that a pulse detonation engine does not use subsonic combustion that is used in a pulse jet engine. In a pulse detonation engine oxygen and fuel combine to generate supersonic combustion through detonation of the fuel-oxygen mixture effectively creating a reoccurring and continuous series of explosions of oxygen and fuel within the engine, rather than burning the fuel -subsonically by deflagration of the fuel, as in a pulse jet engine. By changing the engine operating cycle from burning the fuel-air mixture to an explosive detonation of the fuel-oxygen mixture, the overall operating efficiency of the engine is theoretically increased. The operating efficiency of a pulse detonation engine is increased because a pulse detonation engine uses a supersonic combustion process that burns all the fuel while still in the engine at a high pressure producing a constant volume combustion process for the exhaust gases to be discharged from the engine at high velocity. This inherently increases the burn efficiency of the engine; i.e., the amount of heat produced per unit of fuel, above other types of engines, although conversion of the energy produced within a pulse detonation engine to thrust is difficult. Also, a pulse detonation engine needs to produce a large number of fuel detonations within the engine in a short period of time to sustain the thrust level of the engine, which requires a very short detonation cycle time for the engine. While the overall increase in the engine burning efficiency of a pulse detonation engine is increased over that of an engine using burning of a fuel-air mixture, pulse detonation engines must continuously generate a large number of detonations within the engine and convert the combustion gases into an effective thrust from the engine to power a vehicle.
To ensure that the combustion gases exit aft of the vehicle some types of pulse detonation engines, like a pulse jet engines, use a type of shutter or equivalent valve structure to close the front of the pulse detonation engine preventing the combustion gases from exiting the front of the engine. The timing of the closing of the shutters or valves to force the combustion gases to exit the engine aft in only one direction is an important consideration in pulse detonation engine design.
Pulse detonation engines are designed as either valve-less engines or engines having valves. Some prior art types of pulse detonation engine are set forth in U.S. Pat. Nos. 6,584,765 6,725,646, 6,845,620, and 7,251,928. A pulsed combustion engine is set forth in U.S. Pat. No. 7,100,360.
It is desirable to have a pulse detonation engine that can operate at very high rates of fuel-oxygen detonation to continuously provide thrust for a vehicle.