Pulse detonation engines (PDE) conceptually allow high-speed cruise capability with a low cost reliable system. PDEs incorporate many practical engineering advances over existing engines such as a gas turbine. Pulse detonation involves detonation of fuel to produce thrust more efficiently than existing systems. Pulse detonation is more efficient because of mechanical simplicity and thermodynamic efficiency. For example, PDEs have fewer moving parts, are lighter weight, and require lower cost to maintain and operate.
Application of the pulse detonation cycle requires coupling the high thermal efficiency of the detonation cycle with high propulsion efficiency in a practical device. PDEs detonate combustible mixtures to produce thrust from high velocity exhaust gases within a high pressure and temperature environment. Practical PDE designs include multiple detonation chambers to obtain high aggregate operating frequencies and quasi-steady thrust. Current combustion system models predict high propulsion efficiencies for PDEs and good thrust characteristics from low subsonic to high supersonic type regimes. Pulse detonation technology may be applied to actuators to manipulate fluid flow as well.
One of the key requirements for pulse detonation is that detonation initiation be achieved in as short a distance as possible from the thrust plate. For a PDE operating with a typical gas mixture of JP-10 fuel and air, direct detonation initiation at the thrust wall is not possible since the critical initiation energy is much too high for a practical ignition system. Thus, a need exists to improve mixing of fuel and oxidizer to achieve detonation proximate to the thrust wall. One alternative to direct initiation is commonly referred to as deflagration to detonation transition. This is the process by which a flame accelerates to a velocity on the order of 1,000 meters per second and the detonation initiation occurs in the region between the frame and a precursor shockwave. The low reactivity of prototypic fuel air mixtures causes the detonation run-up distance to be relatively large and thus prohibitive for practical engine designs.
To overcome such problems, solutions consider fuel oxygen mixtures in a pre-chamber approach. Although this may meet the objective of detonation initiation within a short distance, the need for an onboard oxidizer complicates the PDE by adding additional parts with associated cost and weight, while also imposing significant safety hazards. More desirable approaches are required that enhance the detonation process in a fuel air mixture by reducing the run-up distance without the use of additional oxygen.
Various aircraft, such as tactical aircraft, have one or more jet engines that produce thrust corresponding to the exhaust coming from a nozzle of the jet engine. The weight and cost of tactical aircraft exhaust systems have increased at an alarming rate with the incorporation of features for afterburning, thrust vectoring, and advanced shaping. Historically, afterburning and vectoring have required variation of the nozzle geometry. For example, a typical turbo fan engine's nozzle throat area must increase in size when afterburning. Vectoring has required deflection of nozzle flaps, and sometimes rotation of the entire nozzle assembly. Aperture shaping for afterbody integration further imposes the use of less structurally efficient two-dimensional, rather than axis-symmetric, nozzles. These capabilities require greater mechanical complexity in the various systems. A large number of modern jet aircraft employ after burner equipped low bypass turbo fan or turbojet engines. In such engines, fuel is injected into the hot exhaust stream and ignited. The resulting combustion accelerates the exhaust to increase thrust. This solution, while effective, is not fuel efficient as significant amounts of unburned fuel are exhausted.
To simplify the nozzle geometry and complexity, actuators may be incorporated into the engine to allow afterburning, thrust vectoring and advanced shaping of the exhaust flow. These actuators may add some complexity in exchange for reducing the weight of jet engines and their associated nozzle configurations. These actuators inject a cross-flow into the primary flow. For example, U.S. Pat. No. 6,112,512 (the '512 patent) issued to Miller et al., which is hereby incorporated by reference, provides a method and apparatus for pulsed injection for improved nozzle flow control. This flow control uses engine bleed from the compressor of the jet engine to inject air as a pulsed cross-flow into the primary flow in the nozzle. However, bleeding air from the engine takes away mass flow rate of the primary flow, which reduces the thrust and efficiency of the jet engine. Therefore, a requirement exists for solutions that reduce the need for compressor bleed air for controlling the nozzle jet.