BACKGROUND NOTES

Scramjet & PDW engines

1) Scramjet engines

Conventional jet engines rely on turbines to draw in air to mix with fuel. The ramjet has no compressor fans, relying on speed-generated air pressure. Another engine is relied on to reach sufficient operating speed. The scramjet (supersonic combustion ramjet) is similar, but it runs on a hydrogen / air mix and operates at supersonic speeds. It is a clean engine, producing steam as an exhaust gas.

Scramjets are expected to deliver speeds up to Mach 8. After tests in 2001, Australia's University of Queensland succeeded in producing a working scramjet.

2) PDW (Pulsed Detonation Wave) engines

Unlike older pulse jet engines, the Pulsed Detonation Wave (PDW) engine does not have moving parts. It is possible in a PDW engine to use not only the conventional internal thrust chamber, where the detonation wave is started from the rear of the chamber by the ignition circuit, but also external detonation waves, with the fuel mixture contained by the craft's slipstream.

Laser ignition is viewed as a versatile method requiring no previous ignition sequence. With laser ignition, fuel detonation can be started at a preferred spot, at the rear of the chamber or externally.
The precision available with a laser would allow the detonation sequence to begin in different places, using the detonation variations to guide the vehicle.

Acetylene, hydrogen, ethane and other fuels are considered useable.
Sweden's defence research establishment, FOA, has been studying the PDW concept since 1993. The first test rig was run in the spring of 1994 and later demonstrated at a conference in the USA.

The PDW is very compact and is expected to provide good thrust levels. One of the first possible applications is in missiles, UAVs and cheap expendable drones and decoys. A PDW engine may have only 20% of the cost of a jet engine with the same thrust. It could be made small enough to fit into anti-aircraft projectiles.



More Scramjet links:

Scientific American Scramjet Article

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