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Spaceplane air cooling technology 'could revolutionise aero engines'

The technology behind a British attempt to develop an air-breathing rocket engine capable of powering a runway take-off and landing reusable spaceplane could also drive a revolution in the much more ordinary world of subsonic airliners.

Reaction Engine's SABRE rocket engine relies on an exotic heat exchanger capable of cooling intake air - from as much as 1,000˚C (1,832˚F) at Mach 5.5 to an almost-cryogenic -150˚C - to provide the near-liquid oxygen required to provide rocket thrust when mixed with tanked liquid hydrogen.

The technology, formally "signed off" by the European Space Agency in November as viable, will now be the subject of a £250 million ($400 million) investment drive, which Reaction Engines hopes will raise funds to develop a demonstrator.

However, while the company's focus will be on its SABRE concept, Reaction Engines believes its cooling technology, which transfers heat from the air to tanked liquid hydrogen fuel by running it over a huge network of 1mm tubing, could augment a "standard" aero gas turbine in two ways.

Reaction Engines technical director Richard Varvill says a SABRE-style heat exchanger could feed cool air to compressor blades. In current gas turbines, the hot-section blades are running at temperatures above the melting point of the metals they are made from, and have to be cooled by pumping less-hot air through internal holes, the formation of which greatly complicates blade manufacture. Better cooling with colder air may permit even hotter combustion.

Another technique would be to use a heat exchanger to take heat from the exhaust and feed it back into the combustion chamber, thereby getting work from energy that would otherwise be wasted.

Varvill reckons these two approaches could slash fuel burn by 5-10%, a massive improvement. As Varvill notes, waste-heat recuperation is widely used in power station gas turbines, where weight and space considerations clearly do not apply as they do in aircraft. Indeed, recuperation is used in aero-derivative gas turbines, including Rolls-Royce's WR-21, a 25MW unit widely used in ships and derived from the RB211, the first three-spool engine which led to the Trent family.

None of this will happen quickly for aircraft, stresses Varvill, as it would require a new engine architecture rather than any bolt-on approach. But, he notes, aero engine makers have not abandoned hope of bringing in recuperation at some point.

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