Next generation aerospace engine begins pre-cooler testing

Oxford based Reaction Engines is developing a hybrid air-breathing/rocket engine called Sabre, which can breathe air like a jet engine at lower speeds but switch to a rocket engine once it reaches higher altitudes. The test stand will not validate the full Sabre propulsion system, but is its enabling technology - a special type of pre-cooler heat exchanger. During flight as air enters the pre-cooler its temperature will drastically reduce by as much as 100°C. The pre-cooled turbo-compressor provides a high pressure air supply to the combustion chamber. This allows operation from zero forward speed on a runway up to Mach 5.5 in air-breathing mode during ascent. As the air density falls with altitude the engine eventually switches to a pure rocket. The test result shows the flow thorough the pre-cooler to be aerodynamically stable without any significant structural deflection or vibration. The company has built a custom-designed engine test facility at the Culham Science Centre. The facility is designed to be flexible so that other machinery, such as contra-rotating turbines, can also be tested. Contra-rotating turbine technology has advantages in pre-cooled engines both for advanced launchers and for hypersonic civil transport when an air compressor is driven by a helium or hydrogen turbine (giving a large speed of sound mismatch between the turbine and compressor). Selecting a contra-rotating turbine increases relative bladespeeds and eliminates the turbine stators giving a mass saving and efficiency increase.