Researchers at Cambridge University’s Rolls Royce University Technology Centre (UTC) are engineering new materials to make the jet engines of the future.
Current aircraft engines use turbine blades made from nickel-based superalloys containing nickel and aluminium, but with increasing demands for planes to run faster but with reduced emissions, this material is now reaching the limit of the extreme temperatures and stresses it can withstand.
How a jet engine works
- Near the front of the engine is a compressor, which is essentially a large number of vanes that suck in a ton of air in less than a second and compress it to a fiftieth of its normal volume. It is then passed across hundreds of blades rotating at speeds of up to 10,000 rpm that force it as high-pressure into a combustion chamber.
- At this point the air is moving at hundreds of miles an hour. Fuel is injected into the combustion chamber, where it mixes with the fast-moving compressed air and is ignited. The resulting gases are about a third as hot as the sun’s surface.
- The hot gases then pass back at speeds of almost 1,500 km per hour to drive a turbine which, in turn, provides propulsion for the aforementioned compressor. Each turbine blade generates power equivalent to the thrust of a Formula One racing car.
- The remaining energy is expelled from a nozzle at the back of the engine to create forward thrust.
- At the very front of a turbofan engine is a large fan that also sucks air in.
- Some of this air is picked up by the compressor but the rest bypasses the main turbine and is led around to the back of the engine where it supplies additional thrust.
- Because a turbofan relies on the rotating turbine to drive the compressor and fan, and the turbine can’t turn without air from the compressor, it needs help to get started. This is done with compressed air that spins the compressor and fan at such a speed that, when the fuel is ignited, there is enough airflow to ensure the hot gases are thrust backwards and don’t explode.
- To demonstrate how a jet works, hold a high-pressure hosepipe up to the palm of your hand – the pressure of the water squirting out the end will try to push your hand back.
Now, using the periodic table as their ingredients list, a team of Cambridge University researchers are melting together precise amounts of different elements to create a ‘super’ material that can cope with even more challenging conditions.
Dr Howard Stone, one of the researchers on the team, explains; “Even tiny adjustments in the amount of each component can have a huge effect on the microscopic structure, and this can cause radical changes in the superalloy’s properties. It’s rather like adjusting the ingredients in a cake – increasing one ingredient might produce one sought-after property, but at the sake of another. We need to find the perfect chemical recipe.”
They now have have 12 patents with Rolls-Royce, including one that uses a mixture of nickel, aluminium, cobalt and tungsten to make an extremely strong material.
“Instead of the cake being flavoured with two main ingredients, we can make it with four,” explains Stone. “This gives the structure even better properties, many of which we are only just discovering. We’ve also been looking at new intermetallic reinforced superalloys using chromium, tantalum and silicon – no nickel at all. We haven’t quite got the final balance to achieve what we want, but we’re working towards it.”
To find out more about how jet engines work and discover how the team is engineering new ‘super’ materials, watch this fascinating video:
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