Fresher flights

Engine components that promise to help cut aircraft pollution have been devised by a Munich-based company as part of the Clean Air Engine (Claire) technology project.

MTU Aero Engines has reduced the size of an aircraft’s engine by integrating optimised components, including a high-pressure compressor, a geared turbofan and a recuperator.

It claims Claire could help cut carbon dioxide emissions from aviation by 30 per cent by 2035.

MTU has been working with industry partner Pratt & Whitney to develop the components, such as the compressor.

‘We have been developing high-pressure compressors for a long time. We’re presently running one that we developed with Pratt & Whitney at our test centre in Munich, which is looking very promising,’ said Dr Erich Steinhardt, MTU senior vice-president of technology.

The eight-stage, 17:1 pressure ratio module, which was tested last year, consists of Integrally Bladed Rotors (IBR), in which the compressor blades are integrated on to each compressor disc.

Paul Adams, senior vice- president of engineering at Pratt & Whitney, said this design increases strength while reducing the weight of the compressor.

‘IBR technology, coupled with a new rotor design, materials and aerodynamic concepts, will make for a very lightweight and efficient compressor. This will be a great advantage on conventional or advanced geared turbofans,’ he said.

Steinhardt explained how the component would help to reduce pollution from aircraft engines. ‘In our opinion, you need a highly-efficient compressor to cut emissions. With the new compressor, we can achieve a high-pressure ratio, and the greater the pressure, the better the aerodynamic cycle of the engine.

‘In addition, we would reduce the weight of the engine by designing a very low-weight compressor, which would reduce the weight of the aircraft and ultimately fuel burn.’

He claimed another component that contributed to improved engine efficiency is the turbine. ‘The second component is the high-speed, low-spool turbine that we have been working on since the 1990s, for which we developed a counter-rotating fan and an adopted drop fan.

‘High-speed turbines improve engine efficiency by enabling the reduction of aerodynamic loading in a turbine,’ he said.

MTU has also made improvements to the geared turbofan, which has helped reduce noise pollution.

‘A gear system de-couples the fan from the low-spool turbine, which spins about three times as fast as the fan. Separating the components allowed us to build fans with larger diameters that work independently of the turbine and compressor, and these help to improve the propulsion efficiency.

‘We have been working on the geared turbofan in a demonstrator engine and found that the larger fan diameter, the higher pressure ratio created by two counter- rotating fan blades, and high propulsion reduced fuel burn. However, it also reduced noise pollution quite significantly, by about 24dB,’ said Steinhardt.

Attached to a geared turbofan is a recuperator, which helps to recycle heat energy produced by the engine’s turbine.

‘You can use the heat energy at the exit of the low-spool turbine and turn it back into the cycle by using this energy to heat up the compressor, like in a power plant,’ said Steinhardt. ‘It is very efficient, and we’ve developed a compact heat exchanger that can cope with high-pressure differentials and temperatures of 400ºC.’

Although all the components have been put through a number of tests, Steinhardt said more were required.

‘We have run many noise and efficiency tests on a small-size engine model in a wind tunnel in Cologne, so we have got a very broad database of results. But of course there is a lot of work to be done,’ he said.