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Super-efficient engines
Generations of engineers have been improving plane engines over many decades to make them as energy efficient as possible.
‘Already a lot of work has been done on reducing the emissions of jet engines, reaching an energy efficiency of about 97% in some parts of the engine,' says Sylvain Lardeau, an aviation technology expert. ‘But more work is needed to further reduce noise and weight.'
A cross section through one of the latest engine designs. Image: Pratt & Whitney
In the past, engine development has been important for saving cash as fuel costs rise and to reduce noise. But now it matters from a climate-change perspective too - and there's still much work to be done.
Engineers are attempting to optimise a number of elements of engine performance to make them as efficient as possible. They want to improve the ‘bypass ratio' - the rate that air flows through the engine - using the smallest amount of fuel.
Thermal efficiency is also important - so that as much as possible of the heat energy produced from the burning of fuel is transformed into engine power.
Engine evolution
There are lots of trade-offs when it comes to designing engines and scientists need to weigh up things such as weight, power, heat resistance and noise. Open-rotor engines - likely to be implemented in 8-10 years' time - would deliver more propulsion for less fuel on short-haul journeys than conventional engines.
An open-rotor engine. Image: easyJet
Open rotors would be best suited to journeys of less than 3000 kilometres. They would also be larger, and could be relocated above the tail of the plane to shield some of the noise. The turbine would have two sets of specially shaped high-speed propellers that rotate in opposite directions. This helps eliminate the vortex of swirling air that is usually created behind propellers. And because the fan blades would not be contained inside bulky housing, a major source of drag and weight would be removed.
The next generation of plane engines is nearing completion. The engine manufacturer Pratt & Whitney is developing a Geared Turbofan™ engine. All its components have been redesigned, but a key feature is the introduction of a gearbox, like you find in a car. This will allow each part of the engine to operate at whichever speed is most efficient.
‘The Geared Turbofan engine is not only lighter and quieter than today's engines, but it burns 12-15% less fuel, produces 12-15% less CO2 emissions and reduces nitrogen oxide emissions by 55%,' says Matthew Perra from Pratt & Whitney.
One part of the engine where the fuel is burned - the combustor - is particularly responsible for producing nitrogen oxides (NOx). This group of gases help cause climate change by reacting with sunlight to make the greenhouse gas ozone.
Researchers at Georgia Institute of Technology are one group of engineers developing a low NOx combustor. By lowering and evening out the temperature in the combustor and forcing fuel to mix thoroughly with air before it's ignited, NOx can be reduced significantly, maybe even enough to meet the aviation industry's target of 80% cuts.