This solution could cut aviation emissions by up to 30 per cent

In the future, regional flights such as Trondheim-Oslo could become much more environmentally friendly with the help of a hybrid aircraft engine. 

This type of engine combines an electric motor and a combustion engine to drive a propeller. The innovation should be able to reduce CO₂ emissions by up to 30 per cent.

“The principle that causes emissions to decrease is the same as for hybrid cars – a combination of both fuel and electricity,” says SINTEF researcher Torstein Grav Aakre.

Focus on regional flights

Aviation accounts for about four per cent of the EU’s total climate emissions. This solution has the potential to reduce emissions by as much as one per cent throughout the EU, according to the researcher.

The focus is on regional flights because it is easier to make these flights greener using electricity.

“The reason is that batteries for electric engines weigh more than regular fuel. And the longer you have to fly, the more energy the plane needs to carry,” Aakre explains.

Major work underway

A lot needs to be developed to create the hybrid aircraft engine.

Among other things, better aircraft propellers and gearboxes between the electric engine and the combustion engine. Improved electric powertrains, energy management, and energy distribution are also necessary.

“Everything has to be as light as possible in aviation, so one of our main tasks is to reduce the weight of the aircraft engine as much as possible,” says Astrid Røkke.

She works at Rolls-Royce Electrical Norway. They are collaborating with SINTEF.

Researching the heart of the machine

SINTEF and Rolls-Royce are collaborating to develop the electrical insulation for what is called the stator. It is located at the heart of the electrical machine and makes the rotor turn.

“The stator converts current that is sent through coils into an alternating magnetic field that turns the rotor. The coils require insulation to prevent short circuits, and this needs to be as thin as possible – without compromising the insulation’s lifespan,” says Røkke.

Testing the insulation's lifespan with a new method

Building machines that are bigger, more powerful, and have a higher output than before requires using higher voltages and frequencies. 

There are currently no methods to test this.

“The industry does not have standards for calculating service life at such high voltages and frequencies. They only have figures for how much a given insulation material can withstand up to 1 kilohertz. Here, we’re talking up to about 50 kilohertz,” says Røkke.

She explains that Rolls-Royce, as a supplier to the aircraft industry, must know how materials behave at these frequencies in order to be completely certain that the insulation’s lifespan is long enough.

“Otherwise, we might create something that is dangerous to use,” she says.

But a newly developed test method from SINTEF makes it possible to calculate the service life of this important material.

Testing voltage and frequency

Put simply, they test this by connecting a voltage source to test objects that mimic the insulation.

"We turn the voltage on and off at a given frequency until an error occurs, to see the service lifespan of the test objects," Aakre explains.

Based on the test results, the researchers can find out how voltage and frequency affect the service life of the insulation.

“The test method SINTEF has created is something that we’ve needed at Rolls-Royce for a long time, but that we haven’t been able to find or had the expertise to develop ourselves. In other words, SINTEF has solved a real problem for us,” says Røkke.

Many good results

“We’ve had a lot of good results, and the experiments are still ongoing,” says Aakre.

As expected, the researchers have confirmed that the lifespan is shorter with a higher frequency.

“That’s what we thought would happen, but we couldn’t know for sure, because no tests have been published on this before,” says Røkke.

Right now, a demo of the aircraft engine is being built and will be tested in France next summer. The ambition of the research project is to have the new hybrid solution on the market by 2035.

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Read the Norwegian version of this article on forskning.no

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