Rolls-Royce tests jet engine with hydrogen

In Great Britain, Rolls-Royce has conducted tests with a jet engine that runs on hydrogen. This is a first step towards small aircraft flying on this gas.

It was a ‘soil test‘, with a loose jet engine on the ground. Rolls-Royce engineers had made this AE2100 jet engine suitable for hydrogen.

This hydrogen was produced using green electricity, namely electricity generated by the tidal power plant of the European Marine Energy Center on Eday, one of the Orkney Islands, on the northern tip of Scotland.

Adjustments are needed

“You can’t just send hydrogen through an ordinary jet engine, which normally burns kerosene. All kinds of adaptations are needed,’ explains Ivan Langella from TU Delft. The university teacher Flight performance and propulsion is not involved in the Rolls-Royce investigation. Rolls-Royce itself was unable to answer questions The engineer to answer.

Cold

To begin with, hydrogen must be cooled down to around -260 degrees Celsius in order to be transported in liquid form on a plane, says Langella. ‘The cold can negatively affect the materials in the pipes, e.g. Furthermore, hydrogen lacks the lubricating effect that petroleum naturally has. So you have to adapt the design of the jet engine so that parts don’t wear out too quickly’.

But there are also challenges in the jet engine’s combustion chamber. Hydrogen burns very differently from kerosene, says Langella. “The biggest challenge is to keep nitrogen oxides, NO, as low as possiblex.’ After all, CO is not formed when hydrogen is burned2 free, but just like when burning kerosene NOx.

Hundreds of small injectors

To do that, roughly speaking, two routes are possible, says Langella. Which Rolls-Royce uses is not known. ‘The first is by placing hundreds of tiny injectors in the combustion chamber, each injecting a tiny bit of gas. Just before all the gas has been burned in one cycle, hydrogen is injected again. As a result, nitrogen oxides have almost no chance to form.’

More air

The other way to NOxthe formation can be slowed down with so-called ‘lean premixed combustion‘, with proportionately more air than fuel available. “The two are partially mixed before entering the combustion chamber. Because you have excess air, it can absorb some of the heat of combustion, so the temperature stays a bit lower and NOxformation too.’

Different planes

The aircraft engine manufacturer Rolls-Royce collaborated with the airline easyJet for the tests. “We are committed to continuing to support this ground-breaking research. Hydrogen offers great opportunities for a number of aircraft, including the ones we fly,” says CEO Johan Lundgren of that company in a press release.

Decarbonisation of aviation

With their tests, both companies want to prove that hydrogen can play a role in the decarbonisation of aviation. There are two routes to this, both of which are likely to be pursued. On the one hand, hydrogen can be used to generate electricity on board an aircraft, in a fuel cell. Electric motors that drive propellers then run on the green power. We’ve written about it before.

Direct combustion

What Rolls-Royce has now tested is route two: direct combustion of hydrogen in a jet engine. This gives a higher output than with the fuel cell – necessary to power really large aircraft – but it requires further research. The advantage is clear: no CO comes out of the jet engine’s exhaust2 but water as a waste product.

Much larger volume

The disadvantage of hydrogen compared to petroleum is that the volumetric energy density of hydrogen is lower. An airplane therefore needs a much larger volume of it to get as far as with kerosene. Therefore, the use of hydrogen will for the time being be limited to shorter distances. For real long-haul flights, kerosene will still be needed for a while. Being the best option for it for now sustainable aviation fuels (SAFs), which are made from residual products, so there is no extra CO2 comes in the air. In the longer term, much is expected of synthetic petroleum.

2035

After the analysis of this first ground test of the concept, Rolls-Royce and easyJet plan another series of tests. These were to lead to a full-scale ground test with a Rolls-Royce Pearl 15 jet engine. “We are pushing the boundaries to discover hydrogen’s carbon-free potential that could reshape the future of aviation,” said Grazia Vittadini, Rolls-Royce Chief Technology Officer in the press release. The company hopes to deliver engines that run on hydrogen around 2035 and are suitable for small to medium-sized aircraft.

Obviously, hydrogen is one hot topic is in aviation, Langella also says. “A lot of research is being done into it, and it is also very promising. But before hydrogen can fulfill that promise as a suitable alternative energy source, one must look at the whole cycle. It is currently still expensive and slow to produce a lot of hydrogen, but that will hopefully change’.

Opening photo: a researcher near the jet engine used for the test. Photo Rolls Royce

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