Hydrogen-powered engines open up opportunities for fossil-free aviation, and the fuel system is a key component. Hydrogen contains more energy per kilogram than today's kerosene, and also has the advantage that the residual product of combustion is mainly water vapour.
Short and medium-haul flights, for example within Europe, offer the best opportunities for a transition to hydrogen-fuelled engines. A study from Chalmers published earlier this year shows that hydrogen-powered aircraft could meet the needs of 97 percent of all intra-Nordic flights by 2045.
In the transition to hydrogen, industry manufacturers expect to be able to continue using the same type of turbofan engines as in today's aircraft, which means that engine fuel systems will have to be adapted to handle the very low temperature of liquid hydrogen. To keep the weight of the aircraft down, the hydrogen needs to be stored in liquid form, which requires a temperature in the tank of around -250 degrees Celsius, and injecting the fuel for combustion at that temperature means significantly reduced efficiency with increased fuel consumption as a result.
For several years, researchers at Chalmers have been working on various projects to develop a completely new type of heat exchanger, for which a patent application has now been filed by the partner GKN Aerospace. The system utilises the low storage temperature of hydrogen to cool engine parts, and then uses waste heat from the exhaust gases to preheat the fuel by several hundred degrees before it is injected into the combustion chamber. "Each degree of temperature increase reduces fuel consumption and increases range," says Carlos Xisto, an associate professor at the division of Fluid Mechanics at the Department of Mechanics and Maritime Sciences, and one of the researchers involved in developing the new technology.
Impressive improvement of mature technology
In the recently published study Compact heat exchangers for hydrogen-fuelled aero engine intercooling and recuperation, the researchers investigated the effect of the heat exchanger on short- to medium-range aircraft equipped with hydrogen-fuelled turbofan engines. Among other things, they measured a reduction in fuel consumption of almost eight per cent during take-off. The lead author of the study, Alexandre Capitao Patrao, explains why this is a more impressive figure than you might think.
“Eight percent may not sound like much, but in an aircraft engine that is a mature and well-established technology, it is a very good result for a single component. These kinds of improvements also have a reverse snowball effect, as the size and weight of the aircraft is reduced, there are further savings in fuel consumption. With more optimisation, this type of technology in a standard commercial aircraft such as the Airbus A320 could improve range by up to 10 percent, or the equivalent of the Gothenburg-Berlin route.”
Increased efficiency and decreased emissions
Interestingly, the study also describes that emissions of environmentally harmful nitric oxides decreased by 37 percent while engine efficiency increased. To reduce emissions, the engine needs to be cooled, and with traditional technology this reduces efficiency, but in a hydrogen engine with a heat exchanger this does not happen, as the energy is recuperated in the process.
The technology has been developed within the EU project ENABLEH2, and the PATH project which was funded by Chalmers' Transport Area of Advance. The projects ran between 2018-2022, during which time the infrastructure was constructed that has since been used to test new engine components and carry out simulations. Within Chalmers' centre Tech for H2, research is ongoing to further develop the technology.
Contacts
Alexandre Capitao Patrao, previously postdoc at Mechanics and Maritime Sciences, now Senior Aerodynamics Engineer at GKN Aerospace Engine Systems.
alexandre.capitaopatrao@gknaerospace.com
Telephone: +46 700 87 30 96
Carlos Xisto, associate professor, Division for Fluid Dynamics, Mechanics and Maritime Sciences
carlos.xisto@chalmers.se
Telephone: + 46 31-772 14 58
Isak Jonsson, researcher, Division for Fluid Dynamics, Mechanics and Maritime Sciences
isak.jonsson@chalmers.se
Telephone: + 46 31-772 50 79
Tomas Grönstedt, full professor, Division for Fluid Dynamics, Mechanics and Maritime Sciences, Director of Tech for H2.
tomas.gronstedt@chalmers.se
Telephone: + 46 31-772 14 55