Many pathways can lead to climate-neutral air transport

Since the beginning of 2020, researchers at the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt; DLR) have been working together in the Exploration of Electric Aircraft Concepts and Technologies (EXACT) project on designs for climate-neutral commercial aircraft. The concept of a fleet consisting of regional, short-haul and medium-haul aircraft with a wide range of propulsion systems is now available as an interim result.

These include regional aircraft with distributed electric propulsion systems as well as short- and medium-haul aircraft with turboprop and turbofan drives. These can be operated both hybrid-electrically by means of hydrogen fuel cells and by direct combustion of hydrogen or using Sustainable Aviation Fuel (SAF).

"Especially between the technology options based on hydrogen and SAF, a close race is emerging. We would now like to take the aircraft concepts and energy scenarios we have developed forward together with partners from industry and science and deepen them in joint cooperation projects for climate-neutral air transport," explains project leader Johannes Hartmann from the DLR Institute of System Architectures in Aeronautics in Hamburg.

Both the full life cycle of the aircraft and the process of extracting, transporting and providing renewable fuels have now been comprehensively considered in the analysis of the climate impact of the new configurations. The overall goal of the EXACT project is to design new aircraft configurations that can be operational with at least 70 seats and a range of 2000 kilometres by 2035.

The innovative aircraft designs should use new technologies to no longer release carbon dioxide. For this purpose, the project team first examined conventional engines in order to understand them in detail. From these findings, the team was able to develop different propulsion concepts and possible aircraft configurations, as well as evaluate their interaction in an entire fleet of different aircraft sizes.

Climate neutral from start to finish
The cooperation of 20 DLR institutes with their expertise and joint system competence makes it possible to think about and consider the entire life cycle of an aircraft - from production and operation to decommissioning and subsequent recycling. To this end, the project team has designed all the components of the various aircraft in detail and examined how they interact.

"Next, we want to look at the requirements for approval and industrialisation in more detail in joint projects with industry," says Hartmann "Medium-sized companies in particular can use our aircraft concepts to plan the pre-development of their components for delivery to larger industrial companies at an early stage."

In the near future, SAFs could already reduce the climate impact of air transport. In the long term, as is the case with direct hydrogen combustion, they offer the potential to reduce climate impact by up to 90 percent. However, completely different technologies are needed for hydrogen-powered aircraft. In addition, airport infrastructure and maintenance facilities must be adapted, and air transport personnel need to be retrained.

A special focus is also being put on considering the lifecycle not only of the aircraft, but also of the various energy sources. The engineers and scientists are investigating the environmental impact of the individual aircraft types from design to decommissioning.

By environmental impact, the researchers mean not only the emission of carbon dioxide and other greenhouse gases, but also, for example, water consumption or the contamination of soils by pollutants. This means that they also look at the impact on the environment and the climate before an aircraft component is produced and what happens to the materials after recycling.

'Green' energy carriers
In order to produce sufficient 'green' hydrogen, green electricity and water are needed. In specialised industrial processes, the hydrogen can be further processed into SAFs. The EXACT project is also investigating scenarios for transporting the energy carriers to the locations where air transport takes place in the most sustainable way possible.

"The direct coupling of such issues with aircraft design and technology development is completely new in our project. Petroleum has always been extracted from the ground and processed into kerosene in refineries; producing sustainable fuels is much more complex. Solar power, for example, could be generated in the desert, and water is available on coasts. In EXACT, we are researching how these energy resources can be obtained, transported and processed as efficiently as possible so that they can ultimately be used in aircraft," says Hartmann.

The scientists are already taking fuel production into account in scenarios for sustainable energy generation with subsequent production of hydrogen and SAF when planning new types of aircraft. They link this with the necessary infrastructure so that a new air transport system is planned to be sustainable and economically operable right from the start.

In the second half of the project, whole-system solutions are now to be found in which the technology modules interlock optimally. Only then will a reliable evaluation of the various technologies and energy sources be possible with regard to their climate impact.

Related Links
DLR Institute of System Architectures in Aeronautics
Aerospace News at SpaceMart.com

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