Logistic, Mobility & Infrastructure

Flying is harmful to the climate because a lot of CO2 is released when kerosene is burned. One environmentally compatible solution could be to run aircraft on sustainably produced hydrogen in the future. To do this, suitable supply chains must be established. A joint project in which Hamburg University of Technology is involved is investigating what this might look like.

"Above the clouds, freedom must be boundless," sang singer-songwriter Reinhard Mey many years ago. In the meantime, flying has come to stand for high CO2 emissions. But researchers are doing a lot to make the aviation industry climate-neutral. One approach is to use green hydrogen as an energy carrier instead of fossil kerosene. However, current capacities to produce hydrogen are still low, and large amounts of electricity are needed for production. One solution to this problem could be to generate the electricity in offshore wind farms at sea. Green energy forms the basis for splitting water into its components oxygen and hydrogen. Only if the hydrogen is produced from renewable energy sources can its use contribute to climate protection. This is a promising approach, but one that poses major challenges for the aviation industry.

Over the next three years, the joint project "HyNEAT - Hydrogen Supply Networks' Evolution for Air Transport" will conduct research to plan the networks for supplying hydrogen at airports. The focus is on the cost-effective production and transport of green hydrogen, which is a volatile gas. This complicates the planning of delivery networks. For use in aviation, the hydrogen must be liquefied because it has a smaller volume in the liquid state. This requires it to be cooled to at least minus 250 degrees Celsius. There are currently only a few such liquefaction plants in Europe, including one in Leuna in Saxony-Anhalt. For transport and storage, the liquid hydrogen must also be well insulated, otherwise there is a risk that it will evaporate.

Models for the supply of green hydrogen

At TU Hamburg, Professor Christian Thies' Resilient and Sustainable Operations and Supply Chain Management Group is involved in the project and tasked with developing mathematical optimization models for the so-called "Hydrogen Supply Chain Network Design Problem". For this purpose, energy systems and demand are analyzed and individual components are modeled. Finally, the results will be combined and specific solution methods for the complex models will be developed with colleagues from mathematics. For example, they will calculate what sizes the pipelines through which the hydrogen is transported must have, or how many trucks must be used for the transport. "With the help of the knowledge gained, our working group creates various scenarios. We examine them and use them to derive recommendations for action for politics and industry on how to efficiently provide green hydrogen for aviation," says Prof. Thies. "Just as necessary as developing new propulsion systems and aircraft concepts is building the corresponding hydrogen infrastructure. The biggest challenge will be to arrive at competitive costs that enable the operation of new types of hydrogen-powered aircraft," continues the supply chain expert.

The project is looking at and investigating a total of three levels: The researchers are sounding out the global hydrogen potential for aviation. They are calculating whether they can be implemented in the European energy system, with the associated scope extending to Africa and the Middle East. And finally, they describe their findings down to the local level to see what a typical airport must look like.

The joint project is funded by the German Federal Ministry of Education and Research (BMBF) with around three million euros. Participants include Leibniz Universität Hannover, Technische Universität Braunschweig, Technische Universität Clausthal, Technische Universität München, Technische Universität Hamburg, and an industry advisory board whose members include Airbus, Deutsche Aircraft, Lufthansa, Linde, Siemens Energy and Hamburg Airport.

Further information

• Project website: www.hyneat.de
• For more information on the working group, visit www.tuhh.de/oscm

A TU Hamburg project shows that metal aircraft parts created in a 3D printer are much lighter and can be manufactured faster than conventionally produced ones. They help save kerosene and reduce the CO2 footprint of aircraft.

At first glance, it's not obvious what this workpiece is: It is round, open on both sides and there are many holes on the surface. What makes the curious piece special is that it is a metal part made in a 3D printer that is about a meter in diameter. "It's part of an aircraft turbine," says Dirk Herzog, solving the mystery. "And in fact, it is one of the largest individual parts that have been produced additively, i.e. by 3D printing, using a laser process to date," explains the engineer, who is responsible for the project for the Institute for Laser and Systems Engineering at TU Hamburg. But it's not just the size that's astonishing: "Switching from conventional casting to the additive process reduces costs and weight by 30 percent. And that means that its use can save valuable kerosene and thus CO2."

Down with emissions

It is an important step for aviation to comply with the EU's Green Deal. It stipulates that transport emissions should fall by 90 percent by 2050 compared with 1990 levels, and the aviation sector is expected to play its part. One research initiative to develop fuel-efficient aviation technologies was the Clean Sky 2 program funded by the European Commission and the European aerospace industry, which gave rise to the MOnACO project in 2018. In addition to TU Hamburg, which researched the printing process, project partners include Autodesk, which is taking care of design optimization, and TU Dresden. Their experts are building a test rig with state-of-the-art instruments that they will use to validate and measure the flow data after production. The consortium is working closely with the engine manufacturer GE Aerospace in Munich.

In principle, there are particularly stringent requirements in aircraft construction. This also applies to parts suppliers and leads to long lead times and high costs. These challenges and the fact that a turbine center frame is not a rotating part made it an ideal candidate for additive manufacturing. Dirk Herzog's team, which collaborates with the Fraunhofer IAPT in Bergedorf for 3D printing, makes it possible to manufacture the part in one piece, so that 150 individual parts no longer have to be joined together at the end - as is usually the case. This reduces the lead time for the manufacturer from nine to two and a half months.

Micrometer-thin layers

The printing itself takes place in a sealed-off large container. "In a layer of metal powder, in this case a nickel alloy, a laser beam fuses the individual parts of the powder at over 1,000 degrees Celsius," explains Herzog. "The layer is only 60 micrometers thin and sinks after the process. The metal powder is again evenly distributed and the laser exposure allows the next layer to form." The process repeats itself countless times until the turbine part is printed after quite a few days of construction. "A major advantage of additive manufacturing is the freedom in design. Depending on the specification, it can be adapted and rearranged at any time. Air diffusers, curves, channels or grid structures, everything is possible. At the beginning of the project, we mainly tried out how far we could reduce the wall thickness to save as much weight as possible," explains Herzog.

The process used is not limited to aviation. It has been used for medical implants, for example, for some time. But it is in aerospace that the financial benefits of weight reduction are greatest. This is shown by a simple "rule of thumb," which states that in aviation, 1 kilogram of weight saved can save 1,000 euros in fuel costs. Over the lifetime of an aircraft, this corresponds to around 25 metric tons of CO2. In other words, much more than in the automotive industry, where calculations are completely different due to higher unit numbers: Here, savings of 100 kilograms are needed to achieve the same cost effect. Since energy costs have risen across the board, weight reductions are likely to have an even greater financial impact. Herzog explains: "This is also the reason why such projects are often initially tested for the aerospace industry. 3D printing has already become established for individual, smaller engine components such as injection nozzles. But perhaps in the future, large-scale printed components will also be installed in aircraft as standard."

The MOnACO project consists of a consortium of Hamburg University of Technology (TU Hamburg), Technische Universität Dresden (TUD) and technology company Autodesk. It is supporting General Electric AAT Munich in the development and manufacture of a large additively manufactured metal component - the Advanced Additive Integrated Turbine Centre Frame (TCF).