Air travel is harmful to our climate. To change that, the HyFly project is developing a hydrogen-powered propulsion system for light aircraft. What is already available in the automotive industry needs to be completely reinvented for the aerospace sector. The researchers are collecting data at a test stand and are developing solutions for the extreme conditions of aviation.
In 2020, “Flugscham” made it into the Duden dictionary of German language. The word describes the “guilty conscience of travelling by plane as it is harmful to the climate due to high CO2 emissions”. The HyFly project at the THWS location in Schweinfurt contributes to future air travels without the environmental guilt: THWS is researching a CO2-neutral drive train for planes.
In a nutshell: “Our goal is to fly”, says Dr. Isabell Wirth, research associate at HyFly, a co-operative project subsidised by the German federal government. In co-operation with four businesses, the Technical University of Applied Sciences is developing a climate-friendly drive train for ultra-light aircrafts. The technology is based on hydrogen fuel cells.
Hydrogen bears great potential for aerospace applications
Currently, air traffic is responsible for three percent of global CO2 emissions. The industry managed to reduce fuel consumption per passenger kilometre by 24 %, however, CO2 emissions increased by a total of 16 % through a rise in flights. Here, hydrogen represents a solution. The International Council on Clean Transportation just predicted that by 2050, two thirds of all flights could be powered by hydrogen fuel. Then, one third of the mileage would have become climate-neutral.
The HyFly project aims to help bringing about this sustainable change in air travel with hydrogen. The energy carrier can be used in many ways - and it is storable. The energy is generated in a fuel cell: Here, hydrogen and oxygen react to water. The chemical reaction also releases electricity.
However, according to a statistic of the German Hydrogen and Fuel Cell Association, hydrogen is currently mainly produced through steam reforming from natural gas or naphtha. In this case, it is called “grey” hydrogen, which is not climate-neutral. The massive increase in the price of natural gas and the growing climate awareness lead to producers reconsidering their options. “Thus, hydrogen is currently making a transition from grey to green, and it becoming more economical as well”, explains Professor Dr. Johannes Paulus, project manager at HyFly.
Hydrogen air planes demand new ideas
Professor Dr. Paulus is excited for a special moment in autumn 2023: For the first time, a two-person plane equipped with a propulsion system developed at THWS is scheduled to take off. But before this can happen, the THWS scientists have a lot of work to do. Their task is to test a fuel cell along with battery and electric motor on the ground, and to simultaneously develop a battery charging system and a motor control.
Although there already are cars that are propelled by fuel cells, the technology cannot be transferred directly to planes. “The conditions are completely different. We have questions that highly differ from the ones asked in the automotive industry”, Professor Dr. Paulus says. For example, unlike most motorists, pilots are highly-trained personnel, enabling us to engineer the controls very differently and allowing us to include more flight control parameters. "However, our task is to find out what needs to be measured to guarantee safe operation", the project manager says.
The greatest challenge is weight. Planes need to be light, space is limited. A two-person ultra-light plane must not weigh more than 600 kg. Thus, the propulsion system needs to be "simplified" as far as possible, as Paulus explains: “We intend to use as few components as possible for our fuel cell, all it needs to be is functional.” In a car, engineers would use a recirculation loop to lose as less hydrogen as possible, he says. “It’s basically the same for air planes, but with the goal to cut components in order to save weight, a so-called Dead-End Operation is probably the better solution.” This means: As little hydrogen as possible should remain at the end.
The team of researchers is currently constructing a test stand to find out which components can be cut from the propulsion system. In its essence, it is based on the pioneering work of Toni Schott. In his Bachelor’s thesis he covered the planning of the test stand. Now he’s doing his Master’s degree while working as a research associate, conducting the actual tests.
The test stand provides results for new developments
Toni Schott is excited to be part of the research project. “It's a real playground for engineers”, he says. “Only a few people know how a hydrogen-powered air plane behaves in the skies.” The aircraft moves in high spheres, where temperature and humidity are low. The fuel cell reacts very sensitively to such conditions. Particularly, drying out of the fuel cell's membrane is an issue.
At the test stand, Professor Dr. Paulus and his team are now gathering data on the behaviour of the propulsion system under various conditions to integrate it in the system’s digitised twin. “We are sitting in a simulated cockpit to fully analyse the propulsion system during a flight”, he describes his work.
Based on the results they develop new solutions, as there are many questions that state-of-the-art aircraft engineering does not yet know the answers to. Many components need to be redeveloped from the ground up. “The spherical tank made of carbon fibre is an innovation”, Schott says. It is especially light-weight and space-saving; and it is built to withstand the high pressures required to store hydrogen, even when the atmospheric pressure is declining at higher altitudes. The energy source presents many challenges to the researchers, but according to Paulus, one great advantage is that the fuel cell is easily recyclable, which also contributes to climate protection.
The ultimate goal is to provide a propulsion system for small to medium-sized planes. “We dream of also covering long distances”, Wirth says. With an electric motor, you cannot travel that far. But with a hydrogen fuel cell, distances of up to 1,000 kilometres can currently be covered, which is approximately the distance from Schweinfurt to Rome.
Click here to listen to the podcast "Mechanical Engineering: Hydrogen drive for light air planes" (podcast in German/English transcript available)
Climate-friendly solutions are also elaborated for large and passenger aircrafts. Airbus, for example, plans to ship the first hydrogen-powered planes in 2035. The overall forecast by Allied Market Research of 2021 is a global market volume for hydrogen-fuelled air planes of 144.5 billion US dollars in 2040.
Besides researching fuel cells, institutions and the industry are investigating the possibility of using hydrogen instead of kerosene in conventional propulsion systems. At the moment, it is unforeseeable which technology is going to succeed in which performance category in the long run, Professor Dr. Paulus reckons. Schott concludes: "From my point of view, there is no better approach to climate-friendly air travel than hydrogen"