The aviation sector has embraced the challenge of decarbonization. Hydrogen-powered aircraft lead the race toward 2050 environmental targets, but hurdles remain and one big question lingers: will Europe’s ambition take flight or hit turbulence?

Europe's aviation faces a double challenge: the transition to zero-emission, and the opportunity to lead this revolution and to maintain its leadership in such a strategic sector. The environmental stakes are high: the aviation sector is responsible for 3.8 percent of global CO₂ emissions and, without immediate action, these could triple in the next 25 years, according to forecasts by the International Civil Aviation Organization (ICAO). The European Green Deal has set a goal of reducing transport emissions by 90 percent by 2050, but the clock is ticking. One of the keys to meeting these goals is the take-off of hydrogen-powered aircraft.

The use of hydrogen as a fuel in aviation is constrained by its very nature: to be used on board, the lightest chemical element on our planet must be stored in liquid form at cryogenic temperatures (-253°C) and requires new, lightweight, high-efficiency tanks. This is at the heart of the Overleaf project, financed with European funds and coordinated by Emma Celeste Lope Retuerto of Aciturri. "Our main goal is to increase the volume of hydrogen stored while keeping weight and costs under control. After testing the path of liquid hydrogen storage and demonstrating that our solution is valid, the next step will be to turn this process into practical solutions, in order to make these technologies available on the market within a few years. In this way, we will help solve the problem of zero-emission flights by transforming hydrogen into a readily available fuel, and meeting the EU's 2050 recommendations".

Hydrogen has a lower volumetric energy density, a feature that translates into the need for higher on-board fuel storage than in conventional aircraft: in other words, explains Lope Retuerto, "We need to increase the volume of hydrogen in storage devices". She is echoed by Roger Groves of TU Delft University, who collaborates in the research: "To make hydrogen an efficient fuel for large-scale commercial aviation, we are working on a new design for storing hydrogen, which cannot be stored in the location of current aircraft. Additionally, we also need a new type of distribution system to prevent hydrogen leakages and efficiency losses. This is why we are building a new kind of sensor to detect leaks and ensure passengers' security."

The work on Overleaf has reached the final stage with important achievements, both in tank design and in tackling the risk of liquid hydrogen (LH2) leakage, says Jordi Renart, Associate Professor at Universitat de Girona, one of the research institutions involved: "A new concept of tank has been developed, with new materials and through new manufacturing processes, additive manufacturing and automated fiber placement, with new materials". With the support of project’s partners Aciturri and Aimen, Renart’s team has contributed to the design of the tank by performing part of the mechanical numerical analysis by finite elements. It’s been a long procedure, aiming at meeting both the structural requirements and the constrains imposed by the manufacturing process, he says: "We have worked in the design of the geometry, orientations and layup sequence of the materials of the inner and outer tanks, and the joints between them and the external supports." Concerning the leakage issue, one of the main objectives was to quantify the permeability of the hydrogen gas through the tank’s walls, explains Renart: "We are developing inspection techniques to detect cracks in the walls using micro-computerized X-ray tomography. “This technique now allows us to identify potential crack paths where LH2 leakage could occur."

Creating a new tank design is a complex challenge that could not only reduce emissions but also lead to breakthroughs in other sectors. "The technology that we are developing could also have a profound impact in the field of rail transportation, with new materials taking advantage of the ability to work at -253° Celsius," explains Emma Lope Retuerto. "Our new-generation sensors, designed to operate in critical conditions, might be useful for other industry sectors, and thanks to our progress in the Automatic Fiber Placement process, new applications could be envisaged also in the telecommunication sector, where carbon fiber is fundamental."

To speed up the kick-off of the hydrogen-aviation era, the European institutions should take the lead with conviction, exhorts Krisztina Hencz, Aviation Policy Manager at Transport & Environment, an NGO that contributed to crafting the ReFuelEU Aviation regulation. "The EU should create a comprehensive scheme of incentives, clear rules, and appropriate financial mechanisms," she says. "Synthetic fuel mandates must be met, with penalties for those who do not comply, and at the same time, the Clean Industrial Deal can be a unique opportunity to create a real industrial strategy that favors e-kerosene and hydrogen." Governments should seize this opportunity, also to exploit "e-kerosene untapped potential in supporting the e decarbonization of the aviation sector, drive the cleantech transition and deliver green jobs, in an area where Europe is still a leader", adds Hencz. Not to mention that the green fuels market at the moment relies mostly on start-ups, "which would benefit greatly from big oil companies' support via offtake agreements and/or direct investments". Hence, the need for "de-risking mechanisms to address the unique challenges of first-of-a-kind projects, such as low-interest loans, loan guarantees, and risk-sharing mechanisms."

Achieving the environmental targets set by the Green Deal for the aviation sector is possible, says Groves. Still, many challenges are still ahead. "Aviation is a very critical industry from the security standpoint. Any new technology requires extensive certification, and so it takes time to implement solutions in civil aircraft. We also need to rethink fuel depots at airports, and this entails massive investments". The way is marked out and it's now up to Europe to decide whether to lead or to chase, reaffirms Krisztina Hencz. "The EU is taking steps in the right direction. Nonetheless, it still needs to provide stronger support to hydrogen-based synthetic fuels to ensure that the projects being developed get to final investment decision. The contrary would mean making the problem bigger, and reducing the chances of aviation ever meeting its climate goals," she concludes.