Next-Generation Hydrogen Fuel Cell Technology in Aviation

Aviation 5 minute read

The development of hydrogen fuel cells for aviation is picking up speed. Milestone after milestone is being conquered, and commercial zero-emission flights are expected to be a reality in the not-so-distant future. In this article, you will learn about the most important next-generation features of the technology and what innovations are needed to fuel the transition toward full decarbonisation of the aviation industry.

Maintaining fuel cell temperature stability in aircraft

Temperature stability is a crucial feature of a hydrogen fuel cell. In most vehicle applications, the fuel cell would have an operating temperature of about 65-70 °C, and a peak temperature of about 85 °C. Hydrogen fuel cells in aircraft, however, require significantly higher temperatures: about 90-95 °C in general operation, with peak temperatures of 100-105 °C. Having a separate cooling system for the fuel cells in a plane will of course make the whole fuel cell system heavier. Instead, air can be let into the aircraft to cool the fuel cells, but that will create additional drag which results in quite a lot of energy being used just for the cooling. The higher the temperature that the hydrogen fuel cell can withstand while operating efficiently, the less cooling will be required – saving both weight and energy.

How do we best maintain the fuel cells temperature stability? There are two main alternatives: using materials that allow the hydrogen fuel cell to withstand very high temperatures, and making the fuel cell as efficient as possible. The fuel cell will generate both electricity and heat. The greater its efficiency, the less waste heat it will generate in relation to the power produced.

Optimising weight and reliability of an aircraft’s hydrogen fuel cell stack

Weight is an essential aspect of an aircraft. The fuel cell stack can support the overall weight reduction in the plane by having a high gravimetric power density (W / kg), but what truly matters in terms of weight is not the weight of the fuel cell stack itself but the weight of the entire fuel cell system or even the entire powertrain of the plane. This includes not only the thermal management system mentioned above but also the fuel tanks, the power electronics, hybridisation with batteries and many more.

By working closely together with OEMs (Original Equipment Manufacturers) and customers, we are able to optimise the weight and reliability of an aircraft’s hydrogen fuel cell system. This goes for the entire stack design process, but not least when it comes to the stack’s integration with the aircraft’s other systems. For example, to make the stack reliable, we use as many passive system components as possible. Active components, by contrast, are components that may eventually break. By using passive components wherever possible and by developing our fuel cell stacks in close collaboration with our partners, we ensure that the next generation of hydrogen fuel cells can function reliably together with the aircraft’s other systems over time.

Hydrogen fuel cells that meet tough aircraft power requirements

In addition to weight and reliability, the next generation of hydrogen fuel cells need to meet the particularly tough power requirements of aircraft. The power output from these have to be significantly higher than those of most other fuel cell-powered vehicles: megawatts, not kilowatts, even for smaller aircraft. Here, factors like weight and size come into play again. A greater power output requirement means that the hydrogen fuel cell stack has to be both larger and more powerful. Moreover, the gravimetric power density needs to be very high, meaning that the fuel cell stack should produce as many watts per kilogram as possible.

This presents another major step in hydrogen fuel cell development, with the next generation being more powerful than previous ones; and growing even more powerful still. We are already seeing the increased demand for fuel cell stacks with higher power output, from the aviation industry in particular. Balancing that demand with the factors described above is a challenge, but one which can be overcome through collaborative efforts. A key part of that is to look at lessons learned from other applications and industries as well, such as the marine or vehicle manufacturing sectors.

Smarter fuel cell stack housing allows for better system integration

Another interesting development is the integration of more features directly onto the fuel cell stack, through its stack housing. Stack housing helps protect the fuel cell stack from dust and humidity, but it can also have other, technical benefits. The housing can be integrated more with the hydrogen fuel cell stack and the aircraft’s other systems. One example of that could be to install a DC/DC converter on the stack housing, thus reducing the cabling needed to and from the stack. Less components may be used and the weight of the application can be reduced.

While stack housing is nothing new, it has often been more of an afterthought: something added to fuel cell stacks once they have already been developed and installed. And, naturally, adding weight and taking up more space as a result. As the technology and industry keep maturing, we are starting to see better ways of working with stack housing design. By keeping it in mind from the start and through the design phase, we can integrate the stacks and stack housing better and probably start saving precious space and weight instead. It is yet another way in which the next generation of hydrogen fuel cells will meet the unique requirements of the aviation industry.

 

PowerCell Group Enables Sustainable Aviation

Interested in how we’re helping decarbonise one of the hardest-to-abate industries? Explore how our hydrogen fuel cell technology is powering zero-emission aircraft today. Click here to learn more about our solutions for a cleaner, more sustainable future in aviation.

 

Johanna Dombrovskis

Senior Project Manager, PowerCell Group