The H Factor

With hydrogen hype hitting the headlines how does Rolls-Royce see the lightest element in the universe playing a role in its decarbonisation strategy?

It’s official, hydrogen is a hot topic in the world of aerospace. Even with offices closed and no water coolers to chat over, hydrogen is the gaseous substance on everyone’s lips. Already a subject gathering momentum, H received an extra boost when Airbus announced its three new hydrogen powered concepts in a slick webinar in mid-September, and the world’s first hydrogen-powered commercial aircraft took to the skies in the same week.

So what does this mean for Rolls-Royce and how does hydrogen fit into our decarbonisation strategy?

Rolls-Royce is uniquely positioned to play a key role in decarbonising a number of energy sectors not just aviation, and hydrogen can play a key role in this.

In civil aerospace understanding the opportunities and challenges of hydrogen is part of our continuing sustainability strategy, which is built around three pillars: improve the gas turbine; promote SAF; and be at the forefront of developing innovative propulsion technologies.

Hydrogen is primarily part of the innovation pillar as new technologies and infrastructures would need to be developed to fully enable its benefits. It is not a simple drop-in fuel, like SAFs for example, which are already suitable to power our latest generation engines.

We currently have work underway to understand the challenges of hydrogen fuelled propulsion and developing the associated technology roadmaps, and we are working with the  industry to fully explore the potential of hydrogen.

Hydrogen is ideally suited to decarbonise many energy and power sectors but we also recognise aviation has unique challenges - partially due to the specific weight and size constraints of carrying fuel, and also because the industry’s reliability and safety requirements are set very high, which requires very high engineering maturity barriers to be achieved, particularly for passenger-carrying services. While not insurmountable, these requirements mean we need to ensure enough account is taken of the time to transition from prototypes to products.

Timing wise small hydrogen powered aircraft could potentially be available before the end of the decade with regional becoming available early in the next decade (2030-35).

How hard is it to adapt existing aero-engines to run on hydrogen?

We do have some experience in this space as we have successfully tested our Trent engines with a hydrogen/kerosene blend in the past. However, moving to 100% hydrogen would require some adaption to the current gas turbine design.

The biggest challenge would be managing the flame temperature and stability in the combustion system. Then there is the question of adapting the fuel delivery and management system, notably for liquid hydrogen. So it is possible but there would need to be a big focus on redesigning these elements of the current engine design as well as looking at the gas turbine as a complete tank-to-exhaust system and taking a more holistic, overall system level approach.

This total system approach becomes even more viable when you deliver part of the engine power electrically. So our work in electrification and hybridisation as well as in developing embedded motors and starter generators all complements the development of a future propulsion system that could be powered by hydrogen – either deployed using a fuel cell or combusted directly in the engine.

Of course, radical design changes will be necessary in any airframe to create a product that is market-ready. The larger the aircraft the more radical the design change necessary to adapt to hydrogen storage requirements - 1kg of hydrogen has three times the energy of kerosene but more importantly it take up five times the volume.

The industry would also require an entirely new form of infrastructure for the handling and transportation of hydrogen – in liquid form it needs to be kept at -253C – which does not exist today.

How does Hydrogen complement the other technologies that are being developed to help move aviation move towards a more sustainable future?

A future picture seems to be emerging that shows the very smallest range of aircraft powered by batteries; the possibility of batteries, hybrid, all-electric or hydrogen to power the small to mid-range; and even more efficient gas turbines in the larger range aircraft so we should expect to see a combination of solutions as the industry transitions to a more sustainable future for aviation.

Therefore, aero engines as we know them today, or very close derivatives, will still be required but it’s quite possible that they could be fuelled by sustainable aviation fuel or hydrogen. In the longer term gas turbines will continue to evolve and we see a combination of all these technologies turning it into an even more efficient system delivering even better performance. Our vision is a marriage of innovative technologies that will deliver a more efficient mechanical and electrical hybrid system that is potentially fuelled by hydrogen.

In a post COVID-19 world, where sustainability will be a priority, we will need to understand how hydrogen can be used in a wider roadmap to decarbonise our world, not just in aviation but in other forms of transport long-term technology developments.

Within our Power Systems Division we are already actively involved in several hydrogen projects, which are providing us with valuable experience.  We recently announced a partnership with the recently established Daimler / Volvo JV to use their hydrogen fuel cells for stationary fuel-cell generators as CO2-neutral emergency power generators for safety-critical facilities such as data centres. They will offer emission-free alternatives to diesel engines, which are currently used as emergency power generators or to cover peak loads. These can also be used in microgrid solutions.

And our small modular reactor programme will generate zero carbon electricity, which can be used either to supply the grid directly or indeed to drive electrolysers to generate green hydrogen. The hydrogen can then be used as the energy carrier itself or further converted into sustainable aviation fuels.

Whilst there are great attractions to a hydrogen-based economy there are barriers to its realisation including: widescale adoption, production at scale, infrastructure investments, bulk storage, distribution and safety considerations. There is also the issue of how to create a simultaneous demand and supply for hydrogen technologies to ensure the scale up can drive the costs down.

If we want hydrogen to be a sustainability solution, we also need to look at the lifecycle of its production – there is very little truly “green” hydrogen being produced today. Although Rolls-Royce SMRs could be a zero-carbon form of production.

There is a public hunger for action on climate change to happen now rather than in the long term. SAF is ready as a response to that demand – there is no requirement to redesign aircraft. We now need to understand how hydrogen can be introduced to complement that in parallel. We also have to recognise that if there is a demand for people and cultures to globally connect again, then for the long-range market SAF is the only current option (65 per cent of fuel consumed on flights over 1,000nm).

So despite the hype, hydrogen powered aviation is no silver bullet. It will take a combination of different solutions, including SAFs, electric, hybrid and more efficient gas turbines, powering different missions and complementing one another, to help the industry reach its decarbonisation goals.

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