At first glance, the competing technologies for the future of cleaner, greener aviation might seem like the start of a highly disorganised long-distance race. Big players have thrown their names, influence and money behind specific fuels and concepts to green the aviation of today, which are already halfway down the first straight, while others are leaning towards a full rethink of the industry, cutting across the inside of the race track.
To learn more about the runners and riders in this greener aviation technology race, we sat down for a deep-dive with Lukas Kaestner, co-founder and chief operating officer at the Sustainable Aero Lab, the Hamburg-based sustainable technology and policy incubator.
“If you look at efficiency and emissions, the most promising sustainable aviation technology is currently hydrogen,” Kaestner says. “It’s great to see that there are more and more projects coming up in this field, from big OEMs like Airbus to startups such as ZeroAvia — and no less important, that there is the political will to pursue and fund research and development in this field.”
A key challenge for hydrogen is the novelty of the technology and its requirement for a full infrastructure stack to produce, transport and store the fuel — and to do so sustainably. The future cannot be, for example, diesel trucks driving tanks of supposedly green hydrogen around the world. This tech stack will require investment from both public and private sectors.
Moreover, Kaestner says, “hydrogen will most likely concentrate on the short and medium haul segment of commercial aviation, which is also the largest. Currently, the technology is not advanced enough to give an answer for a sustainable long-haul flight segment.”
Taking a regional approach may well make sense here if a particular region’s political and industrial leaders can pathfind the development of hydrogen infrastructure for short- and medium-range flights.
Within the longhaul field, the best answer to the question at least into the mid-term is likely to be sustainable aviation fuels. “One additional advantage of SAF is the reduction of contrails with a strong climate impact. Hydrogen produces even more contrails, at least currently,” Kaestner notes. “You’ll end up with the question of what’s more important: zero emission or climate impact?”
In terms of the industry’s big players, Kaestner summarises, “Airbus is definitely in the game & has set the course into the next decade with its zeroE concepts. If this follows the planned tracks, we can expect to see a first demonstrator fly by 2026, and a serial aircraft in the 2030s. Boeing so far has been shy with committing to anything bold and is currently more focusing on SAF.”
At the other end of the field, battery-electric power is a key focus of the urban and regional air mobility market, with startups like Ampaire, Electra, Heart Aerospace, magniX and ZeroAvia all jostling for position. New market entrants like D328neu and Pipistrel are also working in this space, which looks to change the economics and environmental impact of distant regional air travel especially around relatively inaccessible areas, with the Scottish highlands and islands, British Columbia waterways and rural Nordic areas.
“The third field in terms of airframes is the advanced air mobility market with air taxi startups such as Lilium, Volocopter, Joby Aviation, Archer and more,” Kaestner says. “These companies are currently at prototype stage, with very ambitious timeframes. It will be interesting to see whether they can live up to it.”
Hydrogen’s technologies and powerplant options are inherently linked
Diving into the technology and its production, “Liquid hydrogen is the best option for aviation, but the whole process chain needs a lot of primary energy,” Kaestner notes. “Electrolysis and liquefaction are very demanding and a lot of research has to go into these fields as well. In addition you need carbon dioxide-neutral primary energy to generate hydrogen. It doesn’t make sense to produce hydrogen out of natural gas — currently the main source for hydrogen — but you have to define the complete chain from beginning to end. Political support worldwide is needed to make this happen.”
Once the heavy lifting to source the fuel is secured, the big question becomes which of the propulsion options — or both, in parallel or in series — seems most attractive.
The notionally easier option is to continue to combust hydrogen as fuel inside a gas turbine, which will require significant work but is not an entirely unknown process to the existing players in the propulsion market.
More complex is fuel cells, where the very fundamentals of how an aircraft is powered will change. This will open up opportunities for new players — ElringKlinger is already working with Airbus — to throw their hat into the ring.
One future pathway could be gas turbine-burned hydrogen stored as liquid in tanks by the mid-2030s, with future development of fuel cells into the 2040s and 2050s.
Whichever technologies take the lead, they will be even more digital than today, and with the Airbus A350 already capable of generating a full terabyte of data every flight hour (GE says the same about its latest engines) it will be vital to improve data mining, analytics and processing.
“Aviation can still tap a lot of potential by using more advanced data engineering,” Kaestner says, “for example in the field of artificial intelligence, to constantly monitor, adjust and optimise engine performances as an example. These questions should be a general ‘must’ to the industry, as they are not only beneficial to the environment, but also to the costs of operation.”
Taking account of the bigger picture will be crucial, Kaestner says. “A ‘clean’ hydrogen aircraft is still not very efficient when it circles over England for 45 minutes, before being cleared to land at Heathrow. The optimisation of routes, flight planning, ground operations, et cetera, will be another crucial factor to become truly sustainable.”
Next-generation air traffic management can help here, as can continuing research and development into artificial intelligence to propose new ways of managing growing global traffic.
Fundamentally, Kaestner concludes, “there will be no single factor and no hardware ‘product’ that will become the sole ‘saviour’ for aerospace. As an emission-emitting industry, we need to turn every stone – and find solutions where everything plays together.”
Author: John Walton
Published: 24th June 2021
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