Future zero-emission single-aisle aircraft will likely be powered by engines using direct combustion of hydrogen, as the pace of fuel cell development will not match the timeline for a new aircraft launch, according to former Airbus chief technology officer Paul Eremenko.
Eremenko, who now runs fuel storage and powertrain developer Universal Hydrogen, says that although fuel cells will improve, this will not happen quickly enough to allow the big two airframers sufficient confidence to launch a next-generation narrowbody based on the technology later this decade.
“I don’t think we are going to get there with fuel cells in that timeframe,” he told a webinar organised by consulting firm McKinsey on 27 January.
While a “combustion architecture” would be a “less elegant” solution it is still “better than the alternative and probably the only hope we have as an industry” to tackle the significant carbon dioxide emissions from short-haul flights.
Fuel cell-based powertrains will likely be confined to the 2MW class – around what is required for regional turboprops, he argues.
Eremenko’s view is supported by Robin van Muren, head of strategic development at the EU’s Clean Aviation programme.
He says that regional aviation is “open for the fuel cell approach”, but at present, for a Boeing 737 or Airbus A320 successor, “those with deep pockets will be betting on direct burning of hydrogen”.
There is also some debate on whether gaseous or liquid hydrogen will be more suitable for aviation in the long run.
Val Miftakhov, founder and chief executive of powertrain developer ZeroAvia, says given the relatively short time before its initial system – sized for 19-seaters – enters service, gaseous hydrogen is the “only realistic solution to push through certification”.
Sub-regional aircraft are also better suited to the installation of external storage tanks thanks to existing hard points, he adds, and the resulting drag penalty is “not too extreme”.
However, for larger aircraft cryogenic liquid hydrogen will be required; Miftakhov expects to be able to certificate such a system in the 2026 timeframe.
Eremenko, however, says Universal Hydrogen is designing its intermodal storage capsules for both liquid and gaseous hydrogen. The latter will be suitable for around two-thirds of regional operations, but “in order to get the last third you have got to go liquid”, largely due to its better volumetric energy density.
“There are certification challenges with both and it’s not immediately clear to me that one will get certificated before the other,” he says. Universal sees both its storage systems gaining regulatory approval in 2025.
Eremenko also rails against the “total insanity” of using green hydrogen to produce synthetic sustainable aviation fuel (SAF) – sometimes known as e-Fuel – rather than employing it in a more sustainable manner.
E-Fuels are climate neutral, but still emit CO2, he notes. Synthetic SAF will also require significant subsidies to make it competitive with conventional jet fuel, he says. “It is not the solution for the decarbonisation of aviation.”
