Despite delaying service entry by up to 10 years, Airbus is still pressing ahead with its ZEROe hydrogen aircraft programme and has tweaked the design of a conceptual fuel cell-powered airliner that could carry up to 100 passengers on routes of up to 1,000nm (1,850km).
Planned improvements to the power density and efficiency of its hydrogen fuel-cell propulsion system derived from ongoing testing will enable the design to use four 2.5MW units rather than the six 1.25MW engines seen on earlier iterations.
Unveiling the revised configuration at the Airbus Summit event in Toulouse on 25 March, Glenn Llewellyn, vice-president for zero-emission aircraft, said: “Today we reaffirm our belief that hydrogen can and will fly.”
Doubts over the airframer’s commitment to pursuing hydrogen propulsion emerged last month after it revealed a delay to the ZEROe timeline of five to 10 years – and a 25% cut in annual funding.
It blamed low technology readiness, and the slow progress being made in developing a regulatory framework and a hydrogen production and distribution infrastructure.
Speaking at the summit, Airbus chief executive Guillaume Faury said launching a programme too early ran the risk of developing a “sort of ‘Concorde of hydrogen’, where we would have a solution but one that would not be commercially viable at scale.”
Initially revealed in 2020, the 100-seater was one of three hydrogen-powered concept aircraft – also including hydrogen-combustion designs – drawn up as part of the ZEROe programme. Service entry was tentatively planned for the mid-2030s.
But since that point “we have continued to advance our research,” says Llewellyn.
As part of that effort, Airbus has been developing a 1.2MW fuel cell powertrain that will run on liquid hydrogen.
Ground tests have been taking place at its Ottobrunn facility near Munich since 2023, with the powertrain taken to its full 1.2MW output late that year.
Testing of the full system continued throughout 2024 and is still ongoing, says Hauke-Peer Luedders, head of engine development. “We have created a massive amount of learning,” he says.
Consequently, Airbus has been able to redesign the engine, reducing weight and volume by 15%. Simplification of the architecture, including cutting the number of components by 50%, has also brought “a significant improvement in operational reliability without compromising safety”.
For example, each engine will now incorporate two 1MW electric motors rather than four less powerful units on the version currently on the test stand at Ottobrunn.
Additionally, the engine features a revised thermal-management system using a pair of large side air intakes rather than two side inlets and a scoop on the underside of the nacelle.
Luedders says this has enabled a lighter, simplified internal construction and also allows the unit to take advantage of the air flow from the propeller when the aircraft is stationary but with the fuel cells running.
Airbus is also working how to mitigate contrail production from the water generated by the fuel cells. However, Luedders declines to reveal details, citing pre-patent confidentiality.
Airbus has been developing the fuel cells themselves through its Aerostack joint venture with automotive specialist ElringKlinger. The resulting 1MW stack, using low-temperature proton exchange membranes, is the first such system in the world to have followed “aviation requirements” from the very beginning, Luedders claims.
“We are now starting the journey towards a significant performance improvement and getting the weight down to the [production level],” he says.
Airbus had intended to flight-test the fuel cell propulsion system aboard an A380 testbed later this decade, but that plan has been shelved as part of the wider programme delay.
However, late last year, prior to the change of course, the powertrain destined for flight test passed the critical design review (CDR) milestone, says Luedders.
Concluding the CDR process provided the engine team with “significant learnings on how to really design something aerodynamic and flight-worthy”, he says.
The powertrain previously intended for flight test is currently being built and will now be assembled at Ottobrunn and used a ground-test asset and eventually run on liquid hydrogen from a bespoke stainless tank supplied by an external partner.
Commissioning of that “next-generation” system is likely to begin in 2026, he adds, leading to what Llewellyn describes as “testing of the complete end-to-end system” the following year.
A separate fuel tank, and its associated control system, capable of holding 100kg of liquid hydrogen is also currently being built at Airbus sites in Nantes, France and Bremen, Germany.
Tests of the fuel tank will later take place towards the end of this year at the Air Liquide Advanced Technologies facility in Grenoble in eastern France.
Andy Reynolds, head of hydrogen storage and distribution, says the 100-seat ZEROe concept aircraft would use two tanks, each holding around 750kg of liquid hydrogen.
Llewellyn says Airbus will use the delay to ZEROe to “further improve the performance of the hydrogen technology we are working on”, potentially incorporating new technologies, such as a cryogenic superconductivity, which are at an earlier stage of development.
Although Airbus will “stick within the 100-200-seat [size]” for the concept “we are still working on how far we could push the technology”, he adds.
If a higher-capacity or longer-range aircraft becomes the target, Llewellyn says the propulsion architecture “would need to be different”, incorporating features like a cryogenically-cooled electric motor: “Those kind of technologies would need to be brought in to scale [the aircraft] significantly.”
Another consequence of the changes to the scope of ZEROe is the decision to “focus our efforts on a fuel-cell propulsion system”, says Llewellyn, dropping consideration of a hydrogen combustion engine. Only the fuel-cell powertrain offers the potential for a “close to zero-emission” aircraft, he notes.
Faury insists Airbus is not backing away from hydrogen: “We are absolutely convinced this is an energy for the future,” he says, but “there is more work to be done”.
