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After unveiling its ZEROe concept aircraft nearly 18 months ago, Airbus on Feb. 22 announced it is taking the next step toward its ZEROe initiative by partnering with CFM International to develop a flight test demonstrator based on hydrogen.
The objective of the hydrogen demonstration program is to ground and flight test a direct combustion engine fueled by hydrogen, as part of Airbus’s goal to market a zero-emission aircraft by 2035.
Airbus said during a Feb. 22 press conference that it will use an A380 aircraft as the ZEROe hydrogen combustion demonstrator, equipped with liquid hydrogen tanks that will supply the engine which is located along the rear fuselage of the aircraft. Airbus said the A380 was selected as the demonstrator due to the space available on the aircraft to install the additional systems required for the program.
According to Sabine Klauke, Airbus chief technical officer, a number of changes must be made to the A380 to transform it into a hydrogen demonstrator. First, support will be installed on the aircraft to add a gas turbine for hydrogen combustion. Then, just below the main deck, four liquid hydrogen tanks will be installed and stored in a caudal position. Lastly, “we will install the distribution system right to the engine in order to make it fly,” said Klauke.
The tanks, which will be hermetically sealed, are to be delivered from Airbus’s new zero-emission development centers. Different materials are currently being evaluated for the hydrogen tanks, including CFRP, composite, and metal. In terms of hydrogen capacity, Klauke said 400 kilos of liquid hydrogen will be used on the A380 for this demonstration.
As part of the program, CFM International — which is a 50/50 joint company between GE Aviation and Safran Aircraft Engines — will modify the combustor, fuel system, and control system of a GE Passport turbofan to run on hydrogen. It will be mounted along the rear fuselage of the flying testbed to allow engine emissions, including contrails, to be monitored separately from those of the engines powering the aircraft. CFM will complete extensive ground tests prior to the A380 flight tests.
The U.S.-manufactured GE Passport engine was selected for the program because of its “physical size, advanced turbo machinery, and fuel flow capability,” Airbus said.
Mohamed Ali, vice president of engineering at GE Aviation, explained in detail what hydrogen will mean for the engine and the propulsion system: “To distribute the fuel from the storage tanks to the engine combustor, it will require the development of a new cryogenic fuel delivery system. Before the liquid hydrogen can enter the engine’s combustion chamber, we will need to convert it into gas to be burned cleanly inside the combustor.
“Unlike jet fuel, hydrogen is actually then injected into the combustor as gas, making its mixing with air to actually be easier. But hydrogen burns at much higher temperatures than jet fuel does today,” Ali continued, adding that CFM will build on its current advanced materials, coatings, cooling technology, and developed combustor and turbine parts that can withstand such temperatures.
While burning hotter means greater susceptibility to other emissions, such as nitrogen oxide, Ali said CFM intends to combine the expertise of GE and Safran to minimize nitrogen oxide formation.
Moreover, Ali said hydrogen burns 10 times faster than jet fuel, which will require new designs and technologies to control the flame and make it stable.
“As our next steps, we will modify an existing GE Passport engine for the purposes of this program, adjusting its fuel distribution system, combustor, and controls to work with hydrogen. We will fly the modified engine . . . to prove out the technologies. What we learn from this program will inform us about potential future engine developments.”
While Airbus, of course, is providing the A380 platform to test the hydrogen combustion engine in cruise phase, the OEM will also be responsible for defining the hydrogen propulsion system requirements and overseeing flight testing.
Ground tests have already begun with some of the technological aspects, and the goal is to fly by the end of 2026 — which will prepare the program for maturation into 2035, “as we want to be in the market by then,” said Airbus’s Klauke.
In terms of the certification of hydrogen propulsion, Michel Brioude, Safran chief technical officer, said the U.S. Federal Aviation Administration and European Union Aviation Safety Agency are “really open-minded to working with us” on the hydrogen demonstration program. CFM is currently working with the regulators to determine the key points in terms of certification, as well as the regulatory requirements to demonstrate that they can fly safely.
“It’s our view that hydrogen propulsion is a fundamental part of the long-term solution,” said Jeff Knittel, Airbus Americas chairman and CEO. “And we remain realistic about the challenges that such a transformation of aviation presents. We are committed to this new aviation future, and we fully embrace the opportunity and the challenges that lie ahead.”