One step closer to hydrogen-fuelled planes

Airbus has announced plans to test a hydrogen-fuelled aircraft by the middle of this decade, with a view to launching zero-emissions flights by 2035.

The technology will be tested on a modified A380 jetliner, in a newly-signed partnership with CFM International. 

Hydrogen fuel, touted by some as the fuel of the future, is seen as a potential solution for the deeply polluting aviation and shipping industries in a net-zero world: hydrogen burns cleanly, producing just energy and water vapour.

But while engineers have promoted hydrogen as a possible transport fuel since at least the 1920s, real-world technologies are still in their infancy, thanks to the destructive dominance of fossil fuels over the last century. 

Airbus’ announcement, then, marks an important early step in a move towards making the sector compatible with net-zero.

“This is the most significant step undertaken at Airbus to usher in a new era of hydrogen-powered flight since the unveiling of our ZEROe concepts back in September 2020,” said Sabine Klauke, Airbus Chief Technical Officer, in a statement. 

“By leveraging the expertise of American and European engine manufacturers to make progress on hydrogen combustion technology, this international partnership sends a clear message that our industry is committed to making zero-emission flight a reality.”

How will they do it?

The program’s stated objective is to “ground and flight test a direct combustion engine fuelled by hydrogen, in preparation for entry-into-service of a zero-emission aircraft by 2035”.

According to Airbus, their partner CFM will modify the combustor, fuel system and control system of an engine to help it run on hydrogen, and the engine will be fitted onto the airline’s discontinued A380.

“Our ambition is to take this aircraft and add a stub in between the two rear doors at the upper level,” said Glenn Llewellyn, Airbus’ Vice President of Zero Emissions Aircraft, in a promotional video on YouTube. “That stub will have on the end of it a hydrogen powered gas turbine.”

“Inside the aircraft there will be hydrogen storage and hydrogen distribution, which will feed the engine with hydrogen.”

There will be instruments and sensors around the hydrogen storage unit and engine, to monitor how the system functions both in ground tests and in-flight. Up in the cockpit, instruments will need to be modified with a new throttle to change the amount of power the engine operates at, and a display for pilots to monitor the system.

Why hydrogen fuel? 

Hydrogen, the most abundant element in the Universe, burns cleanly, and can be produced using renewable energy through the electrolysis of water (though it can be produced using fossil fuels, too). 

Given that it’s so abundant, can be made from water, and combusts to produce water vapour, it can be a closed-loop energy system; the definition of renewable. 

It’s also highly reactive: hydrogen gas, made up of two hydrogen atoms, can combust at extremely low concentrations. It can combust in response to a simple spark, and it’s even been known to combust when exposed to sunlight or minor increases in temperature. That’s why it’s a suitable replacement fuel for kerosene, but it’s also why the system needs to be tested for safety.

“Aviation is one of these things that everyone agrees needs hydrogen for decarbonisation, because it’s not going to be possible to electrify long distance air travel in the next few decades,” explains Fiona Beck, a senior lecturer at ANU and convenor of the Hydrogen Fuels Project in the University’s Zero-carbon energy for the Asia Pacific grand challenge. “We just don’t have the battery technologies.

“One kilogram of hydrogen has 130 times the energy of one kilogram of batteries, so in something like air travel, where weight is really important, there’s just no way you’re going to get batteries light enough to directly electrify air travel.”

Is it safe? 

You’ve probably heard of the Hindenburg disaster. On May 6, 1937, the commercial Hindenburg airship, loaded with 7 million cubic feet of hydrogen gas, exploded, killing 35 passengers.

That’s a very high-profile incident in which hydrogen proved deadly, but a proverbial boatload of hydrogen gas encased within a fabric covering is nothing like the fuel cells proponents of hydrogen fuel are creating in the modern era.

Nonetheless, the incident demonstrates why it’s important to ensure the safety and impregnability of fuel storage; a single spark can prove fatal (though that’s the case with existing fuels, too).

“The key will be to have really good storage containers for the hydrogen, and you’re going to have to re-engineer all the fuel delivery lines,” says Beck, “because you can’t assume that the systems that deliver kerosene safely to an engine are going to be suitable for delivering hydrogen.”

Ultimately, Beck says pre-existing, sophisticated hydrogen technologies, even if they aren’t derived from aviation, mean engineers aren’t going into this blind.

“We already use quite a lot of hydrogen in industry, which is very different than flying a plane full of hydrogen, but still, we know how to handle it relatively safely.

“So, it’s just about designers and engineers making sure that they consider all the safety aspects of it. It’s different, but not necessarily more challenging.”

 Two paths to a hydrogen fuelled future of flight?

Beck notes that Airbus aren’t the only commercial entity exploring hydrogen as a fuel type. In fact, Boeing are incorporating hydrogen into their vision of a cleaner future, but in a different way.

“There’s a difference between just getting hydrogen and burning it in a modified jet engine and what Boeing are doing, which is using sustainable air fuels,” she says. 

But what are sustainable air fuels (SAFs)? Beck says they’re made by combining hydrogen with carbon dioxide to make a sustainably-produced kerosene. 

“The difference is that instead of getting fossil fuels and refining them, you start with hydrogen, which you would hope comes from green sources, and then you take some carbon dioxide captured from another industrial process, and you’re cycling the carbon dioxide one more time before it gets released.”

So, CO₂ is still released into the atmosphere, but the individual flight is not adding its own new load of greenhouse gases to the amount. Instead, it essentially piggy-backs off a pre-existing quantity of emissions that were already produced somewhere else.

The type of fuel that wins out remains to be seen.

“It’ll be really interesting to see which approach we go for in the longer term,” Beck muses. “With synthetic air fuels, your plane engine doesn’t need to change at all, nothing about the demand side needs to change – it’s just kerosene.

“But then there’s issues, because you’re still using carbon dioxide.”

Some commentators see Boeing’s bet on SAFs as a more pragmatic approach that may help us usher in a less polluting age, quicker. On the other hand, if successful, the Airbus system can be fully carbon-neutral from fuel production through to combustion.