Video: Megawatt-scale liquid H2 airliner powertrain comes to life

Universal Hydrogen is already flying the world's largest hydrogen airliner – and now the company has started testing swappable liquid hydrogen fuel modules that'll radically boost the range of clean passenger aircraft operations slated for 2026.

Decarbonizing aviation is challenging; you need to carry a lot of energy in the lightest possible form, and it's very hard to compete with jet fuel on that metric. Batteries are currently abysmal, so the last few years have seen a furious pace of development in the hydrogen space, generally taking hydrogen on board as a compressed gas, then running it through a fuel cell to power electric propellers.

Gaseous hydrogen might get your aircraft roughly double the range that a battery can, and that unlocks short-range regional flights with zero emissions. Universal is at the absolute bleeding edge here – last year, the company flew the largest hydrogen fuel cell-powered aircraft ever built, by a country mile. You can see Lightning McClean, a converted Dash-8 airliner, take its first flight in the video below.

Airline operators will need to give up some paying seats to fly clean like this; the Dash-8 can normally take up to 56 passengers, and this gaseous-hydrogen retrofit gobbles up 16 seats. But running on gaseous hydrogen lets operators run flights up to around 460 miles (740 km) in range, and that, says Universal, will cover around 75% of the routes normally serviced by this class of plane.

To go further than that, you'll need to upgrade to cryogenic liquid hydrogen. You need to store it at incredibly low temperatures, below 20 K (-253 °C/-423.4 °F) at ambient pressure levels, to keep it in its liquid phase and stop it boiling off. If you can manage that, it becomes a matter of how much passenger space you give up, but the potential is there to cover nearly all the flights this class of plane handles on jet fuel.

That's amazing, but if gaseous hydrogen is bleeding-edge, liquid hydrogen aviation powertrains are several years behind that, and really just emerging from the research stage. Only last September, H2Fly made the world's first-ever piloted flight of a liquid hydrogen-powered plane, with the remarkable twin-fuselage Pipistrel Taurus shown below.

H2Fly says that moving to liquid H2 has basically doubled the range of the HY4 compared to what it was getting on compressed gas, so the potential here is clear.

Which brings us to now. Universal Hydrogen has been working for some time now to build a modular liquid H2 fuel system at a scale relevant to its megawatt-class propulsion system for mid-sized airliners like the Dash-8 and ATR-72.

We're talking something that looks externally exactly like a regular air freight container, that can be filled at a ground facility, then swapped in and out of an airliner for refuelling using exactly the same equipment you'd normally load cargo with. Here's what it'll look like, although the image below shows the gaseous modules used with Lightning McClean.

Universal Hydrogen

Each liquid H2 fuel module contains a double-walled, vacuum-insulated vessel with a capacity of around 200 kg (441 lb) of liquid hydrogen. Each also has a built-in heat exchange system, which accepts hot coolant from the electric propeller motors and uses it to vaporize the liquid H2, moving it to a gaseous form that can be run through the fuel cells. There's also various boiloff venting facilities and leak detection systems for safety, as well as a "leak-proof quick connect" to plug the thing in once it's on the plane.

Every two of these modules you stick into a converted ATR-72 represents some 575 miles (926 km) of range, on top of all necessary reserves, so airlines will be free to configure their retrofit planes for maximum range, or maximum seats, or somewhere in between.

On Tuesday, Universal announced that it had hooked a liquid H2 module up to its "Iron Bird" ground-based test rig for the first time, at the Mojave Air & Space port. Iron Bird is a functional equivalent to Lightning McClean's propulsion systems, and the team ran it through a full flight test profile without a hitch, providing constant power for an hour and 40 minutes. Check it out:

“This is the largest fuel cell powertrain ever to run on liquid hydrogen,” said president and CTO Mark Cousin, “making it another in a series of ‘firsts’ for Universal Hydrogen."

"This end-to-end demonstration of a hydrogen molecule moving from our filler/dispenser into our storage module and then into our powertrain is the first time that all the pieces of our product portfolio for regional aviation have come together,” added co-founder and CEO Paul Eremenko. “The next step is to upgrade our flight testbed to fly the powertrain fueled by our modules.”

This landmark achievement represents some truly remarkable progress in one of the toughest and most important decarbonization sectors; liquid hydrogen airliners offer an incredibly promising way to clean up our skies. Universal is shooting for this system to be ready for commercial passenger flights as soon as 2026.

And things might not stop there. As we wrote in January, the other leading startup in this space, ZeroAvia, is now working on taking things up another level. Cryo-compressed hydrogen storage will keep the fuel at close to cryogenic liquid temperatures, but it'll also add moderate amounts of pressure to the mix. A lot of factors come into play, says ZeroAvia, but the end result looks like it could provide a 40% airliner range boost over what liquid H2 can offer.

Forgive us for geeking out over hydrogen and other clean aviation options over the last few years; we know it's not the world's sexist topic to bust out at a party. But the rapid advances in this field give us great hope that the ~800 megatons of carbon dioxide a year that aircraft belch into the atmosphere (that's a full 2% of all global energy-related CO2 emissions) can and will be dealt with.

So we're right behind Universal Hydrogen, ZeroAvia, H2Fly and the others working to drive this technology forward, and we wish them the best.

Source: Universal Hydrogen