As the climate crisis deepens, efforts to reduce CO2 emissions intensify across every sector. Commercial aviation contributes 2.4% of global emissions, according to a 2019 study from the International Council on Clean Transportation, with short-haul flights being the most carbon intense. That’s not counting noise pollution and aviation aerosols in the contrails streaking our skies — small particles of soot, sulfur, and nitrogen compounds.
As cars, trucks, and trains speed toward electrification, and governments invest billions to ease the transition, hydrogen fuel cells (HFCs) are increasingly seen as a viable, even essential, solution for decarbonization. And if those vehicles can be retrofitted with HFCs, making them zero emission, why not airplanes?
“Decarbonization is the aviation industry’s existential challenge,” Anna Goranson, chief administrative officer of Universal Hydrogen (UH2), said. “Exponential traffic growth has made aviation one of the fastest-growing sources of greenhouse gas emissions, a trend which is unsustainable. We’re building the end-to-end value chain to enable true zero-emissions commercial services as early as 2025, ushering in a new golden era of flight.”
“Without hydrogen propulsion in single-aisle aircraft, there is no hope for aviation to land anywhere near Paris Agreement emissions targets by 2050,” Paul Eremenko, J.D., co-founder and CEO of the company, said in a statement. Founded in 2020 and based in Hawthorne, California, UH2 is bent on realizing its vision of regional aircraft whose only exhaust is water.
Retrofitting a high-wing, twin-engine airplane for hydrogen propulsion is no simple task. UH2 chose the workhorse of commuter aviation, the De Havilland Canada Dash 8-300, as its demonstrator. “With our experimental test flight coming up in early 2023, we’ve gone through a lot of work to safely retrofit the Dash-8 with our experimental hydrogen powertrain system,” McKenzie Kinzbach, UH2 principal propulsion engineer, said.
“We kept one of the original engines on the aircraft and replaced the other with our powertrain,” she continued. “Basically, we took all of the engine guts out of the nacelle and replaced it with our own parts. It took a lot of design and analysis to get everything to fit and interface correctly with the propeller and a 1-megawatt electric motor. It all had to go in a pretty small space out on the wing.”
The integration team also worked to supply hydrogen to the powertrain. “In the fuselage, we’ve taken out all of the seats, and all the interior structures that aren’t essential for demonstration flight, and put in a set of hydrogen fuel modules,” Kinzbach said. “There’s a whole system of tubes that supply the hydrogen from the modules to the powertrain in the nacelle, where the fuel cells power the electric motor and a high-voltage electrical system. We’re gathering a ton of data from experimental flight tests and have interfaces in the cockpit so the flight crew can see any warnings that pop up from sensors in our system.”
Major suppliers involved include magniX, which supplied the electric motor, and Plug Power, which provided the fuel cells. The Dash-8 will fly out of AeroTEC’s test facility in Moses Lake, Washington.
Safe, efficient, emissions-free flying
Whether gaseous or liquefied, hydrogen as fuel is light, clean, and safe. “We have industry standard practices that limit the concentration of hydrogen we can gather,” TeAnn Nguyen, senior engineer, systems requirements, said. “It’s flammable at 4% in the atmosphere, so we monitor concentration with hydrogen sensors. If the concentration is too high, you need to start venting it out to the atmosphere where it can catalyze with oxygen to form water on its own, or disperse to where it’s less than the ignition point.”
Because hydrogen is 14 times lighter than air, it quickly disperses upward when released, away from people and equipment. Not like jet fuel, which is heavy, toxic, and, in a fire, devastating. In a fuel cell with a platinum catalyst, hydrogen reacts with air from an intake and creates the electricity that drives the powertrain and electric motor. It’s a chemical reaction, not combustion.
Lucie Ravelojaona, principal engineer, advanced projects, noted that the plane’s performance will be the same as a conventional turboprop, with a range of up to 500 nautical miles, with a 45-minute reserve.
“Actually, it’s better, because there’s no emissions,” she said. “Yes, we lose a few rows of seats to the modules, but it can fly 99% of the routes the ATR 72 flies today. Also, when you think of maintenance, an electric motor is easier to maintain and repair than a turboprop engine and will be cheaper for the airlines.”
“We’re working on the architecture, trying to keep the weight the same,” Nguyen added. “Just because hydrogen is lighter than jet fuel doesn’t account for the other bits and bobs that need to be added, like heat exchangers and the fuel cells themselves. Our designs are intended to be at parity or better.”
Once considered too expensive to be practical, green hydrogen will soon be cheaper than jet fuel. And just like solar and wind power components, the cost of electrolyzers and fuel cells will drop further as production scales. “Long before a decade from now,” Eremenko said in a recent “How I Built This” podcast, “you will be able to fly on hydrogen with a major airline in the U.S., Europe, and other parts of the world for a ticket price that’s equivalent or lower, with the comfort of knowing the plane produces nothing but water.”
While testing continues on the Dash-8, UH2 also has an order from Massachusetts-based regional carrier Connect Airlines to convert 75 ATR 72-600 turboprops to hydrogen power, and more orders are coming in. The company is planning for the commuter planes to be certified for passenger service in 2025, and the ATR 72 was recently unveiled at Universal’s new facility in Toulouse, France.
“We will be supplying conversion kits to our customer airlines,” Kinzbach explained. “The airline does a retrofit process to replace the aircraft’s original engines with our hydrogen powertrains. After removing several rows of rear seats in the fuselage to accommodate the fuel modules, they can then get everything connected with the electrical systems — then add all the auxiliary things that let the aircraft fly comfortably for passengers.”
When the plane reaches its destination, empty fuel modules can be loaded out, shipped to and refilled at green hydrogen production sites and then returned to any airport desired using the existing intermodal freight network. Distributing modules and loading them using the airport cargo handling system is convenient. It also sidesteps the need for brand new infrastructure to replicate or convert airport jet-fueling systems to hydrogen, a prohibitively expensive proposition across the world’s thousands of airports.
How green is the hydrogen? “We’re well aware that ‘carbon-free’ energy production is a somewhat misleading term,” Nguyen said. “There’s carbon involved in the creation of a solar panel, for instance. Hydrogen electrolyzed by energy from a coal-burning plant is definitely not where you want to go. Even at this stage, at the experimental level, we’re keeping it as renewable and green as possible.”
A shared vision of cleaner flight
A sense of urgency underscores their mission to make aviation sustainable. “What initially drew me into engineering was rocketry, so I went to school for aerospace engineering,” Kinzbach said. “I learned a ton about aircraft design and operation. I knew I wanted to transition into clean tech, but I wanted to stay in aerospace if I could. To find aviation and clean tech being developed here was perfect.”
Ravelojaona agreed. “I’ve been fascinated by airplanes and aviation since I was a kid, just trying to understand how birds could fly when my two feet were stuck on the ground! So I studied at École nationale de l’Aviation Civile in Toulouse, right in the backyard of Airbus. I wondered how I could make aviation more sustainable, and have more impact on the climate. I was in Silicon Valley when eVTOLs were first being talked about, but that technology felt like it was too far in the future. UH2’s mission really drew me in — and we’re having a positive impact right now, versus 10 years from now.”
Nguyen found her way to UH2 through chemical and systems engineering. “I wanted to use my skills in engineering and science to improve the world. My first job out of college was at Lockheed’s space division, where I worked on antennae manufacturing. It was very cool, one-of-a-kind work.
“But the issues that face us today are immediate,” she said. “Space travel, while it’s given us life-changing technology — GPS for example — isn’t going to save the planet right now. Here, I’m making exactly the kind of impact I want. And when I’m working so hard, my question is always, ‘Am I leaving a legacy as an engineer that I can be proud of?’ Yes — and that’s a great part of my job.”
They’re working for a future without the roar of jet-fueled engines, where aviation powered by hydrogen is normal, not novel. Turning a new page in the rich story of flight, a quiet and clearer sky is on the horizon.
