Reflecting its relatively measured projections for hydrogen power’s role in the aviation industry’s sustainability efforts over the next 10 or 15 years, Boeing continues to promote the advancement of sustainable aviation fuel (SAF) as perhaps the most effective way forward in the near- and medium-term. Although Airbus also advocates for the increased availability of SAF, the European company sees a more prominent role for hydrogen in the nearer term and plans to introduce a hydrogen-powered narrowbody airliner by 2035.
The extent to which the U.S. company’s view on hydrogen contrasts with that of Airbus went on display during a series of media briefings in Seattle in mid-June, as Boeing chief sustainability officer Chris Raymond called for the need to understand the “realities” and relative benefits of various alternative fuel types, including hydrogen and electric.
Reflecting on his company’s considerable experience with fuel cells and cryogenic hydrogen production over the past decade and a half, Raymond didn’t reject those avenues’ potential but cautioned that their large-scale application will require far more development time than some would suggest. He cited Boeing’s own studies on hydrogen power—including the world’s first piloted hydrogen fuel cell-powered aircraft in 2008 and an airplane powered by liquid-hydrogen combustion engine in 2012—as if to underscore the company’s knowledge of its limitations and challenges.
Raymond also cited early lessons learned from studies Boeing and NASA recently completed on a 37,000-gallon carbon-fiber hydrogen fuel tank. “If you convert that to equivalent energy for jet fuel, it's about 3,700 gallons of jet fuel, which is about what powers a regional jet, but the cross-section of [the tank] is about the size of a regional jet,” he explained, highlighting the scale challenges liquid hydrogen presents for application on an aircraft.
“And by the way, the white stuff that you see on there is called frost,” he added, referring to a photograph in his Powerpoint presentation. “So how are we going to deal with that at 30,000 feet? And how are we going to deal with the water that we create with hydrogen fuel cells at 30,000 feet, especially contrails, which are all coming into our vocabulary now as a component of carbon emission? We have to understand how to deal with contrail formation on a hydrogen fuel cell airplane. And we're studying that.”
Raymond also cited the lifecycle challenges associated with hydrogen production, which with the technology now available generates its own greenhouse gasses. Large-scale production of so-called green hydrogen with techniques such as electrolysis and steam methane reforming will take many years and involve an evolutionary, rather than revolutionary, process.
“A lot of it is what you believe about how fast the grids are going to change to renewable electricity,” said Raymond. “I don't believe we're going to just sort of get to this Nirvana state eventually. I think there'll be a migration over the years. And I actually think as we start to introduce things like industrial carbon capture, you can make some of the fuel pathways cleaner…and people are starting to do that now.”
More immediately and even for the near future, though, Boeing has turned its focus to sustainable aviation fuel (SAF) as the most promising avenue for reducing greenhouse gasses, particularly given the volume of fuel burned on long-distance flights. Raymond noted that 50 percent of all flights don’t exceed 1,000 kilometers but they account for only 15 percent of all the fuel used. Meanwhile, roughly 10 percent of all flights extend beyond 2,800 kilometers but they account for half of all the fuel burned. Given that even Airbus acknowledges that hydrogen-powered widebodies won’t become feasible for several years after the first narrowbody propelled by hydrogen reaches the market, the role of SAF as a primary emissions reduction measure will extend far beyond 2035, argues Boeing.
Pledging to ensure all its commercial airplanes can fly on and gain certification to use 100 percent sustainable aviation fuels by 2030, Boeing points to its partnerships with airlines, industry, governments, and research institutions to expand limited SAF supplies and reduce the fuels' cost as evidence of its environmental credentials. The airframer worked with airlines, engine manufacturers, and others to conduct biofuel test flights starting in 2008 and gain approval for sustainable fuels in 2011. In 2018, the Boeing ecoDemonstrator flight-test program made the world's first commercial airplane flight using 100 percent sustainable fuels with a 777 Freighter in collaboration with FedEx Express. Its most recent ecoDemonstrator, a former Singapore Airlines 777-200ER unveiled on June 16, will also test the effects of SAF on emissions reduction along with about another 30 sustainability and safety-related technologies.
Although he didn’t dismiss the potential for hydrogen to serve as one avenue for reaching the industry’s net-zero emissions goals, Raymond clearly sees SAF as the most important way forward, at least for now.
“We have put a lot of our voice on sustainable aviation fuel as one of the forms of that renewable energy,” he said. “There's a lot of room to run in sustainable aviation fuel. There's room to scale up the production of it. And there's also room to scale up the innovation around it. And the fuels we all have in our heads as sustainable aviation fuels today are going to change. There are going to be new feedstocks. We're going to introduce carbon capture into the process. Hydrogen's going to get greener as a component of the process.”