Hydrogen’s potential as a primary aviation fuel makes it one of the most promising prospects for sustainable aviation, Tarsus F&E’s Aviation Sustainability conference in Dubai in late 2020 heard.
Nikhil Sachdeva, project manager at consultancy Roland Berger, who chaired the session on hydrogen, said three broad areas needed to be tackled for the fuel to progress as an alternative propulsion source: technology and technological challenges, perception, largely related to safety concerns, and paradigms, which today involved similar modes of fuel-burn, whether for regional or long-haul aircraft, something that the establishment of hydrogen’s feasibility for jet propulsion would likely change.
Hydrogen’s low viscosity, high buoyancy, diffusivity, and volume, but with lower weight per unit than traditional kerosene, poses several technical challenges. The implications for airliner design are that aircraft will have to have much bigger fuel tanks to cater to hydrogen’s higher volumes.
“That has an impact on the aircraft structure itself as a whole,” said Gabriel Godfrey, product owner sustainable aircraft at industrial risk control outfit Apsys, which in 2001 became 99.2 percent Airbus-owned.
“If we took at the Airbus ZEROe project as an example, it gives us a hint of what hydrogen aircraft may look like. Some [prototypes] look similar to what we have today—they'll probably be the first ones—but even for those, the location of [fuel] storage is quite different to existing aircraft—and they're also working on some ground-breaking new concepts.”
Sami Alawneh, chief of the Safety and Environment Unit at King Hussein International Airport in Aqaba, Jordan, saw a number of obstacles to the practical implementation of hydrogen solutions at airports.
Airports already faced a lack of space, and hydrogen is likely to be a major issue when it comes to creating new fuel facilities or retrofitting existing ones. On the aircraft, stresses on tanks, piping, and handling pumps, as well as refueling hydrants, would mean higher impacts on materials than with current systems. Aqaba faces a dramatic range in temperature, from zero degrees C at night in winter to 50 deg C in summer, likely to increase stresses on materials and procedures.
“I'm expecting a lot of difficulties and challenges,” Alawneh told the panel.
It would make little sense to tackle hydrogen in a silo approach, where airframers focused on the aircraft, airports on airports, and oil and gas firms on producing the fuel and nothing else, said Godfrey. “Aviation has a history of actually being pretty good at working together, but we will have to take this a notch higher. There will have to be a holistic and collaborative approach across the industry,” he said.
Multiple aircraft concepts will emerge under hydrogen, depending on missions and markets addressed. “We will not be able to sustain the 20, 50, or 100 concepts that you see when you Google 'sustainable aircraft' or 'new mobility' today,” Godfrey said. “There will be some level of convergence. The downside of that opportunity is that there's a lot of uncertainty. At this point, [it's too early to discern] the winning concepts.
“We cannot afford, as an industry, to have multiple solutions. Those risks will not be manageable, both logistically and economically. That means that there is a core foundation of topics on which the industry will have to agree, and that is typically best done through standardization.”