Could existing jet engines run on hydrogen?
Since it's already been successfully proven that sustainable aviation fuel can be substituted into existing jet engines, the question now is whether hydrogen could also be a "drop in" fuel.
This is something that Rolls-Royce (which is not associated with the ZEROe program) has been looking at, having successfully tested its Trent engines with a hydrogen/kerosene blend in the past.
"Moving to 100% hydrogen would require adaptation to current gas turbine design," Alan Newby, director of aerospace technology and future programs at Rolls-Royce Civil Aerospace, tells CNN Travel.
But Newby also explains that the biggest challenge would be managing the flame temperature and stability in the combustion system. Then there is the question of adapting the fuel delivery and management system, notably for liquid hydrogen. Another caveat, he notes, is that one kilo of hydrogen has three times the energy of kerosene, but more importantly, it takes up five times the volume.
"So the answer is -- yes, it is possible but there would need to be a big focus on redesigning these elements of the current engine design as well as looking at the gas turbine as a complete tank-to-exhaust system and taking a more holistic, overall system level approach," says Newby.
How these concepts could change commercial aviation
The unveiling of the Airbus concepts symbolizes a milestone in terms of civil aerospace adopting hydrogen at the top tier of industry.
True, ongoing efforts with smaller aircraft and drones using hydrogen and hydrogen fuel cells are plentiful. However, Airbus's announcement signifies a major strategic shift for commercial aviation, whereby hydrogen could become the norm for short- and medium-haul flights for the 2030s and beyond.
"But there's no point in addressing a hydrogen airplane if you're not going to look at the system in which it operates," cautions Gray.
Aviation "needs to address the whole zero carbon issue in a holistic systems way, looking at airports, air traffic control, aircraft, and transport to and from airports," he explains.
Fortunately, the dialogue between stakeholders appears to be underway.
"This is going to create a massive change in the energy and aviation ecosystem," says Airbus's Glenn Llewellyn. "We've already started working with airlines, energy companies, and with airports because this kind of change really requires a teaming across industry and inside the aviation industry in order to make it happen."
This necessity for a holistic approach dovetails neatly with the aspiration among airport operators to reduce their own carbon footprint -- hydrogen could power many aspects of airport infrastructure.
For example, in 2015, Memphis International Airport carried out a two-year demonstration of the world's first zero-emissions, hydrogen fuel cell-powered ground support equipment, saving over 175,000 gallons of diesel fuel and 1,700 metric tons of CO2.
In a separate initiative at Toulouse-Blagnac Airport, a hydrogen production and distribution station is being installed for fueling hydrogen-powered buses.
What makes hydrogen a compelling fuel for airports is the fact that it can be produced on-site as well as from the airport's waste materials.
Finnish airport company Finavia is among those evaluating its practicality.
"We're looking at how we could use the waste streams at Finavia's airports, including the waste from glycol (the fluid used for de-icing airplanes) to generate hydrogen," says Henri Hansson, senior vice president of infrastructures and sustainability.