A new report concludes that fuel-cell powered ATR and De Havilland Canada turboprops could have enough range to cover most typical turboprop routes – but only when carrying far fewer passengers.
For that reason, airlines using such modified turboprops – the designs for which remain unproven and in development – would need to operate many more flights to fill the same market demand, according to the report from the International Council on Clean Transportation (ICCT).
Released on 2 August, ICCT’s study also predicts that hydrogen fueling costs will decline substantially in the coming decades. It says fuel cells using liquid hydrogen – which must be kept colder than -253°C (-423°F), posing another challenge – would provide more range than those using hydrogen gas.
“A fossil-fuelled turboprop aircraft retrofitted with hydrogen storage and fuel-cell propulsion is more energy efficient and less carbon intensive, but more expensive to fuel,” says ICCT, which has offices in Washington, DC. “It would have lower payload and range capabilities but would reduce [greenhouse gas] emissions by 88%.”
A handful of companies are working to bring hydrogen-powered aircraft to market, describing hydrogen – which emits water when converted to energy – as the aviation’s industry’s carbon-cutting solution. Engines can be made to burn hydrogen as fuel, or fuel cells can use hydrogen to produce electricity to power motors.
Players include US firm ZeroAvia, which is developing fuel-cell propulsion systems for aircraft and has flight-tested its system using a modified Dornier 228. Another, Universal Hydrogen, has test flown a Dash 8 powered partly by fuel cells and is also developing the modification for ATRs. In the UK, Cranfield Aerospace Solutions is developing a fuel-cell conversion for a Britten-Norman BN2 Islander.
Despite optimism, large technical, practical and infrastructure challenges remain.
“Retrofit fuel cell aircraft will be a key testbed for hydrogen use in aviation where success would enable larger, clean-sheet aircraft to enter the commercial aviation market,” ICCT says.
Its report examines a fuel-cell modified ATR 72 as a test case, delving into range and capacity limitations imposed by hydrogen as fuel.
Hydrogen has less energy density than jet fuel, with four times the volume per energy unit. As a result, getting enough range from a hydrogen-powered ATR would require the aircraft’s cabin to be fitted with extra fuel tanks. That means removing seats. This “modular hydrogen storage” concept is similar to that envisioned by Universal Hydrogen.
“Carrying more hydrogen increases an aircraft’s maximum range, while reducing its passenger capacity,” ICCT’s report says.
A factory-fresh ATR 72-600, powered by Pratt & Whitney Canada PW127 turboprops, can carry up to 78 seats and has 740nm (1,370km) of range.
By comparison, ICCT estimates a liquid-hydrogen fuel-cell powered ATR 72 carrying 70 passengers would have range less than 250nm. But removing 28 seats and installing hydrogen tanks in the empty rows would give the aircraft, now with 42 seats, 945nm of range – farther even than the factory aircraft.
In practice, passenger limitations mean fuel-cell aircraft could only directly replace 15-20% of the turboprop market. But by adding more flights, such aircraft could capture the majority of the market, ICCT says.
The cost of green hydrogen, which is produced using renewable energy sources, has been a concern as a factor that could hinder its use as fuel.
But ICCT thinks those costs will approach jet-fuel costs in the coming decades, thanks to such factors as availability in the US of cheap renewable energy, and because hydrogen is more efficient than jet fuel.
ICCT estimates green hydrogen “fuelling costs” for an modified ATR would be 29-40% more than for jet fuel in the USA in 2030, but cheaper by 2050.
But green hydrogen purchased in Europe, where it is “expected to be more expensive to produce”, will likely cost about twice as much as fossil-based jet fuel in 2030, and 50% more in 2050. ICCT’s fuel-cost predictions account for the expense of replacing fuel-cell systems, which could need to be swapped out every 3.5 years.
