Hydrogen-electric aircraft propulsion system developer ZeroAvia says it has achieved record-breaking performance while testing the high-temperature proton exchange membrane (HTPEM) systems in its hydrogen fuel cells.
According to ZeroAvia, early testing of the pressurized, 20-kilowatt HTPEM fuel cell stack at the company’s research and development facility in the UK demonstrated a specific power level of 2.5 kW/kg at the cell level, and the company expects to achieve power densities exceeding 3 kW/kg in the next two years. This will make the hydrogen fuel cells powerful enough to enable electric propulsion systems viable for large aircraft that seat more than 100 passengers, such as the Boeing 737 and Airbus A320 families, according to ZeroAvia.
In January, ZeroAvia successfully completed the first flight test of a 19-seat Dornier 228 regional airliner retrofitted with one of its hydrogen propulsion systems. After more than two years of collaboration with the hydrogen fuel cell systems developer HyPoint, ZeroAvia acquired HyPoint in October 2022 with plans to integrate the company’s turbo-air-cooled HTPEM fuel cells into its propulsion systems. ZeroAvia’s powertrain uses hydrogen fuel cells to generate electricity, which powers the electric motors that spin the aircraft’s propellers.
The HTPEM fuel cells ZeroAvia is now testing, with a power output of 2.5 kW/kg, will be ideal for powering ZeroAvia's ZA2000 powertrain for 40- to 80-seat aircraft and could enable new electric propulsion systems for eVTOL aircraft and rotorcraft.
The 19-seat Dornier 228 that the company flew in January utilized low-temperature PEM fuel cells, which the company says work well for sub-megawatt-scale, smaller aircraft, “but the lower stack core temperatures make it harder to remove heat from the larger systems,” ZeroAvia officials said in a statement. “HTPEM technology eliminates a number of components from the fuel cell system and reduces cooling drag, thereby enabling commercially relevant payload and range.”
Traditional LTPEMs cannot be used above temperatures of 80 degrees Celsius (176 degrees Fahrenheit), but HTPEMs can safely operate at up to 200 degrees Celsius (392 degrees Fahrenheit). The higher temperatures result in faster chemical reactions and greater efficiency, making these fuel cells more suitable for transportation applications. HTPEMs are also expected to have a life cycle of 20,000 hours or about four times longer than that of LTPEMs.
“The companies and geographies that seize the lead in high fuel cell temperatures and pressures will lead the industry,” said ZeroAvia CEO Val Miftakhov. “This progression is similar to the story of turbine engines, where ever-increasing temperatures and pressures drove higher and higher performance.
"Hydrogen fuel cell propulsion is the most environmental and economical alternative to existing engines," Miftakhov continued, "and HTPEM is the most promising route to delivering these benefits into large aircraft categories. I am confident that what we are demonstrating now is the core building block to delivering zero-emission flight for all categories of aircraft in the long term.”
ZeroAvia’s plans for hydrogen-powered aviation involve the production of two hydrogen-electric powertrains to retrofit existing aircraft. The company’s 600-kilowatt ZA600 powertrain, which is designed to support nine- to 19-seat airframes with a range of up to 300 nautical miles, was successfully demonstrated during the flight test in January.
The company also aims to deliver a 40- to 80-seat hydrogen-electric aircraft with a range of 700 nm by 2027. The larger aircraft will utilize a two- to five-megawatt ZA2000 powertrain and will run on liquid hydrogen, while the smaller one will use hydrogen gas.
According to ZeroAvia, it now holds provisional order commitments covering around 1,500 of its hydrogen propulsion systems, with between 600 and 700 of these intended for aircraft with up to 19 passenger seats. The company aims to start taking deposits for delivery slots this year.