Hydrogen-powered aircraft

A hydrogen-powered aircraft is an aeroplane that uses hydrogen fuel as a power source. Hydrogen can either be burned in a jet engine or another kind of internal combustion engine, or can be used to power a fuel cell to generate electricity to power an electric propulsor. It cannot be stored in a traditional wet wing, and hydrogen tanks have to be housed in the fuselage or be supported by the wing.

The hydrogen-powered Tu-155 prototype made its first flight on 15 April 1988.

Hydrogen, which can be produced from low-carbon power and can produce zero emissions, can reduce the environmental impact of aviation. Boeing acknowledges the technology potential and Airbus plans to launch a first commercial hydrogen-powered aircraft by 2035.[1] McKinsey & Company forecast hydrogen aircraft entering the market in the late 2030s and scaling up through 2050, when they could account for a third of aviation's energy demand.[2]

Considerable added electrical generation would be needed as the jet fuel energy consumed in 2019 represented 14% of the world’s electricity; and generating the power needed, producing, liquefying and distributing the hydrogen would cost several trillion dollars.[3] MIT's Alan H. Epstein considers investments would be better spent on sustainable aviation fuel than on hydrogen aircraft.[3]

Hydrogen properties
Energy density of fuels: horizontal per mass, vertical per volume. Kerosene is highlighted in red and hydrogen in blue.

Hydrogen has a specific energy of 119.9 MJ/kg, compared to ~43.5 MJ/kg for usual liquid fuels,[4] 2.8 times higher. However, it has an energy density of 10.05 kJ/L at normal atmospheric pressure and temperature, compared to ~31293 kJ/L for liquid fuels,[4] 3114 times lower. When pressurised to 690 bar (10,000 psi), it reaches 4,500 kJ/L,[4] still 7 times lower than liquid fuels. Cooled at 20 K (−253 °C), liquid hydrogen has an energy density of 8,491 kJ/L,[4] 3.7 times lower than liquid fuels.

Aircraft design

The low volumetric energy density of hydrogen poses challenges when designing an aircraft, where weight and volume are critical.[5] To reduce the size of the tanks liquid hydrogen may be used, requiring cryogenic fuel tanks.[5][6] Cylindrical tanks minimise surface for minimal thermal insulation weight, leading towards tanks in the fuselage rather than wet wings in conventional aircraft.[5][6] Airplane volume and drag would be significantly increased by three times larger fuel tanks, highly insulated and spherical or cylindrical.[3] A larger fuselage would add more skin friction drag and wave drag due to the extra wetted area; extra tank weight; and weight and balance variations during flight.

Gaseous hydrogen may be used for short-haul aircraft.[7] Liquid hydrogen might be needed for long-haul aircraft.

Hydrogen's high specific energy means it would need less fuel weight for the same range, ignoring the repercussion of added volume and tank weight.[6] As airliners have a fuel fraction of the Maximum Takeoff Weight MTOW between 26% for medium-haul to 45% for long-haul, maximum fuel weight could be reduced to 9% to 16% of the MTOW, but this would be the case only for the unusual maximum fuel case of the payload-range tradeoff.

Fuel cells would make sense only for general aviation and small commuter aircraft as their engine efficiency is less than half of large gas turbines, but not for usual single or twin-aisle airliners.[3] The efficiency of a hydrogen-fueled aircraft is a trade-off of the larger wetted area, lower fuel weight and added tank weight, varying with the aircraft size. Hydrogen is better suited for short range airliners, while longer ranges may need new aircraft designs such as blended wing body.[8]

Liquid hydrogen is one of the best coolants used in engineering, and precooled jet engines have been proposed to use this property for cooling the intake air of hypersonic aircraft, or even for cooling the aircraft's skin itself, particularly for scramjet-powered aircraft.[9]

Emissions and environmental impact

Hydrogen aircraft using a fuel cell design are zero emission in operation, whereas aircraft using hydrogen as a fuel for a jet engine or an internal combustion engine are zero emission for CO2 (a greenhouse gas which contributes to global climate change) but not for NOx (a local air pollutant). The burning of hydrogen in air leads to the production of NOx, i.e., the H
2 + ½O
2 → H
2O reaction in a nitrogen-rich environment also causes the production of NOx.[10] However, hydrogen combustion produces up to 90% less nitrogen oxides than kerosene fuel, and it eliminates the formation of particulate matter.[6]

If hydrogen is available in quantity from low-carbon power such as wind or nuclear, its use in aircraft will produce fewer greenhouse gases than current aircraft: water vapor and a small amount of nitrogen oxide. Currently very little hydrogen is produced using low-carbon energy sources.[11]

A 2020 study by the EU Clean Sky 2 and Fuel Cells and Hydrogen 2 Joint Undertakings found that hydrogen could power aircraft by 2035 for short-range aircraft.[8] A short-range aircraft (< 2,000 km, 1,100 nmi) with hybrid Fuel cell/Turbines could reduce climate impact by 70–80% for a 20–30% additional cost, a medium-range airliner with H2 turbines could have a 50–60% reduced climate impact for a 30–40% overcost, and a long-range aircraft (> 7,000 km, 3,800 nmi) also with H2 turbines could reduce climate impact by 40–50% for a 40–50% additional cost.[8] Research and development would be required, in aircraft technology and into hydrogen infrastructure, regulations and certification standards.[8]

History

Demonstrations
The hydrogen powered Boeing Phantom Eye UAV first flew on 1 June 2012.
the hydrogen fuel cell-powered HY4 made its first flight in 2016.

In February 1957, a Martin B-57B of the NACA flew on hydrogen for 20 min for one of its two Wright J65 engines rather than jet fuel.[12] On 15 April 1988, the Tu-155 first flew as the first hydrogen-powered experimental aircraft,[13] an adapted Tu-154 airliner.

Boeing converted a two-seat Diamond DA20 to run on a fuel cell designed and built by Intelligent Energy.[14] It first flew on April 3, 2008.[15] The Antares DLR-H2 is a hydrogen-powered aeroplane from Lange Aviation and the German aerospace center.[16] In July 2010, Boeing unveiled its hydrogen powered Phantom Eye UAV, that uses two converted Ford Motor Company piston engines.[17]

In 2010, the Rapid 200FC concluded six flight tests fueled by gaseous hydrogen. The aircraft and the electric and energy system was developed within the European Union's ENFICA-FC project coordinated by the Politecnico di Torino.[18] Hydrogen gas is stored at 350 bar, feeding a 20 kW (27 hp) fuel cell powering a 40 kW (54 hp) electric motor along a 20 kW (27 hp) lithium polymer battery pack.

On January 11, 2011, an AeroVironment Global Observer unmanned aircraft completed its first flight powered by a hydrogen-fueled propulsion system.[19]

Developed by Germany's DLR Institute of Engineering Thermodynamics, the DLR HY4 four-seater was powered by a hydrogen fuel cell, its first flight took place on September 29, 2016.[20] It has the possibility to store 9 kg (20 lb) of hydrogen, 4x11 kW fuel cells and 2x10 kWh batteries.[21]

On 19 January 2023, ZeroAvia flew its Dornier 228 testbed with one turboprop replaced by a prototype hydrogen-electric powertrain in the cabin, consisting of two fuel cells and a lithium-ion battery for peak power.[22] The aim is to have a certifiable system by 2025 to power airframes carrying up to 19 passengers over 300 nmi (560 km).[22]

On 2 March 2023, Universal Hydrogen flew a Dash 8 40-passenger testbed with one engine powered by their hydrogen-electric powertrain. The company has received an order from Connect Airways to convert 75 ATR 72-600 with their hydrogen powertrains.[23]

Aircraft projects

In 1975, Lockheed prepared a study of liquid hydrogen fueled subsonic transport aircraft for NASA Langley, exploring airliners carrying 130 passengers over 2,780 km (1500 nmi); 200 passengers over 5,560 km (3,000 nmi); and 400 passengers over 9,265 km (5,000 nmi).[24]

Between April 2000 and May 2002, the European Commission funded half of the Airbus-led Cryoplane Study, assessing the configurations, systems, engines, infrastructure, safety, environmental compatibility and transition scenarios.[25] Multiple configurations were envisioned: a 12 passenger business jet with a 3,500 nmi (6,500 km) range, regional airliner for 44 passengers over 1,500 nmi (2,800 km) and 70 passengers over 2,000 nmi (3,700 km), a medium range aircraft for 185 passengers over 4,000 nmi (7,400 km) and long range aircraft for 380 to 550 passengers over 8,500 nmi (15,700 km).[26]

In September 2020, Airbus presented three ZEROe hydrogen-fuelled concepts aiming for commercial service by 2035:[27] a 100-passenger turboprop, a 200-passenger turbofan, and a futuristic design based around a blended wing body.[28] The aircraft are powered by gas turbines rather than fuel cells.[29]

In December 2021, the UK Aerospace Technology Institute (ATI) presented its FlyZero study of cryogenic liquid hydrogen used in gas turbines for a 279-passenger design with 5,250 nmi (9,720 km) of range.[30] ATI is supported by Airbus, Rolls-Royce, GKN, Spirit, General Electric, Reaction Engines, Easyjet, NATS, Belcan, Eaton, Mott MacDonald and the MTC.

In August 2021 the UK Government claimed it was the first to have a Hydrogen Strategy. This report included a suggested strategy for hydrogen powered aircraft along with other transport modes.[31]

In March 2022, FlyZero detailed its three concept aircraft:

  • the 75-seat FZR-1E regional airliner has six electric propulsors powered by fuel cells, a size comparable to the ATR 72 with a larger fuselage diameter at 3.5 m (11 ft) compared to 2.8 m (9 ft 2 in) to accommodate hydrogen storage, for a 325 kn (601 km/h) cruise and an 800 nmi (1,480 km) range;
  • its FZN-1E narrowbody has rear-mounted hydrogen-burning turbofans, a T-tail and nose-mounted canards, a 10 m (33 ft) longer fuselage than the Airbus A320neo becoming up to 1 m (3 ft 3 in) wider at the rear to accommodate two cryogenic fuel tanks, and a larger wingspan requiring folding wing-tips for a 2,400 nmi (4,400 km) range with a 450 kn (830 km/h) cruise;
  • the small widebody FZM-1G is comparable to the Boeing 767-200ER, flying 279 passengers over 5,750 nmi (10,650 km), with a 6 m (20 ft) wide fuselage diameter closer to the A350 or 777X, a 52 m (171 ft) wingspan within airport gate limits, underwing engines and tanks in front of the wing.[32]

Propulsion projects

In March 2021, Cranfield Aerospace Solutions announced the Project Fresson switched from batteries to hydrogen for the nine-passenger Britten-Norman Islander retrofit for a September 2022 demonstration.[33] Project Fresson is supported by the Aerospace Technology Institute in partnership with the UK Department for Business, Energy & Industrial Strategy and Innovate UK.

Pratt & Whitney wants to associate its geared turbofan architecture with its Hydrogen Steam Injected, Inter‐Cooled Turbine Engine (HySIITE) project, to avoid carbon dioxide emissions, reduce NOx emissions by 80%, and reduce fuel consumption by 35% compared with the current jet-fuel PW1100G, for a service entry by 2035 with a compatible airframe.[34] On 21 February 2022, the US Department of Energy through the OPEN21 scheme run by its Advanced Research Projects Agency-Energy (ARPA-E) awarded P&W $3.8 million for a two-year early stage research initiative, to develop the combustor and the heat exchanger used to recover water vapour in the exhaust stream, injected into the combustor to increase its power, and into the compressor as an intercooler, and into the turbine as a coolant.[34]

In February 2022, Airbus announced a demonstration of a liquid hydrogen-fueled turbofan, with CFM International modifying the combustor, fuel system and control system of a GE Passport, mounted on a fuselage pylon on an A380 prototype, for a first flight expected within five years.[35]

Proposed aircraft and prototypes

Historical

Projects

See also

References
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  2. "Decarbonizing aviation: Making net zero possible". McKinsey. July 15, 2022.
  3. Alan H. Epstein (January 13, 2021). "Opinion: Leave Hydrogen For Dirigibles". Aviation Week.
  4. "Module 1". Hydrogen Properties (PDF). December 2001. {{cite book}}: |work= ignored (help)
  5. "How to store liquid hydrogen for zero-emission flight". Airbus. 2021-12-09.
  6. "Liquid hydrogen as a potential low-carbon fuel for aviation" (PDF). IATA. August 2019.
  7. Le Bris, G; et al. (2022). ACRP Research Report 236: Preparing Your Airport for Electric Aircraft and Hydrogen Technologies. Transportation Research Board (Report). Washington, DC. p. 21.
  8. Hydrogen-powered aviation (PDF) (Report). EU Clean Sky 2 and Fuel Cells and Hydrogen 2 Joint Undertakings. May 2020.
  9. Segal, Corin (2010). The Scramjet Engine Processes and Characteristics. Cambridge University Press. p. 4. doi:10.1017/CBO9780511627019. ISBN 9780511627019.
  10. Mike Menzies (23 September 2019). "Hydrogen: The Burning Question". The Chemical Engineer. Institution of Chemical Engineers.
  11. "Hydrogen aircraft". H2 Vehicles. Archived from the original on 2012-06-18. Retrieved 2016-05-06.
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  13. Dieter Scholz, Hamburg University of Applied Sciences (19 November 2020). "Design of Hydrogen Passenger Aircraft" (PDF).
  14. "Boeing Prepares Fuel Cell Demonstrator Airplane for Ground and Flight Testing" (Press release). Boeing. March 27, 2007. Archived from the original on 29 April 2007.
  15. "Boeing Flies First Fuel Cell-Powered Airplane" (Press release). Boeing. April 3, 2008. Archived from the original on 6 April 2008.
  16. "DLR motor glider Antares takes off in Hamburg – powered by a fuel cell" (PDF) (Press release). DLR. 7 July 2009.
  17. "Boeing Unveils Unmanned Phantom Eye Demonstrator" (Press release). Boeing. July 12, 2010.
  18. "ENFICA-FC".
  19. "Global Observer, AeroVironment's Extreme Endurance Unmanned Aircraft System, Achieves Historic First Hydrogen-Powered Flight" (Press release). AeroVironment. Jan 11, 2011.
  20. "Fuel cell aircraft HY4 makes maiden flight". The Engineer. 30 September 2016.
  21. "Vil ha kortdistanse flytrafikk over på hydrogen" (in Norwegian). Teknisk Ukeblad. 21 June 2017.
  22. "ZeroAvia Makes Aviation History, Flying World's Largest Aircraft Powered with a Hydrogen-Electric Engine" (Press release). ZeroAvia. January 19, 2023.
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  28. Henderson, Caspar (7 April 2021). "The hydrogen revolution in the skies". bbc.com. BBC. Retrieved 5 August 2021.
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  30. Nathan Harrison (6 Dec 2021). "Zero-carbon emission flights to anywhere in the world possible with just one stop". Aerospace Technology Institute.
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  32. Dominic Perry (11 March 2022). "FlyZero details trio of zero-emission aircraft concepts". FlightGlobal.
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  34. Dominic Perry (1 March 2022). "P&W sees 2035 service entry potential for revolutionary hydrogen powerplant". Flightglobal.
  35. "The ZEROe demonstrator has arrived" (Press release). Airbus. 22 February 2022.
  36. "Airbus looks to the future with hydrogen planes". BBC News. 2020-09-21. Retrieved 2022-11-26.
  37. "H2FLY's HY4 Completes First-Ever Piloted Flight Of Liquid Hydrogen-Powered Electric Plane". www.msn.com. 19 September 2023.
  38. ZeroAvia Conducts UK's First Commercial-Scale Electric Flight, June 23, 2020
  39. This plane powered by hydrogen has made an electrifying first flight, March 7, 2023
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