Hydrogen Planes

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 a propeller. Unlike most aircraft, which store fuel in the wings, hydrogen-powered aircraft are usually designed with the hydrogen fuel tanks inside the fuselage.

Hydrogen, which can be produced from low-carbon power and can produce zero emissions, is considered an important technology for decarbonising aviation. Airbus has announced plans to launch into service the first commercial hydrogen-powered aircraft by 2035 and Boeing has acknowledged the potential of the technology. According to McKinsey & Company, hydrogen aircraft could enter the market in the late 2030s and scale up through 2050, when they could account for roughly a third of aviation’s energy demand.

Hydrogen properties and design considerations

Hydrogen has a specific energy of 120 MJ/kgCollege of the Desert, “Module 1, Hydrogen Properties”, Revision 0, December 200
Hydrogen Properties
Retrieved 2014-06-08. that is times higher than traditional jet fuel (43 MJ/kg), however, it has an energy density which is 3,000 times lower at normal atmospheric pressure and ambient temperature.IOR Energy
List of common conversion factors (Engineering conversion factors)
Retrieved 2008-10-05. Gaseous hydrogen can be pressurised at up to to reach an energy density which is 7 times lower than jet fuel. Alternatively, it can be cooled at , turning into a liquid with an energy density times lower than jet fuel (8.5 MJ/L compared to 35 MJ/L).

The low energy density of hydrogen poses challenges when designing an aircraft, where weight and volume are critical. To reduce the size of the tanks liquid hydrogen must be used, requiring cryogenic fuel tanks. Cylindrical tanks minimise surface for minimal thermal insulation weight, leading towards tanks in the fuselage rather than wet wings in conventional aircraft. This leads to a longer, wider fuselage; adding more skin friction drag and wave drag due to the extra wetted area; extra tank weight; and weight and balance variations during flight.

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. As airliners have a fuel fraction of the MTOW between 26% for medium-haul to 45% for long-haul, maximum fuel weight could be reduced to % to % of the MTOW, but this would be the case only for the unusual maximum fuel case of the payload-range tradeoff.

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 best suited for short and medium range aircraft, while new aircraft designs (such as blended wing body) might be required to make long-range hydrogen aircraft feasible.

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 (a greenhouse gas which contributes to global climate change) but not for (a local air pollutant). The burning of hydrogen in air leads to the production of , i.e., the + ½ → reaction in a nitrogen-rich environment also causes the production of . However, hydrogen combustion produces up to 90% less nitrogen oxides than kerosene fuel, and it eliminates the formation of particulate matter.

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

A 2020 study by the European Commission and the EU aviation industry found that hydrogen could feasibly power aircraft with entry into service by 2035 for short-range aircraft, with an additional cost per person of less than €18 while reducing climate impact by 50 to 90%. Significant research and development will however be required, not only in aircraft technology but also into hydrogen infrastructure and accompanying regulations and certification standards.

History

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. On 15 April 1988, the Tu-155 first flew as the first hydrogen-powered experimental aircraft, an adapted Tu-154 airliner.

The European Union's research project in cooperation with Airbus and 34 other partner companies dubbed ''CRYOPLANE'' assessed the technical feasibility, safety, environmental compatibility and economic viability of using liquid hydrogen as an aviation fuel. This was concluded in 2002 (with the final report published in 2003).

Boeing converted a 2-seat Diamond DA20 to run on a fuel cell designed and built by Intelligent Energy. It first flew on April 3, 2008. The Antares DLR-H2 is a hydrogen-powered aeroplane from Lange Aviation and the German aerospace center. In July 2010, Boeing unveiled its hydrogen powered Phantom Eye UAV, that uses two converted Ford Motor Company piston engines.

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 project coordinated by the Politecnico di Torino.
Hydrogen gas is stored at 350 bar, feeding a fuel cell powering a electric motor along a 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.

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. It has the possibility to store of hydrogen, 4x11 kW fuel cells and 2x10 kWh batteries.

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

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. Project Fresson is supported by the Aerospace Technology Institute in partnership with the UK Department for Business, Energy & Industrial Strategy and Innovate UK.

As of 2021, ZeroAvia is actively developing aircraft with a fuel cell powertrain "capable of carrying up to 20 passengers about 350 nautical miles".

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 of range. 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.

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.
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, 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.

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, for a first flight expected within five years, mounted on a fuselage pylon on an A380 prototype.

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 compared to 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 longer fuselage than the Airbus A320neo becoming up to wider at the rear to accommodate two cryogenic fuel tanks, and a larger wingspan requiring folding wing-tips for a range with a cruise;
* the small widebody FZM-1G is comparable to the Boeing 767-200ER, flying 279 passengers over , with a wide fuselage diameter closer to the A350 or 777X, a wingspan within airport gate limits, underwing engines and tanks in front of the wing.

Proposed aircraft and prototypes

Historical

*Lockheed CL-400 Suntan, 1950's concept, dropped for the SR-71
* National Aerospace Plane, 1986-1993 concept with a scramjet, cancelled during development
*Tupolev Tu-155, 1988 modified Tupolev Tu-154 testbed, flew over 100 flights
*AeroVironment Global Observer, 2010-2011 fuel-cell powered drone demonstrator, performed 9 flights before crashing
* Boeing Phantom Eye, 2012-2016 piston engine powered drone demonstrator, flew 9 times with flights lasting up to 9 hours

Projects

AeroDelft
a student team creating a gaseous and liquid hydrogen fuelled drone and Sling 4
*Airbus ZEROe, presented in late 2020, it aims to create four concept aircraft and launch the first commercial zero-emission aircraft, entering service by 2035
* DLR Smartfish, two seat experimental lifting body; based on the previous Hyfish

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