Hydrogen airplanes have been sought-after for long, a quest that has been reinforced by the world’s efforts to transition towards greener aeronautical technologies that cut down on polluting emissions.
So far, the world’s leading experts in the sector have reached key milestones in the design of the right hydrogen aircraft, with the aim of dethroning fossil-fuel options in the near future. All chief experiments, including those by GKN Aerospace and Airbus, coincide that the first hydrogen airplane might be ready for 2035, while the first ground-based demonstrations could take place in 2025.
As conventional aviation is responsible for 3.6% of EU greenhouse gas emissions (according to figures published by the European Commission), the search for a zero-emission airplane sees a good alternative in using hydrogen to decrease harmful carbon dioxide releases into the atmosphere.
In fact, estimates by the European Commission claim hydrogen-related technologies could significantly decrease these figures: while combustion models would reduce climate impact by 50-75%, fuel-cell technology could reduce them by 75-90%.
How does a hydrogen airplane work and what are the challenges that must be solved in order to guarantee hydrogen planes can effectively replace conventional ones? Keep reading to find out.
Hydrogen-powered aircrafts
A hydrogen airplane is an aircraft that uses hydrogen as a fuel source, instead of conventional jet fuel.
Because hydrogen presents a clean combustion with no harmful emissions, it has represented one of the leading efforts to decarbonize the aeronautical sector, in a similar process to the search to decarbonize the automotive industry.
Today, there are two models for powering a hydrogen powered plane:
- Combustion hydrogen planes: these rely on modified engines that use hydrogen as fuel, in an analogous manner to what fuel airplanes are doing today but with less harmful emissions. Today, this is the most likely option for bigger, long-distance planes.
- Fuel cell hydrogen planes: here, hydrogen is used to generate electricity within fuel cells, which then act as electric propulsion to turn propellers. Heat and water would be the only by-products. This represents the most viable option for smaller planes.
In order to fully develop these technologies, the industry is currently on the look to advance in generating these solutions:
- Adequate storage systems for liquid hydrogen
- Fuel cells able to convert hydrogen into electricity
- The motor structure in charge of turning propellers
- Systems able to control power of fuel cells
At the same time, there are a number of advancements in these areas:
- The HEAVEN is working on developing a powertrain that turns the hydrogen into torque to turn propellers in an efficient manner
- The H2GEAR programme is developing scalable hydrogen electric propulsion technology, generating a system where electrical power from hydrogen in fuel cells is the centerpiece. This same programme has developed innovative propulsion system architecture for medium-sized aircrafts, where fuel cell system integration, an hyperconducting power network and cryogenic motor systems will work in conjunction for making the hydrogen airplane a reality.
- The University of Illinois in collaboration with NASA (as part of the Center for Cryogenic High-Efficiency Electrical Technologies for Aircraft or CHEETA) are in charge of a project to develop an efficient cryogenic hydrogen fuel cell system that would translate into an all-electric aircraft. In this case, cryogenic liquid hydrogen would be in charge of storing energy, which would then be converted to electrical energy thanks to the use of fuel cells. Their research also involves the development of an ultra-efficient electric propulsion system and a model for superconducting energy transmission, where energy waste is eliminated.
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Hydrogen storage: the current solutions
As the top world experts advance in generating a sustainable model for an hydrogen airplane, it’s more clear how the issue of storing liquid hydrogen must be solved before moving forward.
Additionally, hydrogen must also be available at airports for refueling operations (in an analogous manner to hydrogen stations for cars), and adequate piping and tubing systems must be provided both for on-board and off-board provision.
Liquid hydrogen is a cryogenic substance: the gas needs to be frozen down to minus 253°C in order to reach a liquid state. As such, it requires specific cryogenic equipment for its handling and storage.
As such, vacuum-insulated vessels have represented a viable option for large-scale cryogenic storage so far, but designs for hydrogen planes will need to adapt to this particular mode of transport. In addition to this, hydrogen molecules contain less energy than jet fuel molecules, so that more fuel will be needed.
These solutions will also need to take into account that tanks for storing hydrogen need to be pressurized, so that they must be incorporated within the main fuselage. Experts point out extra-large fuselages or the use of blended wings might be involved, so that more fuel storage is available.
Cryogenic technology in hydrogen airplanes
Cryogenic technology will stand at the center of any advancements in designing the hydrogen airplane of the future.
As such, producing, transporting and storing hydrogen are three operations that require cryogenic engineering expertise for generating the necessary supporting infrastructures.
Why does the European Union support hydrogen planes?
The main reason is the need to reduce the aeronautical industry’s outstanding greenhouse emissions.
The hydrogen airplane represents a greener alternative to conventional aircrafts, which today are responsible for around 3.6% of the EU greenhouse gas emissions and 2.5% of global carbon dioxide emissions (larger numbers than the total emissions produced by Germany). This problem is exacerbated by this industry’s production of effective radiative forcing (which is rising global average temperature) and trails left by airplanes, which account for other significant negative impacts for the environment.
Hydrogen planes are considered to be a greener and potentially sustainable alternative, as water is the only emission caused by a hydrogen powered plane.
This, however, will only take place if the production of hydrogen remains environmentally-friendly itself (as we describe further below in this article), an issue that the European Commission has targeted through a dedicated hydrogen strategy to scale up production, distribution and storage of green hydrogen.
The result is a number of European initiatives, backed by public funding, to research the potential of hydrogen planes so that their market launch is accelerated.
Additionally, taking the lead in the development of hydrogen-related technologies could mean Europe remains a top global player in a field with a great economic potential.
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Limitations of hydrogen power
- Clean production of hydrogen remains an issue to be solved. Today, ‘grey hydrogen’ dominates the market, that is, hydrogen that is produced by reforming methane from natural gas, following a process that produces carbon dioxide. While ‘Blue hydrogen’ is a cleaner alternative (as carbon capture and storage or CCUS is used), the ideal production method would be using electrolysis of water, resulting in ‘green hydrogen’. Today, only 1% of hydrogen is produced using this pollutant-free system.
- Hydrogen is more expensive than conventional fuel. This means economic adjustments must also be made to guarantee the hydrogen airplane remains a viable option.
- Adequate technologies must be devised. This includes, as we’ve seen above, new models for pressurized tanks and aircraft architecture, among other needs.
All in all, the cryogenic sector remains a key piece in solving the hydrogen airplane jigsaw, which will surely involve top global players in the coming decades in the search for a sustainable, efficient airplane model.
