The unstoppable growth of air traffic poses a major challenge for environmental sustainability. Aviation, as we know it, is based on the burning of fossil fuels, which generates a considerable carbon footprint. Given this scenario, the aeronautical industry is eagerly exploring cleaner alternatives, and hydrogen is emerging as a candidate with great potential.
Although batteries are presented as a viable solution for small aircraft on short journeys, their limited energy density rules them out for large, long-range aircraft. The alternative of sustainable aviation fuel (SAF), although promising, faces the difficulty of scaling its production to the required levels without generating a negative impact on food security.
It is in this context that hydrogen emerges as an attractive option. Its high energy density makes it an ideal fuel for long-distance flights with high passenger capacity. However, its implementation presents various technical and logistical challenges that are not easy to solve
For this reason, there are many people trying to solve the challenges of sustainable aviation, because the business is huge, and will last a very long time
The main challenges of hydrogen in aviation are:
. Sustainable and large-scale production: The production of green hydrogen, that is, from renewable sources such as solar or wind energy, is currently limited and expensive. Significant investments in infrastructure and technology are required to achieve mass production that meets the demand of the aeronautical sector.
. Storage and transport: Hydrogen must be kept at extremely low temperatures (-250°C) to keep it in a liquid state, which involves complex and expensive storage and transport systems. Alternatives are being explored, such as solid-state storage using metal hydrides, but they are still in the development phase.
. Adaptation of aircraft: The use of hydrogen as a fuel requires significantly modifying the design of aircraft. This includes the development of cryogenic storage tanks, adapted fuel supply systems, and the modification or replacement of current engines.
. Safety: The high flammability of hydrogen requires extreme safety measures at all stages of its handling, from production and transportation to storage and use in aircraft.
Despite the challenges, the aviation industry is making significant progress in research and development of technologies that enable the use of hydrogen as a fuel. Several companies have already presented prototypes of hydrogen-powered aircraft, both in the small commercial aircraft category and in the regional aircraft category.
The first short- and medium-range hydrogen-powered commercial aircraft are expected to enter service in the next decade. Hydrogen can be used with fuel cells to generate electricity and power a small aircraft.
There are already flight tests of small and medium-sized aircraft running on fuel cells and electric motors of up to 1 Mw. of power, and it is expected that they will be on the market in a few years. These are aircraft with very experienced propeller engines, which have had their fuel system and engines changed so that they can fly again without polluting the environment.
For long-distance flights, the development of more complex technologies will require a longer period of time. Since hydrogen is stored very cold, a heat exchanger is needed to heat it before it is applied to the engine. And that is easy to say, but it is very complex.
For large aircraft to fly without polluting, they need to solve several problems:
- Handling hydrogen at low temperatures (-250ºC)
- The heat exchanger to apply hydrogen to the engine at a suitable temperature
- Modifying aircraft engines to run on hydrogen
Work is being done in all three areas, but it will take many, many years before we see large aircraft flying on hydrogen
In short, hydrogen is emerging as a promising alternative to decarbonize aviation and make it more sustainable in the long term. While there are still important technical and logistical challenges to overcome, investment in research, development and innovation, together with collaboration between governments, industry and research centers, will be key to turning the dream of clean aviation into a tangible reality.
And in the meantime, I remain hopeful that within the not-too-distant future we will see regional aircraft flying sustainably.
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