Aviation and fossil fuels
which we manufacture it on an industrial scale. Nevertheless, Airbus has expressed its interest in this technology through its ‘ZEROe’ project, which aims to design a commercial airliner capable of producing zero emissions (Airbus, n.d.). The advantages of hydrogen that have already been listed are added to by Airbus’s proposal to fully exploit this fuel by using it for both combustion and fuel cell power, meaning that it is both burnt in the engines and used to generate electricity, combining to produce an even more efficient hybrid power system (Airbus, n.d.). The second problem with hydrogen is that it has a very low volumetric energy density (Demaco, n.d.). Therefore, whilst it has more energy than regular fuel per Kg, more space is needed to store the same amount of energy. One solution is to liquify the hydrogen. This slightly increases the energy per litre, albeit not back to the levels of kerosene. Liquified hydrogen also needs to be stored at only 20 degrees K or -253 degrees C to prevent evaporation. Storing this fuel onboard is therefore the main problem engineers are facing.
Left: A comparison between different fuels in terms of volumetric and mass energy density. Note the difference between kerosene and liquid hydrogen (LH2). Kerosene therefore has more energy per litre but less energy per Kg. Yin and Rao (2012). Energy comparison of various fuels.
Conclusion
The aviation industry has been unable to adopt sustainable technologies due to the vast engineering challenges posed. Even the most readily available technology such as sustainable aviation fuels still requires an immense amount of research and construction to build the colossal infrastructure network needed to support this global industry. Despite this, there is still cause for cautious optimism. New efficient engines have already made strides towards cutting the carbon footprint of airliners and some hybrid technologies, such as the one proposed by MIT, appear achievable, requiring a feasible amount of engineering to be operating within a decade. Hybrid power and sustainable fuels could bring about a new era in aeronautical engineering but, at best, they can only serve as short-term stopgaps. To bring aviation into a sustainable future, major changes are needed, and these may still be decades away. Therefore, the best way forward is to put in the immense amount of work needed to realize these two simpler technologies in the shortest possible timeframe. Putting them into industrial use would mean an improvement in sustainability, while the immense challenges of alternate power sources, possibly hydrogen, are solved. The sheer scale of such projects and the time pressure they would have to operate under presents a great but nonetheless feasible task. The engineering required would undoubtedly take years, which is why work needs to be started and accelerated wherever possible in order to revolutionize air travel and bring it firmly out of the 20 th century for good.
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