The aviation industry is facing a critical challenge as the world moves towards decarbonization. While planes currently account for only 2-3% of global carbon dioxide emissions, that number is expected to rise to 25% by 2050 [1]. Unlike other sectors that have clear pathways to cleaner technology, the aviation industry has yet to find a way to replace kerosene, the primary fuel used in jet engines. If the aviation sector fails to find a solution to this problem, it could represent as much as 25% of worldwide emissions by 2050 [1].
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The Current State of Aviation Fuel
Currently, most jet engines rely on kerosene, a form of aviation fuel known as Jet A or Jet A-1. The choice between Jet A and Jet A-1 depends on the region, with Jet A primarily used in the United States and Jet A-1 used in the rest of the world [4]. The primary difference between the two is their freezing point, with Jet A-1 having a lower freezing point of -47 degrees compared to Jet A at -40 degrees. This makes Jet A-1 more suitable for colder climates and international routes that fly over the Arctic [4].
Exploring Alternative Fuels
To find a suitable replacement for kerosene, several alternative fuels are being explored. One option is biofuels, such as bioethanol and biodiesel. While bioethanol has a low freezing point, it is volatile and has a lower volumetric energy density compared to kerosene [9]. Biodiesel, on the other hand, has a high freezing point, making it unsuitable for jet engines [9].
However, biofuels can be further processed to create fuels similar to kerosene that can be used in current-generation planes with minimal modifications. Airbus has already conducted tests using a biofuel blend in an A350 powered by Rolls Royce XWB engines, showing promising results in terms of emissions reduction [11].
Another potential future fuel is hydrogen. While hydrogen offers a high gravimetric energy density, its volumetric energy density is significantly lower than traditional fuels [17]. Additionally, storing and handling hydrogen presents challenges due to its corrosive properties and the need for specialized fuel tanks [18].
E-Fuels: A Potential Solution
E-Fuels, which are created by combining carbon dioxide and hydrogen, offer a possible solution to overcome some of the challenges posed by biofuels and hydrogen. This process involves drawing carbon dioxide directly from the atmosphere using direct air capture and combining it with hydrogen to produce methanol [18]. Methanol can then be further processed to create kerosene-like e-fuels. While this approach solves the scalability issues of biofuels, it is currently cost-prohibitive due to the high energy requirements and the challenge of sourcing renewable hydrogen [18].
The future of aviation fuel is uncertain, and multiple factors need to be considered when choosing a suitable alternative. Cost, freezing point, flash point, and volumetric energy density are essential parameters to evaluate potential alternatives [16]. Biofuels and e-fuels may offer a bridge to a more sustainable future, as they are compatible with existing jet engines. However, the aviation industry needs to accept the associated costs and work towards gradually introducing these fuels.
It’s important to note that the aviation industry may also see advancements in electric planes, which are already being explored for smaller aircraft. While the range of electric planes is currently limited, niche markets may develop in the near future [20].
FAQs
Q: Why is the aviation industry facing a crisis?
A: The aviation industry is projected to be responsible for 25% of worldwide emissions by 2050 if a suitable replacement for kerosene is not found [1].
Q: What fuels are currently used in jet engines?
A: Jet A and Jet A-1 are the primary types of jet fuel used in commercial aviation, with Jet A used in the United States and Jet A-1 used in the rest of the world [4].
Q: What are the challenges with alternative fuels like biofuels and hydrogen?
A: Biofuels face challenges in terms of scalability and cost. Hydrogen, while offering high energy density, presents difficulties in storage, handling, and integration into aircraft structures [18].
Q: What are e-fuels, and how do they compare to other alternatives?
A: E-Fuels are created by combining carbon dioxide and hydrogen to produce kerosene-like fuels. While they offer scalability, they require significant energy and hydrogen sourcing, making them currently cost-prohibitive [18].
Conclusion
Finding a suitable replacement for jet fuel remains a complex challenge for the aviation industry. Biofuels, hydrogen, and e-fuels offer potential solutions, but each comes with its own set of hurdles. Balancing cost, performance, and environmental impact will be crucial in navigating the transition to a more sustainable future for air travel.
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