With the Air Transport Action Group (ATAG) having committed to reducing 50% of its CO2 emissions by 2050, and the European Union’s Green Deal to become carbon neutral in the same period, the aviation industry is facing severe challenges to fulfil these ambitious goals.
In light of recent developments within the aviation sector and initiatives to reduce aviation’s climate impact, we are taking a closer look at what is happening within aviation in terms of climate sustainability.
Aircraft manufacturer Airbus has revealed three new concepts for zero-emission commercial aircraft, all based on hydrogen as a primary power source. These concepts include a long-haul option as well as two short-haul options.
It is already well established that liquid hydrogen is used as a rocket propellant, which was first initiated by NASA, the U.S. space agency. One chief reason for choosing liquid hydrogen in the first place was that it burns with extreme density while having the lowest molecular weight. So why is it that the commercial aviation industry is only now developing concepts for hydrogen use?
Unlike existing technology in rocket science, the Airbus concepts modify gas turbine engines running on hydrogen in its gaseous state rather than being liquified. Some challenges that this combustion engine is facing is that hydrogen has only about one-third of the volumetric energy density of methane or natural gas, and not even one-tenth of that of current aviation fuel. Other challenges are hydrogen’s high combustion temperature as well as the highly reactive combustion properties.
Protecting components from overheating caused by flashbacks (uncontrolled upstream propagation of the flame) or autoignition (which is caused by the high reactivity of hydrogen) might be a costly challenge to overcome, especially in more complex burner designs, as needed in high-efficiency turbines. Reducing/eliminating nitrogen oxide emissions of complete hydrogen combustion is possible through keeping the flame below the critical NOx temperature of 1,350oC.
An independent study by consultancy McKinsey shows that hydrogen propulsion could be a significant part of the future propulsion technology mix. Nonetheless, achieving this requires massive investments in R&D as well as a policy framework that guides development in the right direction.
Policies as such already (partly) exist in Europe and are subject to expansion. The EU emissions trading system comprises CO2 emissions from aviation. But the European Economic Area (EEA) is not the only area within the aviation sector that emits emissions, meaning that a scheme similar to the European model needs to be established globally.
Roughly 95% of hydrogen today is produced through steam methane reforming (SMR), which leaves quite a carbon footprint. So-called grey hydrogen has average lifecycle emissions of 0.28 tCO2e/MWh, which is about 60% of that of natural gas. By contrast, green hydrogen is any hydrogen produced with lifecycle emissions of 0.01 tCO2e/MWh or less, which corresponds to an emissions decrease of at least 99.64%.
Besides the challenge of producing green hydrogen, the entire infrastructure from production and transport to storage and plane fuelling is non-existent at airports and needs to be established before we can even dream of concepts like the ones presented by Airbus becoming a reality.
Lufthansa, the German airline group, has committed to reducing its emissions and launched a research group that is looking to create jet fuel in the form of synthesis gas by using concentrated solar, hydrogen or methanol.
In the U.S., San Francisco’s airport obtains part of its jet fuel supply from Nestle, the world’s largest supplier of sustainable aviation fuel. The fuel is delivered via a unique pipeline called “a climate quantum leap” and is made from a mix of renewable and sustainable waste, such as cooking oil and animal fat. This fuel can be used with existing infrastructure and reduces emissions by as much as 80%.
With electric cars on the rise, electric planes are also in the mind of many. Elon Musk said that electric aircraft might be a reality in the next five years, as battery capacities are predicted to rise by more than 50% within the next 2-3 years. Whether or not electric planes will contribute to reducing CO2 emissions is a question that electric cars are also facing in significant dispute.
The financial burden airlines are facing due to COVID-19 has not been an incentive for cleaner power source investments and reducing emissions. Nevertheless, the public shift in mindset that not only COVID-19 but other natural disasters have caused ls leading society and decision-makers to be aware of the immediate need for sustainability to stop climate change. Aviation is not exempt from this scruting.
Considering the impact that air transport has, we wish to see more initiatives and concepts that help reduce emissions and make the entire sector cleaner. This is not an option, but an imperative if we are to stop climate change.