What is the aviation industry doing to de-carbonise?Posted on
The demand for air travel continues to rise and, as a result, the aviation industry is one of the world’s fastest growing industries. If carbon emissions from aviation continue to increase at their current rate, the industry is expected to become one of the largest carbon emitting sectors in the coming decades. There is therefore an immediate need to reduce carbon emissions from aviation. This is not lost on airlines, governments, or manufacturers. In 2021, member airlines of the International Air Transport Association passed a resolution to achieve net zero carbon emissions by 2050. In July of this year, the UK Government announced their plan, ‘Jet Zero’, to achieve net zero carbon emissions from the UK aviation sector also by 2050. Manufacturers continue to invest significantly in decarbonising solutions, including electric propulsion, hydrogen power, and sustainable aviation fuels. This article discusses each of these three solutions in more detail.
Prototype electric aircraft exist today and are currently under development by a number of start-ups and SMEs, as well as being investigated by the likes of Airbus and Rolls-Royce. An electric aircraft typically comprises one or more propellers or rotors driven by one or more electric motors, powered by one or more batteries or hydrogen fuel cells. This means zero ‘tail pipe’ emissions; however, to be completely carbon neutral, an electric aircraft relies on the use of renewable or carbon neutral energy to produce the electricity used to charge its batteries or the hydrogen used to supply its fuel cells. Electric aircraft are also subject to limitations similar to those of electric cars; range is limited by battery or fuel cell storage capacity and recharging time, in the case of battery-powered aircraft, meaning that flight turnaround time is significantly longer than that of aircraft running on conventional aviation fuel. Weight is also much more of a significant factor for an aircraft than it is for a car, as more weight means that the aircraft needs to generate more lift by means of its wings or rotors. The size of an electric aircraft’s battery cannot therefore be easily increased without affecting the design of the aircraft as a whole. For these reasons, it is likely that electric aircraft will be limited to short haul passenger flights, for example to provide an ‘air taxi’ between urban destinations. That being said, electric aircraft are in fact well suited to this purpose, as they do not contribute to local air or noise pollution. Rolls-Royce predict that urban electric aircraft will take to the skies by the mid-2020s.
As well as being used to generate electricity in a fuel cell, hydrogen can be used as a fuel for internal combustion. When burned, hydrogen does not produce any carbon emissions and existing gas turbine engines can be modified to utilise hydrogen. The gravimetric energy density of hydrogen is around three times that of conventional jet fuel, making it seem ideal for long haul and cargo flights; however, the volumetric energy density and the amount of energy per unit mass of hydrogen is low. This means that large tanks are required to store hydrogen on an aircraft and the weight of the fuel is significant. This not ideal, as size and weight are both at a premium on an aircraft. In addition, to be a carbon neutral fuel, the energy used to produce hydrogen needs to be renewable or itself carbon neutral. Hydrogen is also expensive, requires specialist infrastructure to be transported, and is difficult to store. Despite these challenges, Airbus is investing significantly in hydrogen, aiming to develop the world’s first zero-emission commercial aircraft by 2035 using hydrogen propulsion.
Sustainable Aviation Fuels (SAFs)
Perhaps the most promising immediate solution is provided by SAFs. These fuels can be used to fuel current gas turbine aero engines without modification and have the potential to be completely carbon neutral. SAFs fall into two main categories: biofuels and synthetic fuels. Biofuels are made from recycled waste such as used cooking oil, industrial waste, and agricultural and forestry residue. Synthetic fuels are made using electrochemical reactions between water and carbon captured from the atmosphere. In the case of synthetic fuels, if the energy used to produce the fuel is renewable or carbon neutral, and the amount of carbon released into the atmosphere when the fuel is combusted is the same as the amount of carbon captured to produce the fuel, then the synthetic fuel is completely carbon neutral. Another advantage of SAFs is that they can be blended with conventional jet fuel to provide at least some reduction in net carbon emissions. In the US, for example, aviation fuels comprising up to 50% SAF are currently approved for use. The challenges currently facing the widespread use of SAFs include the stringent approval processes that aviation fuels are subject to, and cost and supply. SAFs are currently too expensive to be commercially viable on a large scale and there are currently only a small number of manufacturers producing SAF. The limited supply is also in demand from the land transportation sector, further limiting the amount of SAFs available to the aviation sector.
There is no perfect solution to de-carbonisation within the aviation industry, and a reduction in carbon emissions is likely to be achieved through the use of a combination of the solutions discussed above. Electric propulsion is limited to short haul, passenger applications. Viable hydrogen fuelled aircraft are still some way off. SAFs provide a promising immediate solution, provided the regulatory and supply issues can be addressed. We may also see hybridisation in the short-term, for example utilising hydrogen or electric propulsion in combination with gas turbine engines running on conventional jet fuel. In any event, with the 2050 targets in the not-too-distant future, we are likely to see a lot of exciting innovation within the aviation industry to address the problem of de-carbonisation.
If you would like to discuss any of the issues raised in this article, please contact the author or your usual Barker Brettell attorney.