One of the biggest priorities in the transportation sector is sustainability, and a key to decarbonising carbon-intensive industries such as aviation and heavy freight shipping will be sustainable biofuels.
This requires some adaptations in order to produce and store vast quantities of biofuel suitable for use as jet fuel or in blends with existing kerosene jet, which itself requires tanks with pressure relief valves to manage the varying stages of production.
Industry bodies such as the International Air Transport Association (IATA) have stated that a key strategy to decarbonising aviation and ensuring that the industry can help rather than hinder attempts to reach net zero is through the use of specialist biofuels, but why is this the case?
What is aviation biofuel, how can it help reduce emissions and reliance on fossil fuels, and why is it much more critical here than biofuels in other transport sectors?
What Is Aviation Biofuel?
Aviation biofuel, often known more broadly as sustainable aviation fuel (SAF), is any low-carbon fuel source not based on petroleum that can be used to replace kerosene-based jet fuel.
Jet fuel has particularly complex requirements compared to other transportation fuels, which makes it significantly more difficult to replace with alternatives.
Unlike biodiesel, bioethanol or electrofuels, which can either be adapted for use as a drop-in fuel with conventional cars or used with a flex-fuel car and tend to have a relatively narrow band of operating conditions they are expected to work in, jet fuel needs to be consistent in the midst of extremes.
Whether it is the high initial operating temperature to take off from an airport in a particularly warm country to the freezing temperatures at the edge of space, jet fuel needs to constantly flow safely and in a way that pilots will expect.
Developing biomass-derived fuels suitable for flight is difficult, but there are several methods available that can significantly lower carbon dioxide emissions and reduce reliance on fossil fuels.
They are currently typically blended with fossil fuels, with the aim to transition to fully biomass-derived fuels in the future.
How Can They Help Reduce Carbon Emissions?
Unlike jet fuel, which is made from kerosene and derived from crude oil which is acquired at tremendous environmental cost, biofuel is far less carbon intensive, and depending on the methods used to extract and produce the fuel, could potentially only produce carbon emissions once used.
Whilst the technology is still being developed and maximised, biofuels derived from algae with the ability to photosynthesise could potentially produce just two per cent of the carbon emissions of Jet-A1, one of the most commonly used types of jet fuel.
Other sources include non-food crops, Jatropha oil and waste oil from tallow and deep-fat fryers.
These provide fewer emissions savings by volume but can provide a greater benefit overall due to the development of technology to convert the materials into biofuel and their wider accessibility in general.
As with other biofuels, sustainability is crucial, as growing crops for biofuel at the expense of food production can have a counterproductive effect.
What Are The Challenges With Aviation Biofuel?
Creating 100 per cent drop-in jet fuels that have identical properties is possible but SAF is currently facing significant supply constraints with key ingredients such as hydrotreated esters and fatty acids (Hefa).
Increased demand with limited supply increases costs exponentially, which harms the economic case for aviation biofuel and can cause issues with adoption in the long run.
Whilst there was a hope that one per cent of all jet fuel used in aviation would be SAF, just 0.3 per cent was produced and used, something the IATA describes as “significantly below previous estimates”.
Part of this is issues with incentives, which still make fossil oil an attractive option for many operators, whilst another aspect is issues with scaling the production of SAF fuel.
Another issue is with avoiding contaminants. The United States Air Force reported in 2016 that bacteria and fungi critical to the production of some types of biofuel were found in their fuel tanks, requiring extensive disinfection through pasteurisation methods to fix.
Are There Any Alternatives?
Unlike with roadgoing transportation, where a shift is being seen away from petrol or diesel cars entirely towards battery electric vehicles, a transition away from fuel-based aircraft itself is far more difficult if not impossible for passenger airliners.
Weight is a major consideration with flight, and the notorious weight of batteries and their currently limited capacity makes electric airliners extremely difficult if not impossible with current battery technologies, although there are some prototypes in development.
