In a research facility on the outskirts of a business park near Sheffield, Ihab Ahmed, a researcher at the University of Sheffield, is preparing to test a small jet engine.

Originally used as an auxiliary power unit for a commercial airliner, the engine now serves as a key testing device for innovative fuels developed in the adjacent laboratory. This setup is the heart of Sheffield University’s Sustainable Fuels Innovation Centre (SAF-IC), a cutting-edge research hub where synthetic fuels can be produced and tested on a small scale before transitioning to larger-scale production.

From a control room filled with computer screens, Ihab can closely monitor the engine’s activity as it fires up with a burst of flame. Real-time data from sensors help analyse the engine’s performance and the exhaust gases emitted, providing essential feedback on the effectiveness of the new fuels.

These sustainable aviation fuels (SAF) are synthetic alternatives to conventional fossil fuels, created from renewable sources such as waste cooking oils, vegetable fats, agricultural waste, and even captured carbon dioxide. Unlike fossil fuels, SAFs offer a significant advantage: they don’t add to the overall carbon dioxide levels in the atmosphere.

The carbon they emit has only recently been captured from the environment, either by plants or through chemical processes, making their use far more sustainable compared to fossil fuels, which release carbon that has been stored in the Earth for millions of years.

For the aviation industry, SAFs present a potential game-changer. Both Airbus and Boeing predict that the global airliner fleet will more than double in the next two decades as air travel demand grows, particularly in emerging markets like India and China. Simultaneously, airlines are under pressure to meet the ambitious target of net-zero carbon emissions by 2050, a goal endorsed by the International Air Transport Association (IATA).

While gains in fuel efficiency can be achieved by replacing older planes with modern ones—newer models are 15-30% more fuel-efficient—this will not be enough to meet the rising demand for air travel. Long-term solutions, such as hydrogen power and electric planes, are promising but face significant technological and logistical hurdles.

Hydrogen, for instance, poses challenges in terms of storage and production. It must be stored as either a highly compressed gas or a very cold liquid, and for it to be truly sustainable, it needs to be produced from renewable energy sources, which are currently limited.

“We believe we could bring a small hydrogen fuel cell aircraft to the market between 2035 and 2045, technically,” says Arjen Meijer, chief executive of the Brazilian jet maker Embraer.

“But the question that needs to be answered is: will there be sufficient hydrogen to feed those aircraft? These things need to come together. They can’t happen separately.”

Electric planes, on the other hand, suffer from the issue of energy density—batteries are far too heavy to power large aircraft for long distances, making them impractical for widespread use in commercial aviation.

This leaves sustainable aviation fuels as the most immediate and practical solution. SAFs can be engineered to have the same chemical properties as conventional jet fuel, allowing them to be used in today’s aircraft with minimal modifications. Current regulations require that airlines use a blend of SAF and regular jet fuel, with the SAF component capped at 50%.

However, modern aircraft are capable of running on 100% SAF, as demonstrated by a groundbreaking flight in 2022, when Virgin Atlantic flew a Boeing 787 from London to New York using only fuel derived from waste fats and plant sugars.

“The technologies are already available and certified for use in aircraft,” explains Julie Kitcher, chief sustainability officer at Airbus.

“The challenge with sustainable fuels is really about getting it produced at scale, across the globe, because this is a global industry, at an affordable price.”

The primary hurdle for SAF adoption is supply. Currently, SAF makes up just 0.05% of the fuel used in the European Union, and it costs three to five times more than conventional jet fuel. To address this, governments are introducing mandates to increase SAF usage. In the UK, a “SAF mandate” requires that 2% of all jet fuel supplied in 2025 must be SAF, rising to 10% by 2030 and 22% by 2040. The EU has similar targets, with a goal of 63% SAF usage by 2050. While the U.S. does not have mandated requirements, it offers subsidies to lower SAF prices.

Despite these efforts, scaling up SAF production remains a major challenge. There are multiple pathways to produce SAF, including biomass-based methods that utilise waste cooking oil, energy crops, wood, agricultural residues, and even human waste. However, concerns have arisen about the environmental impact of using certain feedstocks, such as the risk of deforestation or diverting land needed for food production toward fuel production.

An alternative production method, called power-to-liquid, involves breaking down water and carbon dioxide, then recombining the carbon and hydrogen to create liquid fuel. While this method could theoretically produce unlimited amounts of SAF, it requires vast amounts of renewable energy and advances in carbon capture and storage technology, both of which are currently expensive and limited in scale.

“There are good SAFs, and there are bad SAFs, but the brutal truth is that right now there is not much of either,” says Matt Finch, UK head of campaign group Transport & Environment.

“Conversely, right now there are thousands of new planes on order from airlines, and all of them will burn fossil fuels for at least 20 years.

“Actions speak louder than words, and it’s clear that the aviation sector has no plans to wean itself off its addiction to pollution.”

The aviation industry is calling for more investment to increase SAF production and bring down costs. At the recent Farnborough Airshow, several major players announced significant initiatives related to SAF. A consortium including Airbus, AirFrance-KLM, Qantas, and others pledged $200 million to a fund aimed at investing in mature SAF production technologies, particularly those utilising waste-based feedstocks.

Boeing, meanwhile, has partnered with investment firm Clear Sky to promote a method developed by British company Firefly that turns human waste into SAF. This process uses heat and high pressure to convert waste into a usable substance for fuel production, humorously dubbed the process of “powering planes with poo.”

In conclusion, while SAF holds immense potential to decarbonise the aviation industry, the road to widespread adoption is filled with challenges. Significant investments in technology, infrastructure, and production capacity will be necessary to scale up SAF usage and meet the industry’s ambitious climate goals.

 

 

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