Will sustainable aviation fuel take off?

In a building on the edge of a business park outside Sheffield, researcher Ihab Ahmed is preparing to fire up a small jet engine.

Originally used as an additional power unit for commercial aircraft, it has been turned into a testbed for new fuel developed in the laboratory next door.

The arrangement is the centerpiece of the University of Sheffield’s Sustainable Fuels Innovation Center (SAF-IC), a research facility set up to allow synthetic fuels to be prepared and evaluated on a small scale, before being put into large-scale production.

On the bank of computer screens in the nearby control room, Ihab can monitor the engine as it starts with a burst of enthusiasm and power up.

Sensors tell you what the engine is doing in real time – and allow exhaust gases to be continuously analysed.

Sustainable fuels are synthetic alternatives to fossil fuels, made from renewable sources.

This can include waste cooking oil, vegetable fat and agricultural waste, as well as captured carbon dioxide.

The advantage of burning this kind of fuel is that it does not increase the overall carbon dioxide load in the atmosphere.

The carbon that is emitted is only recently removed, either by plants or chemical processes. In contrast, burning fossil fuels releases carbon that has been stored in the earth for millions of years.

“From an environmental perspective, it’s day and night,” Mr Ahmed said.

“In principle, CO2 should be net zero, so that no carbon dioxide is added to the atmosphere, but the other benefit is the non-CO2 part.

“For example, reducing the particles or smoke that comes out of the engine, which can affect your lungs, also contributes to the creation of contrails.”

For the aviation industry, this could be a game-changer.

According to forecasts from Airbus and Boeing, the global aircraft fleet is expected to more than double over the next two decades, as the middle class in countries like India and China expands, and demand for air travel increases.

At the same time, members of the International Air Transport Association, which represents airlines, have committed to achieving net zero by 2050.

Some gains will be made by replacing old aircraft with new ones. The most modern aircraft are between 15 and 30% more fuel efficient than before. But if the industry is to continue to grow, more is needed.

In the longer term, new technologies such as hydrogen power and electrification may play a role, at least on shorter routes. But there are difficult challenges to overcome.

Hydrogen, for example, is abundant and difficult to store in large quantities. It must be stored as a highly compressed gas or as a supercooled liquid. In order to be sustainable, it must be made in a “clean” way, from renewable sources – and the current supply is very limited.

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

“But the question that needs to be answered is: will there be enough hydrogen to feed the plane? These things have to come together. They can’t happen in isolation.”

Batteries, at present, are very heavy in terms of the energy they contain. This makes them unsuitable for powering large aircraft, or for use over long distances.

This means that hydrogen and hybrid, or fully electric, aircraft remain years away. Sustainable aviation fuel, by contrast, can be created in a laboratory with the same characteristics as conventional fuel derived from crude oil, making it suitable for use in today’s aircraft.

There are limitations. Airlines must now use a mixture of SAF with regular fuel, with the SAF component not exceeding 50%.

However, modern aircraft can burn 100% SAF. In a specially approved flight test last year, Virgin Atlantic flew a Boeing 787 from London to New York using fuel produced exclusively from waste plant fats and sugars.

“The technology is already available and certified for use in aircraft,” said Julie Kitcher, chief sustainability officer at Airbus.

“The challenge with sustainable fuels is about producing them at scale, worldwide, because it’s a global industry, at an affordable price.”

And that is very clear to catch. The current supply of SAF is minimal. According to the European regulator EASA, only 0.05% of the fuel is used in the EU. They also cost between three and five times more than “regular” jet fuel.

The government wants to change this. In the UK, the “SAF mandate” has been established, which states that from next year, 2% of all jet fuel supplied must be SAF, rising to 10% in 2030 and 22% in 2040.

The EU has a similar mandate, though until 2050 – when the SAF usage target is 63%. The US has no minimum requirements but offers subsidies to reduce sustainable fuel prices.

But if the use of SAF increases, production must also be increased dramatically.

There are many different ways, or pathways, to create sustainable fuels. It can be made from biomass, such as cooking oil waste, energy crops, wood, agricultural residues and also human waste.

However, there are concerns that this will not provide all the fuel that the market will eventually need. Some feed materials may need to be avoided, to prevent environmental degradation such as deforestation, or to prevent the land needed to grow food from producing energy.

An alternative is to use a method called power to liquid, where water and carbon dioxide are split, with the result that carbon and hydrogen are combined to make liquid fuel.

This could produce an unlimited supply of fuel, but to be sustainable it would require large amounts of renewable electricity, as well as increasing the amount and storage of carbon.

Both processes – using biomass or energy for liquids – are currently very expensive. As a result, the airline industry demanded action to increase production, and reduce prices with economies of scale.

However, environmentalists question whether this is actually possible.

“There are good SAFs, and there are bad SAFs, but the truth is that there aren’t many at the moment,” said Matt Finch, head of the Transport & Environment campaign group.

On the contrary, there are currently 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 is clear that the aviation sector has no plans to break its addiction to pollution.”

However, at the recent Farnborough Airshow, there were some important announcements related to the SAF.

A consortium including Airbus, AirFrance-KLM, Associated Energy Group, BNP Paribas and Qantas among others announced plans to invest $200m (£151m) in a new fund that will invest in “technologically mature SAF production projects using examples based on waste. raw material”.

Meanwhile, Boeing said it had formed a partnership with investment firm Clear Sky to promote its SAF production method pioneered by the British company Firefly.

The method involves taking human waste and using heat and high pressure to convert it into a substance that can then be used to make SAF.

In other words, allow the plane to be powered by poo.