Successful flight tests from biofuel aces plane and helicopter

A biofuel got from used cooking oil could slash aviation-related carbon emissions—if its unblended form can operate with existing aircraft.

Two flying machines partially powered by unblended sustainable aviation fuel, or SAF, made successful test flights in France this fall. An Airbus A319neo plane and an Airbus H225 helicopter all fueled one of their two engines with unblended SAF when flights that lasted three and two hours, respectively.

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Aviation sector is investigating various kinds of SAFs in

The aviation sector is investigating various kinds of SAFs in hopes of eventually making flying carbon-neutral. “The similar hydrocarbon molecule is present in both SAF and regular jet fuel.

As a result, the CO₂ emissions of both fuels [in engine exhaust] are not so much changed. However, the difference between the two fuels is the origin of the carbon,” says Massimiliano Materazzi, senior research associate at University College London, who is not included in the test flight project.

“The carbon in SAF is from biomass

This means the carbon that is emitted is exactly the similar that was extracted from the atmosphere by the biomass to grow.” In other information, the living sources managed to provide SAF really take carbon out of the atmosphere; therefore, burning the material merely represents the return of that same carbon back to the air, making the overall process close to carbon-neutral.

“With the best SAF production pathways, you can have between 80 to 90 percent reduction of CO₂ emissions over the fuel’s whole life cycle, compared to the traditional aviation fuel,” says Nicolas Jeuland, an expert on future fuels and manager at Paris-based aerospace company Safran, which is a part of the test project.

Jeuland tells aircraft engines are already certified to use SAF blended with regular jet fuel at ratios of up to 50 percent, and some airlines currently use SAF at ratios between 10 and 15 percent.

“However, we want to ensure that anyone wanting to use more than 50 percent SAF can do so in the future without any technical limitations,” he continues. That is why Safran is partnering with organizations including Airbus and TotalEnergies, which provides the fuel, on these test flights. They mark the start of a series of tests that will continue in 2022.

The goal is to measure both on-ground and in-flight SAF emissions and to study existing engines’ agreement with this type of fuel. “Engines usually stay in service for between 20 to 30 years,” Jeuland points out. If existing engines can run happily on SAF, airplanes can go green now rather than waiting for new, ultra-efficient aircraft that are not programmed to join the fleet until early in the next decade. “That’s why we have to prepare for the compatibility of the engine with 100 percent SAF now,” he says.

Assembling the SAF worked in these test flights involves sourcing used cooking oil and other waste fats from restaurants, industries, and other facilities, and treating it with hydrogen.

The hydrogen breaks down these substances’ fatty molecular chains into straight chains of carbon and excludes some of their small stable structures. “At the end, you have a clean fuel that doesn’t include aromatic compounds and sulfur,” Jeuland explains. Without sulfur, the emissions are cleaner, and without those aromatic compounds, SAF also emits much less particulate material than traditional fuel.

Jeuland predicts this lack of particles will also reduce airplane contrails, which have been identified as adding to global warming. “With SAF, we believe that the contrails—which are formed due to water condensing on tiny particles emitted by burning the traditional jet fuel—will be completely reduced,” he answers.

However, SAF’s lack of aromatic compounds could also affect its compatibility with some aircraft currently in use. Although Jeuland says existing engines should be able to run on unblended SAF without any major modifications, peripheral fuel systems may have to change slightly.

“For instance, the elastomers [a type of stretchy polymer] that we currently use in fuel lines to stop leakages can be incompatible with lower aromatic fuel,” he notes. “So we may have to potentially change the elastomer seals for SAF use,” Jeuland says developing new elastomers is not a great deal—but adds that the new complex question is whether existing fleets can be retrofitted with the latest elastomers. “This is something Safran is working on with Airbus and other partners,” he answers.

The extra problem is SAF’s still relatively high price.

Depending on how well-developed the production pathways are, such fuels price between two and 10 times as much as private fuel. Given the lack of integrated industries for producing SAF, Jeuland says this currently high price tag is entirely understandable.

“Traditional jet fuel, which costs less than milk or beer, is the result of fully integrated industrial processes that have been developed over decades,” he answers. “In the future, as we build more and bigger production plants, increase the efficiency of collecting biomass, and diversify the sources of biomass, [SAF’s] price will potentially go down.”

One way to make costs could be to get additional SAF sources. “By 2050 the need for SAF is expected to reach 500 million [metric tons] each year. At the time we are between 0.2 and 0.5 percent of that figure,” Materazzi says.