Scientific American explores a frontier of carbon-neutral industry – a way to make airplanes and helicopters fly without so many greenhouse gases in their exhaust:
Two flying machines partially powered by unblended sustainable aviation fuel, or SAF, performed successful test flights in France this fall. An Airbus A319neo plane and an Airbus H225 helicopter each fueled one of their two engines with unblended SAF during flights that lasted three and two hours, respectively.
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“The same hydrocarbon molecule is present in both SAF and traditional jet fuel. As a result, CO2 emissions of both fuels [in engine exhaust] are not much different. 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 involved in the test flight project. “The carbon in SAF is from biomass. This means the carbon that is emitted is exactly the same that was removed from the atmosphere by the biomass to grow.”
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Producing the SAF used 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 removes some of their less stable structures. “At the end you have a clean fuel that doesn’t contain aromatic compounds and sulfur,” [Safran-employed future fuels expert Nicolas] Jeuland explains. Without sulfur, the emissions are cleaner, and without those aromatic compounds, SAF also emits much less particulate matter than traditional fuel. Jeuland predicts this lack of particles will also reduce airplane contrails, which have been identified as contributing to global warming.