Used frying oil lowers aircraft fuel emissions

Used frying oil can be turned into an additive that makes aircraft fuel more environmentally friendly, according to a study reported by ERR and involving Estonian and French researchers.

Researchers from the Estonian University of Life Sciences, Tallinn University of Technology, the Estonian Aviation Academy and KBFI, together with French scientists, combined zinc compounds with old rapeseed oil that had been used to fry 10 batches of French fries at 190 degrees Celsius.

The low-temperature synthesis produced special nanoparticles, which were tested in a real TA-8 gas turbine engine after being added to standard Jet A-1 aircraft fuel.

The particles produced at 130 degrees Celsius performed best. Adding just 10 parts per million of the new additive reduced harmful nitrogen dioxide emissions by 3 percent in engine tests. Particles made with clean rapeseed oil produced an even better result, cutting nitrogen emissions by nearly 18 percent.

The nanoparticles did not settle at the bottom of the fuel mixture and remained stable for at least four months. Tests also showed that the small quantity of particles did not affect the fuel’s basic properties. Its density, flash point and viscosity all remained within aviation standards.

Researchers said further long-term testing is needed before the solution can move beyond the laboratory.

They attributed the reduction in emissions to chemistry at the microscopic level. Molecules from the used frying oil attach themselves to the surface of the zinc particles, forming a protective layer that prevents the particles from clumping together in the fuel. This helps the fuel atomise more effectively in the engine. Smaller fuel droplets evaporate faster and mix more evenly with air, allowing combustion to take place at a more uniform temperature.

The zinc compounds also require substantial energy to break down, which directly cools the combustion process and suppresses the formation of harmful nitrogen oxides.

The researchers published their findings in the journal Materials Today Sustainability.