Hot core processing of jet engine lubrication oil can enhance contrail nucleating particle numbers

Contrails contribute to atmospheric warming and form via ice particle formation on soot particles emitted from jet engines. With the development of lean-burn engines and sustainable aviation fuels reducing soot emissions, lubrication oil droplets will likely play a more important role in contrail formation. Here we show that the oil venting strategy can strongly affect contrail nucleating particle emissions. We sampled oil droplets from a gas turbine breather vent and used an expansion chamber to count ice crystals that formed under contrail conditions. When we experimentally replicated oil passing through the hot core of a lean-burn engine, ice particle formation increased 29 ± 10 times relative to venting the oil directly into the atmosphere (overboard). Our contrail modelling shows that the amount of oil emitted and the choice of lubrication oil venting strategy may offer opportunities for reducing contrail warming and should be considered for engine certification and emissions regulations.