UNREAL Project : Unveiling nucleation mechanism in aircraft engine exhaust and its link with fuel composition

Abstract : Aviation emissions are not limited to greenhouse gases like CO2 or water but include as well other gases like nitrogen oxides (NOx) or sulfur oxides (SOx) and volatile and non-volatile particulate matter (vPM and nvPM respectively). nvPM is defined as particles present in the engine exhaust at temperatures higher than 350°C and consists essentially in soot particles produced by the incomplete combustion of the fuel. vPM is formed by nucleation from gaseous precursors in the cooling exhaust gas downstream the combustor, when the concentration of preexisting particles has decreased, favoring homogeneous nucleation versus heterogeneous one (absorption of gases onto preexisting particles). Sulfuric acid formed in the engine exhaust seems to be linked to the formation of vPM. However, the amount of sulfur present in the fuel converted to sulfuric acid in the exhaust is too small to explain the amount of vPM observed. Chemi-ions and organic compounds emitted by the engine are one of the most suitable candidates to explain the formation of vPM in the engine exhaust, but the molecular mechanism behind this phenomenon is still unknown...