Effects of fuel sulfur content and nvPM emissions on contrail formation: A CFD-microphysics study including the role of organic compounds

Abstract

Aviation-induced contrails impact the climate significantly by altering atmospheric properties at cruise altitudes. Understanding the formation and evolution of ice crystals in aircraft engine plumes is essential for improving contrails prediction and mitigating their climate effects. This study introduces an innovative CFD-microphysics coupling methodology to simulate ice crystal formation in the near field of a turbofan engine plume. A 2.5D axisymmetric Eulerian-Lagrangian framework was employed, integrating gas-phase chemistry (60 reactions with 22 reactive species) and a detailed microphysical model. The model accounts for soot surface activation, condensation of organic vapors and sulfur species (H₂SO₄ and SO₃), as well as freezing and deposition processes. Results demonstrate that colder ambient temperatures (e.g., 212 K) enhance water supersaturation, accelerating ice crystal formation and growth, with soot-derived ice crystals reaching mean radii of up to 680 nm. Lower FSC increase the number of ice crystals due to the accompanying higher water supersaturation, while higher FSC promote larger ice crystals through enhanced condensation on soot particles. Organic compounds were shown to play a critical role in soot particle activation and growth, particularly under high FSC and lower temperature conditions, where they dominate the surface composition as compared to sulfur species. The soot emission index significantly influences the ice crystal number and size, with a soot emission index of 1.38 × 10¹³ #/kg-fuel producing the largest soot-derived ice particles due to reduced competition for available moisture. Hydrates and volatile particles exhibit peak concentrations of 10¹³ #/cm³ under high FSC, reflecting the role of sulfuric acid in their growth.