Characterization of aircraft engine soot: unique properties and cloud impact
Résumé
Aircraft engine soot collected at the outlet of a D30KU combustor is comprehensively characterized by numerical experimental techniques: TEM, EDS, AFM, FTIR, GC-MS, ion and liquid chromatography and gravimetry. Physical properties (morphology, microstructure, particle size, surface area, porosity) and chemical properties (elemental composition, water soluble/insoluble organic and inorganic fraction, surface functional groups, and volatility) are examined. The water uptake by engine soot is analyzed in a wide range of the relative humidity from 0.01 to 100% and temperatures from 233K to 295K. Engine soot exhibits unique features and especially a high hydrophilicity (20ML of adsorbed water at 240K) and an heterogeneity of its composition. Comparison with laboratory–made kerosene flame soot indicates that engine soot particles separates into two fractions: an hydrophobic main fraction which contains a reduced amount of sulfur and an hydrophilic fraction of impurities with large amounts of iron, oxygen, sulfur and potassium. These results allows us to estimate the environmental conditions able to develop aircraft engine soot indirect effects with respect to ice nucleation modes proposed for contrail and cirrus formation. Our finding of two fractions in engine soot leads us to suggest that the main fraction of aircraft – generated soot may initiate a sulfur-independent heterogeneous nucleation mode in the UT while the fraction of impurities is responsible for contrail formation.
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