The laboratory combustion technique operating on a typical combustor of a gas turbine engine is used for soot sampling. Soot particles are derived by combustion of a hydrocarbon mixture at typical cruise C 3 H 8 Èn-C 4 H 10 conditions. Size, morphology, microstructure, surface area, porosity, and the chemical nature of the soot surface particles are studied by transmission electron microscopy (TEM), Raman and Auger electron spectroscopies (AES), volumetry and gravimetry. Structural irregularities such as micropores determine the speciÐc adsorbability of non-polar gases such as Kr, and With respect to water adsorption, CH 4 C 6 H 6. aircraft combustor soot is far from being hydrophobic. Initial water adsorption on polar heterogeneities leads to pore Ðlling at increasing pressures. The microstructure of soot particles is easily transformed under the inÑuence of adsorbates, giving rise to swelling e †ects. Due to its speciÐc physico-chemical properties aircraft combustor soot may act as contrail condensation nuclei at low sulfur content in the jet fuel.

[1] Morphology, microstructure and surface chemistry of laboratory made kerosene soot used as an aircraft soot surrogate have been studied to establish the correlation between the porosity and the mechanism of water adsorption on the soot surface. The quasielastic neutron scattering (QENS) technique has been used to characterize the dynamics of water confined in the soot pores network. Spectra above and below the water triple point T m describe the translational and rotational diffusion of water molecules adsorbed in 0.5 nm micropores, 2 nm supermicropores and !2 nm mesopores. Below T m an appreciable amount of liquid water exists in the soot micropores down to the lowest tropospheric temperatures. The depression in freezing temperature is related to the pore dimension. Water confined in the micropores appears to freeze completely only at T below 200 K showing that the nucleation process depends on the specific microporosity. At the saturation plume conditions ffi30% of adsorbed water has been transformed into ice. These results show that, in the upper troposphere, soot particles presenting the above-mentioned properties will contain stable water/ice components inside the pores with 25% of unfrozen water.

No abstract

Quasi-elastic neutron scattering (QENS) and neutron diffraction (ND) experiments were conducted to characterize the dynamics and structure of water/ice confined in a well-defined kerosene-soot pores network at 40, 60, and 100% relative humidity and at temperatures from 283 to 204 K. The QENS spectra indicate that about 35% of the adsorbed water is in an amorphous solid-like state at T = 283 K and that an appreciable amount of liquid water exists in the soot supermicropores down to the lowest temperature investigated, i.e., 204 K. The depression in freezing temperature is related to the pore dimensions. At T [Formula: see text] 260 K ND shows a mixture of amorphous ice, probably located in the soot mesopores coexisting with ice Ih at the surface of the soot primary particles. The results are discussed within the context of aircraft-generated soot aerosols in the upper troposphere as candidates for heterogeneous ice nucleation responsible for contrails and cirrus formation. PACS Nos.: 82.33Tb, 92.60Mt, 81.05Rm, 61.12-q

No abstract