Modelling of cluster formation of jet fuel oil molecules
Le résumé fourni par la source
Aviation activities are considered an important source of ultrafine particles. Recent studies suggested that lubricating oil emitted from jet engines plays a neglected role in new particle formation. However, the molecule-level mechanism for this process remains unclear. In this thesis, pentaerythritol tetrahexanoate (PT), a typical polyol ester molecule in aviation lubricating oils, is selected as a representative compound for jet engine emissions. Several other relevant species, trans- and cis-sulfuric acid (SA), SO2, and HNO3, are also considered. Quantum chemical calculations are employed to simulate particle formation processes. Extensive sets of candidate structures are first generated using a custom configuration sampling algorithm. The structures are initially optimized at the GFN2-xTB level. Their single-point energies are evaluated using the B97-3c method for preliminary filtering. Selected candidate structures are further explored using the CREST algorithm to identify low-energy configurations. The representative structures are subsequently optimized, and calculated their frequencies are calculated at the B97-3c level, with thermodynamic corrections evaluated at a temperature of 573.15 K. Finally, high-level single-point energy calculations are performed at the DLPNO-CCSD(T)/def2-TZVP level to refine the electronic energies, from which the Gibbs free energies of cluster formation are obtained. The results indicate that PT can form thermodynamically favorable clusters with itself and the selected species. Among the investigated clusters, the PT dimer exhibits the highest stability, which indicates a strong tendency for clustering of PT. In addition, PT-transSA and PT-cisSA clusters also show relatively high stability due to the network of multiple hydrogen bonds between carbonyl oxygens of PT and SA. In comparison, the stability of PT–HNO₃ and PT–SO₂ clusters is relatively weak. This study reveals the potential mechanism by which aviation lubricating oil vapor forms stable molecular clusters at the molecular level. This provides a theoretical basis for understanding the formation of ultrafine particulate matter in aviation emissions.
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