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ABSTRACT: The engine internal emission reduction of commercial vehicles has been very im-pressive during the last ten years. The mass related reduction of the soot emission is a result of the reduced number of particles also with regard to those <50nm. The microstructures in atomic scale and the bonding states (electronic structures) of soot particles emitted by advanced commercial vehicles engines will be elucidated by means of TEM, HRTEM and EELS. Core-shelled spheroidal primary particles are found as described in the literature, but more primary particles do not exhibit a defined structure. The high-resolution imaging reveals irregular shaped primary particles with a deformed fullerenoid structure (size between 10 and 20nm) and fullerene-like clusters or molecules on the surface of the primary particles [Sum03]. XPS, FTIR (DRIFTS) spectroscopy are applied to reveal the functional groups on surface and the bulk composition of the soot particles. The surface of the soot is highly covered with oxygen containing functional groups Giant PAHs, e.g. hexabenzocoronene, are volatilized to form an aerosol containing GPAH clusters similar in size like primary soot particles. This aerosol is used to study the reactivity of a chemically well defined model soot. Models for BSU stacks (size~2nm) are detected by MALDI-TOF-MS. The largest cluster found is (C96H30)6 with the mass 7098 u. The microstructures of soot particles are related to the chemical reactivity against the oxidizing agent nitrogen dioxide, NO2 by kinetic measurements. The obtained knowl-edge will be applied in the practice for minimizing the soot particle emission of diesel en-gines and for increasing the activity of exhaust aftertreatment with PM-KATâ and GD-KAT systems. The investigation of the formation and the properties of diesel soot of advanced commercial engines is just at the beginning. We expect that the chemical properties of the surface and the microstructure of soot emitted from advanced diesel engines will re-define toxicity (threshold value of secondary genotoxicity) and relevance of physical measurement methods.