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Ultrafine (<100 nm) particles related to traffic are of high environmental and human health concern, as they are supposed to be more toxic than larger particles. In the present study transmission electron microscopy (TEM) is applied to obtain a concrete picture on the nature, morphology and chemical composition of non-volatile ultrafine particles in the exhaust of state-of-the-art, Euro 6b, Gasoline and Diesel vehicles. The particles were collected directly on TEM grids, at the tailpipe, downstream of the after-treatment system, during the entire duration of typical driving cycles on the chassis dynamometer. Based on TEM imaging coupled with Energy Dispersive X-ray (EDX) analysis, numerous ultrafine particles could be identified, imaged and analyzed chemically. Particles <10 nm were rarely detected. The ultrafine particles can be distinguished into the following types: soot, ash-bearing soot and ash. Ash consists of Ca, P, Mg, Zn, Fe, S, and minor Sn compounds. Most elements originate from lubricating oil additives; Sn and at least part of Fe are products of engine wear; minor W ± Si-bearing nearly spherical particles in Diesel exhaust derive from catalytic coating material. Ultrafine ash particles predominate over ultrafine soot or are nearly equal in amount, in contrast to emissions of larger sizes where soot is by far the prevalent particle type. This is probably due to the low ash amount per volume fraction in the total emissions, which does not favor formation of large ash agglomerates, opposite to soot, which is abundant and thus easily forms agglomerates of sizes larger than those of the ultrafine range. No significant differences of ultrafine particle characteristics were identified among the tested Gasoline and Diesel vehicles and driving cycles. The present TEM study gives information also on the imaging and chemical composition of the solid fraction of the unregulated sub-23 nm size category particles. [ABSTRACT FROM AUTHOR]

The definition of a sufficiently resolved heat transfer model with spray cooling effect as a function of each droplet kinetic and thermal parameters is a key factor in the numerical simulation of aqueous urea (AUS) based Selective Catalytic Reduction (SCR) exhaust after-treatment systems. A consolidated spray-wall interaction model [1] has been implemented on the open source 3D finite volume software OpenFOAM and a critical investigation of its behaviour in engine representative conditions is reported. A simplified test case is used to highlight the influence of the chosen model on the numerical simulation of the system, reducing the importance of the other spray sub-models in the Lagrangian-Eulerian computational framework. The coupling between the droplet evaporation heat flux and the gas-solid interface thermal boundary condition has been studied, pointing out the significance of each contribution. The main focus of this work is to present reference conditions to simulate the spray-dry wall spray impingement behavior to determine the 'onset of wall wetting' thermal conditions. [ABSTRACT FROM AUTHOR]