Microscopic investigation of soot and ash particulate matter derived from biofuel and diesel: implications for the react
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RESEARCH PAPER
Microscopic investigation of soot and ash particulate matter derived from biofuel and diesel: implications for the reactivity of soot Anthi Liati • Alexander Spiteri • Panayotis Dimopoulos Eggenschwiler Nina Vogel-Scha¨uble
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Received: 21 May 2012 / Accepted: 26 September 2012 / Published online: 5 October 2012 Ó Springer Science+Business Media Dordrecht 2012
Abstract Investigation of soot and ash particulate matter deposited in diesel particulate filters (DPFs) operating with biofuel (B100) and diesel (pure diesel: B0 and diesel80/biofuel20 blend: B20) by means of optical microscopy, scanning electron microscopy, and high resolution transmission electron microscopy (HRTEM) reveals the following: the rapeseed methyl ester biofuel used for this study contributes to ash production, mainly of Ca–S– and P-bearing compounds ranging in size between 50 and 300 nm. Smaller ash particles are less common and build aggregates. Ash is deposited on the inlet DPF surface, the inlet channel walls, and in B100-DPF at the plugged ends of inlet channels. The presence of Fe–Cr–Ni fragments, down to tens of nanometers in size within the ash is attributed to engine wear. Pt particles (50–400 nm large) within the ash indicate that the diesel oxidation catalyst (DOC) upstream of the DPF shows aging effects. Radial cracks on the coating layer of the DOC confirm this assumption. The
A. Liati (&) A. Spiteri P. Dimopoulos Eggenschwiler Laboratory of Internal Combustion Engines, EMPA, Swiss Federal Laboratories for Materials Testing and Research, Ueberlandstrasse 129, 8600 Du¨bendorf, Switzerland e-mail: [email protected] N. Vogel-Scha¨uble Laboratory of Solid State Chemistry and Catalysis, EMPA, Ueberlandstrasse 129, 8600 Du¨bendorf, Switzerland
B100-DPF contains significantly less soot than B20 and B0. Based on the generally accepted view that soot reactivity correlates with the nanostructure of its primary particles, the length and curvature of graphene sheets from biofuel- and diesel-derived soot were measured and computed on the basis of HRTEM images. The results show that biofuel-derived soot can be more easily oxidized than diesel soot, not only during early formation but also during and after considerable particle growth. Differences in the graphene sheet separation distance, degree of crystalline order and size of primary soot particles between the two fuel types are in line with this inference. Keywords Diesel soot Diesel ash Soot nanostructure Graphene Soot oxidation Biofuel
Introduction The detailed investigation of emissions from diesel engines is gaining importance, on the one hand due to enhanced measures for the reduction of air pollution and on the other through improvement of aftertreatment strategies, engine performance, and fuel efficiency. Given the fact that trucks are operating with diesel fuel and that the demand for personal diesel cars continues to rise, bio-derived fuels have been applied in recent years as an alternative to diesel. Application of biofuels aims primarily at redu
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