Microscopic investigation of soot and ash particulate matter derived from biofuel and diesel: implications for the reactivity of soot

Abstract

Investigation of soot and ash particulate matter deposited in diesel particulate filters (DPFs) operating with biofuel (B100) and diesel (pure diesel: B0 and diesel 80 /biofuel 20 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-Sand 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 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.

Micro- and Nanostructural Characteristics of Particles Before and After an Exhaust Gas Recirculation System Scrubber

“…A lattice spacing of 4 Å was observed by Merchan-Merchan et al (2012) for pure diesel in an open air diffusion flame. The observed lamella length in our study (2.0 nm) is in average longer than the values (1.6 nm) reported by Müller et al (2007) and the tortuosity of 1.19 differs from those reported by Vander Wal et al (2010) (1.3) and Liati et al (2012) for diesel engine soot. It is suggested by Merchan-Merchan et al that diesel soot collected at flame temperatures of 655…”

Investigation of the Oxidation Behavior of Soot in Diesel Particle Filter structures

“…A further series of works has studied the inluence of particulate composition and nanostructure (nanometer and subnanometer scales) as well as of the primary particles and agglomerate sizes on the reactivity [7,8,9,10,11,12,13,14,15]. The term nanostructure refers to the dimensions, relative orientation and curvature of the graphene layer segments.…”

“…While the former may be somehow constant over the regeneration, the determination of the latter requires knowledge of the regeneration evolution. Here several approaches have been followed, based on geometrical reasoning, [17], BET (Brunauer-Emmett-Teller surface measurement technique based on physical adsorption of gas molecules on a solid surface) soot surface measurements, [18], as well as using micro-and nanostructural aspects of the soot primary particles and agglomerates, [9,10,11,12].…”

Physicochemical property changes during oxidation process for diesel PM sampled at different tailpipe positions

“…The hugest changes of diesel particle diameter may partially explain the maximum drop of burn out temperature for sample 3. [26,33,34]. PM formed at high temperature tends to be void core structures, as shown in references [35][36][37][38].…”