Chemical and nanostructural characteristics of the particulate matter produced by renewable diesel fuel in an automotive diesel engine

Renewable diesel (RD), a paraffinic fuel produced by the hydrotreating of palm oil, was used neat and blended at 10% and 30% (by volume) with ultra-low sulfur diesel (ULSD) to generate particles in an automotive diesel engine operating at two engine speeds (1890 and 2410 min(-1)) under the same engine load (95 Nm). Particulate matter was characterized using thermogravimetric analysis (TGA), Raman spectroscopy, X-Ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), and X-Ray photoelectron spectroscopy (XPS). Oxidation profiles showed that diesel soot is slightly more reactive than the soot produced by RD and its blends, independently of the engine speed (the maximum mass loss rate temperature -MLRTmax - was 6.6 degrees C lower for ULSD than neat RD). This behavior was in agreement with the active surface area (ASA) of the particles, which varied between 10.8 m(2)(g for RD to 13.9 m(2)/g for ULSD at the same engine speed. Soot nanostructure (ratio of Raman peaks) and interlayer distance show a slightly higher degree of order of the particles when RD was added into diesel fuel. The mean primary particle diameter of neat RD soot was around 26 nm and fractal dimension of the agglomerates was around 1.66, which were both lower in comparison with ULSD (32 nm and 1.97, respectively). Fringe analysis applied to HRTEM micrographs revealed no clear trend in the fringe length and tortuosity among soot samples. Finally, it was found that, independently of the fuel tested, all particle samples gathered at 2410 min(-1) were slightly more reactive and smaller than those collected at 1890 min(-1). From this engine configuration and specific experimental setting, it can be expected that the use of RD blends would not markedly affect the performance of aftertreatment devices like diesel particulate filters. (C) 2019 The Combustion Institute. Published by Elsevier Inc, All rights reserved.