Search

Soot particles generated by a liquid-fueled miniCAST burner, supplied with diesel B7, was characterized for the first time over a total of 34 operating points covering an overall equivalence ratio (ϕ) range of 0.103–1.645. To characterize the gas and particulate phase emissions, electron microscopy images, mobility-equivalent size distributions and mass concentration of the soot aggregates were recorded, and optical extinction/absorption coefficients of the exhaust were measured. The burner produces soot aggregates with geometric mean diameter size in the range 45-105 nm with primary particle size in the range 18-39 nm. The Ångström absorption exponent (α) was evaluated in the range 400-1000 nm and was found to increase with ϕ and vary in the range 1.05–2.25. The interposition of a catalytic stripper in the sampling line was found to (i) flatten the shape of the size distribution of aggregates, (ii) oxidize most of the gas phase thus impacting optical extinction coefficients particularly below 400 nm and (iii) decrease α. The soot volume fraction (fv) was determined by three independent methods: optical absorption, mass deposit and mobility size distribution combined with morphology data. fv evaluated from size mobility data accounting for morphological aspects agreed within 13% with fv measured optically and within 25% with fv evaluated from mass concentration measurements. The precise methodology developed to characterize engine-like soot particles produced by a liquid-fueled miniCAST can now be transposed to study other regular, renewable, and surrogate liquid fuels to investigate their physical and optical properties before considering their large-scale use. Copyright © 2023 American Association for Aerosol Research

International audience; The transformation process in sooting flames leading to the formation of nanoparticles in the condensed phase from molecular precursors in the gas phase (soot nucleation) is not yet fully understood [1]. Information on the physical chemical properties of the nascent particles is difficult to accessexperimentally but also essential for the validation of the hypotheses on soot nucleation currently being examined by the scientific community. In this work, we characterize the molecular precursors and the soot particles formed in a laminar diffusion methane flame by combining several in situ and ex situ diagnostics (fluorescence, incandescence, secondary ion mass spectrometry and Raman spectroscopy) with the goal of inferring the chemical composition and the structure of the nascent particles. The presented work highlights that several of the investigated physical chemical properties suddenly change within a narrow flame region that acquires the character of a discontinuity point correlated to the soot nucleation process. Notably, the obtained data shows evidences of the transition from flat to curved molecular structures, and the progressive apparition of finite size, sandwiched graphene like layers. Furthermore, the fraction of atomic hydrogen features a local maximum immediately upstream the detection of nascent soot particles consistent with the increasing in flame rate of C-C covalent bonds formation postulated by the major hypotheses explaining the nucleation of soot particles.References[1] J.W. Martin, M. Salamanca, M. Kraft, Soot inception: Carbonaceous nanoparticle formation in flames, Progress in Energy and Combustion Science. 88 (2022) 100956.https://doi.org/10.1016/j.pecs.2021.100956.