Comprehensive characterization of particulate matter emissions produced by a liquid-fueled miniCAST burner

Abstract

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.