Characterisation of soot agglomerates from engine oil and exhaust system for modern compression ignition engines

The characteristics of soot in oil samples extracted from lubricating oil and exhaust system of a modern common rail compression ignition engine were studied. The morphological parameters of the soot agglomerates were calculated from micrographs obtained by a High-Resolution Transmission Electron Microscopy (HR-TEM). The morphological analysis indicated that the soot in oil agglomerates have a larger average primary particle size and overall larger agglomerate size (determined by the radius of gyration) compared to the agglomerates sampled in the exhaust system. This can be a consequence of the dehydrogenation of hydrocarbon (HC) chains from the oil around the soot agglomerates. The shape of the agglomerates is quantified by fractal dimension. The soot in oil agglomerates presented a slightly larger fractal dimension than those studied in the exhaust system. Therefore, it seems that soot in oil agglomerates were more compact than those found in the exhaust system. The impact on lubricating oil properties should be further investigated.