Morphological Characterisation of Diesel Soot-in-Oil and the Associated Extraction Dependence

Paper #:
  • 2018-01-0935

  • 2018-04-03
The size and morphology of soot particles and agglomerates extracted from samples of lubricating oil drawn from the sump of a diesel engine have been investigated using Transmission Electron Microscopy (TEM) and Nanoparticle Tracking Analysis (NTA). Soot from the sample was prepared for imaging by both centrifugation and sample dilution with heptane, followed by washing in diethyl ether to investigate the associated extraction dependence. The size and shape of agglomerates were defined from measurements of skeleton length and width, as well as shape factors such as circularity. It was shown that centrifugation increases the extent of agglomeration within the sample, with 15% of the agglomerates above 200 nm compared to 11% in the solvent extracted soot. It was also observed that the width of centrifugation extracted soot was typically 10 nm to 20 nm larger than that of solvent extracted soot, suggesting that centrifugation forces the individual agglomerate chains together. Centrifugation also fails to extract a large percentage of particles below 50 nm. In the centrifugation extracted soot only 4% of the agglomerates were smaller than 50 nm while agglomerates in the solvent extracted sample accounted for 19 %. TEM can be an expensive characterisation tool for high throughput testing required by industry. In this work NTA is also used as an alternative method of measuring particle size due to its lower cost and faster sample turnaround than the more widely used TEM. It was found that results generated by NTA correlated well to those of TEM, however NTA cannot detect scatter from soot particles below 50 nm. The morphological characteristics of two commercial carbon blacks were also measured using both techniques and compared to select the most suitable soot surrogate.
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