Comparing Physical and Chemical Properties of Soot from Laboratory Tests and Heavy-Duty Engines Used in Field Operations

Morphology, nanostructure, and composition of soot extracted from the oil sump of different heavy-duty engines operated under dynamometer and field conditions were investigated. Soot characteristics were then compared to a carbon black sample. Soot was extracted from used oil for transmission electron microscopy (TEM) analysis. Energy-dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analyses were also performed to assess soot composition. Two soot classes, I and II, can be identified based on their appearance under the TEM. Carbon black and class I particles have graphitic structures, while class II samples have a more sludge-like appearance. Similar aggregate sizes were observed among the samples. In all samples, the primary particle size distribution ranges from 16 nm to 22 nm in terms of mean diameter. Differences in the length and tortuosity of the graphitic fringes between the samples were observed. The findings suggest a greater degree of interaction between class II samples and the lubricating oil, and consequently, a different wear behavior may be expected depending on the specific soot characteristics.