Impact of Diesel Engine Oil Additives–Soot Interactions on Physiochemical, Oxidation, and Wear Characteristics of Soot

Carbonaceous soot accumulated in crankcase oil is known to have an adverse effect on diesel engine performance, durability, and fuel efficiency. The current study is focused on determining the influence of engine oil additive package and soot interactions on crankcase soot chemistry, structure, and oxidation. The soot was extracted from the crankcase oil of Mack T-12 dynamometer diesel engine tests and characterized using X-ray absorption near edge structure (XANES) spectroscopy, high-resolution transmission electron microscopy (HR-TEM), high-temperature X-ray diffraction (HT-XRD), and energy dispersive spectroscopy (EDS). Additionally, four-ball wear bench tests were conducted to study the effect of several interactions like antiwear additive–soot, dispersant–soot on lubricity of formulated engine base oils. XANES and HR-TEM analyses suggest the presence of chemical compounds originating from engine oil chemistry as either adsorbed/embedded into the turbostratic nanostructure of soot. The HT-XRD method was employed to map variations in interplanar spacing of basal plane (002) of turbostratic soot with temperature, indicative of the degree of disorder and ease of oxidation. The oxidative reactivity of crankcase soot is found to be strongly dependent on the changes in the physical and chemical makeup of carbonaceous soot structure. Wear assessment proved that the increase of soot concentration in formulated oils significantly increases wear of sliding surfaces. Results indicate that the soot-induced wear occurs through an abrasive wear mechanism, where soot antagonistically interacts with protective antiwear additive-formed tribofilms and exacerbate wear of engine components.