Soot wear mechanisms in heavy-duty diesel engine contacts

Abstract

In this study, the wear mechanisms of a used, soot-containing oil drained from an engine test are investigated. As reviewed at the start of this paper, many wear mechanisms have been proposed for soot-containing oils. Often these studies were conducted using fresh oils with added carbon black as a soot mimic which do not always accurately represent the oxidation pathways in engines. Hence, we apply a range of tribometer tests and surface analyses techniques to assess the wear performance of engine-drained oil on AISI 52100 steel. Results suggest that this used oil gives rise to the corrosive-abrasive wear mechanism involving repeated cycles of anti-wear film formation and subsequent removal by soot abrasion. The role of different additives in mitigating/exacerbating this mechanism are studied by testing lubricant samples with key additives omitted. This reveals that detergent helps to form a strong, soot-resistant tribofilm, while ZDDP prevents wear provided it can form a strong film but can also increase wear in a used, abrasive, soot-containing oil.