Influence of Antiwear and Dispersant Lubricant Additives on Soot Wear

Due to incomplete combustion, high levels of soot can accumulate in engine oils between drain intervals. This soot can promote wear of rubbing engine parts such as chains, cam systems and piston rings. Such wear was used to be confined to diesel engines but in recent years it has also become an issue in direct injection gasoline engines. Previous studies have shown that soot wear can be exacerbated by the presence of anti-wear additives such as zinc dialkyldithiophosphate (ZDDP) in the engine oil, so that under some conditions lubricants that contain both soot and ZDDP actually give more wear than ones from which the anti-wear additive is left out [1, 2]. This has been ascribed to a corrosive-abrasive wear process in which the soot nanoparticles continually abrade the ferrous sulphide/phosphate tribofilm that is initially formed when ZDDP reacts with rubbing surfaces. This type of wear is also called polishing wear. This study focuses on the exploration of possible mechanisms of the impact of soot on wear in order to understand the interaction of engine oil formulation using anti-wear and dispersant additives on soot induced wear.