Interactions of Engine Oil Additives

Abstract

Modern engine oil formulations usually contain many kinds of additives, such as detergent-dispersants, antioxidants, VI improvers, rust inhibitors, and friction modifiers. However, what these additives do in the crankcase is not yet fully understood. As a first step in clarifying the complex mechanisms of engine oil performance in the crankcase, the interaction of engine oil additives was studied on the basis of surface chemistry. Metallic detergents form rigid micelles in oil, whereas ashless dispersants associate moderately and form small micelles in oil. No interaction was found between metallic detergents and zinc dithio-phosphate (ZDP), but there were strong interactions between ashless dispersants and metallic detergents and between ashless dispersants and ZDP. The adsorption onto an iron surface, the solubilization of sludge, and oxidation inhibition by engine oil additives are strongly influenced by the state of solution of these mixed systems.