Boundary Lubricant Film Modeling of Ester Mixture Lubricants in Severe Sequestration Environments

Abstract

In recent years, environmental pollution and the depletion of energy resources have become problems, and there is a growing demand for high-efficiency technology. Lubricating oil is used in gasoline vehicle transmissions to reduce friction, and ester mixture lubricating oil is used in boundary lubrication conditions where solid contact is severe. Ester mixture lubricants increase oil film thickness and reduce friction by adhering to metal surfaces, but it is known that esters containing unsaturated fatty acids undergo thermal denaturation during friction. In this study, we elucidated the effect of thermal denaturation of esters on friction properties. Friction tests were conducted at 23°C, 40°C, 60°C, and 80°C using lubricating oil containing unsaturated fatty acids (TMPTO) added to base oil (PAO), and oil film thickness was calculated from reflectance obtained simultaneously. The viscosity of the mixed layer of TMPTO and its thermal denaturantion was calculated from the obtained oil film thickness using an original formula. The viscosity was found to be higher than that of TMPTO in bulk form at all temperatures. The viscosity increase can be attributed to the formation of multimolecular films by surface adsorption and thermal denaturation.