Friction assessment of ultralow viscosity lubricant formulations based on a validated elastohydrodynamic simulation

Abstract

High-performance engines are highly optimized machines; therefore, any identification of potential improvement requires a detailed study to assess different performance scenarios, working fluids and engine configurations. Simulation tools are among the best ways to study all possible options. In this framework, a validated elastohydrodynamic (EHD) simulation model of the connecting rod journal bearing is used to assess the performance of different lubricant formulations in mixed lubrication scenarios. To simulate a realistic scenario, a finite element analysis (FEA) is performed, where the assembly of connecting rod and shaft supports are modelled with finite element models (FEM) to account for elastic deformations on journal bearings. Furthermore, a set of oil properties is measured and collected to import into GT-Suite commercial software. This set enables us to consider the dependence of variables such as viscosity, density, specific heat transfer, and coefficient of friction on the shear rate, pressure, temperature, and air solution. Moreover, a friction assessment methodology is presented to choose the best lubricating oil for severe working conditions. This test method accounts for several factors: tribology, rheology, wear, and lubrication regime. The results are presented for three ultralow viscosity lubricants and the reference oil from validation. This assessment gives a complete comparison of lubricants performance, where lubrication regime and tribological losses are key factors to select the best candidate.