Modeling the Viscoelastic Behavior of Engine Oil in the Crankshaft-Journal-Bearing of High Torque Low-Speed Diesel Engine

Abstract

Journal bearing is used to carry the cyclic and impact loads in many applications such as internal-combustion engine’s crankshaft. During engine operation at lower speeds, the main end of the crankshaft is more vulnerable to inadequate film thickness generation resulting in adhesive wear. For high torque low speed engines, use of non-Newtonian lubricant gives more robust bearing design as compared to Newtonian lubricant. Polymer addition to mineral oils result in non-Newtonian viscoelastic behavior of the lubricant. There are three types of non-Newtonian lubricants out of which viscoelastic lubricant is the most prominent cause of improvement. In this research continuity and Navier-Stokes equations are solved to ensure conservation of mass and momentum of the lubricant flow. After determining the film thickness between the bearing and the crankshaft 2-D Reynolds equation is used to model the behavior of the lubricant. The constitutive equations exhibiting viscoelastic characteristics are coupled with the momentum conservation equations to generate simulation results for non-Newtonian lubricant response. The steady state wedging and transient squeeze effects are studied for a viscoelastic engine lubricant at low speed. Parametric studies at various engine speeds and radial clearances are studied for useful engine design. The simulation results for Newtonian and viscoelastic engine lubricants are compared. The results show that at a low initial speed the Newtonian lubricant does not produces sufficient hydrodynamic pressures due to thin hydrodynamic films. For the same configuration viscoelastic characteristics of the lubricant contribute towards improving the pressure and film thickness profiles of a high-torque low-speed engine. It reduces the chances of breakdown of lubricant film and enhances the life of crankshaft by preventing adhesive wear.