No abstract

Elastohydrodynamic lubrication (EHL) is critically essential to minimize engine wear at low engine start up speeds. During the normal engine operations at medium to high speeds, non-Newtonian characteristics of multigrade engine lubricants enhance engine life by preventing adhesive wear. By incorporating viscoelastic effects of a non-Newtonian lubricant and focusing on different low engine start up speeds, this study models EHL fluid flow in the initial engine start up conditions. A 2-D non-Newtonian piston skirts lubrication model and analysis at the time of engine start up is presented based on the upper convected Maxwell viscoelastic model. The analysis of a non-Newtonian lubricant between piston and cylinder liner by using characteristic lubricant relaxation times in all order of magnitude analysis is done by using a perturbation method. The EHL film profile is predicted by solving the two-dimensional Reynolds equation using the inverse solution technique and the finite difference computational method in the fully flooded lubrication conditions. At different low engine start up speeds, the effect of viscoelasticity on lubricant velocity and pressure fields is examined and the influence of film thickness on lubricant characteristics is investigated. Numerical simulations show that piston eccentricities, EHD pressures and film thickness profiles are functions of low range of engine start up speeds. This study suggests that the initial engine start up speed at low range can be optimized as viscoelasticity produces a beneficial effect on piston skirt lubrication in the initial engine start up.

This paper presents the results of a transient analysis of hydrodynamic lubrication between piston and cylinder surfaces in engine Initial startup conditions with a Non Newtonian lubricant under oscillatory motion. Effects of different multi-grade oil viscosities are also investigated in the simulation. The time dependent Reynolds equations use a Maxwell type model to analyze fluid rheology. A perturbation scheme is used to derive coupled non linear partial differential equations to obtain the fluid velocity. The oil film profile is predicted by solving the two-dimensional Reynolds equations using the finite difference computational method. The piston velocities in engine secondary motion are adjusted by using fourth order Runge-Kutta technique. Using different oil viscosities, the effect of viscoelasticity on lubricant velocity and pressure fields is examined and the influence of film thickness on lubricant characteristics is investigated. Numerical simulations show that piston eccentricities and film thickness profiles vary under different multi grade oils at engine start up conditions.

In the normal high speed engine operation at small piston-to-bore radial clearance, elastohydrodynamic lubrication (EHL) of skirts and non-Newtonian lubricant behavior prevent adhesive wear, but in the initial engine start up, the large clearance, low speed and absence of EHL, cause start up wear. This study models 2-D upper convected Maxwell viscoelastic EHL of piston skirts at small radial clearance in a few initial low speed engine start up cycles by solving the Reynolds equation and using the inverse solution technique. The numerical analysis incorporate characteristic lubricant relaxation times and a perturbation method to predict and compare hydrodynamic and EHL pressures and film profiles. The effects of viscoelasticity on the lubricant characteristics, transverse eccentricities of piston, film thickness, and pressure fields in the hydrodynamic and EHL regimes are investigated. This study suggests that EHL film is formed at very small piston-to-bore radial clearance at low start up speed under assumed conditions to prevent start up wear as viscoelasticity produces a beneficial effect on piston skirts lubrication in the initial engine start up.