Low viscosity shear heating in piston skirts EHL in the low initial engine start up speeds

Absence of elastohydrodynamic lubricating (EHL) film causes piston wear in low speed cold initial engine start up, while shearing of low viscosity lubricant in few cycles affects its load carrying capacity. Shear heating effects are incorporated in 2-D hydrodynamic and EHL model by solving 2-D heat equation. EHL pressures are calculated using inverse solution technique. Comparative analysis is based on viscous dissipation coupled with piston motion, changes in pressure, film thickness and viscosity. This study suggests that the increase in temperature varies with speed to affect piston eccentricities, viscosity and film thickness. This optimizes low start up speed for a few engine cycles.

► Numerical modeling of shear heating effects at low speeds in cold engine start up.
► A slightly high start up speed minimizes adhesive wear in the EHL regime.
► Increasing low start up speed enhances viscosity and load carrying capacity of oil.
► Shear heating reduces film thickness as the low engine start up speed increases.
► Optimization of low start up speed to minimize wear and to enhance the engine life.