Double-Newtonian rheology in a model piston-ring cylinder-wall contact

In automotive engines, lubricants have undergone important changes over the last decades. Oil companies have added more and more additives to ensure correct performance of specific engine contacts, whilst increasing engine performance. Polymer additives are amongst these, used to increase viscosity at high temperatures and thus to flatten the viscosity temperature curve. This viscosity increase occurs at low shear rates, but at high shear rates the viscosity diminishes and tends to a lower value. iscosity reduction at high shear rate is due to the distortion and alignment of the polymer molecules, and their breakage for extreme shear rates. aper analyses the influence of the double Newtonian rheology on friction and load carrying capacity in a model piston ring cylinder wall contact. It is found that the friction coefficient changes with increasing shear rate, as the contact goes through the non-Newtonian transition.