Due to large temperature variation in the internal combustion engine, viscosity index improver agents are added to lubricants to improve their viscosity-temperature behavior. As a side effect, this causes the lubricant to exhibit both shear thinning and unequal stress normal differences in simple shear. In the present analysis the shear thinning effect is modeled by the power-law constitutive equation and application of the resulting theory is made to the piston ring lubrication problem.; A general analysis of the flow problem in a thin slit is made using the power-law constitutive equation. The analysis is valid not only for Couette dominated flow but also for Poiseuille and squeeze flows. The slit has a lower plate and an upper surface whose shape and translational motion can be arbitrarily specified.; Using data for two power-law lubricants, the analysis is applied to the piston ring lubrication problem. The consistency and power-law indices as well as the temperature variation along the cylinder liner are taken into consideration. It turns out that the more shear thinning lubricant for most of the stroke gives less minimum-oil film thickness and friction force in this study.; An investigation of the pressure boundary condition is presented. Using a combination of lubrication theory and the Boundary Element Method, the slider bearing is analyzed employing data for two power-law lubricants. The pressure distribution within the fluid under the bearing is found to be very different from that computed by lubrication theory only using conventional ad hoc pressure boundary conditions. The load carrying capacity and friction force, however, differ by no more than 5%. The greater shear thinning lubricant gives less load and friction in this analysis. This conclusion is not general as it depends on the operating shear rate of the bearing.
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