Consideration about dynamic conduct of viscosity index improver in the share field

Abstract

Engine oil is one of the factors that contribute to the improvement of fuel efficiency, and the smaller the viscosity change over a wide range of temperature, the better the fuel efficiency. The aforementioned oils are called high viscosity index oils, and they have been developed by lowering the viscosity of the base oil or by adding viscosity index improvers (VII). This study simulates the behavior of viscosity index improver (VII) in a system that imitates the sliding environment of an actual engine and verifies its effectiveness. The simulation is based on a combination of the lattice Boltzmann method and Brownian dynamics. As a result, it was found that the VII was dragged into the high velocity region, as in the Poiseuille flow, but the trend was stronger at lower shear rates. This indicates that the behavior of VII in a narrow gap under shear is opposite to that of VII at rest. It was similarly shown that the effect of VII is not expected in the region near the center of the engine cylinders where the shear rate is high because it depends on the shear rate. This study shows the behavior and effect of VII in the shear field.