Applications of Ultra-Shear Viscometry to Fuel Economy Optimization
The correlation between high-temperature high-shear (HTHS) viscosity and crankcase fuel economy has been well documented in the literature. However, most reported work to date has been conducted using measurements made at a single shear rate (10E6 s-1) and fixed temperatures (typically 80, 100 and 150C) (i.e. a point measurements). The technology exists to conduct flow measurements over a limited shear rate range and a temperature range between 80 and 150C, allowing 3-dimensional flow surfaces (temperature, shear stress, viscosity) to be generated. The range of shear rates sampled can be extended by experimental means and time-temperature superposition principles, providing flow surfaces that can show relative differences in lubricant performance for shear rates between 1E4 and 1E8 s-1. These extended flow surfaces provide new insights into potential fuel economy benefits resulting from lubricant formulation changes.