Rheological Properties of Lubricants and Their Correlation With Fuel Economy Performance

One of the least expensive pathways to achieving improvements in vehicle fuel economy is through changes to engine lubricant viscosity and composition. Driven by ever more stringent emissions regulations, OEMs are therefore requiring engine oils to continue protecting engines at lower viscosities and reduced friction.
Different engine operating conditions represent a range of lubrication conditions, and to better understand the full impact of engine lubrication process, one must understand how oils perform in these conditions. In general, additives in lubricants help to provide the right balance of fuel economy while maintaining durability protection. The focus of the present study is on the hydrodynamic lubrication regime, and the rheological properties of oils were investigated and correlated to their fuel economy performance in different engines, Mercedes Benz OM 501 LA and Detroit Diesel DD13, and driving cycles, WHTC (World-Harmonized Transient Cycle) and modal.