Different formulations of lubricating oil have been evaluated in a Design of Experiment (DoE) approach to examine the effect of their viscometric properties on engine fuel economy. The performance of the oils has been evaluated on a transient test bed over the New European Drive Cycle (NEDC) using a production automotive Diesel engine. The main viscometric properties investigated were cold cranking shear (CCS), kinematic viscosity at 100°C (Kv100) and high temperature high shear (HTHS). Results have shown that CCS is dominant during the first phase of the NEDC (ECE15) whilst HTHS and Kv100 become more dominant during the second phase (EUDC). The viscometric changes for the aged oils evaluated showed a 3.5% fuel economy reduction over the NEDC when comparing the 0W30 grade with 10W40 oil. A DoE analysis confirmed the observed trends and facilitated the creation of a multi-dimensional response model which can be used to predict brake specific fuel consumption (BSFC) over the NEDC based on changes in oil viscometrics.
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