Lubricant viscosity and viscosity improver additive effects on diesel fuel economy

This work verifies the impact of lubricant viscosity and viscosity improver additives on diesel fuel economy. Eight lubricants were tested in a single-cylinder, four-stroke, direct injection diesel engine mounted on a dynamometer, under different load and speed conditions. Engine friction power was also investigated through Willans’ line. The results demonstrate that fuel economy obtained from multigrade viscosity oils is higher than that obtained from monograde viscosity oils. A linear relationship was obtained between the high temperature high shear viscosity and specific fuel consumption. The lubricant which provided lower fuel consumption also required lower friction power. ► Monograde oils showed higher viscosity and fuel consumption than multigrade oils. ► High shear stable polymer additive reduced oil viscosity and fuel consumption. ► The lowest specific fuel consumption was noticed at moderate speed and load. ► Specific fuel consumption increased linearly with lubricant HTHS viscosity. ► Engine operation with a low viscosity multigrade oil produces lower friction power.