To study the mechanism of the effect of low-viscosity oils on engine friction
loss reduction so as to improve the vehicle fuel economy of the Worldwide
harmonized Light vehicles Test Cycle (WLTC) by upgrading the Society of
Automotive Engineers (SAE) viscosity grade of the factory fill oil from 5W30 to
0W20, eight 0W20 oil samples were blended with different doses of base oil,
viscosity modifier (VM), and friction modifier (FM).
Theoretical analysis by AVL-EXCITE simulation of the key friction pairs combined
with practical engine friction torque test and vehicle WLTC fuel consumption
tests were carried out. The results showed that 0W20 oils can effectively reduce
the engine friction torque by 5.64 Nm and the friction loss by 11.95% with the
throttle fully opened; while with the throttle closed, the friction torque
decreased by 3.53 Nm and the friction loss by 11.26%, resulting to the
improvement of the vehicle WLTC fuel economy by 2.08%. Without deteriorating the
durability of the engine, the application of 0W20 engine oil can help to achieve
carbon dioxide (CO2) emission reduction and the Corporate Average
Fuel Consumption (CAFC) score accumulation.
Low viscosity plays a leading role in the WLTC low-speed and medium-speed
segments, while VMs and FMs contribute more in the high-speed and extra
high-speed segments, indicating that the oil viscosity is not the only key
factor to reduce engine friction. The coordination of the whole oil formulation,
low viscosity combined with different additives, is the key to reduce friction
loss and achieve fuel economy.