High Viscosity Index Petroleum Base Stocks - The High Potential Base Stocks for Fuel Economy Automotive Lubricants

A high viscosity index (HVI) petroleum base stock (VI=125), which is produced by a severe hydrocracking process, has been used in formulating an advanced SAE 5W-30 oil meeting API SG, EC-II and current ILSAC performance requirements in order to demonstrate potential fuel economy benefits of this oil. The oil was formulated by blending the HVI base stock with a small amount of a solvent-refined base stock to obtain an “optimal aromaticity”, a dispersant VI improver, an optimized combination of detergent and inhibitor, and a conventional ashless friction modifier. The fuel economy performance of this oil has been compared to that of a similarly formulated solvent-refined SAE 5W-30 oil using the Sequence VI test, a motored engine friction test, a new fired/motored friction test, and the EPA road simulator fuel economy test. The SAE 5W-30 HVI oil exhibited an improved fuel economy performance in the above tests, despite of higher HTHS viscosity of the HVI oil. The better fuel economy performance of the HVI oil has been attributed 1) to a superior oxidation stability of base oil blend that allows to maintain its good friction reducing effect during the engine testing and 2) to desirable rheological properties exhibited by better pressure-viscosity behavior. It was demonstrated that at the same high temperature high shear viscosity the HVI oils provide substantially better fuel economy performance than the solvent-refined oils. In addition to a good fuel economy performance, the HVI oils exhibited better volatility characteristics and good low temperature fluidity. The results of fuel economy engine testing showed that additional fuel economy benefits can be derived when using the low viscosity SAE OW-30 HVI oil containing similar additive system as the 5W-30 HVI oil. The SAE OW-30 HVI oil gave EFEl of 3.4% in the Sequence VI test. The fuel economy of the HVI oils was alternatively improved by using an effective sulfur containing metal complex friction modifier, while retaining HTHS viscosity at 2.9 mP·s at 150 °C and 1O⁶ s^-1, and meeting all other performance requirements of the ILSAC standard. In the Sequence VI test, the 5W-30 HVI oil containing the metal complex friction modifier gave EFEl of 3.9%.