The performance and mechanisms of organic polymeric friction modifiers in low viscosity engine oils 2019-01-2204
The requirement of OEMs to reduce CO2 emissions is leading to a reduction in viscosity of engine oils with 0W20 approved oils now common. 0W 16 approvals are growing in popularity and will be further supported in the US by the introduction of ILSAC GF-6B. Japanese OEMs are driving the development of 0W- 12 and 0W08 grades which will be supported by JASO GLV-1. These low viscosity engine oils can contain MoDTC with very high levels of 1000+ppm molybdenum to achieve the fuel economy improvement required to pass engine tests such as Sequence VIE. Molybdenum usage at this level contributes to sulphated ash increase. It can also have a negative impact on deposits.
This paper examines the performance and mechanism of two ashless polymeric friction modifiers in a 0W20 formulation. These polymeric friction modifiers have been shown to give fuel economy benefits in Sequence VIE engine tests. The aim of this work is to better understand the influence and interaction of these polymeric friction modifiers in the presence of ZDDP as well as other additives, in tribological testing. Specifically, how the friction and wear benefits observed in MTM testing correlate to the chemical composition of the tribofilm as characterised by X-ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy.
Further work detailing the combination of polymeric friction modifier and MoDTC was conducted on the MTM, including surface characterisation for potential synergistic properties in the reference oil.
Evidence of the polymeric friction modifier on the surface, and throughout the depth of the tribofilm, was observed, even in the presence of molybdenum containing additives. This work proves the good surface affinity and film forming properties of polymeric friction modifiers and highlights the differences in the tribofilm composition depending on the friction modifier(s) used.