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Low‐temperature rheology of engine lubricants subjected to mechanical shear: Viscosity modifier effects
Author(s) -
Covitch Michael J.,
Weiss Joseph,
Kreutzer Ingo M.
Publication year - 1999
Publication title -
lubrication science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.632
H-Index - 36
eISSN - 1557-6833
pISSN - 0954-0075
DOI - 10.1002/ls.3010110403
Subject(s) - viscosity index , shearing (physics) , rheology , shear rate , isoprene , viscosity , materials science , temperature dependence of liquid viscosity , apparent viscosity , shear (geology) , composite material , shear thinning , polymer , crankcase , copolymer , thermodynamics , chemical engineering , relative viscosity , mechanical engineering , engineering , scanning electron microscope , base oil , physics , internal combustion engine
It is well known 1–5 that the viscosity of crankcase lubricants decreases in the early stages of use due to shearing of the viscosity modifier (VM) and, depending upon the type of service, fuel dilution. This paper examines the effects of VM chemistry on the shearing process, and particularly how both high‐temperature and low‐temperature viscosities can change as a result of mechanical shear in the Kurt Orbahn injector test and during a passenger car fleet test. Commercial olefin copolymer, styrene/butadiene, styrene/isoprene, and radial isoprene polymers were included in this study, as a way of representing the major VM chemistries used in motor oils throughout the world. The rate of change of kinematic and high‐temperature, high‐shear‐rate viscosity with time, as well as low‐temperature cranking and pumping viscosity changes, were found to be characteristic of particular VM chemistries.