In 2005, the growing emphasis on fuel efficiency coupled with
the long-recognized negative effects of viscous friction caused by
engine hydrodynamic lubrication, led to considerations of the
benefits of lower viscosity engine oils by the SAE Engine Oil
Viscosity Classification (EOVC) Task Force. More recently these
considerations were given further impetus by OEM enquiry regarding
modification of the SAE Viscosity Classification System to include
oils of lower viscosity specification than that of SAE 20.
For the EOVC Task Force, such considerations of commercially
available, significantly lower viscosity engine oils, also produced
a need to reassess the precision of high shear rate viscometry of
such engine oils as presently practiced at 150°C - as well as
interest in temperatures such as 100° and 120°C believed more
representative of engine operating conditions.
This paper presents studies of the precision of high shear rate
viscometry on lower-viscosity simulated engine oils at temperatures
of 80°, 100°, 120°, and 150°C at a shear rate of one million
reciprocal seconds (1.0⋅10⁶s-1) using the Tapered Bearing
Simulator (TBS) Viscometer. These viscosity values were then
analyzed for conformity to the MacCoull, Walther, Wright
viscosity-temperature and the ability to interpolate high-shear
rate viscosities. Lastly, the ability to determine the high shear
rate viscosities of oils at various chosen temperatures was applied
in appraising the fuel efficiency benefits of such oils by
determining the Viscous Fuel Efficiency Index. These values are, in
turn, compared both to one another and to the Index values of
several hundred North American engine oils collected by the
Institute of Materials in 2008 and 2009 for their yearly engine oil
database.
