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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.

The SAE Engine Oil Viscosity Classification (EOVC) Task Force has been gathering data in consideration of extending SAE J300 to include engine oils with high temperature, high shear rate (HTHS) viscosity below the current minimum of 2.6 mPa⋅s for the SAE 20 grade. The driving force for doing so is fuel economy, although it is widely recognized that hardware durability can suffer if HTHS viscosity is too low. Several Japanese OEMs have expressed interest in revising SAE J300 to allow official designation of an engine oil viscosity category with HTHS viscosity below 2.6 mPa⋅s to enable the development of ultra-low-friction engines in the future. This paper summarizes the work of the SAE EOVC Low Viscosity Grade Working Group comprising members from OEMs, oil companies, additive companies and instrument manufacturers to explore adoption of one or more new viscosity grades.

Modern engines rely more and more on the engine oil to serve increasingly complex hydraulic functions such as, for example, controlling cylinder deactivation - a means of significantly increasing fuel efficiency. However, the success of hydraulic methods of activating mechanical responses in engines (or other devices) is dependent on the degree of incompressibility of the hydraulic fluid. As a consequence, those engine oil properties that impart susceptibility to foam formation in areas of hydraulic operations of the engine are detrimental to the engine's performance and durability. This paper is an initial study of aeration, air entrainment, and air release under pressure decrease using a simple bench test. The preliminary information reported suggests the potential application of the instrumental approach developed to measure the rate of foam formation from the air entrained in engine oils and the resistance of such foam to collapse.

Low-temperature engine oil pumpability has been a concern for OEMs, engine oil formulators, and additive manufacturers for a number of years particularly since a significant number of air-binding failures in 1980 and '81. On careful investigation of the cause of such field failures, it was found that oil sensitivity to a particular combination of weather conditions was responsible. The experience also suggested that many other low-temperature weather conditions might produce engine-damaging gelation. Thus, it seemed desirable to develop a bench test that would induce and measure gelation that might form in engine oil by continuously measuring slowly cooling oil over an extensive low-temperature range. This led to the development of the Scanning Brookfield Technique (SBT) first reported in 1982.

Viscometry has been closely associated with the lubricating properties of engine oils since the development of the reciprocating engine. With the advent of non-Newtonian multi-grade engine oils, a new dimension of viscometry was introduced - viscometry at high shear rates and high temperatures. In view of the importance of the critical hydrodynamic lubrication that engine oils provide - and the toll on engine efficiency that these oils extract - it was thought timely and practical to review the initiation and application of high shear rate engine oil viscometry and to discuss subsequent development.

Previous studies have shown that there is a lack of correlation between engine oil phosphorus volatility with both oil volatility and the initial level of phosphorus in the engine oil. On the other hand, these and more recent studies have illustrated that phosphorus volatility is related to temperature, other additives in the oil, and the chemical composition of the zinc di-organo di-thio phosphate (ZDDP) used. This paper reports the results of continued studies associated with engine oil phosphorus volatility, with the ultimate goal of reducing the amount of phosphorus that deposits on catalytic converters adversely affecting catalyst function.

The rheology and related low-temperature pumpability of engine oils used in modern heavy-duty diesel engines are markedly affected by the presence of high levels of soot. This paper presents results of studies of the rheological condition of highly soot-laden oils using two protocols of the Scanning Brookfield Technique as investigative tools.