Continued from page 8
parts, and yet being low enough to improve fuel economy by internal friction reduction. Therefore control and reduction of both PVL and TVL is desirable, and the viscosity loss profile5 helpful tool in designing and choosing VI Improvers.
is a
Summary Modern Industry and OEM specifications stipulate increasingly stringent Rheological Characteristics in Lubricants. Examples of these are Robust Low temperature performance requirements in tests such as the CEC L 105 and Viscosity Stay In Grade requirements after 90- cycle Kurt Orbahn Shear. Increasing focus on Greenhouse Gas Reduction and Fuel Economy Improvement is leading to a preference for lower SAE grades and higher lubricant temperature. High Temperature Sheared Viscosity has a direct correlation to fuel economy performance and also engine durability. Increasing lubricant temperature can increase engine wear unless High Performance level optimized lubricant formulations (DI + VII + Base Oil) are used.
Figure 9
The ability of oil to retain its viscometric properties is particularly important in Heavy Duty Engine Oil applications to prevent wear and maintain intended levels of oil pressure. It is known that mechanical shearing of the oil, fuel dilution, oil oxidation and soot level all affect the aged oil viscosity. Sims et al7
have
investigated the effect of polymer chemistry and structure on extended shear stability of lubricating oils and have reported the advantages in retaining viscosity after extended shear in the Kurt Orbahn (KO) test. With OCP-VIIs, the rate of viscosity loss diminishes to a plateau after 90 cycles in the KO test whereas for SIP chemistry, viscosity loss continues at a high steady rate even up to 720 cycles in the KO test. While it is well known that soot generated during engine operation, as well as oil oxidation, can cause a rise in engine oil viscosity over time, fuel dilution and shearing can cause a decrease in viscosity over time. VII choice may therefore impact the oil viscosity after extended drain in HDEOs, in particular the contribution of extended mechanical shear. This is of particular importance to reduce decreasing after shear HTHS viscosity. As shown in Figure 10, the OCP samples maintained HTHS viscosity after extended shear, but some other VIIs with HSI technology did not. Base oil selection also plays an indirect role in influencing shear stability of finished oils by nature of base oil VI. Higher VI oils will require less VII to meet viscometric requirements for a given oil, which result in an overall more shear stable product.
OCP chemistry is found to provide advantages in retaining viscosity after extended shear in the KO test. With OCP, the rate of viscosity loss diminishes to a plateau after 90 cycles in the KO test. Base oil selection also plays an indirect role in influencing shear stability of finished oils. Higher VI oils require less VII to meet viscometric requirements for a given oil, which result in an overall more shear stable product.
References 1. Olefin Copolymer Viscosity Modifiers. Michael J Covitch 2. Viscosity Index Improvers with Optimized Structure and Performance in Lubricating Engine Oils. SAE/KSAE 2013 International. Pritesh A. Patel, Alexander Boffa, Maryam Sepehr
3. Role of certain OCP Viscosity Modifiers in gel formation and filter blocking tendencies of engine oils. JSAE 20077141-SAE 2007-01-1960. Jai G. Bansal, Kwok-Leung Tse and Stuart P. Briggs
4. Low Viscosity Lubricants for Improved Fuel Economy in Heavy Duty Engines while Maintaining Lubricant and Engine
Durability.Technische Akademie Esslingen, January 2012. Wim van Dam, Trevor Miller, Keith Narasaki, Gary Parsons, Ruud ter Rele
5. High Shear Rate Rheology of Lower Viscosity Engine oils over a temperature range of 800C to 1500C using the Tapered Bearing Simulator Viscometer. SAE 2010-01-2288. T.W. Selby
6. The expanding dimensions of High Shear Rate Viscometry. SAE 2008-01-1621.
T.W.Selby
7. Extended Shear Stability of Viscosity Index Improvers in Lubricating Oils. 14PFL- 0682. Carrie Sims, Maryam Sepehr, Alexander Boffa, Mark Sztenderowicz
LINK
www.oronite.com
Figure 10
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LUBE MAGAZINE NO.124 DECEMBER 2014
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