Viscosity Prediction for Multigrade Oils

Sorab, Jagadish; Holdeman, Hollianne A.; Chui, Granger K.

doi:10.4271/932833

Cited by 23 publications

(8 citation statements)

References 14 publications

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“…m is a constant, with a typical value lying in the range of 0.5-1.0. Subsequent works by Moore 21 and Sorab et al 22 have essentially come to the same conclusions, although Sorab used a Carreau equation to describe the viscosity shear rate variation, rather than a Cross equation. Bair 23 has also used the Carreau-Yasuda equation for describing the shear rate behaviour of lubricants in journal bearings.…”

Section: Lubricant Viscosity Variationmentioning

confidence: 86%

Shear rates in engines and implications for lubricant design

Taylor

Kraker

2017

Proceedings of the Institution of Mechanical Engineers, Part J:

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By combining shear rate range data in engine components with measured viscosity shear rate curves on lubricants (at different temperatures), useful insights have been obtained on how the viscosity shear rate curve of a lubricant should be “designed” to give low friction (and hence improved fuel economy). A brief review is carried out of typical shear rates in key engine components, which is backed up by the authors’ own calculations (using in-house lubrication software that includes realistic viscosity/temperature/shear rate data). It is found that shear rates in journal bearings are typically in the range of 105 to 5 × 106 s−1, whilst peak shear rates for the piston rings can be as high as 2 × 107 s−1, and for the valve train, peak shear rates can reach 2 × 108 s−1. Accurate viscosity shear rate curves have been measured for different temperatures using a range of viscometers, including a novel mid-shear capillary viscometer that is capable of measuring viscosities in the shear rate range of 104 to 106 s−1. The use of such a viscometer is crucial to obtain good fits to the measured data (since usually, viscosity data are only usually available at low shear rates, 102–103 s−1, and extremely high shear rates, > 106 s−1, and such data are difficult to use for accurate viscosity/temperature/shear rate fits). The implications of the above data are then discussed for the design of low friction lubricants which give improved fuel economy. It is highlighted that the traditional high temperature high shear viscosity, HTHS150, measured at 150 ℃ and a shear rate of 106 s−1, although adequate for bearing durability purposes, is probably not the ideal parameter to use for estimating the fuel economy potential of an oil (since shear rates in engines are usually much greater than 106 s−1, and also because oil temperatures in fuel economy engine tests are usually much lower than 150 ℃). Other possible high shear viscosity parameters are discussed which may be an improvement on HTHS150. The work also highlights that the choice of viscosity modifier, and the amount used, can have a substantial impact on the fuel economy performance of a lubricant.

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Section: Lubricant Viscosity Variationmentioning

confidence: 86%

Shear rates in engines and implications for lubricant design

Taylor

Kraker

2017

Proceedings of the Institution of Mechanical Engineers, Part J:

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“…For the piston assembly, the strongest correlation between the fmep contribution and viscosity is achieved when viscosity is evaluated using liner temperatures at the mid stroke position [5].This is illustrated in Figure 1 by the better consistency of results from tests at different start temperatures compared to cases where the bottom or top liner positions have been used as the reference location. Dynamic viscosity values µ (in mPa.s) for the SAE 5W/30 oil were calculated using the Vogel equation [7], given by:…”

Section: General Observationsmentioning

confidence: 99%

Investigations of Piston Ring Pack and Skirt Contributions to Motored Engine Friction

Shayler¹,

Leong²,

Pegg³

et al. 2008

SAE Int. J. Engines

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An experimental study has been carried out to examine the influence of ring tan load and piston skirt modifications on piston assembly friction under motored engine conditions for initial temperatures of -20, 0 and 30 o C and motoring speeds within the range 400 to 2000 rev/min. The study has been carried out using the block, crankshaft and pistons of a 2.4l, 4 cylinder diesel engine with a bore and stroke of 89.9mm and 94.6mm respectively. The pistons examined are typical of current designs for light duty diesels. A range of ring pack and piston skirt modifications have been tested, in each case as part of a complete piston assembly. The first changes produced reductions in fmep of between 5% and 38%. The reduction was due to improved skirt and ring pack designs in equal measure, each giving improvements of up to 20%. From this baseline eliminating the tan load of the piston rings was projected to give a further reduction in fmep of between 10% and 20%. Increasing the piston diametric clearances by close to the difference between minimum and maximum grade clearance gave smaller improvements of between 2% and 10% relative to the baseline, and reducing skirt roughness to perfectly smooth gave a projected reduction of typically 4%, and more at low oil viscosities.

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“…This meant that the shear thinning behaviour of VM solutions could not be fully explored. Typical flow curves of engine oils up to 10 6 s −1 can be found in [8][9][10][11]. This limitation has recently been addressed by the development of the PCS ultrashear viscometer (USV) that is able to reach 10 7 s −1 .…”

Section: Introductionmentioning

confidence: 99%

Shear Thinning and Hydrodynamic Friction of Viscosity Modifier-Containing Oils. Part I: Shear Thinning Behaviour

et al. 2018

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Viscosity versus shear rate curves have been measured up to 10 7 s −1 for a range of VM solutions and fully formulated oils of known composition at several temperatures. This shows large differences in the shear thinning tendencies of different engine oil VMs. It has been found that viscosity versus shear rate data at different temperatures can be collapsed onto a single master curve using time-temperature superposition based on a shear rate shift factor. This enables shear thinning equations to be derived that are able to predict the viscosity of a given oil at any shear rate and temperature within the range originally tested. One of the tested lubricants does not show this time temperature superposition collapse. This fluid also exhibits extremely high viscosity index and shear thins more easily at high than at low temperature, unlike all the other solutions tested. This unusual response may originate from the presence on the VM molecules of two structurally and chemically different components. In a companion paper, the master shear thinning curves obtained in this paper are used to explore how VMs impact film thickness and friction in a steadily loaded, isothermal journal bearing [1].

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Viscosity Prediction for Multigrade Oils

Cited by 23 publications

References 14 publications

Shear rates in engines and implications for lubricant design

Shear rates in engines and implications for lubricant design

Investigations of Piston Ring Pack and Skirt Contributions to Motored Engine Friction

Shear Thinning and Hydrodynamic Friction of Viscosity Modifier-Containing Oils. Part I: Shear Thinning Behaviour

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