Relating High-Temperature, High-Shear-Rate Viscosity to Engine Operation

Spearot, James A.

doi:10.1520/stp23002s

Cited by 11 publications

(4 citation statements)

References 19 publications

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“…10 6 s -1 ) than those that can be achieved with modern rheometers. 4 The dynamic behavior of lubricants under these extreme conditions is generally unknown and cannot be predicted easily. The viscosity of the fluid at these conditions is the key element in determining whether the lubricant can sustain a sufficient fluid film between moving parts.…”

Section: Introductionmentioning

confidence: 99%

“…Real lubricants operate frequently under conditions of high pressure, temperature, and shear rate. The pressures encountered in the elastohydrodynamic lubrication regime (EHL) often exceed 1 GPa, and the shear rates can be orders of magnitude higher (≫ 10 6 s -1 ) than those that can be achieved with modern rheometers . The dynamic behavior of lubricants under these extreme conditions is generally unknown and cannot be predicted easily.…”

Section: Introductionmentioning

confidence: 99%

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Impact of Molecular Architecture on the High-Pressure Rheology of Hydrocarbon Fluids

and

Maginn

2000

J. Phys. Chem. B

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Molecular dynamics simulations are conducted on three C18 poly-α-olefin isomers under extreme conditions typical of traction fluids or lubricants under elastohydrodynamic lubrication conditions. The viscosity, self-diffusivity, and rotational relaxation times of the molecules are computed at pressures ranging from atmospheric to as high as 1 GPa. The dynamics of all three isomers are slowed as pressure increases, but a highly branched isomer shows a more dramatic reduction in mobility with pressure than does a linear or singly branched isomer. In particular, the viscosity of the highly branched molecule exhibits a much larger increase with pressure than does the viscosity of the other isomers, indicating that the highly branched molecule should exhibit more favorable traction properties than the other isomers. An explanation for the differences in dynamic properties between the isomers is given in terms of a reduction in liquid void volume coupled with the greater backbone stiffness of the highly branched molecule. A free volume analysis is conducted and shown to provide a better means of correlating the pressure dependence of diffusivity and viscosity than commonly used engineering models.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Impact of Molecular Architecture on the High-Pressure Rheology of Hydrocarbon Fluids

and

Maginn

2000

J. Phys. Chem. B

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“…In particular, the oil should be warmed as fast as possible to its optimal range (where efficiency is high but Λ still acceptable), and then even more critically, oil temperature should be capped at a level where Λ does not drop to the level at which wear will occur at significant pace. Zaretsky 23 suggests a value of Λ=2 would be a an approximate value for this point, with theoretically zero frictional wear occurring at Λ≥3. 23 Also, the impact of lubricant temperature on its lifespan is important; lubricant life is doubled for every drop in 10℃ oil temperature.…”

Section: Discussionmentioning

confidence: 99%

“…Zaretsky 23 suggests a value of Λ=2 would be a an approximate value for this point, with theoretically zero frictional wear occurring at Λ≥3. 23 Also, the impact of lubricant temperature on its lifespan is important; lubricant life is doubled for every drop in 10℃ oil temperature. 24 However, great care must be taken with the additive packages, as some do not function at low temperatures as they operate by a chemical reaction method.…”

Section: Discussionmentioning

confidence: 99%

Effect of lubricant temperature and type on spur gear efficiency in racing engine gearbox across full engine load and speed range

Douglas

Thite

2015

Proceedings of the Institution of Mechanical Engineers, Part J:

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Energy losses are of great significance to the automotive and motorsports industries. Many of these losses are incurred during power transmission through the gearbox. There has been considerable research in this area; however, generally gear losses are not calculated at part load condition, nor are so-called dry sump systems considered outside of motor racing. The method developed by Anderson & Loewenthal, which considers efficiency over part-load conditions is used here to calculate geartrain losses with varying speed, load and temperature conditions in a spur gear type gearbox for motorsport application. Both oil bath (wet sump) and oil jet (dry sump) systems of lubrications are considered. The Changenet method is used to calculate the churning losses in the typical oil bath lubrication system. Seventeen different mineral and synthetic oils were evaluated. At 75 kW engine output, 1200 W were lost in the dry sump gearbox whereas 1320 W were lost in the wet-sump gearbox -in first gear at 10,500 r/min engine speed. The oils studied showed a spread of total drive efficiency of 97.8% to 99% in the most extreme temperature case. From the observation of how efficiency and film thickness relate to operating temperatures, it is clear that tight temperature control is critical to obtain the potential benefits available from oil optimisation. The dry sump gearbox is predicted to be more efficient only above 5000 r/min engine speed.

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