GF-5, economy, Striebeck curve, and modern oils

[Shannow]

Following discussion in other threads on HTHS affecting fuel consumption (it certainly does), I thought that the following might be interesting.

http://www.infineum.com/sitecollectiondo...ns%20051209.pdf

PDF, so I can't link pictures, but shows the different tests under the VID, and where the oils of varying viscosity sit in the different tests.

Backed up with HTHS 100 and 150 regressions, which show a virtually linear saving of fuel versus the reference lubricants...interesting should one extrapolate the line.

http://www.infineum.com/sitecollectiondocuments/notebooks/gf5/ResearchReport.pdf

Gives a bit more detail on the tests themselves, and why the test engines was chosen...in part to explore the fuel economy savings that are applicable with friction modified lubricants, running in boundary regimes, versus the older test mule.

Section around table 20/and figure 57 shows the conditions under which this engine is operating under boundary/mixed lubrication, and it's not that onerous a duty point in general.

Thus, I re-assert that modern engines and oils are not always operating in the hydrodynamic range, and that the quest for economy has reduced the operational viscosity margin even further, with routine operation in mixed/boundary mode.

OEMs are choosing lubrication regimes for their customers that will deliver their economy requirements, at the expense of ultimate engine protection...probably enough for 95% of the drivers of said vehicles to get their money's worth out of them.

http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=3023259

Note before people reply...this is NOT pointing at a pile of failed engines in the corner...

 

[JHZR2]

As boundary lubricants get better, viscosity needs go down. As surface finish gets better, viscosity goes down.

Ive siad it a few times, surface finish of parts, rather than "clearances" IMO are a major basis for being able to drop and still maintain hydrodynamic lubrication, with reduced surface roughness allowing for for getting closer to mixed lubrication and even boundary.

 

[Shannow]

Have to agree there...

 

[buster]

Good stuff, thanks.

 

[OVERKILL]

Great stuff Shannow, thank you

 

[d00df00d]

Cheers, Shannow!

 

[spasm3]

Originally Posted By: JHZR2
As boundary lubricants get better, viscosity needs go down. As surface finish gets better, viscosity goes down.

Ive siad it a few times, surface finish of parts, rather than "clearances" IMO are a major basis for being able to drop and still maintain hydrodynamic lubrication, with reduced surface roughness allowing for for getting closer to mixed lubrication and even boundary.


Is there a point at which the surface is too smooth to hold an oil film effectively, causing more startup wear ?

 

[fpracha]

Thanks for the great info!

 

[JHZR2]

Originally Posted By: spasm3
Originally Posted By: JHZR2
As boundary lubricants get better, viscosity needs go down. As surface finish gets better, viscosity goes down.

Ive siad it a few times, surface finish of parts, rather than "clearances" IMO are a major basis for being able to drop and still maintain hydrodynamic lubrication, with reduced surface roughness allowing for for getting closer to mixed lubrication and even boundary.


Is there a point at which the surface is too smooth to hold an oil film effectively, causing more startup wear ?


Without motion, you don't have a hydrodynamic wedge. So an oil film is not an issue, its a matter of boundary lubrication, which is all surface chemistry.

 

[Shannow]

I think that the inference was that in order to have hydrodynamic lubrication, it requires zero relative motion between the lubricant and the wetted surfaces that are in relative motion...can a surface be made to slick such that there is relative motion between the lubricant and the shaft/bearing ?

 

[CATERHAM]

Originally Posted By: JHZR2
As boundary lubricants get better, viscosity needs go down. As surface finish gets better, viscosity goes down.

Ive siad it a few times, surface finish of parts, rather than "clearances" IMO are a major basis for being able to drop and still maintain hydrodynamic lubrication, with reduced surface roughness allowing for for getting closer to mixed lubrication and even boundary.

Reduced surface roughness increases the viscosity margin before the onset of mixed/boundary lubrication. This in turn allows a lower viscosity oil to be used and still maintain the same desired viscosity margin. Consequently for this and other reasons such as better control of maximum oil temp' and improved shear stability of modern oils, when a lower viscosity oil is specified I see no reason to conclude that an engine will automatically be operating any more in mixed/boundary lubrication mode than they once did. If anything I'd posit, since engine are lasting much longer today than they once did, the time spent in boundary lubrication has been reduced despite the trend to lighter oil grades.

 

[Shannow]

Originally Posted By: CATERHAM
Reduced surface roughness increases the viscosity margin before the onset of mixed/boundary lubrication. This in turn allows a lower viscosity oil to be used and still maintain the same desired viscosity margin. Consequently for this and other reasons such as better control of maximum oil temp' and improved shear stability of modern oils, when a lower viscosity oil is specified I see no reason to conclude that an engine will automatically be operating any more in mixed/boundary lubrication mode than they once did. If anything I'd posit, since engine are lasting much longer today than they once did, the time spent in boundary lubrication has been reduced despite the trend to lighter oil grades.


Did you actually READ the articles ?

Your last statement is the "pile of failed engines" strawman played backwards...

If you take the time to read them, you'll see that the new test mule was chosen specifically because it has a higher amount of operation in mixed/boundary regimes than the old, in view of modern trends and designs.

 

[Shannow]

BUMP...

Original article...
http://www.infineum.com/sitecollectiondocuments/notebooks/gf5/ResearchReport.pdf

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