Explain the HTHS/Viscosity at 100c relationship to me

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Originally Posted by JAG
I'll repeat the key point already stated: it is due to temporary shear thinning...temporary viscosity loss at high shear rate. It regains its viscosity when the shear stress goes away. A Newtonian fluid does not have a shear thinning behavior since its viscosity does not vary with shear rate. To be Newtonian, polymer VIIs must NOT be present. Having "shear stable" VIIs does not change that. "Shear stable" VIIs refers to how well they avoid permanent viscosity loss, not temporary loss.


Following on from that JAG, I'll throw in some history... When oils were made with polymeric viscosity index improvers, it was found that they did not provide the "protection" that their grade should have indicated...studies ensued, including the one that generated the first of these charts, particularly interesting as they used an engine in which they access and tap into one main bearing, and supply the bearing with a constant supply pressure of a bunch of oils.

As JAG stated, Newtonian oils do not change the viscosity with shear rate. Oils with polymeric viscosity improvers "flatten" the VII with shear rate, and give an apparent viscosity in the bearing that is lower than the viscosity measured at lower shear rates.

Bearing Viscosity.JPG


shear rates in engines.JPG
 
Why is it important ?

It's the driver of MOFT in the high shear areas. While the above displayed the shear rate around the oil feed hole (as did CATERHAM's oil pressure testing which was very good, albeit the conclusions wrong), the film itself where the load is carried (Minimum Oil Film Thickness - MOFT) is definitely in high shear.

First chart shows the MOFT versus HTHS at a steady state, and the second one at variable speeds and loads, using a modified Somerfeld number (SO being the bearing design point, and you should recognise half of this dimensionless number as being the X axis for the Stribeck curve.

moft hths line.jpg


MOFT HTHS So.jpg
 
Originally Posted by Shannow
Oils with polymeric viscosity improvers "flatten" the VII with shear rate, and give an apparent viscosity in the bearing that is lower than the viscosity measured at lower shear rates.


Pertinent to the topic, temporary shear is related to temperature as well...well temperature insofar as viscosity is affected by temperature. At higher viscosities, the polymers are sheared more than at lower viscosities, so there is more Temporary Viscosity Loss at the lower temperature.

First chart demonstrates this, in that the Temporary (it gets it back) viscosity loss is higher as a percentage for the 100C case than the 150C case.

The second one is permanent, and is useful in the discussion as it shows that the HTHS loss as a percentage of the KV100 loss...it's a LOT less than the KV100 loss (which to ME indicates that you don't have to go way overboard on HTHS).

Third is an industry peeing competition...it's a way old M1 0W40 recipe, I think back in the trisyn days, which we observed usually became a 30 grade before heading back to 40 grade in extended drains.

Last one is for gigs...it's my Mobil were able to claim that their 5W20 offered the same protection as a 10W40...their 5W20 was a monograde, the chart shows viscosity loss over time (distance)



hths 150 100.jpg


HTHS Loss KV.JPG


sheared 0W40.jpg


M1 1978.jpg
 
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Yep, and when the 0w40 once again became a 40 grade in extended drain examples, the 0W part was no where to be found.

What is the true driver of fuel economy, KV100C, or HTHS? For example SAE 30; KV100C 11.0, HTHS 3.5 compared to a 5W30 with a higher KV100C, but a lower HTHS.
 
Originally Posted by userfriendly

What is the true driver of fuel economy, KV100C, or HTHS? For example SAE 30; KV100C 11.0, HTHS 3.5 compared to a 5W30 with a higher KV100C, but a lower HTHS.


Steady state, HTHs is the driver...during warmup, it still is sortof, using the behaviour that I described where at higher viscosities the polymers are stressed more and the viscosity loss due to shear is greater.

For a given HTHS, they are using Viscosity Index to drive economy gains during warmup. FMEP is the normalised "power loss" due to friction. Sometimes measured by motored testing, sometimes measured by fuel/spark cut and inertial run-down. (It's like bmep is Brake Mean Effective Pressure - normalised measure of horsepower.

warmup shear.JPG
 
Originally Posted by JAG
Great posts, Shannow. I hope Patman makes this thread a sticky.


That's a great idea, lots of great info in this thread!
 
Originally Posted by userfriendly
What is the true driver of fuel economy, KV100C, or HTHS? For example SAE 30; KV100C 11.0, HTHS 3.5 compared to a 5W30 with a higher KV100C, but a lower HTHS.

Larger than normal fuel economy is achieved with presence of larger viscosity differentials between two oils, hence it's prominent at low temperature regimes.
Smaller than normal fuel economy is achieved with smaller viscosity differentials between two or more oils, at high temperature regimes.
A multigrade in 5W30 with pour point depressants, high Viscosity-Index low viscosity base oils and larger dosages of low-molecular weights VII's etc trumps a monograde SAE 30 in fuel economy.
Ratio of low temperature:high temperature regime durations is assumed constant.
 
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Originally Posted by SonofJoe
I suspect the primary reason for this behavior is the type of VII used. Although it's not an absolute certainty, the 5W30 & 5W40 are likely to use OCP VII (Olefin CoPolymer). These have relatively poor cold flow (as in CCS) properties but are pretty robust in terms of HTHS.

Because of their poor cold flow properties, it's virtually impossible to make a 0W40 with OCP so you're forced to using expensive HSD VIIs (Hydrogenated Styrene Diene). Although these have far superior CCS performance, they are relatively poor in terms of HTHS.


So Joe, in your opinion, which is the superior VII, if subzero temperatures are not a factor? And why? Your posts are great info but I feel there is even more to be learned if you are kind enough to share this knowledge. Thanks!
 
HSD VII tends to be polymerically more efficient than OCP. You need less of it for a given viscometric balance. HSD oils also tend to have lower Noack volatility (a very useful property for 0W oils). However it is a very expensive VII to produce which counteracts much of it's technical advantage. Overall OCP, made from cheap & widely available ethylene & propylene, is more cost-effective and way more widely used. HSD tends to only be used in top tier 0W/5W oils which are less sensitive to price.

That said, my personal preference has always been for OCP. There are times when cheaper is actually better. I've always seen OCPs as robust and HSDs as 'fragile'. Take for example HTHS. Make two similar oils, one with OCP, one with HSD & both with equal viscometrics. For the same KV100, the oil with the OCP will have higher HTHS (by about 0.3 cP). It will also be less sensitive to thermal degredation & the 'real-life' shearing you'll get in an actual engine.

Hope that helps...
 
Originally Posted by ZeeOSix
...
Here you go ... you can see the trend, but yes there are some cases where it's not a perfect correlation. But generally speaking a higher KV100 will also give a higher HTHS. Of course having the official specs on the specific oil is what you want to go by.
Somebody might wanna check the axis labels on that scatter chart. ( http://www.bobistheoilguy.com/forum...mber/1033/filename/KV100%20vs%20HTHS.JPG )
 
Originally Posted by CR94
Somebody might wanna check the axis labels on that scatter chart. ( http://www.bobistheoilguy.com/forum...mber/1033/filename/KV100%20vs%20HTHS.JPG )


Thanks ... corrected the reversed axis labels and re-posted below - plot lines still fine.

Originally Posted by CR94
Originally Posted by ZeeOSix
... Here's where the raw data came from: https://www.bobistheoilguy.com/foru...hs-influence-on-oil-pressure#Post4717505
Somebody might wanna recheck the axis labels on that plot.


That chart in the other thread is fine ... the x-axis is oil pressure and the y-axis is either KV100 or HTHS. Data plot key is shown below the x-axis. Raw data is also shown so shouldn't be any confusion.

KV100 vs HTHS.JPG


Mobil ESP - KV100 vs HSHS.JPG
 
Thanks to wemay pointing out the good web site that Mag 1 has, I noticed that it shows the HTHS at both 100 C and 150 C. We can use the former along with the kinematic viscosity at 100 C to calculate how much temporary viscosity loss occurred at 1e6/sec. shear rate and 100 C temperature. HTHS viscosity units are cP and we need it in cSt, so I will divide the viscosity in cP by the specific gravity. I'll do this for Mag 1 synthetic 5W-30, which has the following values:
Specific gravity: 0.8502
HTHS viscosity at 100 C: 6.9 cP, or 8.12 cSt
Kinematic viscosity at 100 C: 10.9 cSt

% viscosity loss = 100x(10.9-8.12)/10.9 = 25.5%
That's a lot!

https://mag1.com/products/33/pds/
 
Jag,
error in your calcs, is that the specific gravity is at 15.6...at 100C it's 0.7882
https://planetcalc.com/2834/

Makes it 8.75Cst - 19.7% loss.
Harman Index (does the same at a predicted 150C) is 0.907.

Like I said, earlier, more shear when the oil is thicker.

If you do the search (through google) on Supertech 5W30 data sheet on BITOG, you can find that we had some HTHT100 number to mess with back then....If I can get browser to work, I'll dig it up.
 
Yeah, I almost posted the caveat that I didn't adjust the specific gravity for the temperature but I figured it was close enough to make the point. I can't find it but I posted a link to a paper within the last year that showed a nice 3-D surface plot of viscosity vs temperature and shear rate. It nicely showed what you said, that at lower temperatures, temporary viscosity loss is greater than at higher temperatures. That is because, as you said, shear stress is higher in colder-thicker oil, causing the polymers to distort in a way that reduces their contribution to viscosity.
 
This one ?

Yes, it's named "grail" in my files, I giggled like a school girl the day I found that.

grail.JPG
 
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