High Shear Rate Viscosity index - one step closer.

[Shannow]

Paper the Expansding Dimensions of High Shear Viscometry.

http://www.savantlab.com/images/TBS_Paper_-_SAE_2008-01-1621_The_Expanding_Dimensions....pdf

As some of you know, I've been trying to get a handle on what the viscosity index in the high shear regime is for just about ever, not to a great deal of success.

This is another Selby paper, which is a typical go to for good guts work.

Explains the role of VIIs, and how they work, and has this chart...

It's a range of multigrade engine oils from the US, on the LHS axis is the temporary viscosity loss at 150C high shear conditions, and on the bottom axis is the same shear rate at 100C. Temporary viscosity loss is the delta in viscosity with high shear rate, as the polymeric VIIs get stretched with increasing shear rate.

For those following along it's precisely (1- the Harman Index)

It appears looking at the chart that the loss of viscosity due to high shear at 100C is about 1-1/2 times the loss at 150C (Paper says 30% more, but chart looks steeper).

There's an explaination for that. Remember that multigrades are typically a lighter base-stock, with VII added. There are two phenomenon at play here.
1) the temperature is lower, so the VII aren't as fluffy, and therefore have less impact in increasing the viscosity.
2) the oil is thicker, drags the polymers more, and they flatten out earlier.

So the high shear at lower temperatures is even closer to the base oil viscosity than at 150C.

Yonks ago, someone posted a supertech 5W30 data sheet, which had the rare gem of HTHS 100C
https://bobistheoilguy.com/forums/ubbthreads.php/topics/3307068/Walmart_SuperTech_Synthetic_sp

So messing with it, and this chart, I calculated a few things (black is source data, pink is calculated). I've included the calculators that I always use to calculate density and viscosity on it.

So the high shear 100C viscosity is about 60% more at 100C than at 150C...about consistent with the chart.

What does this mean ?

That the High Shear Viscosity Index, as it relies on both the base oil (Newtonian VI), and the changing nature of VIIs with both temperature and shear rate...is actually higher than the kinematic viscosity index...

 

[Shannow]

Which means that the operating temperature viscosity loss in a multigrade is more than the HTHS...helping with economy, and reducing MOFT in the bearings and rings et.al.

And if you do the math, Citgo 20W20 is almost spot on the same viscosity in the bearing surfaces at 100C as the Supertech 5W30. Citgo 20W20 also has pretty close to the same HTHS at 2.9Cp.

Which, if you look at my previous commentary of the 0W16s, appearing to be almost monogrades in their vasestock like VIs rather than unicorn VIs in the (some) 0W20s, makes much more sense too.

 

[Shannow]

OK, and to back the above (been bagged for a few of those statements by the usual crowd)...

Here's the Supertech 5W30 versus Citgo 20W20...

Has been my traditional position...7.26Cp versus 7.33Cp at high shear in the bearings at 100C...near identical...Yes, HTHS is a little lower, but still at the HTHS minimum for 30 grade, and no permanent shear at all in the monograde.

Now for the board darling, TGMO, which I compared previously to Ravenol 0W16, making the sttement that if I had a car speccing 0W20, I'd be more inclined to take the 0W16, as it's less impacted by VIIs...

Note the viscosity loss for the Ravenol is close to zero...next to (or actually) NO VII effect in this oil
Note also that the HTHS 100s (both calculated figures) are comparable, so therefore same MOFT between the two.

I rest my case, and still maintain that the Japanese have learned their lesson with uber high VI 0W20s to get their economy gains, and have dropped "down" to essentially VII free 16s, less deposits, less volatility.

And re-iterate that I'd rather run a 0W16 than TGMO...

 

[Ducked]

Sounds like you're saying the wheel of progress is turning back to monogrades.

Like that, since I've been heading that way too, though mine are a bit thicker.

Are those "unicorn VIs in the (some) 0W20s" very rare?

 

[SR5]

Nice a HTHS or rather HS-Viscosity VI table, so to speak.

Forgive my ignorance, but what is the difference between the HS Vis and the Newtonian Vis, they are both in cP.

I take it the 100C HS for the 20W20 is 7.33 cP

 

[Shannow]

SR5,
a "Newtonian" fluid is one that has a constant viscosity regardless of shear rate...aka the viscosity index is basestock only, and there are no VII polymers.

Oils with VII polymers were introduced a long time ago, and it was when the (rubbish) 10W40s of the day started doing some strange stuff, like wearing out engines, and filling sumps with rubber that had to be cut out, that people realised there was a problem.

It was found that when the shear rate was high enough, the VII polymers started to "lay flat" for want of a better description, and no longer fluffed up the viscosity...the author of the linked paper was one of the researchers who was at the pointy end of it.

Here's a couple of visual representations...

That shows visually what's going on in this discussion...each "isobar" for a monograde would be flat, no dip.

This is an early one where they started referring to the "apparent" viscosity, aka that which provides bearing protection (test was an engine that they could access main bearing 4 oil gallery, isolate it, and inject the test oil at 40psi...the rate that the oil flowed through the bearing indicated it's "apparent" viscosity, rather than it's KV", chart to the left shows a few points and the difference, an "apparent" loss of 25% in viscosity in the high shear range...the chart on the right shows the "first" and "second" Newtonian ranges, where viscosity doesn't change with speed. First is fluffy VIIs that aren't all bent out of shape, second shows the flattened ones that can't flatten any more.

Yes, the 20W20, being a monograde, I didn't have to flip it back into the other line...it is what it is, and I didn't want to make that couple of percent error in the Harman Index (is 100 for monogrades) flow back into the answer.

 

[Shannow]

Originally Posted By: Ducked
Are those "unicorn VIs in the (some) 0W20s" very rare?


TGMO, Mazda, and Sustina IIRC.

My belief (strong) is that the Japanese engine manufacturers were stuck with J300, and could only market oils that went to "20", which had the HTHS minimum stuck at 2.6. So from their own statements, introduced high VII oils that had lower frictional losses during warmup.

CATERHAM's testing showed some of them seemed to be intentionally not shear stable to drop HTHS in as little as 400 miles.

Honda just went their own way, and created a lower viscosity oil that didn't meet the (then) J300, while they lobbied to extend and break up the sub 20s.

 

[Jetronic]

Interesting calculations, but wether or not the viscosity loss through shear is higher or lower at 100°C is a bit moot since engine parts will not be in that temperature region for long, especially not the high shear areas. And the HS viscosity will always be higher than at 150°C obviously.

But it does mean care has to be taken by those who run thinner than recommended oils because their engine "runs cool anyway", like in winter.

Also, what does this mean if there's a significant amount of fuel contamination, either gas or diesel? Part of the base oil would be replaced by even thinner base oil? As I take your first post it means the high shear viscosity effects are smaller than a simple kv calculation would have you believe. In that way VM chemistry could be a good thing?

 

[SonofJoe]

On a slightly different note, I recently stumbled upon an old 1998 paper from Lubrizol India entitled 'Shear Stability Of Polymers Used As Viscosity Modifiers In Lubricating Oils'.

Here's the link (just download the PDF, it's free)...

http://nopr.niscair.res.in/handle/123456789/30861

Mr Ghosh and his co-workers were investigating the permanent (as opposed to temporary) shear of VII polymers. He was doing this using the KO30 shear test beloved by ACEA and the Europeans and more or less ignored totally by the API and the Americans (for PCMO). This artificially severe test repeatedly pumps hot oil through a fuel injector to induce mechanical shear of the VII polymer chains. He expresses his results in terms of Permanent Shear Stability Index (PSSI) which is simply the loss of KV100 due to shear over the initial gain in KV100 due to the VII, expressed as a percentage.

What intrigued me about this study was he tested OCP (by far and away the most common VII) in a range of mineral base oils ranging from very thin (100N) to very thick (500SN). What I saw was that the PSSI increases with VII treat rate (which I sort of knew anyway) and that PSSI tends to increase with the thickness of the initial base oil (which I didn't).

It's impossible to analyse this paper properly without access to the raw KV data but my gut feel is that this implies that the absolute viscosity of an oil plays a role in the degree to which it permanently shears. Which is interesting. It might suggest that the sort of real-life oil shearing you saw back in the day in the US with all mineral 10W40s might be a thing of the past given that thinner oils are now the norm. Maybe we're all been fretting over nothing!

 

[Jetronic]

downloaded, and already rom the abstract I can see this will be interesting reading. Let's see how the (presumeably) shellvis VI in my oil of choice performs...

 

[Jetronic]

Unpredictable results when mixing it seems, as all react differently to base oil composition.

 

[Shannow]

Originally Posted By: Jetronic
Unpredictable results when mixing it seems, as all react differently to base oil composition.


I think I know a bloke who's been saying that for a while...

 

[Jetronic]

Don't celebrate too soon, that guy was saying the results of mixing were unpredictable because of the polymers, but this paper suggests it's because of the base oils

 

[SonofJoe]

I'm wondering if the problem is that Mr Ghosh et al haven't analysed the basic data enough to yield proper predictions of this particular viscometric system.

In the past, I've found that most simple engine oil properties (KV, CCS, MRV, Noack, HTHS, etc) are predictable provided you dig deep enough into the data to find the fundamental mathematical relationships.

Also, I might be wrong, but some of the data looks decidedly 'off' (particularly on the SIP VM). I'd want some of that data queried and rechecked before I believed it.

 

[Jetronic]

Well, they dismissed what they called outliers... of course, if you go in with a certain but wrong expectation, you might be keeping outliers and dismissing valid data...

 

[userfriendly]

As is, the VI does not tell the whole story such as cold cranking & pumping performance (W grade) or extreme hot performance like HTHS or NOACK of an engine oil.

Would a high shear rate viscosity index be a graph between two temperatures, maybe 100C & 150C ?

 

[SR5]

Originally Posted By: Shannow
SR5,
a "Newtonian" fluid is one that has a constant viscosity regardless of shear rate...aka the viscosity index is basestock only, and there are no VII polymers.......


Thanks Shannow, every time I talk to you, you make me want to start running monogrades. Pity most of them around me are SG rated mineral oils.

BTW why is that ?
Castrol RX Mono 30 is API CF / SG
Caltex Delo Silver SAE 30 is API CF / SJ
Penrite Mono Truck SAE 30 is API CF / SG and E1

They all seem to have reasonable TBN (7 to 9) and the Castrol has a regular Sulphated Ash of 0.9%, and the Delo a regular zinc of 940 ppm. Their Noack would be on the low side, so what's missing ? What can't they be SL or SN ?

 

[Shannow]

To quote (well paraphrase) a friend there's no glory (or $) in a GrII low NOACK 2.9-3.1 HTHS 10W20.

There IS the desire to produce other than supercheap air compressor oils in othe rmarkets.

Here's a good one from G-Man...

https://bobistheoilguy.com/forums/ubbthreads.php/topics/1174209/Valvoline_20w20,_3500_miles,_C

 

[MolaKule]

Originally Posted By: SHANNOW
Oils with VII polymers were introduced a long time ago, and it was when the (rubbish) 10W40s of the day started doing some strange stuff, like wearing out engines, and filling sumps with rubber that had to be cut out, that people realised there was a problem.


Some time ago I posted that I was working with the company that was producing PIB thickeners for the lubricant industry in which it's quality was way below par. A large batch (many train car loads) was sent out before proper testing and vetting. I was called in to determine the cause and raise the bar on testing.

It was determined that a console that controlled the PIB creation process was being affected by a two-radio system that interfered with the hardware that controlled the process programming. I.E., this was a RFI/EMI problem.

The radio system was moved and a new control console was built to mitigate this problem.

 

[MolaKule]

Quote:
Some time ago I posted that I was working with the company that was producing PIB thickeners for the lubricant industry in which it's quality was way below par. A large batch (many train car loads) was sent out before proper testing and vetting. I was called in to determine the cause and raise the bar on testing.


Should have read:

Some time ago I posted that I had worked with the company that was producing PIB thickeners for the lubricant industry in which it's quality was way below par. A large batch (many train car loads) was sent out before proper testing and vetting. I was called in to determine the cause and raise the bar on testing.