GTL = higher PVC = a lot less wear says Chevron

[Gokhan]

This very interesting Chevron patent claims that GTL base stocks have a higher pressure - viscosity coefficient (PVC), which means a lot thicker oil film under pressure (a lot higher oil-film strength, which results in an a lot higher EHL [elastohydrodynamic lubrication] film), which in turn means a lot less wear. Patent also emphasizes that the effect has nothing to do with the base stock's viscosity index (VI). Note that PVC is the exponential coefficient that relates a base stock's viscosity under pressure (such as thousands of atmospheric pressure produced when squeezed between moving parts) to its atmospheric-pressure viscosity reported in the specification sheets (KV40 and KV100).

I am now considering the switch to the new generation of oil technology using GTL base stocks, currently available in Pennzoil Platinum PurePlus products.

Chevron patent: Lubricating oil with improved wear properties

 

[turtlevette]

But I thought you guys, the core group here, say oil is oil and minimum oil film thickness is proportional to viscosity and nothing else.

 

[Gokhan]

Originally Posted By: turtlevette
But I thought you guys, the core group here, say oil is oil and minimum oil film thickness is proportional to viscosity and nothing else.

That's for hydrodynamic lubrication (HL), when the minimum oil-film thickness (MOFT) is still very large, such as journal bearings not subjected to heavy load and/or RPM that is not too low, as MOFT is inversely proportional to load and directly proportional to RPM, in addition to being directly proportional to HTHSV. In the valvetrain, parts of the rings and cylinders, and in the bearings when the load increases and/or RPM decreases, you go into the elastohydrodynamic (EHL) lubrication, where the oil film gets minimally thick and you are almost having metal-to-metal contact. That's when the PVC (oil-film strength) becomes very important. But that's the most worrisome lubrication region anyway; therefore, PVC (oil-film strength) is crucial in determining wear in general.

 

[4wheeldog]

Originally Posted By: Gokhan
This very interesting Chevron patent claims that GTL base stocks have a higher pressure - viscosity coefficient (PVC), which means a lot thicker oil film under pressure (a lot higher oil-film strength, which results in an a lot higher EHL [elastohydrodynamic lubrication] film), which in turn means a lot less wear. Patent also emphasizes that the effect has nothing to do with the base stock's viscosity index (VI). Note that PVC is the exponential coefficient that relates a base stock's viscosity under pressure (such as thousands of atmospheric pressure produced when squeezed between moving parts) to its atmospheric-pressure viscosity reported in the specification sheets (KV40 and KV100).

I am now considering the switch to the new generation of oil technology using GTL base stocks, currently available in Pennzoil Platinum PurePlus products.

Chevron patent: Lubricating oil with improved wear properties


Well......Since there is virtually no measurable wear using good quality oil available today.....It would seem the the best way to utilize this new(er) technology would be to use it in thinner grade oils........Thus achieving improved economy and still getting virtually no wear.

Could this be a key to the new SAE 16 grade, and other even thinner grades?

 

[Gokhan]

Originally Posted By: 4wheeldog
Originally Posted By: Gokhan
This very interesting Chevron patent claims that GTL base stocks have a higher pressure - viscosity coefficient (PVC), which means a lot thicker oil film under pressure (a lot higher oil-film strength, which results in an a lot higher EHL [elastohydrodynamic lubrication] film), which in turn means a lot less wear. Patent also emphasizes that the effect has nothing to do with the base stock's viscosity index (VI). Note that PVC is the exponential coefficient that relates a base stock's viscosity under pressure (such as thousands of atmospheric pressure produced when squeezed between moving parts) to its atmospheric-pressure viscosity reported in the specification sheets (KV40 and KV100).

I am now considering the switch to the new generation of oil technology using GTL base stocks, currently available in Pennzoil Platinum PurePlus products.

Chevron patent: Lubricating oil with improved wear properties

Well......Since there is virtually no measurable wear using good quality oil available today.....It would seem the the best way to utilize this new(er) technology would be to use it in thinner grade oils........Thus achieving improved economy and still getting virtually no wear.

Could this be a key to the new SAE 16 grade, and other even thinner grades?

Of course, going to thinner thinner viscosity grades (xW-20, xW-16, etc.) without sacrificing wear protection is the primary motivation of this patent.

However, even if you are using thicker viscosity grades, improved wear protection is important in certain engines, such as high-performance engines, older engines, and heavy-duty diesel engines. Also, less wear in more driving condition helps in any engine regardless of the viscosity grade that is used.

 

[Jetronic]

from the data I've seen, doubling the KV also doubles the oil film thickness under EHD regime, when using newtonian fluids.


Quote:

3.2 Elastohydrodynamic Lubrication
There are many rolling or sliding contacts in engineering where high loads are spread over small contact areas, for example in gears and bearings. In such nonconforming contacts, called elastohydrodynamic (EHD) or concentrated contacts, the lubricating film is exposed to extreme conditions of pressure and shear. In refrigeration compressors, EHD contacts can be found in the rolling element bearings, gears, rotors, or wherever rigid counterformal surfaces are loaded and move relative to one another. The pressures generated in EHD contacts can be on the order of 0.5 to 2.4 GPa. The high pressures within the contact have two beneficial effects, elastically flattening the surfaces, and hence reducing contact pressure, and increasing
oil viscosity in the contact. The overall effect of these two is to permit the formation of thin EHD oil films in such contacts, typically 50 - 1000 nm (0.05 - 1 micron) thick. This is of the same order as the roughness of engineering surfaces which makes EHD oil film thickness an important practical value in predicting the performance of bearings and gears.


from Elastohydrodynamic Lubrication with Polyolester
Lubricants and HFC Refrigerants

 

[wemay]

Excellent read! Thanks Gokhan

 

[lubricatosaurus]

Getting back to the Chevron patent, the phrasing "[00071] Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of the invention. Other objects and advantages will become apparent to those skilled in the art from a review of the preceeding description.".... sounds wishful, and renders this patent useless. I'll bet Shell (Pennzoil) is not paying any royalties to Chevron for using GTL's physical properties. It's like Chevron is trying to patent basic fluid physics here. Crazy

 

[Gokhan]

Originally Posted By: Jetronic
from the data I've seen, doubling the KV also doubles the oil film thickness under EHD regime, when using newtonian fluids.

The point is that in the EHD regime, pressures are much higher, and the KV that applies is not the atmospheric KV but the high-pressure KV, which is determined exponentially by the former and PVC. This is also a low-shear quantity and has nothing to do with non-Newtonian effects (VIIs, HTHSV, etc.), and it's a Newtonian base stock effect. It applies to all (Newtonian) base stocks.

 

[lubricatosaurus]

Originally Posted By: Gokhan
Originally Posted By: Jetronic
from the data I've seen, doubling the KV also doubles the oil film thickness under EHD regime, when using newtonian fluids.

The point is that in the EHD regime, pressures are much higher, and the KV that applies is not the atmospheric KV but the high-pressure KV, which is determined exponentially by the former and PVC. This is also a low-shear quantity and has nothing to do with non-Newtonian effects (VIIs, HTHSV, etc.) and it's a Newtonian base stock effect. It applies to all (Newtonian) base stocks.


Wait, the whole concept of an ideal Newtonian fluid is viscosity independence from stress variations. This entire PVC discussion is founded on GTL being close to independent of temperature, not stress, so this would apply whether the base oil (here GTL) is Newtonian or not.

 

[d00df00d]

Interesting indeed. Thanks for posting, Gokhan!

 

[geekster]

I'm just going to be very honest and say that I think I understand about 20% of this. Sometimes I wish Bill Nye was a member here and had associated videos on YouTube.

I have been reading this site for around 6 years and I am always surprised at some of the conversations that go on here. (I mean that in a nice way)

 

[goodtimes]

You don't need to understand more than 20% because it is marketing. Each company will make you a disciple of their oil if they can. They have whole departments working on selling what they make to you. Go to the next company, and suddenly all the euphoria is shattered about the other as they gather you in.

 

[lubricatosaurus]

Originally Posted By: Gokhan
This very interesting Chevron patent claims that GTL base stocks have a higher pressure - viscosity coefficient (PVC), ......


The Chevron patent didn't claim that at all.

"More particularly, the present invention employs base stocks exhibiting low temperature sensitivity of the Pressure- Viscosity-Coefficient (PVC) to obtain improved wear properties." from the patent indicates they only have observed a lack of sensitivity to temperature in their GTL basestocks, not that it has a higher PVC.

 

[Gokhan]

Originally Posted By: lubricatosaurus
Wait, the whole concept of an ideal Newtonian fluid is viscosity independence from stress variations. This entire PVC discussion is founded on GTL being close to independent of temperature, not stress, so this would apply whether the base oil (here GTL) is Newtonian or not.

If there was no pressure-viscosity coefficient, in other words if the viscosity didn't greatly increase with pressure, any engine would be destroyed in a few minutes. This has nothing to do with Newtonian or non-Newtonian oil. All base stocks (Group I, II, III, IV, V, and GTL) are Newtonian. Non-Newtonian effects are only a result of the viscosity-index improvers VIIs) that are used in multigrade oils. In a non-Netwonian (multigrade) oil, oil temporarily shears at increased shear rates and the viscosity temporarily drops. This is called the dynamic viscosity or HTHSV, which is always slightly lower (not higher as in the pressure-induced viscosity) than the kinematic viscosity. For Newtonian (monograde) oils, viscosity doesn't drop with high shear, so KV and HTHSV are the same (when measured in the same units).

However, PVC is always an important quantity for both Newtonian and non-Newtonian oils. See the reference below studying PVC in Netwonian oils if you still think that PVC = 0 for Newtonian oils:

http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467588

 

[Shannow]

Originally Posted By: turtlevette
But I thought you guys, the core group here, say oil is oil and minimum oil film thickness is proportional to viscosity and nothing else.


Are you being deliberately disingenuous, or just troll baiting ?

As Gohkan pointed out, bearing MOFT is HTHS related...that's where those relationships and discussions are centred.

EHD isn't engine bearings (and it's not 540Rat's tests either)

BTW, you missed some more of me posting other people's work

http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3829734/Cams_and_Lubrication#Post3829734

 

[turtlevette]

Originally Posted By: Shannow
Originally Posted By: turtlevette
But I thought you guys, the core group here, say oil is oil and minimum oil film thickness is proportional to viscosity and nothing else.


Are you being deliberately disingenuous, or just troll baiting ?

As Gohkan pointed out, bearing MOFT is HTHS related...that's where those relationships and discussions are centred.

EHD isn't engine bearings (and it's not 540Rat's tests either)

BTW, you missed some more of me posting other people's work

http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3829734/Cams_and_Lubrication#Post3829734


That's OK and expected. Backpedaling and rear end covering again and again. I've always argued with you that a properly designed synthetic would wear protect better than a heavier grade conventional.

You are a terrible loser. I tried to have respect for you but stuff like this makes it impossible.

 

[Garak]

I think we're getting overly wound up about film strength in base stocks. For even thinner oils, as you point out, it might be a bit of an issue.

 

[Gokhan]

Originally Posted By: lubricatosaurus
Originally Posted By: Gokhan
This very interesting Chevron patent claims that GTL base stocks have a higher pressure - viscosity coefficient (PVC), ......

The Chevron patent didn't claim that at all.

"More particularly, the present invention employs base stocks exhibiting low temperature sensitivity of the Pressure- Viscosity-Coefficient (PVC) to obtain improved wear properties." from the patent indicates they only have observed a lack of sensitivity to temperature in their GTL basestocks, not that it has a higher PVC.

That's because PVC decreases with temperature. (See, for example, this reference.) They are trying to find base stocks with higher PVC at higher temperatures so that they will have thicker EHL oil films at higher temperatures that various parts of the engine experience during normal or severe operation. By keeping the ratio of PVC100/PVC40 close to 1, they are ensuring that they have a small variation of PVC with temperature and have a high PVC at high temperatures.

It's like a "PVC index" analogous to the viscosity index. The latter ensures that the viscosity stays high and the oil-film thickness stays large when the temperature increases and the former ensures that the PVC stays high and the oil-film strength stays high when the temperature increases.

 

[Jake777]

ok I am going to ask the question. But first let me say I don't understand 10% of what you guys are saying but I do hear you saying film strength and it just so happens that I heard that same statement from the RAT guy who does his oil testing and shows what he says are the film strengths of various oil as tested on his rig. NOW many people on here said he was full of it even though I said if indeed film strength was stronger from one oil to another why is that not a good thing and not an indication of a strong point in the oil. Can anyone who has commented so far please help me out with this? Am I hearing that film strength is important and that as such tests like what RAT did showing various film strengths could have some actual usfal info?

for ref... https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/