Influence of kinematic and dynamic viscosity on wear shaft in bearing.

[Jetronic]

I've come across an interesting research article by Repsol (Spanish Lubricant Manufacturer) where they tried to develop a wear prediction algorithm. The interesting bit for me come toward the end, where they compare a commercial 0W-20 with full grp IV/V lubricants of differing viscosities and different levels of Viscosty Modifier concentration, in an actual shaft in bearing test.

The research article is called
Wear protection assessment of ultralow viscosity lubricants in
high-power-density engines: A novel wear prediction algorithm

This study shows kinematic viscosity also matters.

From the data presented in this study, the clear
standout candidate is Oil C, which demonstrates the
lowest wear depth values and area. It is followed by a
tie between Oil B and Ref 0W-20, which exhibit similar
results. Oil A performs the worst in terms of wear
protection throughout the proposed wear cycle.

Oil C was a thin xW-30 oil, 40% PAO, 50 % gp IV and 10% VM.

Oil B was formulated as an xW-20, oil A as straight 20.

Note that all oils were fully formulated and to have similar HTHS at the test temperature.

 

[Klutch9]

Interesting. I wonder why this is. I didn’t read the study, but based on your notes, I’m trying to understand how kinematic viscosity affects anything if all oils present were tested at a temp where their HTHS viscosity was the same/similar.

 

[Jetronic]

Interesting. I wonder why this is. I didn’t read the study, but based on your notes, I’m trying to understand how kinematic viscosity affects anything if all oils present were tested at a temp where their HTHS viscosity was the same/similar.

HTHS is measured at a specific shear rate, and the shear rate here wasn't as high, so you end up with a viscosity in between kinematic (0 shear) and HTHS, for non newtonian fluids. That's how my brain processed it anyway.

edit: a similar situation could happen in an engine that is lugging, or with pretty high boost at low rpm.

 

[Jetronic]

Also want to add, a speed boat illustrates the concept aswell. When it's going fast it lifts itself largely out of the water (high shear rate) but when it slows down, it sinks deeper. And that is despite it doesn't weigh any more than at full speed (load is the same).

If the water is higher viscosity, or higher density, it will lift up more at a lower speed.

 

[MolaKule]

I've come across an interesting research article by Repsol (Spanish Lubricant Manufacturer) where they tried to develop a wear prediction algorithm. The interesting bit for me come toward the end, where they compare a commercial 0W-20 with full grp IV/V lubricants of differing viscosities and different levels of Viscosty Modifier concentration, in an actual shaft in bearing test.

The research article is called
Wear protection assessment of ultralow viscosity lubricants in
high-power-density engines: A novel wear prediction algorithm

This study shows kinematic viscosity also matters.



Oil C was a thin xW-30 oil, 40% PAO, 50 % gp IV and 10% VM.

Oil B was formulated as an xW-20, oil A as straight 20.

Note that all oils were fully formulated and to have similar HTHS at the test temperature.

Here is the link to the complete paper:

https://link.springer.com/article/10.1007/s40544-023-0854-3