Effect of viscosity on hydrodynamic engine bearing

[CT8]

Originally Posted By: userfriendly
I couldn't help notice that the flow rate @ 7500 rpm didn't change much with incremental grade changes to thinner engine oil.
I would assume then, that oil pressure from one grade to the next, would not change at all.

If I throw this discussion back to oil pressure vs viscosity, vs oil pump capacity and relief pressure setting, very little would change at high rpm with viscosity changes.
My take; The pump then, if properly sized for the engine regardless of viscosity, should be operating at relief pressure at high rpm.

The oil pumps move a [chunk] of oil so no matter the viscosity of the chunk the chunk will be the same size. pressure is the resitance to flow and thinner oil leaks out of the bearings faster.

 

[Shannow]

Thinner oil leaks though the clearances in the pump (gears to housing) more than thicker, so actually delivers less (slightly to a lot) depending on delivery pressure too

 

[Jetronic]

Originally Posted By: Mitch Alsup
It seems to me that really small bearing clearances are at least as good as thinner oils in saving power.

Did anyone notice a savings of 600W--this is less than 1HP.


When you only need 18 hp to maintain a cruise speed, that's a 5% fuel gain right there... so highway MPG could be very much impacted

 

[ZeeOSix]

Originally Posted By: Jetronic
Originally Posted By: Mitch Alsup
It seems to me that really small bearing clearances are at least as good as thinner oils in saving power.

Did anyone notice a savings of 600W--this is less than 1HP.


When you only need 18 hp to maintain a cruise speed, that's a 5% fuel gain right there... so highway MPG could be very much impacted


Typically the engine will be around the 2000 RPM range in high gear when just "cruising" down the highway to maintain highway speed. So in reality the HP savings is more like 25W (0.034 HP) with 0W-5 vs 10w30 and 70W (0.094 HP) between 0W-5 vs 10W-60 (which nobody uses anyway). That's using the 0.004" bearing clearance data points.




So if the required HP was at 18, then the power savings is realistically more like 0.034/18 = 2%

More accurately, the HP required to cruise at a constant 65 MPH on flat ground is more along the lines of 24.5 HP for a 3500 lb vehicle. 12.4 HP from wind resistance and 12.1 HP from rolling resistance. So in that case, the power savings would only be 0.034/24.5 = 0.14%.

 

[userfriendly]

Exactly why I don't believe thin engine oils alone will save the whales. Instead, smarter application of fuels we already have.
It makes no sense to import oil and export LNG, or convert coal fired power plants to CNG and leave surface transportation vehicles fuelled by gasoline & Diesel fuel.

 

[Ohle_Manezzini]

Would it sell more oil, since thin oils are consumed several times more than thick, specially at highway cruising? At Cold start thinner helps on fuel economy. You need to know what driving habits prevail in each case.

 

[CT8]

Originally Posted By: Shannow
Thinner oil leaks though the clearances in the pump (gears to housing) more than thicker, so actually delivers less (slightly to a lot) depending on delivery pressure too
True but how much for the discussion that it would make a difference.

 

[CT8]

Originally Posted By: userfriendly
Exactly why I don't believe thin engine oils alone will save the whales. Instead, smarter application of fuels we already have.
It makes no sense to import oil and export LNG, or convert coal fired power plants to CNG and leave surface transportation vehicles fuelled by gasoline & Diesel fuel.
What would happen to the coal then?

 

[userfriendly]

Clean coal technology does not buy green votes. Ontario, Canada is a good example of energy & politics gone wild.

https://en.wikipedia.org/wiki/Clean_coal_technogy

http://science.howstuffworks.com/environmental/green-science/clean-coal.htm

 

[Shannow]

Originally Posted By: CT8
Originally Posted By: Shannow
Thinner oil leaks though the clearances in the pump (gears to housing) more than thicker, so actually delivers less (slightly to a lot) depending on delivery pressure too
True but how much for the discussion that it would make a difference.

 

[ZeeOSix]

Huge difference between 1 cP and 100 cP. How about the difference between 5W-20 and 10w30 oil both at 100 deg C (only 2.5~3 cP difference) for a more realistic comparison.

If at 40 deg C, oils would be where the red lines are drawn. 1 cP and 100 cP oils aren't even on the chart at 100 deg C. SAE 140 gear oil is only 40 cP at 100 deg C.

1 cP = 1 cSt

 

[Shannow]

FFS...

For illustrative purposes...did I say anywhere that ANY engine oil was 1cp anywhere?

 

[Shannow]

Originally Posted By: ZeeOSix
1 cP = 1 cSt


Your fluid dynamics pedigree is really showing now...i.e. absent.

You don't know the difference ????

 

[ZeeOSix]

Originally Posted By: Shannow
Originally Posted By: ZeeOSix
1 cP = 1 cSt


Your fluid dynamics pedigree is really showing now...i.e. absent.

You don't know the difference ????


Look at the table.
http://www.engineeringtoolbox.com/viscosity-converter-d_413.html

Update - I now see the table is based on fluids with a specific gravity of 1 - my bad. But the two tables you showed are two different fluids with different densities, so would have to compare on equal viscosity baselines to adjust for the density difference.

 

[ZeeOSix]

Originally Posted By: Shannow
FFS...

For illustrative purposes...did I say anywhere that ANY engine oil was 1cp anywhere?


Then why even use that example?

 

[Shannow]

Originally Posted By: ZeeOSix
Update - I now see the table is based on fluids with a specific gravity of 1


Difference in dynamic and kinematic viscosities is obvious to a first year engineer, let alone an elite secret agent fluid dynamiscist such as you claim to be.

here, it's explained...

https://bobistheoilguy.com/forums/ubbthreads.php/topics/3742278/Cp_and_Cst_-_the_confusion_bet

No-one past first year would ever claim that 1Cp = 1Cst, as it applies to oils...it's not a "my bad" from reading "engineering toolbox" for the first time, it's a fundamental principal.

As to the chart, it shows graphically what happens with difference viscosities.

As you'd be familiar with the sizing of pumps from various hydraulic manufacturer's you would be aware that they have curves for slip based on DP and viscosity...the one that I showed (water on the left hand axis) shows graphically that pump capacity and power requirement vary related to volume, RPM, and yes, viscosity, lower viscosity causes "Positive Displacement" pumps to flow less...regardless of magnitude.

 

[ZeeOSix]

Yes, it was 'my bad' ... at least I admit it when I'm wrong.

But let's back up a little bit. Your example is a bit skewed comparing water (at room temp = 1 cP) to an oil that's 100 cP, which would be close to a 10W at room temperature. If the oil was a 10W at 100 deg C (normal operating oil temp of most IC engines), then in that example the pump performance curves would be much closer to those when pumping water at room temperature.

Yes, agree on the fact that PD pumps can have pumping "slip" based on the variables involved. It also depends on how tight the pump tolerances have been designed and manufactured - some pumps will slip more than others based on physical tolerances if viscosity is changed drastically. There is probably more slip difference in the pump going on when the oil is cold vs hot, then there is between say a xW-20 vs xW-30 going on when both are fully hot.

In actual use at full operating temp (100 deg C), the difference in pump slip between running say a xW-20 vs a xW-30 or xW-40 in an IC engine isn't going to be enough to cause any oil flow/delivery issues. The delta in viscosity between those oils when fully hot isn't that drastic. Most pumps are over designed anyway, so any small increase in slip isn't going to make any difference impacting proper lubrication.

 

[Shannow]

Originally Posted By: ZeeOSix

In actual use at full operating temp (100 deg C), the difference in pump slip between running say a xW-20 vs a xW-30 or xW-40 in an IC engine isn't going to be enough to cause any oil flow/delivery issues. The delta in viscosity between those oils when fully hot isn't that drastic. Most pumps are over designed anyway, so any small increase in slip isn't going to make any difference impacting proper lubrication.


Exactly my point all along...

Pump only ever has to supply enough volume for the bearing's make-up requirements at the worst point, and operating point of the engine...the excess delivery is seen as "oil pressure".

Oil pressure may well be necessary when having to cool pistons, run actuators and the like...well at least that's per Honda's papers for street engines say as they reduce viscosity.

 

[userfriendly]

Thanks Zee06; For some reason it seems that we have come full circle with this logical explanation;

https://en.wikipedia.org/wiki/False_equivalence or, "1cP = 1 cSt"

 

[Shannow]

Originally Posted By: ZeeOSix
Typically the engine will be around the 2000 RPM range in high gear when just "cruising" down the highway to maintain highway speed. So in reality the HP savings is more like 25W (0.034 HP) with 0W-5 vs 10w30 and 70W (0.094 HP) between 0W-5 vs 10W-60 (which nobody uses anyway). That's using the 0.004" bearing clearance data points.




So if the required HP was at 18, then the power savings is realistically more like 0.034/18 = 2%

More accurately, the HP required to cruise at a constant 65 MPH on flat ground is more along the lines of 24.5 HP for a 3500 lb vehicle. 12.4 HP from wind resistance and 12.1 HP from rolling resistance. So in that case, the power savings would only be 0.034/24.5 = 0.14%.


Couple of quick questions...

How many road going engines have you seen with:
* 0.004" bearing clearances (mains or rods, doesn't really matter).; or
* only one bearing per engine ?

The latter would make it a fairly "uni"que design pardon the pun.

Go back here for catch-up.