Effect of viscosity on hydrodynamic engine bearing

[Shannow]

Originally Posted By: d00df00d
So, in sum: While pump delivery may affect flow rates through the bearings and generate oil pressure, that doesn't mean the purpose of an oil pump is to positively generate those flow rates and that pressure.

Shannow, is that a fair reading of what you're saying?


Yep, for the bearings, the pump is simply there to provide sufficient oil quantity to replace that lost to side leakage, and with sufficient pressure to get it there.

 

[d00df00d]

In that case, I have no idea what the argument is about. What you're saying seems comprehensible enough. Hard to imagine how ZeeOSix is arguing with you.

FWIW.

 

[ZeeOSix]

Originally Posted By: d00df00d
In that case, I have no idea what the argument is about. What you're saying seems comprehensible enough. Hard to imagine how ZeeOSix is arguing with you.

FWIW.


I guess you didn't read the dozens of posts in 3 or 4 different threads discussing this where I showed that pressure fed bearings flow more oil than un- pressurized bearings. Shannow still thinks that a journal bearing will flow the same amount of oil regardless if it's supplied with oil at 0 PSI (ATM pressure) or if it's supplied at 200 PSI by the oil pump. If you believe that also, then you've been brain washed into a misconception.

 

[Shannow]

Originally Posted By: ZeeOSix
Shannow still thinks that a journal bearing will flow the same amount of oil regardless if it's supplied with oil at 0 PSI (ATM pressure) or if it's supplied at 200 PSI by the oil pump. If you believe that also, then you've been brain washed into a misconception.


No, I DO NOT THINK THAT...

you keep telling me and others that that's my belief, and I keep telling you that OF COURSE more pressure creates more flow...

Why do you keep up lying about my position ?

Your initial premise was that oil is "pushed through" bearings to provide lubrication and cooling, and the links that you provide (industrial not automotive) start with the premise that IF the "natural flow" is insufficient, then you can force more through it...you are claiming that the designers of all of these engines can't even get the basics right, so rely on pressure as a crutch.

They don't...

All of the papers that I link to start with the short bearing approximation to find the required flow rate to make up for side leakage, then you add enough volume to get a safety margin for wear and operating conditions, and a minimum pressure to get the oil where it needs to go and supply hydraulics

 

[d00df00d]

Don't bother, Shannow. You've made your position abundantly clear. Anyone who has the wherewithal to follow this conversation should be able to discern your meaning.

 

[ZeeOSix]

Originally Posted By: Shannow
Originally Posted By: ZeeOSix
Shannow still thinks that a journal bearing will flow the same amount of oil regardless if it's supplied with oil at 0 PSI (ATM pressure) or if it's supplied at 200 PSI by the oil pump. If you believe that also, then you've been brain washed into a misconception.


No, I DO NOT THINK THAT...

you keep telling me and others that that's my belief, and I keep telling you that OF COURSE more pressure creates more flow...

Why do you keep up lying about my position ?

Your initial premise was that oil is "pushed through" bearings to provide lubrication and cooling, and the links that you provide (industrial not automotive) start with the premise that IF the "natural flow" is insufficient, then you can force more through it...you are claiming that the designers of all of these engines can't even get the basics right, so rely on pressure as a crutch.

They don't...

All of the papers that I link to start with the short bearing approximation to find the required flow rate to make up for side leakage, then you add enough volume to get a safety margin for wear and operating conditions, and a minimum pressure to get the oil where it needs to go and supply hydraulics



Let's get a few things straight. For starters, I've never claimed that journal bearings NEED to be pressure fed. All I've ever claimed is that they flow MORE oil if pressure fed, and that extra flow from a pressurized oiling system COULD be used to help keep the oil film temperature down IF REQUIRED. It's not out of the realm as a design parameter when designing journal bearings.

Go back and re-read all of these discussions. I challenge you to go find a post of mine where I said journal bearings absolutely NEED to be pressure fed to survive. You didn't even grasp the concept that pressure fed bearings flow more oil until we got deep into these discussions. After lots of going back and forth, you dig up a comprehensive equation that shows that fact, agree to it all, that then turn around and keep making statements that the oil pump doesn't force flow through journal bearings.

I'm not "lying" about your position. If anything, you're lying about the statement that "you've always believed pressure fed bearings flow more", which is not true based on all of these discussions. If you believed that, you wouldn't have argued in 4 different threads with me about the difference between ATM fed bearings and pressure fed bearings. I've posted plenty of information showing that there is no question they flow more with increased supply pressure - doesn't matter if it's an industrial or an automotive journal bearing application. I can go find two dozen quotes of yours that shows you think journal bearings flow the same regardless of how much oil pressure is supplied to them. You've said many times that "the bearings only draw/suck what they need from the gallery to make us side leakage, and the pump doesn't force any oil through the bearings." If that was really the case, then the bearing would flow the same regardless if there was 5 PSI or 500 PSI of supply pressure in the gallery. In a pressurized oiling system the total flow is more than just side leakage make-up.

I could accept that you now agree after all the discussions that pressure fed bearings flow more oil, but I don't agree that "you've claimed they flow more with pressure all along" - that's pure rubbish. The discussions in these threads doesn't support that claim one bit. If you believe what you claim you do, then stop making statements saying the pump doesn't force oil flow through the bearings. Every car on the road with a PD oil pump pressurized oiling system forces more oil through the bearings than they would naturally flow simply from their rotational speed - regardless if they need the extra flow or not. That's my whole point.

 

[ZeeOSix]

Originally Posted By: d00df00d
Don't bother, Shannow. You've made your position abundantly clear. Anyone who has the wherewithal to follow this conversation should be able to discern your meaning.

So do you think journal bearings flow more oil as the supply pressure goes up? Or do you believe they will only flow what leaks out the sides regardless of the supply pressure?

 

[userfriendly]

Z06;
If we have low oil pressure in our car engine, and switch to a thicker engine oil, the pressure will rise.
Would that increase in oil pressure also increase the oil flow through the bearings?
If the oil pressure is so high that the pump pressure relief is open, would switching to a thinner oil be a good fix, as more oil would flow through the bearings?

 

[Jetronic]

Higher oil viscosity results in a thicker MOFT. Thicker MOFT results in less clearance on the unloaded side of the bearing, so you'll get less side leakage there, especially as the viscosity will also be higher.

With bearing clearances as low as 0.024mm on the one example I just pulled, a variation in the MOFT can have a significant impact on the side leakage just by itself.

 

[d00df00d]

Originally Posted By: ZeeOSix
Originally Posted By: d00df00d
Don't bother, Shannow. You've made your position abundantly clear. Anyone who has the wherewithal to follow this conversation should be able to discern your meaning.

So do you think journal bearings flow more oil as the supply pressure goes up? Or do you believe they will only flow what leaks out the sides regardless of the supply pressure?

I think you can't tell the difference between an effect and a purpose. Or you're intentionally ignoring the distinction for some reason.

This thread is a classic example of why the real experts mostly left this site or stopped posting years ago. All it takes is one guy with a full head of steam and a slight lack of discernment, and the thread becomes a circus that buries the real expertise under pages and pages of vitriol and presumption.

 

[ZeeOSix]

Originally Posted By: d00df00d
Originally Posted By: ZeeOSix
Originally Posted By: d00df00d
Don't bother, Shannow. You've made your position abundantly clear. Anyone who has the wherewithal to follow this conversation should be able to discern your meaning.

So do you think journal bearings flow more oil as the supply pressure goes up? Or do you believe they will only flow what leaks out the sides regardless of the supply pressure?

I think you can't tell the difference between an effect and a purpose. Or you're intentionally ignoring the distinction for some reason.

This thread is a classic example of why the real experts mostly left this site or stopped posting years ago. All it takes is one guy with a full head of steam and a slight lack of discernment, and the thread becomes a circus that buries the real expertise under pages and pages of vitriol and presumption.


Ignoring the distinction? ... do you know the reason why these discussions have occurred? If you don't know the whole history behind these discussions over multiple threads then I suggest you go read all the other threads before jumping in.

And you never answered my question - what's your "discernment" on the subject matter concerning pressure fed bearings? BTW, nobody is always a "real expert" with "real expertise" ... that includes everyone here. Everyone here has something to learn at some point, regardless of how much of an "expert" they think they are.

 

[userfriendly]

Zee0six;
Try un-plugging yourself for a minute, then plug yourself back in.
If that doesn't work, try 78 rpm for a minute, then 33 1/3 and back to 45 rpm.

 

[ZeeOSix]

Originally Posted By: userfriendly
Zee0six;
Try un-plugging yourself for a minute, then plug yourself back in.
If that doesn't work, try 78 rpm for a minute, then 33 1/3 and back to 45 rpm.


Maybe someone should play a different record instead, and take the one he's been playing and throw it against the wall.

 

[Shannow]

Originally Posted By: ZeeOSix
I could accept that you now agree after all the discussions that pressure fed bearings flow more oil, but I don't agree that "you've claimed they flow more with pressure all along" - that's pure rubbish. The discussions in these threads doesn't support that claim one bit.



Zee0Six, if you go back outside the threads tht you've hijacked, you will see that I'm pretty conversant in managing bearings, and some big ones, and have a sound unsderstanding on how to push flows around for temperature control for various purposes.

e.g.
* a 500MW turbine, new bearing installed at the design point, and it ran hotter than I wanted, so reviewing the oil supply system, couldn't play on supply side, so removed the top cap, skimmed 0.002" off the top, reinstalled and got the temperatures back where I wanted them (sub 90C outlet temps, 45C rise across the bearings)...clearly, increasing "flow", or side leakage if you will reduced the operating temperature of the bearing...see, I get it .

Another turbine, this one considerably larger, and we were having issues with it's stability (it was close to the unstable region in bearing characteristic number. In that case, we did some experiments with oil supply temperture, and found that increasing the supply temperature (average film temperature, and thus lowered viscosity and MOFT) could cause the shaft whip impact on the bearing spectrum to reduce markedly. On THAT one, changing the bearing design to increase temperatures would have narrowed the clearances, increasing MOFT, so the solution was supply pressure. Bearing supplied by a header at 45(ish) psi, and eac bearing supplied through an orifice. Dropping the orifice size by around 20% (YES, reducing the supply pressure AT the bearing), increased the average operating temperature, dropped the viscosity (in that bearing only), stiffened the oil wedge, and eliminated the whip that was occurring.

Clearly, I've got runs on the board in thermal management of bearings, and can/have changed any of the bearing characteristics to achieve my goals.

So your claim that I don't understand them is plain wrong...I've got the runs.

 

[Shannow]

OTOH,
introducing Hagan Poussielle stationary shaft equations, and being fixated on stationary shaft and pre-oiler zero speed examples, and considering that all flow paths were purely resistive (rotational speed irrelevent, you only picked up the speed part late in that game) would indicate that your ACTUAL experience in this area is limited, and it was grasping at textbooks for the time that you told me to

Originally Posted By: ZeeOSix
First of all, learn how to do quotes.


I knew it was going to be downhill right from that very first snide...you weren't (and as evidenced by the threads you hijack aren't) interested in anything but slamming and discrediting me.

 

[Shannow]

Hope I get these quote things right...

Originally Posted By: ZeeOSix
Go back and re-read all of these discussions. I challenge you to go find a post of mine where I said journal bearings absolutely NEED to be pressure fed to survive.


Originally Posted By: ZeeOSix
What do you think the whole purpose of a PD oil pump is on an engine? It's to FORCE FEED the bearings. Modern high HP engines have to have FORCE FED journal bearings to make them handle the load and heat and last way longer than if they were not pressure fed.


I know that NEED and "have to" are spelled differently, but they are synonymous in this...

 

[ZeeOSix]

Originally Posted By: Shannow
Originally Posted By: ZeeOSix
First of all, learn how to do quotes.


I knew it was going to be downhill right from that very first snide...you weren't (and as evidenced by the threads you hijack aren't) interested in anything but slamming and discrediting me.


First of all, if you go back and re-read all the threads you'll find that it was you who started with the snide remarks. You think you can do that and not have some in return?

 

[ZeeOSix]

Originally Posted By: Shannow
Hope I get these quote things right...

Originally Posted By: ZeeOSix
Go back and re-read all of these discussions. I challenge you to go find a post of mine where I said journal bearings absolutely NEED to be pressure fed to survive.


Originally Posted By: ZeeOSix
What do you think the whole purpose of a PD oil pump is on an engine? It's to FORCE FEED the bearings. Modern high HP engines have to have FORCE FED journal bearings to make them handle the load and heat and last way longer than if they were not pressure fed.


I know that NEED and "have to" are spelled differently, but they are synonymous in this...


In those quotes I was specifically talking about high performance engines - high specific HP and overall high HP levels. In many other posts I made, I specifically said that not all engines need pressure fed bearings (ie, low HP, low RPM, etc). There was even discussions about why hot rodders used high pressure / high volume oil pumps to cure crank and rod bearing failures. I maintain that engines like those do need to have more oil flow forced through the bearings than they would naturally flow only due to their rotation in order to survive any reasonal amount of time in their extreme use (ie, more than one short race).

If you now claim you agree that pressure fed bearings flow more oil than not, then don't make statements like:

1) "The oil pump is only supplying oil to make up for the bearing's inherent side leakage, which is influenced by viscosity, RPM, speed, diameter, length, load, and diametrical clearance...it's not "flowing" oil through the bearings."

2) "Again, bearing parameters determine the oil make-up requirement...which is what the pump needs to supply, NOT jamming oil through it... "

3) "Again, the function of the oil pump is to provide oil to the bearings, it's not to force it through them.
Bearings draw off from the supply what they need, and the artifact of them needing less than the pump delivery is oil pressure.
No, you don't use pressure to pump the oil through, in spite of how you FEEL it works."

4) "You do not pump oil through a bearing at all..."

5) "The bearings draw oil from a pressurised gallery, to suit their own needs...more pressure won't make the bearing take more within reason."

Here's a graph from one of the links you posted. Note that the bearing flowed 40%~60% more oil with a 1 bar (14.5 PSI) increase in oil supply pressure (2 bars vs 3 bars). As you know, reducing the film temperature increases the oil viscosity and helps maintain a better MOFT which could mean the difference between a bearing failure or not, especially if the bearing is being pushed towards it's limits. As I mentioned before, using supply pressure to force more oil through the bearing certainly can be a design parameter to be used if the temperature can't be controlled effectively in any other ways.

https://www.ricardo.com/Documents/Downloads/pdf/ringpak_comparison_of_predicted.pdf

 

[Shannow]

Originally Posted By: Shannow

I told you, squirter oil flow is based on pressure applied to it, not RPM...asking for an answer to a nonsensical question ?

But here's how much oil a bearing draws...

Pick an L/D ratio (that's length to diameter, make it 1/4 because that's close to engine bearings....make viscosity, make clearance (c), Radius (r), and load (P) and viscosity (u) constant, and change RPM...upwards, and you can see that the normalised flow drops with RPM...

The bearings require less oil, draw less oil from the galleries to make up for side leakage...in bug turbine bearings, they will draw a couple of psi vacuum to attain that make-up flow.

So bearings, all things being equal draw off less normalised flow as RPM increases.

PD pumps provide a linear volume RPM relationship.

So providing a linear flow availability (PD pump) to a reduced requirement for make-up (the bearings) creates more backpressure with increasing RPM, which you read as oil pressure...

Simple, isn't it ?

As can be (very) simply deduced, looking at the slopes of the curves, a cam turning at half speed has a different change in flow characteristic as the mains.

The squirters, obeying regular laws of physics, flow more with this increasing pressure, and the ratio of squirter flow to bearing flow therefore increases...the percentages change, and are not fixed.

Again, asking a nonsensical question (% change in squirter flow versus RPM) in and of itself clearly identifies that you really haven't had the opportunity to grasp fluid dynamics...

Is your position based on science or belief ?

By asking the proverbial nonsensical question, I'd posit that you lean towards the latter.

(and science has proven that when your beliefs stop working, the centres in your brain that respond to pain light up, and you reject it).

 

[ZeeOSix]

Originally Posted By: Shannow
Simple, isn't it ?

Again, asking a nonsensical question (% change in squirter flow versus RPM) in and of itself clearly identifies that you really haven't had the opportunity to grasp fluid dynamics...

Is your position based on science or belief ?

By asking the proverbial nonsensical question, I'd posit that you lean towards the latter.

(and science has proven that when your beliefs stop working, the centres in your brain that respond to pain light up, and you reject it).


The King of making snide remarks.