Sources of engine heat and effects of oil viscosity

[bbhero]

Originally Posted by PimTac
Originally Posted by BrocLuno
This whole thick/thin thing is way to "emotional" ... Folks are making oil decisions based on a "feeling" that it will do XYZ ... It's like brand loyalty - fan boys/girls.

What does the engine want? It's based on actual bearing numbers (clearances, wear, operating environment), piston to wall clearances, and type of valve train. If you live in Minnesota it can be one thing. If you live in San Diego, it can be another.

% heat generated by increased viscosity is somewhat pertinent to operating environment, but offset by HTHS capability.

It's all about keeping the metal bits from actually touching in the operating range under the loads that are being experienced. If a NASCAR engine could live on 0W-20, those guys would have made the switch years ago. Drag Racers are trying to live with "light oils" as they know it means less drag ("free HP"), but they are paying a steep price to learn how.

Almost all engines are actually designed around the equivalent of SAE 30. BMW have tried to tighten bearing clearances to allow constant use of thinner oils, ditto Audi. But in both cases it has not been an overwhelming success. Fine for mom chasing the kids and doing in-town errands. But falls on its face when pushed hard for hours on end like cruising across the US western deserts at elevated speeds with the AC on. Which is why all the makes have some caveat somewhere to use heavier oil on track days, etc. It's about the Operating Environment ...



Thank you for this excellent comment BrocLuno. This should be nominated for comment of the year.



Agree PimTac... Great, great post by Brocluno.

 

[benjy]

i am still learning, but oils used in racing as well as race engines are different animals, heck i would think real synthetics would be different. i just read where a PAO base oil transfers 10% more heat, machinery lubrication had the article. even though i only understand some its still good reading IMO

 

[Shannow]

Can you link to the article ?

 

[OilUzer]

Shannow,

I like the energy flow diagram!

Is the brake power (useful energy outout) what's transferred to pistonds mechanically and the rest of fuel energy is wasted?
If so then on top of that there is internal friction from other engine moving parts so another part of "useful" energy is lost due to that? Is that correct?

 

[Shannow]

"Indicated" power is the amount that is actually turned into shaft rotation (you will see references to Indicated Mean Effective Pressure IMEP)...that is evolved from "indicator diagrammes" on steam engines. they would use a chart that had pressure and volume to work out the incremental power "slices" that the piston made throughout the stroke.

"Brake Power" gains it's name from the application of the power unit on a "brake dynamometer". Engine is loaded against a brake and torqu and RPM tell you the power...that's BHP.

So the gap between the Indicated and brake, per the chart is friction.

Indicated is what gets to the pistons, brake is what comes out the crankshaft mounting bolts.

 

[ZeeOSix]

Originally Posted by Shannow
So the gap between the Indicated and brake, per the chart is friction.

Indicated is what gets to the pistons, brake is what comes out the crankshaft mounting bolts.


Yep, it does show that well in that figure. Great find there, it really shows everything that's going on.

Eyeballing the "total friction" branch, it looks like about 2/3 of the total friction heat is from piston friction that gets absorbed into the cooling system. And that piston friction heat is about 1/4 of the total energy absorbed by the cooling system.

 

[CR94]

Originally Posted by OilUzer
I like the energy flow diagram! ...
I agree.

It's important to keep in mind that this sort of breakdown typically assumes an engine at or near its best BSFC (efficiency). At light loads, throttling loss (not broken out separately in this diagram) rears its ugly head. Of course, when you're idling at a stoplight, losses eat everything.

It's amusing that power to drive the oil pump, which some people assume is a major factor, isn't large enough to be broken out separately either.

 

[Shannow]

Oil pump power is (another of) my BITOG hate memes.

The pump takes very very little power...the new variable volume pumps save about the same amount of energy as having a headlight out (but it's still there)...it's the bearing surface friction that the lower viscosity is chasing.

I LOVE those flow diagrammes...they are hard to find

 

[ZeeOSix]

Shannow - thought you said some place that Honda was chasing piston friction, which makes sense if it's 2/3 of the total friction like the flow figure showed.

How was Honda going to further reduce piston friction? Typical methods are to reduce ring size and tension, but doing too much there can lead to oil consumption issues. Reducing the length of the piston skirts and coating the skirts for less friction and to reduce piston slap is another method. So does Honda have anything new up their sleeves?

 

[Shannow]

That was one paper from that R and site I shared.

That was the one mentioning increasing bearing size and block stiffness to allow lower viscosity...which hinted that they are chasing that piston effect, and will reach the bottom of the bathtub, any further reduction in piston friction not meeting the bearing increases.

 

[ZeeOSix]

I would think lower viscosity oil would also reduce some piston friction, but maybe at the expense of more ring and cylinder wear. Maybe higher tech anti-friction oil additives work well for reducing piston friction, and that's were oils are heading since it seems engine design is near maximized.

 

[ka9mnx]

Piston coatings and mid-stroke thermal liner coatings are the future for engine warm-up efficiency. Problem is thermal coatings are anti-productive after engine warm-up.

 

[Bryanccfshr]

Originally Posted by bbhero
Originally Posted by Bryanccfshr
Very Interesting and reassuring that as long as cooling capacity is not exceeded, oil temperature will quickly come down towards coolant temp when rpms drop in water cooled reciprocating engines.

Originally Posted by Shannow
Will try another demonstration using the big end flows...

Take the big end for example...
* 2.38ml/sec oil flow
* 51W heat generation within the bearing
* 147C exit temperature (taking the shell temperature).p

For the exercise, we'll assume that ALL of the oil that leaves the bearing as it passes TDC strikes the piston crown and is heated to 250C (ring belt temperarture).

1.19ml/sec, 1 g/sec roughly, 100C temperature rise.

That scenario would add 167W to the oil...versus the 245W due to friction (148W+97W)

But clearly, not all the oil on the TDC swing hits the piston, most of it hits the walls, transferring the 147C temperature to the jackets, and being cooled a bit before returning to the sump.




Really good point...

And Shannow great post and pictures are very helpful as well.

Qucik question... Do you really work in Mentone?? That is in the least populated county in the lower 48... Loving county.. That is quite aways from Galveston... Needless to say

Yes I am a health and safety professional working as a consultant in the Delaware basin. Started here in May after 10 years in Durango and Farmington. I work a rotational schedule 2 weeks on 2weeks off so the distance is not that bad. Years ago I worked on the Alaska north slope while living in Texas rotationally. Which was much further.

 

[OilUzer]

Originally Posted by ZeeOSix
Shannow - thought you said some place that Honda was chasing piston friction, which makes sense if it's 2/3 of the total friction like the flow figure showed.

How was Honda going to further reduce piston friction? Typical methods are to reduce ring size and tension, but doing too much there can lead to oil consumption issues. Reducing the length of the piston skirts and coating the skirts for less friction and to reduce piston slap is another method. So does Honda have anything new up their sleeves?


What kind of oil or additive sticks better to a mirror like cylinder walls?

I've read that cylinder walls can't be designed like mirror (to reduce friction) because oil needs something to cling on! Is that true? If true, doesn't "Coating the skirts for less friction" goes against that theory!

I'm sure there is always a trade off somewhere!

 

[ZeeOSix]

^^^ Piston skirt coatings - LINK

 

[OilUzer]

Interesting article.

Was hoping someone explain how frictionless can you go without running to issues (the need for oil to cling on to something)

If hypothetically speaking , a zero friction design (piston/skirt/cylinder) was available, would that cause issues or not? This is just a question idk!

Race car application may be different since don't they rebuild or change engine every time?

 

[Shannow]

It's not to cling, it's little tiny reservoirs in the hatching or alusil bores.

 

[PimTac]

Just a hypothetical thought, but if an engine had a zero friction design, would we even need oil?

This might be construed as blasphemy here on BITOG.

 

[OilUzer]

Good point!

 

[OilUzer]

Originally Posted by Shannow
It's not to cling, it's little tiny reservoirs in the hatching or alusil bores.


Alusil .... This alloy was created in 1927 by Schweizer & Fehrenbach of Baden-Baden Germany and further developed by Kolbenschmidt. ...

Germans again ... and I just heard about it

So the garbage i read on the net about not wanting to have mirror like walls so oil can cling on to something is what you get when you read stuff on the net without verifying it. Trust but verify. I wonder where I heard that before