Valvetrain wear...what Rat DOESN'T do...

[Shannow]

And some tests on ACTUAL valve trains that run contrary to those tests.

http://papers.sae.org/860374/

Quote:
The mechanism of overhead valve train wear in moderate to low temperature service was studied using a modified fired V-D test and a motored V-D cam and cam-follower rig. High wear and Sow wear used oils from the fired test gave the correct relative wear in the motored test, indicating the motored test is a valid tool for studying wear mechanisms. Key factors affecting valve train wear were isolated and selectively introduced in a series of motored engine tests. Results from this study showed the expected increase in wear with a decrease in viscosity of unformulated lubricants. Added zinc diaikyldithiophosphate (ZDDP) reduced wear in a low viscosity lubricant and a used oil as anticipated. A high detergent, high wear oil, in an unused state, did not produce significant wear in the motored test even if all of the ZDDP was removed. Significant wear resulted only after exhaust gases (simulated blowby) were fed into the motored engine sump containing the high wear oil. Laboratory simulation of blowby effects showed the importance of wear resulting from oil aging by chemical reactions between the lubricant and blowby gases. This effect is important even when the viscosity of the lubricant is otherwise sufficient to preclude wear. Active ZDDP depletion by thermal and oxidative routes contributes to wear. Viscosity losses in the Sequence V-D test and in the fired test were large due to fuel dilution and Viscosity Index Improver shear which can lead to further increases in wear.


http://pij.sagepub.com/content/226/4/306.abstract

Quote:
In the last three decades, there has been a resurgence of interest in reducing friction in the engine valve-train for better fuel economy and improved emissions. Research studies and scientists have developed complex mathematical models and advanced test rigs to understand the interaction between cam and tappet. Most of the experimental valve-train work has been carried out on motored test rig assuming there is less difference in valve-train friction under motored and fired conditions. For complete understanding of the difference of camshaft friction under motored and fired conditions, experiments have been carried out on a real engine under both conditions allowing for the first time the detailed study of the effect of cylinder pressure on exhaust camshaft friction. A new method of directly measuring camshaft friction that offers excellent accuracy is described in this article. The technique uses strain gauges to measure the torque exerted upon the camshaft drive pulley sprocket. The advantage of this method over previous techniques is the instantaneous valve-train friction as a function of crank angle can be measured, simultaneously for both inlet and exhaust camshafts, under motored and fired conditions. Experiments have been carried out for both motored and fired conditions on a single-cylinder gasoline engine. Results are presented for instantaneous and mean valve-train friction as a function of engine speed and oil temperature, indicating a decrease in friction with increase in engine speed and an increase with increase in temperature. A significant difference in valve-train friction between motored and fired conditions was found, especially for the exhaust camshaft.

 

[Trav]

It may be time to look at doing something with the desmodromic valve system again.

 

[Cujet]

And,,,

This is why frequent oil changes remain necessary. We really did not need a test to illustrate that combustion gasses AKA "blowby" contaminates oil and results in much higher wear. This is something many aircraft mechanics and every light aircraft engine overhaul facility know. [100 hour oil changes result in high wear, 25 hour changes lead to extremely long life]

It's also evident in oil lubricated machinery with no combustion process. Transmissions, air compressors and production machinery may be good examples. As they often can be lubricated with modest viscosity oils without ZDDP or other additives and infrequent oil changes. All while exhibiting very long useful life.

GM failed in this, by extending engine oil change intervals of low viscosity oils out to the point which the oil was so contaminated, excess wear and warranty clams were the result.

The solution remains the same as it has ever been. Choose a proper viscosity oil, with proper additives and change it appropriately.

 

[demarpaint]

Originally Posted By: Cujet
And,,,



The solution remains the same as it has ever been. Choose a proper viscosity oil, with proper additives and change it appropriately.

Pretty simple actually.

 

[artificialist]

Originally Posted By: Trav
It may be time to look at doing something with the desmodromic valve system again.
I have heard that making variable valve timing in those engines can be a challenge. That may be why it is on motorcycles but not on cars.

 

[Trav]

They are also very loud at high RPM, that why i said take a look at them again. New technology in hydraulics might offer some solutions that were not available years ago.

 

[userfriendly]

The last sentence in the 2nd quote says it all.
The exhaust valve is opened against cylinder pressure in the "fired engine".
The engine oil is also hotter and therefore thinner.

My conclusion from the two quotes Shannow posted, is that engine oil viscosity plays a major roll in valve train wear.

Case in point, the exhaust valve train in a two-stroke locomotive engine surviving with a zinc-free lubricant.

 

[RoadRaceJosh]

Those 2-stroke-cycle EMD engines do open the exhaust valves against residual cylinder pressure. If they didn't the exhaust would go into the cylinder ports. They also have roller followers and don't need the ZDDP for anti-wear. https://www.youtube.com/watch?v=kVxmRQL4pO4

 

[turtlevette]

Originally Posted By: userfriendly

The engine oil is also hotter and therefore thinner.

.


Naw, shannow will tell you its the shear that causes the real heat.

 

[userfriendly]

Yeah, I thought of that after I posted.
OK, the engine parts, in this case the cam & followers are hotter on a running engine.
Maybe not hot enough to activate the additive package when the oil runs over them, but hot enough to spring the VIIs which result in temporary shear, making mono-grades the best. (again)

 

[Lex94]

I remember a study posted by Shannow....

The 40 grade oil with no AW additives did better than the 30 grade oil with AW additives. Makes one want to go to a mono-grade with low NOACK, HTHS >3.5, and change more often.

Maybe I will just run Mobil 1 FS 0w40 in everything if it proves shear-stable.

 

[Shannow]

Originally Posted By: turtlevette
Originally Posted By: userfriendly

The engine oil is also hotter and therefore thinner.

.


Naw, shannow will tell you its the shear that causes the real heat.


You've left absolutely zero comment on anything that I've posted the last week to answer your questions...

Firstly, you've never explained why my Caprice, at 100km/h, exactly the same road load, has 30C+ increase in oil temperature at 4,000RPM in "2" versus 1,700RPM in "D"...all in the space of a 10 minute drive...you pull in some "fire" "frequency" thing, but can't pull it together into a cogent argument.

But given that my experience/measurements can be overwritten by your "feel" for what things "should" look like...

http://wrap.warwick.ac.uk/3494/1/WRAP_THESIS_Fenton_1994_1.pdf

Quote:
The results of these tests showed that the rise in oil temperature was more greatly influenced by higher engine speeds than by an increase in load. Similar results were found by Andrews et al, whose work on Spark Ignition (SI) engine warmup and the influences of water and oil temperatures on engine emissions. Both papers attributed the influence of the engine speed on overall oil temperature, to the increase in oil temperature within the bearings.The rise in oil temperature of the oil film in the bearings was a result of the increase in oil film shear at high rotational speeds.


Quote:
A comprehensive series of engine tests was carried out on a Renault F2N 4 cylinder 1.7 petrol engine to validate the model and to provide the required temperature measurements. The results from the simulation runs and the engine tests indicated similar results to those of Hayashi and Andrews et. al. It was found that the lubricant temperature during warmup was influenced much more by engine speed than engine load.



Quote:
The authors conducted tests on a 1.3 litre petrol engine to analyze the heat transfer paths in crankshaft bearings. The oil flow to the connecting rod was found to be significantly less than through the main bearing. Thus, the big-end bearings ran at higher temperatures than the main bearings, although the temperature difference was controlled by the thermal conductivity of the crankshaft. It was found that 30-50% of the heat generated within the connecting rod was conducted through the crankshaft to the main bearings. The oil flow through the main bearings carried away most of the additional heat.

 

[Shannow]

Originally Posted By: userfriendly
Yeah, I thought of that after I posted.
OK, the engine parts, in this case the cam & followers are hotter on a running engine.
Maybe not hot enough to activate the additive package when the oil runs over them, but hot enough to spring the VIIs which result in temporary shear, making mono-grades the best. (again)


Been trying to find a PDF of the papers quoted for my stash.

Motored engine, the best that the exhaust valve has to open against is the residual pressure from an (near) isentropic compression, a bit of heat addition/loss, and another isentropic expansion back to the valve opening point.

In a fired example, there's the near vertical on a PV diagramme that is the heat addition before the isentropic expansion phase kicks in.

Don't have the paper for this one, but the fired peak cylinder pressure is clearly more than double the motored, and turning up well after TDC, there has already been some expansion and work generated...


Difference between motored and fired is a couple hundred pounds at the cam/lifter interface.

 

[Garak]

That's interesting, Shannow. I downloaded the thesis. I was surprised that load didn't play a more prominent role than it did. Of course, the role of RPM certainly makes sense. I would assume load is significant in the grand scheme of things, of course, but obviously not the primary driver. My air compressor example certainly had steady RPMs, but the heating was higher under load. Of course, the role of RPM is hard to tell there when that's held completely steady.

 

[Shannow]

Garak,
note that I've never once said that the heat of combustion doesn't impact oil temperatures...that's a strawman argument that turtle and his two compatriots use to belittle my statements when they clearly don't have a grasp of the science.

Heat needs to be gotten rid of, and yes, some is transferred to the oil through the bottoms of the pistons and the cooling jets if there...but clearly, the greatest contributor to changes in oil temperature are RPM, regardless of load at the time.

Your compressor example is a bit odd, as compressors are all work, and have no expansion...you get the heat of compression, but then no energy recovery and cooling on the "expansion stroke".

engines with cylinder deactivation rely heavily on the fact that the trapped gas gives some of that energy back on the downstroke.

While on that tangent, if you make a refrigeration system that works solely in the gaseous form, you can compress and heat the gas, cool it, and expand it through a needle valve to get a lo temperature. If you expand it through an expander (like a turbine, but mechanically sealed), you use less power, and get colder temperatures.

 

[slo town]

I'm just glad my BMWs have large sumps (6.9 quarts), and that I use top quality oil, and that I do 3K OCIs on my E46, 5K OCIs on my wife's E90, and 5K OCIs on our 4.5 quart sump Ford and Honda.

Problem solved.

Scott

 

[turtlevette]

Originally Posted By: Shannow
[

You've left absolutely zero comment on anything that I've posted the last week to answer your questions...

Firstly, you've never explained why my Caprice, at 100km/h, exactly the same road load, has 30C+ increase in oil temperature at 4,000RPM in "2" versus 1,700RPM in "D"...all in the space of a 10 minute drive...you pull in some "fire" "frequency" thing, but can't pull it together into a cogent argument.

But given that my experience/measurements can be overwritten by your "feel" for what things "should" look like...




I've been out driving the trans am checking my jetting changes.

Your car makes the oil hotter in a lower gear because you have excess fuel being burned to make the same amount of power. This excess fuel creates more combustion waste heat in the pistons that is carried away by the oil.

You're on some sort of kick right now on the heat of oil shear. It's there but you're making too much out of it.

I've warned you against taking overly simplistic approaches in explaining anomalies. To say that the engine is doing the same amount of work is true but you neglect to change the efficiency parameter. Like taking an ideal pump equation to calculate an unrealistically low number because you're neglecting the fluid friction.

I have a "feel" for things because I have a great deal of experience in a number of areas in addition to having a high level of mechanical aptitude. Do you deny that some people have natural ability?

 

[Shannow]

Confidence and Competence are spelled differently for a reason.

 

[Garak]

Oh, that's true. You never did say that combustion is irrelevant, and no one should take it that way.

The compressor example might have something to do with a couple matters. For one, compressing air puts basically the same amount of heat in a smaller volume, increasing temperatures - the heat of compression, as you say, and that heat isn't going far away. Also, under load, and you know this more than anyone, what is the impact on the bearing and the lubricant?

Now, turtlevette mentions more fuel being burned under high RPMs. So, that has at least some contribution. More RPMs also mean much more friction, as you've mentioned before. From a physics and engineering perspective, how would the work be calculated, at least looking at components of the overall work? While your car is still going the same speed and its mass hasn't changed, nor has your distance travelled change, the distance your pistons have travelled over that time and distance has changed. Essentially, your crankshaft is doing more spins to give your driveshaft the same number of spins as the previous trip. And, in getting those extra crankshaft spins, we also know there is more friction to overcome.

Assuming I'm not getting ahead of myself or totally flubbing up, this is where we have to watch our frame of reference. The driveshaft is ensuring that the same amount of work is being done on the vehicle as a whole. A certain number of driveshaft spins give you a certain number of tire spins, regardless of what the engine is doing to accomplish this. But, from the crankshaft perspective, we're having more spins and overcoming more friction.

 

[Shannow]

Garak,
yes, there's more fuel being burned at 4,000RPM 100km/h than at 1,800RPM 100km/h.

As you say, the vehicle mass hasn't changed...the driveshaft revs per mile is a constant, so the motive power/tractive effort is exactly the same.

The sum of differences then points to only a single factor remaining...losses due to increased engine (and transmission) speed.

The extra fuel burned is burned primarily to overcome the friction that occurs due to the higher RPM...and also to overcome the lesser throttle plate angle and the pumping losses associated with it..