Subthread 32:1 vs 50:1 (heat data)

[timberwolf]

Well I tested the head and muffler temps with 32:1, 40:1 and 50:1.

Can anyone explain, I dont have an explaination why more oil = more heat?

Used the same test as for the 260 muffler mod test.
0 degrees C outside today as oposed to 5 C yesterday.
measured oil with a empty syringe

500ml 91 octane gas 10.1ml Stihl oil =~ 50:1
500ml 91 octane gas 12.8ml Stihl oil =~ 40:1
500ml 91 octane gas 16.1ml Stihl oil =~32:1


32:1 with Stihl 260
-----
Idle temp muffler 52 C
Idle temp head 58 C
3 cut test muffler 150 C
3 cut test head 93C


40:1 with Stihl 260
-----
Idle temp muffler 50 C
Idle temp head 53 C -9.4%
3 cut test muffler 145 C
3 cut test head 85C -9.4%


50:1 with Stihl 260
-----
Idle temp muffler 51 C
Idle temp head 50 C -10.9%
3 cut test muffler 147 C
3 cut test head 81 C -11.5%


I repeated the test with an 066 in reverse order

50:1 with Stihl 260
-----
Idle temp muffler 71 C
Idle temp head 45 C -11.1%
9 cut test * muffler 162 C
9 cut test * head 78 C] -10.3%


40:1 with Stihl 066
-----
Idle temp muffler 71 C
Idle temp head 47 C -6.4%
9 cut test muffler 163 C
9 cut test head 80C -7.5%

32:1 with Stihl 066
-----
Idle temp muffler 72 C
Idle temp head 50 C
9 cut test muffler 165 C
9 cut test head 86C


* note had to change 3 cut test to 9 cut test as 3 cuts in an 11- 12" spruce was not even warming up the 066 the extra cuts also equalizes the cut total cut time between the two saws to about 20-25 seconds each three 7 second cuts for the 260 or nine 2-3 second cuts for the 066.

Obsevations

Observed higher head temps with higher oil ratios, exaust temp did not change as much and no significant or measurable change in cutting time or RPM.

Not much heat diference between 40:1 and 50:1, a little more heat at 40:1 (2-3%) but about 10% increase at 32:1.

Timberwolf

 

[StIhL MaGnUm]

Thats some good info to keep in mind...Why more oil more heat because I think the more oil in the mix the less the octane rating will be kinda like trying to run high compression on 87oct it will ping and run really hot at least thats my thought.I know it's like that with cars atleast cause I know my 13:1 compression race car motor will not run on 87,only 110.

Later Rob...

 

[Dagger]

Very good work Wolf..but look out...I tried to explain why this happened a couple a months ago and got scalded by several who just refused to believe it!

Anyway..the "why" is because that gasoline is simply a better cooling medium than oil...80 % or so of the cooling on a 2 cycle is accomplished by the new fuel charge hitting that hot combustion chamber..not the air flowing thru the fins.it is the evaporitive effect that of the fuel that cools the piston.

evaporitive cooling effect can be demonstrated in a simple way by just sticking your finger in a can of gas and then removing it..it feels cool....that is the gas taking the heat out of your finger as it evaporates.
stick your finger in oil and then remove it.....no cooling felt there.
Similiar techniques are cooling/ tempering a bit or a blade in oil vs water. Oil has a lessened cooling effect.
this is of course not exactly how it happens in the saw...but you will understand the cooling effect of gasoline.
now...more oil in the gas...means less gas in the fuel mix...so there is one influnceing factor. less gasoline to cool the piston.
Also less gas in the mix is like running it leaner to a small extent
less parts of gas per parts of air, increasing the burn temp somewhat.

There are hundreds of servicing dealers out there who have been witness to the same test we showed them at service schools across the midwest for years. 3 cans of gas..different mix ratios..and one saw....
higher heat for any IC engine usually means shorter life dont it?


Now......Walker....Ive been thinking on the synthetic deal....
if the lubrication properties of the syn stuff are better than bright stock oils...which they surely must be...why dont we use even less of it than the "old fashioned stuff"? This question is the one that I am pondering now.

 

[Lobo]

Their is a minimum and maximum thickness oil film acceptable. Actually the oil protection film is really suppose to be thin (microcospic) especially with todays tighter tolerances. If you do not have enough of an oil film the rings and cylinder walls will create friction which creates heat. However too thick an oil film causes friction also and also creates additional heat as the film build up between the two fully fills the microscopic space.

 

[timberwolf]

now...more oil in the gas...means less gas in the fuel mix...so there is one influnceing factor. less gasoline to cool the piston.

50:1 is 98% gas 2% oil, 32:1 is 97% gas 3% oil, that is 1% diference. At that if oil as you say is about half as efective as gas in the cooling the effect, the factor is cut in half.

I'm not thinking this 0.5% is the main factor, though it may well contribute. The leaner concept may be a bit more influencial, as chainging the mixture 1% could be more significant.

I did not slightly, I mean maybe 20-40 rpm increase from 32:1 to 40 or 50:1, but I kind of tossed that out as varience.


I need to think on this one.
Timberwolf

 

[bwalker]

its pretty apparent to me why the saw ran hotter. You didnt change the carberator settings yet you decreased the amount of fuel flowing throught the carb by adding more oil. Thats also why your rpms went up slightly.

because I think the more oil in the mix the less the octane rating will be kinda like trying to run high compression on 87oct it will ping and run really hot at least thats my thought.

Rob, Since octane has no influence(accepted scientific fact) on burn temp provided the saw was not detoniting or preigniting what you suggest is not true.

...which they surely must be...why dont we use even less of it than the "old fashioned stuff"? This question is the one that I am pondering now.

My question for you is why would you want to when much peer reviewed evidence exists that suggest that more oil equals more power and less wear. The studies where done. Since you are a engineering guy, Dagger. look up the SAE papers written on the subject. Further more you mentioned oils cooling abilities when quenching hot metals such as done during the process of hardening steel. Doesnt a oil quenched piece yield different properties by drawing heat out faster?


Also this may be out in left field...but what if the engine external temps are higher because the increased oil in between the cylinder piston interface allowed more heat to be leached out of the piston and into the cylinder causeing the higher temp readings. Oil is used as a heat transfer fluid in industry.

Anyhow, with the crude nature of saw carbs and the inability to mantain a constant fuel air ratio between tests I dont see how this test is in anyway valid.

 

[timberwolf]

walker

Good point on the heat transfer, even though it shows a higher temp on the surface of the head, it could be a whole different world inside. Though I would have thought exaust temp would have dropped if more heat was being transfered to the head.

A more advanced test setup would be required here to prove much, oxgine probe to set mixture by and some way of getting an internal temp from the engine.

As you state the fuelil ratio messes with the fuel air mixture and would scew the test.

At least I got some more saw practice, and made a bunch of kindling.

Timberwolf

 

[Crofter]

Wish you had noted wide open throttle no load rpm's for each premix ratio and then repeated everything with the carb set to as near as possible same degree of lean and again measured temps with each gas/oil ratio. If the rpms were slightly higher with the higher oil content mix it would seem to indicate a leaner gas to air ratio despite the higher oil content. I am beginning to think that the evaporative cooling effect on the bottom of the piston might be the explanation for the temperature difference. Wouldn't it be nice to have an exhaust gas analyser to bring the air / fuel issue to a common ground. Makes it so difficult with the oil being both an unburned lubricant and also part of the burning charge. We also tend to feel that since a little bit of oil is good a whole lot should be better. I'll bet your wife wishes you would quit playing with the chainsaw and go back to cutting wood in 16" lengths so she could pile it properly!

 

[Dagger]

Yup..Bwalker is right about the rpms Wolf...they went up because the fuel mixture was leaner.
can aslo say from expierience..that the saw was running pretty rich anyhow if all you got was that small an rpm increase.
Usually you get 150 to 200 rpms from 50 /1 to 32/1
this ,obviously can be cured by simply adjusting the jets to compensate, if you have adjustable jets.

another factor for the higher heat is the increased viscosity of the fuel mixture cause less volume to flow thru the jets/carb at the same manifold vacuum and impulse pressue
Now these are all small factors...but they all add up, and not a single one is in the right direction for less heat.

BWalker...no, oil quenching takes the heat out slower than water quenching...But I must admit to never trying gasoline quenching when tempering!
I am sure however that it would quench faster than water even . however..fluid quenching /heat removal/ is directly related to a fluids evaporitive rate.


I am thinking of something here....just thinking, is the reason that you should use synthetics at a higher ratio because they dont have as good a friction reducing qualities as bright stock?...but we can do this successfully because they burn at a lower temp, and cleaner?...these are questions..not statements...got me wondering about the "why" now!

 

[bwalker]

am thinking of something here....just thinking, is the reason that you should use synthetics at a higher ratio because they dont have as good a friction reducing qualities as bright stock?

Dagger, Contrary to what the amsoil peddlers will say Syns are not "slicker". As I am sure you are aware there real advantage is higher flashpoints, there decomposition path, viscosity index, etc.

BTW I would bet that if you hooked a cylinder head temp gauge up and a lamda sensor to control mixture that you would no differance in burn temps.

 

[timberwolf]

The 260 was a bit rich, I had set it back after the muffler mod. I did not tach the 066 because It is a bit of a pain to hook it to that saw, I will have to pick up one of thouse handy inductive ones you set beside the saw.

As for cooling, it is the change of state that sucks the heat out, water absorbs a little more than 5 times the heat form it's suroundings when it is turned into steam than it does going from 1 C to 99 C (latent heat of vaporization). If the oil is not vaporized until it is ignighted as part of the fuel air mix then it adds nil to evaporative cooling.

Another small factor that comes to mind is oil being a higher order hydrocarbon having longer carcon chains and more carbon liberations during combustion has a higher radiated heat component. hydrogen and methane would be at the oposite end of the spectrum having fewer carbon atoms with gasoliene somewhere in between.

TW

 

[bwalker]

If the oil is not vaporized until it is ignighted as part of the fuel air mix then it adds nil to evaporative cooling.

The oil MUST be vaporized before it will burn. Thats why I theorised that it would draw more heat during the evaporation process than gasoline. The theory may be full of holes.I dunno.

 

[Crofter]

bwalker----- True the oil must be vaporized before it burns but the temperature necessary to vaporise much oil is not reached in a saw till after ignition so the energy is supplied from the burning charge, thus little evaporative cooling effect from the oil. The gasoline, having a phase change temperature in the 150 F. range starts to have an evaporative cooling effect immediately from the venturi, till ignition. The boiling point of a mixture of two liquids with different boiling points will be somewhere in between, so the oil will also hamper the cooling effect of the gasoline portion of the charge. I wonder if this is what is at work here. ????! I still feel that more oil should make the saw run cooler - I wish these statistics would stop interfering with my intuition.

 

[bwalker]

With the temps a aircooled saw runs at I doubt there would be any unevaporated oil in the combustion chamber. Further more if it indead did leach heat to evaporate the oil after ignition would it not lower the combustion chamber temp and ultimatley the saws temp?

 

[Crofter]

Originally posted by bwalker
With the temps a aircooled saw runs at I doubt there would be any unevaporated oil in the combustion chamber. Further more if it indead did leach heat to evaporate the oil after ignition would it not lower the combustion chamber temp and ultimatley the saws temp?

After ignition the temperature is going to rise to approx 2000 F. Any heat gain by the oil would be from here, not from the saw (path of least resistance ). But the phenomenon we are looking at is higher operating temperatures with more oil, not the reverse. Could it be as Timberwolf suggested that the different burning characteristics of an oilier mixture creates a flame that radiates more heat into the head and piston?----But why mommy, WHY? I want to know.

 

[bwalker]

Crofter, I thnk we may be looking into this way to far. I believe its a simple case of leaner mixture with more oil.

 

[Crofter]

Originally posted by bwalker
Crofter, I thnk we may be looking into this way to far. I believe its a simple case of leaner mixture with more oil.

You could well be right. Sure would be nice to have exhaust gas analyser and a fuel use meter that would show actual volume used per rev. otherwise its a lot of guesswork.

 

[bwalker]

I already have a racepak egt, cht, and rpm digital gauge pack. Somebody find a bosch lamda sensor/assoicited hardware and we will be in business

 

[stihltech]

walker

Go to it walker. I would like you to do these tests. you need to prove everybody wrong, so do it.

Thanks again timber for taking the time and posting your tests.

 

[bwalker]

you need to prove everybody wrong, so do it.

Stihltech, I just want to see a valid test thats all.