Oil Mix Ratios and Cylinder Head Temperatures

[Jonny Quest]

I'm looking for real-life empirical data showing the relationship between oil mix ratios and cylinder head temperatures. We've all heard statements like: more oil in the mix means less fuel -- so the air/fuel mixture is leaner and that makes more heat". Or: "I run 32:1 oil to provide more lubricity and I've never had a saw fail due to a lean mixture condition". I would like to see a real-world scientific evaluation that documents the cylinder head temperature change when running 50:1 vs. 40:1 vs 32:1. Same saw. Same base fuel. Same oil. Same ambient temperature. There seems to be a lot of strong opinions on this matter, but I wonder how much of the various opinions are anecdotal, hearsay, or culturally motivated. Myth or Fact? This might be a good test for Project Farm on YouTube.

JQ

 

[82F100SWB]

More oil can = more heat. But not because of less gas in the mix.
This is how I see it, with a heavy heating background (primary oil heat) as well as a heavy snowmobile background, where serious drag racers measure BTU value and adjust clutching and jetting accordingly.
Mix oil is a higher BTU/gallon than gasoline, so having more of it in your mixture is going to mean your mixture has more potential energy.
This is always going to mean that for the same volume of mixture consumed, there is more potential heat in said mixture.
We all know that some of that oil in the mix drops out of suspension and stays in the bottom end; and not all of it is burnt completely so the increase in heat with increased input BTU isn't going to be as direct as it is in heating, but it will be there nonetheless.
At the same time, richer air/fuel is still going to be colder and lean hotter, that isn't going to change.

 

[Ebarry77]

Check on you tube there was a guy I don't remember his name but his title is your question he did jug Temps at all the mixes.

 

[capetrees]

I'm looking for real-life empirical data showing the relationship between oil mix ratios and cylinder head temperatures. We've all heard statements like: more oil in the mix means less fuel -- so the air/fuel mixture is leaner and that makes more heat". Or: "I run 32:1 oil to provide more lubricity and I've never had a saw fail due to a lean mixture condition". I would like to see a real-world scientific evaluation that documents the cylinder head temperature change when running 50:1 vs. 40:1 vs 32:1. Same saw. Same base fuel. Same oil. Same ambient temperature. There seems to be a lot of strong opinions on this matter, but I wonder how much of the various opinions are anecdotal, hearsay, or culturally motivated. Myth or Fact? This might be a good test for Project Farm on YouTube.

JQ

 

[Ebarry77]

It's a good question I run 40:1. 2 Stroke oil just raises your octane level so it does increase heat but your not going to burn your saw up. But it would be better if he found the answer he wanted himself just trying to help him find it.

 

[buzz sawyer]

More oil = less fuel so you compensate by setting the carb richer which equals more mix and more cooling. I would be surprised to see an appreciable difference in cyl. temp with different mixes.

fwiw, higher octane fuel burns more slowly - to prevent pre-ignition.

 

[82F100SWB]

Octane is resistance to preignition(knock,) just increasing octane level alone isn't going to increase the temperature the fuel burns at, it just makes it harder to light.
It can however delay the start of combustion enough that higher EGT'S will be seen as the combustion event is happening longer after the exhaust port opens.

Often though, higher octane fuels also have different blends and/or additives so they may indeed have increased BTU values. Blanket statements get weird on this one.

 

[burnses]

really reluctant to get into this...but if your rally gonna do it i think you need and EGT in the muffler and a repeatable test procedure......

good luck

 

[bwalker]

fwiw, higher octane fuel burns more slowly - to prevent prpre-ignition.

No, it doesn't.

 

[bwalker]

Octane is resistance to preignition(knock,) just increasing octane level alone isn't going to increase the temperature the fuel burns at, it just makes it harder to light.
It can however delay the start of combustion enough that higher EGT'S will be seen as the combustion event is happening longer after the exhaust port opens.

Often though, higher octane fuels also have different blends and/or additives so they may indeed have increased BTU values. Blanket statements get weird on this one.

No. Higher octane doesnt have anything to do with how easy the fuel ignites.
All pump gasoline have pretty much the same BTU content.

 

[lone wolf]

What burns cooler Ethanol gas or non Ethanol gas. I would worry more about that.

 

[Jonny Quest]

Per Post #3 above, I did a search on YouTube.com and came up with the following:



That was a pretty good test and it provides one data point that appears to support the argument that a higher oil-to-fuel ratio produces more heat during combustion. I intend to continue my search to find other tests that may provide additional data. Regardless of what I find, it is highly doubtful that I will find one definitive and absolute test that kills all discussion. Then we can go back to arguing about synthetic vs. non-syn and Stihl vs. Husqvarna and auto-tune vs. manual. Won't that be nice...

JQ

 

[Ebarry77]

Thus could get fun.

 

[82F100SWB]

No. Higher octane doesnt have anything to do with how easy the fuel ignites.
All pump gasoline have pretty much the same BTU content.

It's easier to explain using those terms to most; but Octane is its resistance to compression inside an engine. The higher the number the more compression it will resist before detonating.

I agree that the majority of non race gas is approximately the same BTU.

 

[rwoods]

Per Post #3 above, I did a search on YouTube.com and came up with the following:



That was a pretty good test and it provides one data point that appears to support the argument that a higher oil-to-fuel ratio produces more heat during combustion. I intend to continue my search to find other tests that may provide additional data. Regardless of what I find, it is highly doubtful that I will find one definitive and absolute test that kills all discussion. Then we can go back to arguing about synthetic vs. non-syn and Stihl vs. Husqvarna and auto-tune vs. manual. Won't that be nice...

JQ

It is hard to conclude anything definitive from that test. I don't know if it was the wood, the chain, the operator, the mix, or some combination thereof, but the saw struggled in the last large wood test - 57 seconds of cutting with 50/1 and 72 seconds of cutting with the 25/1. Until it reaches a terminal temperature, the longer a saw runs the hotter it should get.

Ron

 

[ericm979]

I didn't have the patience to sit through a 15 minute video. Did he retune the carb? If not it's kind of bogus because of course you'd tune the carb properly for each ratio.

Gordon Jennings (motorcycle tuner and writer) did a oil ratio test where he held the engine temp constant on a dyno and saw slightly higher power for the highest oil ratio: www.bridgestonemotorcycle.com/documents/oilpremix6.pdf

Since power and temperature are related when all other factors are the same, you can deduce that the highest oil ratio would run slightly cooler at the same power.

 

[bwalker]

Per Post #3 above, I did a search on YouTube.com and came up with the following:



That was a pretty good test and it provides one data point that appears to support the argument that a higher oil-to-fuel ratio produces more heat during combustion. I intend to continue my search to find other tests that may provide additional data. Regardless of what I find, it is highly doubtful that I will find one definitive and absolute test that kills all discussion. Then we can go back to arguing about synthetic vs. non-syn and Stihl vs. Husqvarna and auto-tune vs. manual. Won't that be nice...

JQ

You can't make more power without heat.

 

[Moondogg73]

Less oil equals less heat. I've tried 25:1 and 50:1. It's a noticeable jump in cyl heat. Might even try Amsoil's 80:1 someday.

 

[Pioneer]

The test winds up being meaningless if he didn't retune it, as the saw will lean out with a thicker oil mixture.

The video did prompt me to start putting my laser temperature gauge in my toolbox though, I should start using it on my saws instead of just my wood stove. Would be nice just to be able to compare their running temperatures.

 

[Porosonik]

Just throwing out a few factiods here:
1). gasoline has about 18,800 BTUs per pound.
2). Ethyl alcohol has 13,000 BTUs per pound.
3). lube oil has quite a bit more latent heat energy than gasoline- I'd guess around 20,000 BTUs per pound.
4). "octane rating" has to do with the speed in which combustion propagates (the rate combustion spreads from molecule to molecule). In a recip engine this is usually said to be 90 feet per second from the point of ignition in normal combustion. Propagation during detonation or "knock" is a lot faster (and HOTTER!). In the old days, they expressed the resistance of a fuel to pre ignition by comparing it to a fuel made up of a ratio of iso octane (which was at that time the most pre ignition-resistant fuel known) to normal heptane (which was about 100% pre-ignition). So, a fuel with an octane rating of 87 would behave the same as a mixture of 87 iso octane and 13% normal heptane. This is why "octane" only goes to 100. For anything higher, resistance to pre-ignition is expressed by "performance number". Octane has nothing to do with latent heat value.

Soooo..... having hard numbers to work with a number of conclusions can be drawn. If you cut 18,800 BTU gas 10-15% with 13,000 BTU alcohol, the result will be a fuel with less BTU value than gasoline- iE: less heat energy available. If all else remains the same, combustion temps will be lower.

Lube oil burns hotter than gas- but the difference between 50:1 (2% oil) and 32:1 (3% oil) isn't all that much. You can do the math and get a good idea what the final effect on combustion temp will be.

Burn speed will be effected by both octane rating and mixture. If the fuel/air mix burns slower, there will be less heat absorbed my the cylinder wall and head, and more downstream by the exhaust port and muffler, given the ignition timing remains the same. This will effect the EGT (greatly!).

Octane rating, since it controls the spread of combustion between molecules, has an effect on burn speed, which has an effect on where in the process combustion happens- in the cylinder or in the muffler.

Sorry for the long winded presentation- I had to know all this stuff to get my Aircraft Mechanics licences 40 years ago.

Porosonik.