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

[weimedog]

It isn't about absorbing heat, it is about transferring heat to the cylinder.

I love Symantec wars..

Actually I have to say there really wasn't a lot shown..a sample and now extrapolations and a bunch of speculation.. Certainly a way to start good discussion and build a virtual model of what might have happened in the slice in time..nothing anyone should take too seriously right now..but good conversation just the same.

 

[weimedog]

I will qualify this post with, "I am not a chainsaw mechanic", but do know a little about physics and scientific method.

So:


A. Ounce for ounce, gasoline does not have the heat content of 2 cycle oil. i.e. less BTUS. Much like diesel fuel having more energy than a gasoline. So it stands to reason that the temps would be less elevated.



My 2 cents.

So does this mean that with a two stroke oil that can burn more completely over the short span of time, there is more heat released into the system? Does releasing that heat from the oil possibly both add energy to the system and also promote a more efficient combustion with the combined mix & ultimately a bit more power? This is what I get from your point..is that the message?

A belief I had for years was the even though there may be more BTU's available per unit volume, because of the burn characteristics (rate of combustion) they couldn't be released in time to actually make a positive impact (therefore less btu's available per ounce during the time of combustion & more residue left to be deposited throughout the exhaust system), in fact the energy used to promote the burning of oil along with a slower combustion characteristic taxed the system during the time of productive combustion.

If what you say is true, that might be why my motors running oils like Bel Ray H1R that left way less residue in the exhaust port also seem to run .."crisp" for lack of a better word compared to conventional mixes. I never made the connection. I also never had any dyno data to either confirm or deny..

 

[edisto]

I love Symantec wars..

Actually I have to say there really wasn't a lot shown..a sample and now extrapolations and a bunch of speculation.. Certainly a way to start good discussion and build a virtual model of what might have happened in the slice in time..nothing anyone should take too seriously right now..but good conversation just the same.

I wasn't trying to argue semantics, just trying to get a concept across. Most of the discussion seems to focus on the general phenomenon of heat gain. If it were the result of combustion differences between the fuels, one would expect an equivalent or higher gain in the temperature measured at the muffler.

An increase only in the cylinder temperature is consistent with the piston shedding more heat to the cylinder, which is a good thing.

If you want to argue semantics, what I did was not an extrapolation, just a best fit line through the observed data points...:msp_biggrin:

 

[c5rulz]

So does this mean that with a two stroke oil that can burn more completely over the short span of time, there is more heat released into the system? Does releasing that heat from the oil possibly both add energy to the system and also promote a more efficient combustion with the combined mix & ultimately a bit more power? This is what I get from your point..is that the message?

A belief I had for years was the even though there may be more BTU's available per unit volume, because of the burn characteristics (rate of combustion) they couldn't be released in time to actually make a positive impact (therefore less btu's available per ounce during the time of combustion & more residue left to be deposited throughout the exhaust system), in fact the energy used to promote the burning of oil along with a slower combustion characteristic taxed the system during the time of productive combustion.

If what you say is true, that might be why my motors running oils like Bel Ray H1R that left way less residue in the exhaust port also seem to run .."crisp" for lack of a better word compared to conventional mixes. I never made the connection. I also never had any dyno data to either confirm or deny..

Well the fact that oil is not being ejected out the muffler is good evidence that the oil has in fact been consumed. Many have said that richer mixtures of oil have in fact produced more horsepower, (work) than leaner mixtures. Some of this additional power could be contributed to better sealing of the rings, however the mixture having more energy could also explain this.

 

[weimedog]

I wasn't trying to argue semantics, just trying to get a concept across. Most of the discussion seems to focus on the general phenomenon of heat gain. If it were the result of combustion differences between the fuels, one would expect an equivalent or higher gain in the temperature measured at the muffler.

An increase only in the cylinder temperature is consistent with the piston shedding more heat to the cylinder, which is a good thing.

If you want to argue semantics, what I did was not an extrapolation, just a best fit line through the observed data points...:msp_biggrin:

Those words just have too many letter for a farmer like me to understand...

I don't totally accept (or totally reject actually) the first premise and there fore don't accept the concussion. Don't accept the second one either as there is a lot more surface area exposed over time to the combusted mixture (than just the piston crown) and there maybe changing boundary conditions related to the mixture and the heat transfer does...take time. Also burn rates effect pressure and heat...a derivative of PV=nRT I don't reject your concept either...think all of this is in fact related to the differing burn/combustion characteristics of the change in oil gas mix rations... For that matter it would seem to me (at a simplistic level) if there is more oil between the piston and the cylinder..wouldn't that insulate?

Yours has to be a point to consider in the mix of this discussion though, as the rate of heat transfer thought components to the cooling surfaces have to effect the exhaust temps at some level as they are part of the total system..the question is which makes more difference. (The mechanics of heat transfer or Gas law...pressure heat time all related and must be effected by heat transfer away from the system as that changes temperature..therefore pressure...a big nasty equation to solve that is in constant change over time)

The real question is after all is said and done is the net effect positive or negative over the life of the saw?

 

[edisto]

Those words just have too many letter for a farmer like me to understand...

I grew up around farmers...the one's I knew were a clever lot.

I don't totally accept (or totally reject actually) the first premise and there fore don't accept the concussion.

If it comes down to head injuries, we're all taking this too seriously.

Which premise do you reject? That there is less of an effect on muffler temp, or that an increase in cylinder temp without a corresponding increase in muffler temp is consistent with better heat transfer?

Don't accept the second one either as there is a lot more surface area exposed over time to the combusted mixture (than just the piston crown) and there maybe changing boundary conditions related to the mixture and the heat transfer does...take time.

From what I have read, the majority of the heat is absorbed and transferred by the piston.

Also burn rates effect pressure and heat...a derivative of PV=nRT I don't reject your concept either...think all of this is in fact related to the differing burn/combustion characteristics of the change in oil gas mix rations...

Then why no increase at the muffler?

For that matter it would seem to me (at a simplistic level) if there is more oil between the piston and the cylinder..wouldn't that insulate?

I'd guess it would be a nonlinear relationship...a thin layer transfers heat better, but also generates more heat from friction.

It also could be a simple (?) matter of creating a better ring seal, which should also increase heat transfer to the cylinder.

Yours has to be a point to consider in the mix of this discussion though, as the rate of heat transfer thought components to the cooling surfaces have to effect the exhaust temps at some level as they are part of the total system..the question is which makes more difference.

At some level yes...but in a simplified view, it is a matter of where the piston dissipates the heat...to the cylinder or the charge in the crankcase.

I found a dissertation on heat fluxes in an air cooled 4-stroke that had thermocouples in the cylinder in 4 evenly spaced areas. Cooling the sump oil cooled all quadrants, but there was much less of an effect on the exhaust side. Conversely, an increase in mean effective pressure produced a large increase in the radial heat flux on the exhaust side, but affected the rest of the quadrants only slightly.

 

[weimedog]

I grew up around farmers...the one's I knew were a clever lot.



If it comes down to head injuries, we're all taking this too seriously.

.

LOL that would be why I farm..the concussion thing.

 

[weimedog]

I grew up around farmers...the one's I knew were a clever lot.

Which premise do you reject? That there is less of an effect on muffler temp, or that an increase in cylinder temp without a corresponding increase in muffler temp is consistent with better heat transfer?

That an increase in cylinder temp without a corresponding increase in muffler temp is consistent with better heat transfer as the entire answer to the anomaly.

I would think that is a part, but a smaller part of the equation than the changes relative to different burn characteristics, unless you factor in a better ring seal increases working pressures that will in turn raise the combustion temps as well as slightly increase the heat transfer mechanics. The reasons are along the lines of the speed of heat transfer process relative to the speed of the burn. I don't see that changing a lot because the piston & cylinder remained constant. SO in addition to a possible better conduction "connection" from the piston to the cylinder; a way to get that additional heat is to in fact have a greater delta of temperatures across that heat transfer system, therefore a hotter cylinder OR a longer time at a higher temp in the combustion chamber. Problem for me again is around the relative times it takes things to get to steady state and the speed of this actual process of cycling thru the combustion process. The mechanics might change a little but I suspect the burn characteristics change more than the heat transfer mechanics.

There are a lot of variables I don't begin to understand such as the cooling relative to expansion in the exhaust, the exhaust temps relative to the speed of combustion that would be effected by the duration and intensity of the burn. Since there is so much energy being released from that process, that's where I see the greatest potential for variations along with the fact that the primary change is relative to the combustible material.

It also could be a simple (?) matter of creating a better ring seal, which should also increase heat transfer to the cylinder.

.

Yea...it could be as simple as that...as that would both effect heat in the process by raising the working pressures and changing the heat transfer characteristics. I could certainly buy the combination as a plausible answer...but have a feeling that the fuel/oil ratio's changing both the rate and the amount BTU's release during the combustion process have a role too. How much? No idea. Sort of like changing the timing just a hair. Reminds me of the discussion around ballistics and the characteristics of gun power. Or the discussions relative to Octane and the speed of burn with different gasoline's..as the burn process is a dynamic thing throughout the combustion chamber, where the peak pressures / temperatures happen along the process have to effect the temperature variations around the cylinder. Wonder how many fractions of degree of rotation different peak pressures occur with one mixture vs. the next due to changes in the rate of burn and where in the chamber those peak temperatures are seen due to the actual location of the burn...Also how much the rate and duration of burn effects the exhaust gas temps...If you think all three (( Heat transfer relative to ring seal, burn characteristics..everything from the speed, duration (and there fore temperature and location), and working pressures due to better ring seal )) of these combined account for what was seen..we are on the same page and now the discussion is about the relative amounts each brings to the equation...but

Ultimately the question boils down to what more or less oil does over the life of the saw..more or less wear, more or less power, more or less life.

 

[Trx250r180]

i havent read this thread completely ,so sorry if someone said this ,my old 2 stroke atv engine builders told me 32:1 oil is leaner than the 50:1 so without rejetting you will create more heat ,pour the oil over your finger ,then the gas ,which is cooler ?the oil is only there to lube the bearings and the thicker 32:1 mixture is not going to go through the same size jet hole as fast as the thinner mixture so is actually creating a lean condition ,does this make sence ? the gas actually cools if more is going into the engine ,sounds backwords you would think more oil is richer ,but if less fuel is going through the carb ,will make more exhaust heat

 

[edisto]

I would think that is a part, but a smaller part of the equation than the changes relative to different burn characteristics, unless you factor in a better ring seal increases working pressures that will in turn raise the combustion temps as well as slightly increase the heat transfer mechanics.

The increase in oil in the mix will not improve the burning characteristics.

The reasons are along the lines of the speed of heat transfer process relative to the speed of the burn. I don't see that changing a lot because the piston & cylinder remained constant. SO in addition to a possible better conduction "connection" from the piston to the cylinder; a way to get that additional heat is to in fact have a greater delta of temperatures across that heat transfer system, therefore a hotter cylinder OR a longer time at a higher temp in the combustion chamber.

Again, the additional oil should produce a lower temp because of a less efficient burn. The push to leaner mix is, in part, to reduce emissions.

Problem for me again is around the relative times it takes things to get to steady state and the speed of this actual process of cycling thru the combustion process. The mechanics might change a little but I suspect the burn characteristics change more than the heat transfer mechanics.

Not in a way that would explain increased cylinder temperatures with constant muffler temperatures.

There are a lot of variables I don't begin to understand such as the cooling relative to expansion in the exhaust, the exhaust temps relative to the speed of combustion that would be effected by the duration and intensity of the burn.

If the intensity of the burn is enough to raise the cylinder temp, it should also raise the exhaust temp.

Since there is so much energy being released from that process, that's where I see the greatest potential for variations along with the fact that the primary change is relative to the combustible material.

Which is less combustible with more oil...

Ultimately the question boils down to what more or less oil does over the life of the saw..more or less wear, more or less power, more or less life.

I just reviewed Bell's description of his test looking at changes in hp using 27:1, 20:1, and 16:1 ratios of Castrol R40 In a Suzuki RM125C. Power went up with more oil in the mix. In his words:

"Interestingly, the piston was much cleaner, and the rings showed no signs of gumming up. This indicated that with more lubricant the rings were transferring more heat out of the piston crown, and they were sealing better."

Jennings found the same trend using bean oil as well...more hp and cleaner pistons with more oil in the mix.

More power, less wear, more life.

 

[edisto]

LOL that would be why I farm..the concussion thing.

Like they say, you have to have something wrong with your head to try and make a living buying retail and selling wholesale!

 

[one.man.band]

an observation about the data: could not determine if timberwolf re-tuned the saw during mix ratio trials.

timberwolf posted a data graph on an 026 which i referenced for EGT temps. (have the graph saved somewhere on my PC, but it is lost).

my belief, that similar data graph that lists CHT and EGT's vs. mix ratios is necessary for more accurate conclusions, (if any could actually be made).

we are talking a difference of a couple of tablespoons per gallon.

 

[weimedog]

The increase in oil in the mix will not improve the burning characteristics.

I not as certain as you on this. How do you know? Or is this just a base assumption..I can't just go there and be all happy joy joy that the mystery is solved and I could report to the world with authority I understand the system... It's a simplistic concision and would make sense...but there is evidence to the contrary and I don't think the better ring contact theory by itself makes sense.....sorry. Its an order of magnitude relative to timing thing I haven't yet resolved. So we move on and agree to disagree I guess. Just been around the block enough to know when things are that complex, simple answers are easy and probably have a bit of truth; but usually too...simple. And therefore I have learn over time to be open to look for other things that might effect the outcome....since the fuel mixture has changed, obviously it has some impact on the system. The speed at which this process happens almost approaches a series of adiabatic processes and is why you almost have to look at the mixture differences for part of the answer. I do believe (but don't know) that the increase in oil helps with working pressure and that may have an impact on heat transfer. I do know By changing the working pressure you do effect burn characteristics, adding an altered fuel, those two things alone might generate the anomaly. Also as I said before I'm would be curious about the duration of the burn as a result of either the mixture changes, working compression, or both in concert.. in a simple explanation it might get hotter & build pressure faster and then as the heat is transferred and converted to work the mixture cools..fast enough not to show measurable differences in the exhaust..I don't know, but I would look there if I could.

Not in a way that would explain increased cylinder temperatures with constant muffler temperatures.
.

Haven't heard a clear explanation yet...still wonder about the combination of things I articulated before...better compression, different burn characteristics, possible more efficient heat transfer, possible changes to the duration/ timing of the burn effecting the timing of peak pressures and therefore temperature both to the cylinder and out the exhaust.

If the intensity of the burn is enough to raise the cylinder temp, it should also raise the exhaust temp.
.

Not really..depends of the timing, efficiency, and duration of the burn...

Which is less combustible with more oil...

.

Maybe maybe not..I not as certain as you on this. I simply don't know.

I just reviewed Bell's description of his test looking at changes in hp using 27:1, 20:1, and 16:1 ratios of Castrol R40 In a Suzuki RM125C. Power went up with more oil in the mix. In his words:

"Interestingly, the piston was much cleaner, and the rings showed no signs of gumming up. This indicated that with more lubricant the rings were transferring more heat out of the piston crown, and they were sealing better."

Jennings found the same trend using bean oil as well...more hp and cleaner pistons with more oil in the mix.

More power, less wear, more life.

Doesn't mean his thermodynamic analysis of the process is any more in depth than what we have seen here as he was more interested in the effects, empirical data...so yet again maybe; but I'm not nearly as certain as you.

You can be more efficient in the postings by boiling down to a discussion of the thermodynamics of different burn characteristic possibilities as a result of different oil ratios & mechanical characteristics..or in your case assuming they are not favorable to more heat..save you a lot of cut and pasting! :msp_tongue:

By the way; his findings relative to both power and cleanliness on tear downs is something I seen myself and has been the base for my mixing 32:1 vs. leaner oil mixes for years. (As I have posted over and over again) Nothing has yet shown me I should change, in fact more and more reported information supports that plan as time goes on.

One thing to consider as I think was posted before by another person, there is more energy potential in a unit volume of oil vs. a unit volume of gasoline.....a table one of my old text books has defines it as follows:
Energy content in fuels:

1 lb of Gasoline: 2.2 x 10(to the seventh power..don't have a way to type that notation!)
1 lb of Oil: 2.4 x 10 (to the seventh)


You add oil and thru more efficient combustion get that energy...you will see a heat increase. You have that combustion cycle happen fast enough and complete enough, there won't be as much change in the exhaust...

 

[weimedog]

an observation about the data: could not determine if timberwolf re-tuned the saw during mix ratio trials.

timberwolf posted a data graph on an 026 which i referenced for EGT temps. (have the graph saved somewhere on my PC, but it is lost).

my belief, that similar data graph that lists CHT and EGT's vs. mix ratios is necessary for more accurate conclusions, (if any could actually be made).

we are talking a difference of a couple of tablespoons per gallon.

Bingo. I couldn't agree more. But empirical data has shown me over and over for years that more oil to a point is better than less...I settled on 32:1

 

[Terry Syd]

Getting more hydrocarbons into the cylinder usually isn't the problem, it's getting the air in there to burn the hydrocarbons that takes some effort.

Bugger if I know what increases the head temp. I am reminded of what happens when you add oil to gas and try to run it in a 4-stroke. It lowers the octane and the engine becomes more prone to detonation. Perhaps that may be what is happening, the octane is lowered and the flame front speed increases. That would push extra heat into the engine.

It's interesting to look at Blair's work on combustion speeds in two-strokes. There is a lag of about 10 degrees before the flame front takes off. The best power is achieved when 50% of the mixture has finished burning by 5-10 degrees ATDC. Maybe we are looking at an increase in flame speed that lessens the lag and burn time.

 

[one.man.band]

very good points have surely been made by all, enjoy reading the replies.

trying not to be a party pooper. the data presented leaves as many possible questions, as explanations.

both saws were idled for an unknown amount of time before, and between test runs. i would wager that oil buildup within crankcase during idle time would increase. the high RPM speed under load conditions were of 7 second or 2 to 3 second duration. could that possibly be enough time to clear the engine of latent oil?

blow-by, has not been mentioned yet. not knowing if the saws were at operating temperature could skew results. effect on piston/ring seal is unknown.

agree that more oil is necessary at higher RPM, and higher oil %'s equate to better ring seal. from what reference material i have had the opportunity to read, this has been confirmed.

 

[edisto]

Getting more hydrocarbons into the cylinder usually isn't the problem, it's getting the air in there to burn the hydrocarbons that takes some effort.

From what I've read, the hydrocarbon emissions from 2-strokes with oil mixed in the fuel are about twice that of 2-strokes with sump lubrication.

Bugger if I know what increases the head temp. I am reminded of what happens when you add oil to gas and try to run it in a 4-stroke. It lowers the octane and the engine becomes more prone to detonation. Perhaps that may be what is happening, the octane is lowered and the flame front speed increases. That would push extra heat into the engine.

But wouldn't it push heat out of the exhaust as well?

Turbulence of the flame front has a lot to do with flame front velocity...I wonder if that is a factor with added oil. Increased viscosity should decrease turbulence though.

 

[Brushwacker]

Old thread and still a lot of deep thoughts on the subject.
Early on I believe it was established no carb adjustments were done to tune the saw to the mix ratio and 200 to 300 rpms was gained with more oil and higher temps was a result. I think 1 thing overlooked that would add heat is your spark plug is firing each revelation, thats 200 to 300 times more combustions. per minute burning, certain to make your exhaust hotter and transfer more heat. That and the fact that it flows slower making the hotter burning 0xygen a higher portion explains the heat. Adjust the carb to the same rpm and the Oxygen ratio should be near the same, the amount of combustions per minute being = tempertures will be significantly reduced compared to the original test results.

 

[Terry Syd]

"But wouldn't it push heat out of the exhaust as well?"

Nope, think of when an engine goes into detonation. The cylinder head temp rises and the egts drop. The heat is being forced into the engine components.

 

[c5rulz]

Old thread and still a lot of deep thoughts on the subject.
Early on I believe it was established no carb adjustments were done to tune the saw to the mix ratio and 200 to 300 rpms was gained with more oil and higher temps was a result. I think 1 thing overlooked that would add heat is your spark plug is firing each revelation, thats 200 to 300 times more combustions. per minute burning, certain to make your exhaust hotter and transfer more heat. That and the fact that it flows slower making the hotter burning 0xygen a higher portion explains the heat. Adjust the carb to the same rpm and the Oxygen ratio should be near the same, the amount of combustions per minute being = tempertures will be significantly reduced compared to the original test results.

Excellent point, if more RPM's are realized, it stands to reason that as more fuel is consumed, work done, temps would go up in the same amount of time.