2 cycle pre-mix oil

[MolaKule]

Well, I respectfully disagree with the good doctor.

The oil and fuel mix are a "solution." In the above post of 10/8, 12:53, I should have used the word "solution," in place of "suspension."

For example, powdered moly disulfide is "suspended" in gear oil where Moly DTC is in "solution" in engine oils.

As such, the oil is not suspended or being floated in the mix, as in buoyancy, but the mix is one homogeneous mass of differing molecules in solution.

This would imply that the activation energy of fuel was greater than that of oil, and that is not the case.

 

[blano]

Molakule, Thk about it this way. What happens when a mixture of volatile hydrocarbons and unvolitile hydrocarbons is intruduced to a high temp environment. Of coiurse the gasoline part of the mixture evaporates and the oil part is deposited on internal pasrt. Why do you think things like oil migration charts have relevance? Because they chart how long it takes this deposited oil to reach all parts of the engine. Also Why is it that everytime you tear down a two cycle the bottom end is soaked with oil, but not gasoline?

 

[MolaKule]

quote:

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What happens when a mixture of volatile hydrocarbons and unvolitile hydrocarbons is intruduced to a high temp environment. Of coiurse the gasoline part of the mixture evaporates and the oil part is deposited on internal pasrt.

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Both the oil and gas are hydrocarbons in solution that becomes combusted at or right before the compression stroke has completed.

quote:

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Why do you think things like oil migration charts have relevance? Because they chart how long it takes this deposited oil to reach all parts of the engine.

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Oil migration is due to the film tension of the oil. The gas/oil mixture has enough oil and additives in it to lubricate the pin bearings as the crankshaft rotates. The piston/liner also sees this oil/gas solution an a thin film of this solution is deposited to provide lubrication.

quote:

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Also Why is it that everytime you tear down a two cycle the bottom end is soaked with oil, but not gasoline?

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Think about what you just stated. If this were true, the crankcase would fill with oil over time and the mixture would become a very rich oil mixture. You are forgetting that the fuel/oil mix is continually flowing through the engine as a complete mix or solution of hydrocarbons, past the bottom end for lower lubrication and that this same mixture is being compressed and combusted for power. As for the oil in the bottom end, the hot soak associated with the cool down evaporates some gasoline leaving the heavier hydrocarbons behind.

The fuel/oil mix is combusted as one complete entity - no separation.

 

[blano]

"The fuel/oil mix is combusted as one complete entity - no separation."
Mola, You are forgeting that the crank case is a very turbulant place with the general flow being up the tranfers and out the exhaust. This is how oil migrates. It is absolutely deposited in the way I have described. You also dodged the question about the different boiling point components(gas,oil) recating to intense heat-IE crankcase.

 

[blano]

Mola,I for got to ad. Are implying that when the mix reaches the combustion chamber in a liquid state(finedroplets) that it is combusted? If so you would be in for a horably inefficant combustion cycle as changing the liquid premix to a vapor state in order to be combusted would leach huge amounts of heat out of the chamber and provide for really poor throttle response.

 

[userfriendly]

Blano;
1. Have you considered pre-mixing 80:1 AND retaining the oil injector system on the polaris?
2. I have a hard time imagining oil not seperating out of a two stroke pre-mix solution. A 50:1 gasoline/oil mixture could hardly be considered a lubricant.
3. If anyone believes that a 50:1 pre-mix is a lubricant, let them try that mix in the crankcase of their car engine.
4. The gasoline is the carrier of a two stroke lubricant. A solvent delivery system.
5. The oil will burn when the engines get warmed up, until that point, blue smoke.
6. Not all of the oil gets seperated out of the pre-mix, eventually the crank case gets saturated and a balance is reached. The exhaust pipe drips oil if it is not combusted.
I tried 50:1 in MX bikes and quickly went back to 38-42:1. That was all the shell ultra could handle with X rider on X track at X RPM, on X motorcycle.
Better riders on longer tracks and hotter days, 28-32:1.
The 50:1 mix made more noise than power. Lots of RPM, but the engines did not pull. Ring-ding-ding-ding, instead of Bwaaaaaaa.
Point being is the rings will not seal without a lubricant, and a 50:1 gasoline/oil mixture is not a lubricant.

 

[cousincletus]

The 80 something to 1 of the Amsoil 100:1 mix seems to be plenty lubrication for lawn and garden equipment. For the boat, I mix at 100:1. No problems in the five years I've been doing this. Keep in mind that a 2 stroke engine is a completely different design as a car engine and doesn't need the same type of lubrication. Basically, the crankcase is used as an intake, where the gas/oil mix is circulated throughout the engine before it is burned. The engines have needle bearings which require less lubrication. The only thing I have that isn't a premix system is my Seadoo jetski, and I mix an extra ounce of oil per gallon of gas in the tank just to be safe, as it gets run pretty hard.

 

[Blue99]

User – Yes, one of functions of the oil in a 2 stroke engine is to enable the rings to seal & generate compression.

And yes, the optimal mix ratio can vary anywhere from 24:1 to 40:1 for a 2 cycle engines used in MX bikes.

But I don’t understand your point about 50:1 is not a lubricant.

The outdoor power equipment segment of the 2 stoke engine market is huge. The majority of this equipment runs on 50:1 pre-mix. These 2 cycles probably consume more fuel on a daily basis than any other 2 cycle application.

Are you implying that 50:1 is not a valid mix ratio?

 

[MolaKule]

I did not imply that the mix in the combustion chamber was pure liquid, but it is a pretty darn rich vapor consisting of both gasoline and oil molecules. Thanks to turbulence and heat in the crankcase, the fuel/oil mix gets "turbulated" or mixed with air in the crankcase.

"You also dodged the question about the different boiling point components(gas,oil) reacting to intense heat-IE crankcase."

In the most basic 2-cycle engine, an inclined reed valve (or equivalent) allows the liquid mixture to be sucked into the lower crankcase chamber on the upper portion of compression upstroke, since at this time there is a lower pressure in the crankcase. Some of the liquid fuel/oil is mixed with air and so forms a fuel/oil "mist" in the crankcase. Also at this time, this mist lubricates the needle bearings, the piston wrist pin, and the crankshaft end bearings. Because the viscosity of the mix is so low (0.25 to 0.75 cSt), only special ball bearings or needle bearings are used. Due to the turbulence associated with the motion of the crank/piston, and due to convected heat, the energy of the mist is raised. But again, this mixture contains both both gas and oil and is stoiciometrically very rich. After combustion, the piston moves down to expose the exhaust port where a "portion" of the burnt gases are expelled. AT the same time, with the downward motion of the piston, the volume in the crankcase is reduced (compression of mist below the piston in the crankcase) and the fuel/oil mist is further heated. As the piston decends further down in the crankcase, the intake port is exposed and the previously compressed mixture flows into the combustion chamber. Heat of combustion from the previous combustion cycle and heat of compression in the crankcase raises the energy levels of the rich fuel/oil mist, which allows better burning of this rich mist/vapor.

You have to also realize that when the mix is sucked into the crankcase, the fuel/oil mix lowers the crankcase temperature somewhat due to some evaporative cooling. In addition, the crankcase temperature never reaches the temp of the upper combustion chamber, i.e., the head. If it did, fuel vapors would buld up and it would explode. If this were the case, the only hydrocarbons getting to the combustion chamber would be the oil hydrocarbons, which would result in intense smoking, signifying incomplete combustion.

BTW, I am still waiting for a 2-cycle diesel chainsaw which has a little roots blower (for better scavenging), fuel and compressed air injection (for better combustion), and electronic valve timing.

[ October 09, 2003, 11:49 AM: Message edited by: MolaKule ]

 

[userfriendly]

Mola..
So instead of the four strokes going: suck, squeeze, bang, blow,
We have the two strokes going ....bang, blow/suck, suck/squeese, bang, blow.
Now Blano added the expansion chamber bag-pipe wave reflection sound effect, and the crank case transfer, so we end up with something like this:
Bang, blow/bounce/ram, suck/swap, squeeze, bang, blow.

 

[Cujet]

I know for a fact that the oil lubricates the 2 stroke engine in much the same form as it comes out of the bottle. I have seen through transparant windows into the crankcase of 2 strokes. I have also seen 2 strokes run at power without exhaust pipes. There are droplets of oil going everywhere.

Chris

 

[yungman]

Originally Posted By: blano
"Do you tinker with the oil pump output on these as well?"
Yes, although not on all sleds as some pump a exceptable amount. For instance my 98 xcr 440 used a little bit more than a quart of oil per ten gallons of gas. This is right around a 32:1 ratio. My 97 polaris xc 700 with a big bore kitted motor however used less than a quart per ten gallons till I turned up the oiler. I try to shoot for 32:1 as it seems to work well in most motors. I have ran as rich as 18:1 (125 mx bike that was ice raced) in certain applications where I was reving the heck out of the motor in high load conditions. BTW I beleive polaris oil injection pumps are suppose to pump 40:1 at wide open throttle. I would just ditch the injection sytems altogether if it where not for the fact the Polaris injects oil directly into each crank bearing. Good system IMO.


Hi Blano
I am glad you join in this post. I have been reading your comments dated back to 2004. It was very interesting. Can you clarify to me about the flash point of the oil. Is low flash point indicate more solvent in oil or just lighter oil? Do you know anything about the Stihl Ultra whether it is low or high flash point. Is the oil good?

I want to get the maximum longivity from my Shindaiwa C4 engine. I don't care about power at all. I just want to get maximum protection without worrying about carbon buildup, not needing to tear the engine apart. Fouling plugs don't bother me at all. I can change it easily. As I nmensioned, I have Shindaiwa One, Amsoil Saber, Stihl Ultra and Echo Power Blend, anyone I can safely use at 32:1 without ill effect?

Thanks for your time, I was going to sent you a reply on one of the 2004 post after I finish reading that. I'm glad you join in.
Thanks

 

[yungman]

Hi Cujet
I read your post about the Honda GX31 vibration was so bad that the crankcase crack on max rpm. I just bought a new trimmer with this engine and it bother me a lot. I went on the RCuniverse to ask. They are the ultimate engine proving ground. They hot rod engines, they modify engine to the extreme. I ask the vibration problem. The reply is no vibration problem at all. They really hot rod this engine and ran at full throtle all the time. They race those engine, never heard of vibration problem. If the engine can survive that kind of extreme condition, Why is the engine blow up on your test which supposing to be a stock engine only at 8:1 ratio. I am not saying that is not true, but, I did model plane flying before, anything survive them, can survive anything. I might be new in lawn equipment, but I did spend years on cars, hot rod. I do know the basics of engines.
I can understand why professional lawncare people don't like 4 cycle because it is heavier. But for normal consummer like me which is a bigger market, 4 cycle is so much quieter, healthier to use for the operator. Don't have to worry about the mix. I rather choose the 4 cycle. We weekend warrior don't run it hours on out, weight is not a problem. 4 cycle start a lot easier, my Troy Bilt, Shindi C4 and Honda can start at 2 to 3 pulls, My Echo, my Echo, it has been always a workout.

For someone that insist on the good smell of the 2 cycle, more blessing for them. They can also smoke 2 packs of cigarette a day also. But the big segment of market will be consummer that care for their health and don't want to blow up a 2 cycle just because forgetting to put oil, too little oil or the wrong oil.