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You know how when you pull the cylinder off, there is that nice sheen of oil in
the bottom end? How does the oil separate from the gas and stay behind?
One would think that as it is fully mixed with the gas, it would just continue on
and get burnt. Does it fall out when it reaches a certain temperature? Or is
there a density/weight difference at the micro level that causes it to separate
with the turbulence?
the bottom end? How does the oil separate from the gas and stay behind?
One would think that as it is fully mixed with the gas, it would just continue on
and get burnt. Does it fall out when it reaches a certain temperature? Or is
there a density/weight difference at the micro level that causes it to separate
with the turbulence?
Thats exactly what oil in gas does. It doesnt “mix” with the gas. It gets dispersed evenly in the gas container - totally seperate from the gas.
The oil lubricates the cylinder by sticking to the walls. Thats the entire purpose of it. Over time it will just run down the walls to the crank and pool up. Its not supposed to burn off completely. If that happens youll seize your motor.
If the gas and oil do not mix, then the oil and gas would separate out into two phases in the container which should not happen. Assuming the oil and gas are compatible to begin with, then you should never see it separate in the container and/or the engine.
Anyone have a more tech heavy answer to this?
The Shop
Nothing at all like guy said about vegetable oil. If that were the case, your fueling would be inconsistent and engine would seize up very quickly. It's probably partly why they call it premix.
The majority of the oil is burned with the gas. The majority of the unburned oil is blown out the exhaust.
There's a reason why you have to "clear it out" when you first start up or let a 2 stroke idle for too long and it's because there is not sufficient heat or intake charge velocity to keep the gasoline/oil vapor moving through the engine as a vapor cloud.
Definitely the oil and gasoline mix and go into solution with each other if they are compatible. Once they are in solution it requires some form of energy (eg distillation) to separate the solution back into its starting components.
Gentlemen, thank you for the replies. I finally wrote to Maxima and got the piece of info
that helped clear it up in my pea brain. You guys that said it separates due to a higher flash point
are correct, according to the folks at Maxima. .
The part I couldn't understand was- the fuel charge enters the crank area, then
transfers up to the combustion chamber. So while the charge is in the bottom end, some of
the oil stays behind. There is no burning taking place in the crank area so how does the oil drop out at that point?
But the deal is it separates in the combustion chamber then literally flows down to the bottom end. "Migrates" is the term they use. Some of the oil is burnt, some gets spit out the exhaust
port and some stays behind coating the cylinder and migrates to the bottom end. I suppose y'all were trying to tell me that so I appreciate it but it was the migration explanation that finally cleared it up for me. Thank you!
port and some stays behind coating the cylinder and migrates to the bottom end. I suppose y'all were trying to tell me that so I appreciate it but it was the migration explanation that finally cleared it up for me. Thank you!"
I'm not completely convinced they are correct with the migration from the combustion chamber theory. Every top end I have pulled off I have always observed "clean" two stroke oil pooled in the crankcase area, not black or oil that has come into contact with any of the combustion products.
The fuel/oil droplets which are in the air charge coming through the crank will absolutely collect on the surfaces over time, and that is why you often see a small pooling of that product on the crank.
Most of the oil is vaporized in the combustion process and sent out the exhaust port. What remains is pushed out in subsequent burn cycles (remember that 2-strokes aren't terribly efficient per piston cycle).
Post a reply to: Two stroke oil question- how does it separate?