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Posted by Joe Cimoch on Monday, October 27, 2008 at 20:56:20 :
Got this from David:
We deal with partially miscible (soluble) liquids all the time.
As you suspect, the cloudiness is simply the two liquids separating. It's due to tiny droplets of one liquid dispersed in the other.
I'm not sure exactly what's in furnace oil or home heating oil, but it's a mixture of heavy (high molecular weight) hydrocarbons.
Ethanol is miscible with gasoline and kerosene, which is a mixture of 12 to 18 carbon chain hydrocarbons. It is not fully soluble in very heavy things such as motor oil. It may be or may not be fully miscible with furnace oil. The denaturant is usually methanol or methyl isobutyl ketone.
Here's the thing though. Depending upon the source, hardware-store denatured ethanol may contain 4-5% water, depending upon whether it's derived from petroleum (hydration of ethylene) or from fermentation and distillation. The latter can't eliminate the last 4-5% of water because there is what's called a minimum-boiling azeotrope at about 95 or 96 % ethanol. This mixture, the balance of which is water, boils at a lower temperature than pure ethanol, so that's what comes over into the condenser (the denaturant- a few percent- is added next). (There are ways to remove the water but that's additional cost.) A little water is OK for some things such as alcohol stove fuel or shellac thinner, but if the total water amounts to more than say 5% or so, it would take a lot of ethanol to render the oil and water a one phase mixture- perhaps more than 50% (I'm guessing here). Ethanol is more hydrophilic (polar- meaning charge separation in the molecule, like water) than hydrophobic. If any water is present, a large amount of ethanol may be removed from the oil into the more polar phase of the mixture because the ethanol closer to water in these properties than to oil.
Methanol is usually used to dry gasoline. It may be (I should do a test in the lab) that methanol, which is even more polar than ethanol, works by forming a small amount of [methanol + water + some gasoline] which nevertheless separates from the rest of the gasoline, however this solution is probably flammable enough to keep the engine from coughing too much. Ethanol would actually be better than methanol for complete 1-phase solution of the water in the fuel- if the source is pure. It's more difficult to compatible-ize water with heavy hydrocarbons.
The clear layer floating on top sounds like it is mostly ethanol. The fact that it easily ignites suggests this. So it looks like the oil is denser than ethanol (gasoline is not). The fact that the flame is slightly luminous tells me that some oil has dissolved into the ethanol even though it contains some water- which I would expect.
If your engine runs OK I'd not worry about the ethanol. If you keep the tank from getting too low then the ethanol-rich layer will only occasionally get into the engine when it sloshes around and reaches the intake, and eventually it'll disappear. If the engine bucks, the first thing I'd do is add more furnace oil, and in time the ethanol will disappear since some goes into the oil each time you fill up.
Let me know how it goes. If it is a problem you could try a more
hydrophobic alcohol such as isopropanol, but be SURE it is anhydrous-
not the usual pharmacy stuff. (Acetone would do the same thing but it
could damage the seals and/or fuel pump.) I'm not sure how "fussy" a
diesel is about the fuel mixture. Since it uses high compression and
temperature it might handle ethanol better than a gasoline engine, which
I have observed is very "fussy" and will not run well if the ethanol
concentration gets over 50% or so (yes I've tried it) unless adjustments
are made.
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