this is a reply i got from a similar question on performance forums...
"It should have been obvious when others said that it "washes right off with gasoline". Why would something that ethanol is selectively dissolving wash off with gasoline? If this were something in rubber or from our fuel tanks, wouldn't that imply that gasoline would dissolve it even more readily than E85?
Alright, so what is this stuff? It is a appears to be a very large petroleum based hydrocarbon, similar to Vaseline. There isn't a single hetero-atom in the molecule (ie, the entire molecule is comprised of hydrogens and carbons), but the molecule is very large. It is also completely aliphatic (ie, only single bonds in the structure - no double or triple bonds). Where did it come from? I can only think of two different sources it could be coming from. It is either something that is mixed in with the rubber hoses that is meant to dissolve away in the gasoline, or it is a trace impurity in the 15% gasoline that is in E85 that wasn't separated during the fractional distillation process. Because it is such a large molecule, it wouldn't be very soluble in ethanol and could easily crash out of solution at the injector.
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Well, here is what I did just so everyone is clear. I filled a 40mL vial with E85 and blew it dry with nitrogen gas and mild heating (about 150*F). After there was no fuel left, I placed it under high vacuum to remove any remaining volatiles for about an hour. I was left with a clear sticky residue that smelled bad - like nasty frying oil. I dissolved this sample in the NMR solvent and analyzed it and it IS the same goo that was on the injector. There was smaller amounts of some other stuff in it as well, but the same peaks I saw in the black goo were in this residue. The black goo IS coming from the E85. It isn't naturally black, though. I suspect it just has soot mixed in with it that is giving it the color.
So the next challenge is figuring out why is this crap in our fuel, and if it is in everyone's fuel (particularly people who aren't having this problem).
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Gum in E85!
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Ok, it isn't chewing gum, of course. I think gum is a generic term for high MW sticky solids. Anyway, if you look at table 1 in this article, it mentions that there is up to 5mg of "solvent-washed gum content"/100mL and up to 20mg "unwashed gum content"/100mL. It think this might be what is sticking to our injectors.
Later in the article it also mentions that mixing E85 and pump gas WILL cause additives to crash out and stick to the injectors and intake runners. I don't think this is what we are seeing since I saw the molecule in a clean sample of E85, but it does open that possibility for others who are mixing.
(link to doc that didn't work)
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So I'm in a brief meeting intermission, but I really am convinced that this stuff is the "gum" mentioned in that article. I found another paper that defined the gum as the residue left after evaporation of the fuel. I'm going to see if I can get ahold of the author of that paper and see if I can figure out exactly what the "gum" is to verify that this is what we are seeing.
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Thiazole, I think have a lead on an exact chemical name to follow up on in solving this mystery. Read the following:
"Overuse of additives with E85 may result in poor vehicle operation. RFA has also made certain recommendations about appropriate detergent treatment of E85. Some detergents, such as polyisobutylene amine, have performed poorly in FFV operation. At some blend levels, these additives may precipitate out of the blend resulting in excessive fuel system deposition."
This info was taken from a pdf I found while researching for a graduate project on E85 I am currently doing, http://www.afdc.energy.gov/afdc/pdfs/41853.pdf
So polyisobutylene amine might be the gum that is precipitating and this is a straight up fuel quality issue and not a fuel environment based one...
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It wouldn't surprise me if gasoline evaporates faster than ethanol in which case you could see this stuff crash out (since it isn't soluble in ethanol). I doubt it happens in the gas tank, though, or the entire fuel system would be covered in this gunk, which I haven't seen. What probably happens is after turning the engine off, whatever E85 is left on the tips of the injectors and in the intake manifold evaporates off leaving behind this gum. After doing this several times, you get a significant amount of gum formation.
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It is dissolved in the E85, but just barely so that it readily crashes out at the injector tip. You can't filter it. It would be like filtering out hard water to remove hard water stains. It can't be done until after it crashes out, but by then it is too late.
You wouldn't want to filter this out even if you could, anyway. The E85 I'm buying has about 10mg of this gum/100mL which means it has about 6000mg per tank. The amount of gum required to clog up an injector is probably only 20mg. The amount to clog a fuel filter would probably be about 1000mg or less. If you could filter it, you'd be clogging several filters per tank. When we scale up the synthesis of a drug, if there is an intermediate that forms a gum and requires filtration, it can actually kill that synthesis and send us back to the drawing board. Gums SUCK and there really aren't many good ways to deal with them other than just dissolving them away.
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Q from someone: I was just thinking that if the gum is a component of the gas that's added to the ethanol to make the E85 (the other 15% that's not ethanol) then adding a little more gas that is more highly refined might push the cross over point far enough that we'd never see it... ?
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Yes - I suspect that when they add the gasoline to the ethanol that the gum is at or very near the saturation point. If you consider that 10 gallons of E85 only has 1.5 gallons of gasoline in it, adding another 1.5 gallons of non-gum containing gasoline like racing gas would decrease the relative concentration of the gum to gasoline by 50% away from saturation. I think this alone would make a big difference and be pretty affordable if it works "
