Letter Re: Advice on Storing E85 Ethanol Fuel

As far as I know, [modern] E85 vehicles [with fuel flash point sensing] can run on pure ethanol (E100 fuel). You can assume there will never be a commercial supply of E100, though, since someone would inevitably try to drink the stuff.As you note, alcohol is hygroscopic, and “If enough water is absorbed, the alcohol separates from the gasoline and goes into solution with the water.” For E85, “enough” is around 20%, so this generally isn’t going to be a problem. – PNG

JWR Replies: Even E10 (10% ethanol) blended gasoline is highly hygroscopic and can absorb 50 times more water than traditional non-blended gasoline. This can be enough to cause hard starting or even engines that won’t run. Water absorption is of particular concern to boat owners. According to fuel-testers.com, one risk with ethanol blends is phase separation. They assert: “With the process of phase separation, two layers of liquid are visible. An upper ethanol-deficient gasoline layer and a lower ethanol-rich (up to 75% ethanol) water layer. It occurs because ethanol is completely soluble in water but only marginally soluble in hydrocarbons. After phase separation, the gasoline layer will have a lower octane number. The fuel also is less volatile.”

And as for someone attempting to drink E100, as long as it is prominently labeled “denatured” and just a small percentage of gasoline or kerosene is added, that is all that is needed to make it unpalatable. Well, perhaps a wino that is already plastered might try it…