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JC76, I know this is an old thread, but no one actually answered your question correctly.
What you have at your favorite station is "up to 10% ethanol. The ethanol is added at the individual stations, and the actual content can vary from day to day. The suppliers keep the ethanol separate from the gasoline because ethanol is a contaminate and degrades the fuel and the equipment. Some stations will cheat and exceed 10%. Also, depending on the storage, ethanol contaminated gasoline will absorb water (which can cause rust inside your engine in certain conditions). Just because a sign says it contains up to 10% ethanol does not mean that is what you are getting.
When I have compared the actual content with constant highway driving in my SUV's, I find that the difference in mpg is negligible if ethanol is less than 5%. At 7.5%, I get about a 10% drop in mpg. At 10% mpg, I get a 15% drop. I have experienced as high as a 20% drop, so someone's storage tank was over the label or it had water in it.
It is absolutely true that the energy content per volume of ethanol is less than gasoline. This is basic high school chemistry. It is a bit more complicated into how that gets turned into useful work.
Your assumption that your 7-11's have 10% ethanol and the other stations have less is not a valid assumption.
Just for fun, try this for an experiment. Get a measure, say 6 oz, of nearly pure ethanol (190 proof everclear or some kinds of moonshine), or even rubbing alcohol will work. Get an equal measure of water. Then mix the two together and measure how much liquid you have. You will find that 6+6<12 because the alcohol and water absorb each other. It is fun to do this to middle school kids who think they know that 6+6=12, and see their puzzled look when it does not.
The same thing happens with small amounts of water and the alcohol in gasoline. The water disappears into the fuel, even though hydrocarbons and water do not normally mix.
You can also do the opposite. If you mix larger amounts of water in gasoline, it will pull alcohol out of the gas. (Not suitable for fuel anymore, because some water is still left in the fuel)
Ethanol blend may be less expensive but you get worse mpg's and the stations that actually carry this type of fuel (around me anyway) are far and few. Doesnt make sense to me to use it. You have to drive further just to put it in your tank and get less mpg, so in the end it probably all evens out.
Thanks for the info. Strange though because my Civic and my old Taurus got about an extra 30 miles per tank with the Ethanol blend. I never got less like some of you are claiming, actually the opposite. When I use non-Ethanol blend my mileage drops and my car does not perform as smoothly.
Quote:
Originally Posted by Checkered24
There is less energy density in ethanol, so ethanol blend gas should result in slightly reduced mileage compared to non-ethanol blend.
The only think I can think of is that the car that is getting better mileage on ethanol might be seeing reduced on the non-e because of a computer controlled timing being set for ethanol, and the car not being run long enough on non-e for it to relearn the optimum timing and spark advance/retard for the different fuel. Being of equal octane, I wouldn't have anticipated changes in timing be needed, but I am also not sure what else would cause it.
i believe checkered is right on the money. since the OP is using primarily E10 fuel, the computer has optimized the system outputs, and when you change the fuel it takes time for the computer to reoptimize the system outputs for the different fuel, and one or two tanks of fuel will not do that, thus timing and fuel mixtures are going be off.
Just for fun, try this for an experiment. Get a measure, say 6 oz, of nearly pure ethanol (190 proof everclear or some kinds of moonshine), or even rubbing alcohol will work. Get an equal measure of water. Then mix the two together and measure how much liquid you have. You will find that 6+6<12 because the alcohol and water absorb each other. It is fun to do this to middle school kids who think they know that 6+6=12, and see their puzzled look when it does not.
The same thing happens with small amounts of water and the alcohol in gasoline. The water disappears into the fuel, even though hydrocarbons and water do not normally mix.
If I add 6oz of fluid, no mater what the fluid is, to 6oz of some other fluid, no matter what they may, be you have 12oz of fluid. Just because one or both fluids are dispersed-or absorbed the other does not make the volume any less.
There's less BTU energy content per unit volume of ethanol than gasoline.
Ethanol has the advantage of a higher anti-knock index than the lower grade gasolines, so it's an easier way to achieve an improved anti-knock rating than to use the costly fractions that have higher resistance to detonation. Tetraethyl lead was an inexpensive way to improve anti-knock characteristics, but it has other drawbacks which lead to it's being banned for motor vehicle fuel, although it's still in AVGAS 100LL due to the fed's having mandated that as the fuel to be used in general aviation and the manufacturers designed their engines around this fuel spec (as opposed to older engines designed for 80 Octane or 130 Octane AVGAS). My older engine, designed for 80 Octane AVGAS, actually runs better and cleaner on 91 Octane motor fuel without ethanol than it does on the mandated 100LL).
Since we buy our fuel measured by the gallon, that means we're buying less energy, which is what is used to drive the pistons down in the burning gases expansion in a combustion chamber.
I can still buy non-ethanol gasoline in my area, and my OBD2 vehicles are delivering 29-32 mpg on it in my normal driving.
When I travel regionally, and can only purchase ethanol added gasoline, the fuel mileage drops significantly. Since I drive enough miles to need several tankfulls of fuel before I return to my home marketplace, the ECU has enough start/stop cycles on it to re-learn the optimal fuel economy strategy on the ethanol fuel. It never comes up to what I was getting on the gasoline only fuel. In my marketplace, due to the high altitude, regular gas is rated 85 octane and my Subie's do just fine on it.
Around us it is very hard to find gasoline with no ethanol in it, and it costs a lot more, but it is worth it. Better mileage and less long term maintainence/repair. Ethanol gunks up your fuel system more.
There's less BTU energy content per unit volume of ethanol than gasoline."
This is confusing. snofarmer says "ethanol is less efficient than gasoline" and then sunspirt says "No, you are wrong, ethanol is less efficient than gasoline."
It takes 1.5 gallons of ethanol to provide the energy content of 1 gallon of gasoline.
A gallon of ethanol has 76,000 British thermal units while conventional gasoline has 115,000 Btu. A blended gallon of gas that contains 10 percent ethanol gets 111,100 Btu.
That amounts to a 3.4 percent reduction in energy, which over the course of a year of normal driving would take an additional 40 gallons of E-10 to go the same distance as conventional gas.
Mileage can suffer by about 25 percent with E-85, according to AAA.
Flex-fuel vehicles designed to run on higher ethanol blends (E85 or 85 percent ethanol) do experience reduced miles per gallon.
As a high-octane fuel additive and substitute for MTBE, ethanol enhances engine performance and adds oxygen to meet requirements for reformulated gasoline.
Last edited by snofarmer; 05-04-2012 at 11:46 AM..
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