straight gas vs. 10% ethanol blend

[kit352]

while vacationing down in the carolina's I noticed i could get gas without the ethanol added to it. I didnt have my test car with me so i couldnt use it but what types of gain would i have seen in regards to mpg. It was only a few cents more per gallon so it may be worth it for people living down there. may also explain why some people have a natural advantage over others who cant get it.

[kit352]

quick checks look like it ends up costing anywere from 3-5% in mpg to use the ethanol blend. for me that equals to about 2mpg. wish i could get it all the time.

[theholycow]

I think it probably varies by vehicle, where some vehicles see a real gain like you describe and others don't, probably due to different technologies and programming.

[kit352]

looks like newer vehicles take better advantage of the ethanol blends while older vehicles like mine suffer more.

[Wyldesoul]

Even with the best vehicle, E10 simply has 3% less energy in it than gasoline, so it is impossible to get any better than a 3% drop in fuel mileage when dealing with E10 vs E0.

http://www.gassavers.org/showthread.php?t=12669

[theholycow]

The energy in ethanol is not extracted exactly the same way as the energy in gasoline. Looking at it from the other point of view, an engine designed to run most efficiently on pure ethanol would lose efficiency when switching to gasoline despite gasoline's increased energy content. Optimum injector size/fuel pressure, compression, and timing are different, as well as probably other things.

So, the actual energy content is only part of the equation.

That said, I really don't buy it when someone says they lose 25% of their fuel economy on E10 vs. straight gasoline. In a very old vehicle I could potentially believe 10%...I imagine it'd have to be more than 30 years old, since my 30 year old car is designed for E10.

[Wyldesoul]

Originally Posted by theholycow

The energy in ethanol is not extracted exactly the same way as the energy in gasoline. Looking at it from the other point of view, an engine designed to run most efficiently on pure ethanol would lose efficiency when switching to gasoline despite gasoline's increased energy content. Optimum injector size/fuel pressure, compression, and timing are different, as well as probably other things.

So, the actual energy content is only part of the equation.

That said, I really don't buy it when someone says they lose 25% of their fuel economy on E10 vs. straight gasoline. In a very old vehicle I could potentially believe 10%...I imagine it'd have to be more than 30 years old, since my 30 year old car is designed for E10.

Even so, a car with an engine which is tuned to run perfectly on E10, vs the exact same car with the exact same engine, but tuned to run perfectly on E0, the engine that runs on E10 is utterly incapable of doing any better than 3% less mpg than the engine running on E0.

E10 simply has 3% less energy in it than E0. You cannot use energy that doesn't exist. If your car is getting less mpg on E0 than on E10, it needs a tune-up, as there is something wrong.

[theholycow]

I agree about the energy content, but in an internal combustion engine most of the energy is wasted. Small differences in waste can result in large efficiency differences.

[slogfilet]

Originally Posted by Biffmeistro

Even so, a car with an engine which is tuned to run perfectly on E10, vs the exact same car with the exact same engine, but tuned to run perfectly on E0, the engine that runs on E10 is utterly incapable of doing any better than 3% less mpg than the engine running on E0.

I think the assumption here is that the same engine, when tuned to perform ideally on both fuels, would have the same efficiency on both. If it does, then yes, E0 wins every time. However, if increasing ro decreasing the amount of ethanol changes the efficiency of your engine, all bets are off.

Most of the BTUs in gasoline (E0, E10, or otherwise) are wasted as heat. If we had engines that operated at 100% efficiency, then yes, E0 would always be better. But since engine efficiency *itself* is a variable, it is possible that a given car could get better mileage on E10 than on E0.

My argument only states that we cannot give a fixed number for the difference in economy between the two fuels. I would agree that in general, E0 will yield better economy. It is very likely, but far from a given.

[SpeedKnight]

To the O.P., where in the Carolinas were you that you found unspiked gas?!? I'd like to lay hands on some to run in my lawn equipment and my motorcycle. My 1995 VW GTi might benefit, as well.