Is Ethanol Robbing Me Of MPG?

[The Baron]

As you may know, the Commonwealth of Virginia mandates 10% ethanol in every station's fuel tanks.

I've been told this costs us about 10% on efficiency.

What do the experts here say?

[Shawn D.]

Yes. Ethanol provides less energy per unit volume, and the A/F ratios are not the same, so more ethanol is consumed.

This has been known since carburetor days when larger jets had to be used when running ethanol.

[The Baron]

Bollocks!

Is it harder on an engine that isn't a "FlexFuel" vehicle? I'm pretty sure the German engineers who designed my car in the 1980's didn't do so with 10% ethanol in mind.

[Shawn D.]

It'll make it run a bit leaner, but probably not 10% leaner, as the ECU has adjustment available. I don't think 10% counts as "flex fuel" anyhow.

[Daox]

10% seems like a bit much. I loose about 2 mpg or so on the Matrix when using E10. They do this because ethanol burns cleaner than gasoline.

[PaleMelanesian]

Comparing the energy content of ethanol and gas, E10 has 3.2% less energy per gallon. It raises the octane, though, so, as always, YMMV. Studies have shown reductions in the 2-3% range.

[Shawn D.]

Originally Posted by PaleMelanesian

Comparing the energy content of ethanol and gas, E10 has 3.2% less energy per gallon. It raises the octane, though, so, as always, YMMV. Studies have shown reductions in the 2-3% range.

Higher octane than necessary reduces efficiency, as the burn is cooler. Increased octane is of no benefit if there is no pinging/detonation or the ignition can't be advanced to take advantage of it.

[SVOboy]

Originally Posted by Shawn D.

Higher octane than necessary reduces efficiency, as the burn is cooler. Increased octane is of no benefit if there is no pinging/detonation or the ignition can't be advanced to take advantage of it.

While this is true, I think it's fair to say 87 octane e10 is 87 octane in the same was the 87 octane non-ethanol gas was 87 octane before the ethanol mandates.

[NeilBlanchard]

Hello,

I believe that ethanol adds some necessary oxygen to the mix, so it burns cleaner. Whatever the reason, it is there -- something has to replace the MBTE since that crap was/is messing up the groundwater.

[PaleMelanesian]

Interesting to note, MTBE has about 80% the energy of gas, while ethanol has about 67%. So moving from an MTBE mix to ethanol is about the same drop as moving from straight gas to MTBE.

http://www.epa.gov/otaq/regs/fuels/ostp-3.pdf

As can be seen in Table 3-1, the theoretically expected decrease in fuel energy as a result of oxygenate use is in the 2% to 3% range when compared to gasoline. This corresponds to 0.5 to 0.8 miles per gallon for a car that averages 27 miles per gallon. As can be seen from the works cited below, research in this area indicates that any fuel economy loss experienced as a result of oxygenate use agrees with the theoretical prediction for fuel energy loss. Thus, it is reasonable to conclude that any fuel economy loss experienced with oxygenate use is solely a function of the change in fuel composition and the resulting slight decrease in energy content of the fuel.

http://tonto.eia.doe.gov/oog/info/twip/twip.asp

MTBE and ethanol contain about 80 percent and 67 percent, respectively, of the energy in conventional petroleum-based gasoline. The result is that typical oxygenate blending reduces the Btu content of gasoline by two to three percent.