When running in the midwest, I got about a 10% increase in fuel milage when running the ethanol mixture, and cooler engine temperature, compared to the 91 unleaded fuel available in California and west of the Rocky Mountains. Likely due to the oxygen atom in the alcohol radical.
Ralph-
This seems counter to what I would expect. As Ice correctly states, alcohols contain significantly less energy per unit volume than gasoline. In the extreme, think, if I mix water with my gasoline would I expect to get less performance? Certainly. But the alcohol industry has sold us on it’s “greenness” and championed legislation federally to allow our regular gasoline to be blended with up to 10% of this product. (They are now lobbying for higher concentrations as well).
For reference, since the energy content (BTU/Lbm) of pump grade gasoline is hard to quantify without specific testing and because many refining variables can affect this value, we can equate the energy content of gasoline to that of isooctane, 20,556 BTU/Lbm, higher. By contrast Methanol has an energy content of 9,770 BTU/Lbm, higher and Ethanol has a value of 12,780 BTU/Lbm, higher. Thus both blending alcohols bring less energy to the combustion party, resulting in less power output for a given volumetric fuel input. The mechanical efficiency of our engine is fixed by its design so I would expect that feeding the engine a fuel with less energy content would result in more fuel consumption for a given power output and thus less fuel mileage (at the same power conditions).
Ethanol (C2H5OH) as its molecular formula suggests does “carry” with it an Oxygen atom which helps provide more oxygen for a better combustion process. Ergo it is green because its use promotes a more complete combustion process and less unburned hydrocarbons when the exhaust valve opens to reject the products of combustion. And ethanol does carry a high octane rating (107 Research / 89 Motor) which resists combustion detonation but one can only capitalize on this if the ignition timing is advanced to take advantage of this attribute. I might note here for our readers that even though ethanol has a high octane rating it also has a significantly lower energy value thus exposing the widely held misconception that octane somehow means the fuel is more “powerful” (a myth by the gasoline producers to sell product) which is clearly not the case.
Without modifying an engine (which can and is done, note the Indy cars all run on alcohol for crash/fire protection and run 220+ mph) for a specific gasoline/ethanol mixture, the engine using a fuel without alcohol will make more power and deliver better performance than that same engine using a alcohol blended fuel.
