180Marty wrote:30% ethanol would raise the octane rating about 7.5 points. If you were a engine designer, doing eco boost technology in Detroit, would you rather design for 84 octane that the oil companies like to make or 91.5?
There is a common misconception that octane rating=power rating. It does not, and the two are not even particularly related. Alcohol has 1/3 less energy per unit volume than gasoline. Alcohol has less energy per stoichiometric fuel/air charge than gasoline by a wide margin as well. Adding alcohol to gasoline with the same compression ratio will reduce engine work output. This is due to the enthalpy of the alcohol and the stoichiometric differences. E-30 typically means a power loss of 10% on the same engine at the same volumetric fuel flow. You step on the gas slightly more as a result, and this leads to a higher volumetric fuel consumption. http://en.wikipedia.org/wiki/Gasoline_gallon_equivalenthttp://en.wikipedia.org/wiki/Ethanol_fuel
In addition, ethanol production only yields 30% more energy than it takes to make it. if we all switched to E-30, our national gasoline energy consumption would actually go up by a factor of over two. That's because the EROEI (energy return on energy invested) of gasoline is around 10:1 at present, while for alcohol, it's 1.3. So it works out to (10/1.3*30%)=230% of present gasoline energy consumption to replace 30% of our gasoline with ethanol. You'll find similar conclusions elsewhere- greenies choose lower ethanol EROEI's, the oil folks like to use the best imported oil EROEI numbers.
Brazil can come out way ahead with alcohol- they have an ethanol EROEI of 8:1. The US has not figured out a way to do this.
To use alcohol effectively, one needs to boost the compression ratio of the engine to achieve higher Carnot thermal efficiencies. It's as simple as that. And you can't really bring gasoline fractions in ethanol blends along for the ride. An engine set up for alcohol has a high compression ratio to take advantage of high thermal efficiencies. An optimized alcohol engine will be more efficient than gasoline. A conventional gasoline Otto cycle engine today cannot optimally exploit the Octane number advantage of the alcohol. Newer designs can make progress.
These 'eco boost' engineers in Detroit know full well the limitations of alcohol with conventional engines. What we have today is not a result of stodgy bureaucracy, but real limitations. They would rather design an engine as revolutionary as they can dream it, at a price they can sell. That's what engineers do.
As for mileage with E-blends (page 6), it follows my own experience very closely: http://www.ethanol.org/pdf/contentmgmt/ ... Report.pdf