Ethyl alcohol has been used for many years as a motor fuel when blended with
gasoline, particularly in Europe. From 5 to 20 percent anhydrous alcohol is
used in commercial blends. Alcohol has an octane number of 99 and a higher heat
of vaporization than gasoline, both of which are technologically desirable.
Despite alcohol having only two-thirds the caloric value of gasoline, blends of
up to 15 percent alcohol provide slightly more power and lower fuel consumption
than straight gasoline. This anomaly is explained on the basis of a higher
fuel/air ratio for the alcohol blend. In countries that imposed compulsory
mixing, gasoline/alcohol blends were not readily acceptable by the public.
However, gasoline/alcohol/benzen blends were acceptable, as indicated by
experience in France with a blend consisting of 75 percent gasoline, 15 percent
alcohol, and 10 percent benzene.
Don't argue with me about it, I am just quoting a respected and highly used
"Mark's Standard Handbook of Mechanical Engineers" published by the McGraw-Hill
Book Company, Eighth Edition.
Theodore Baumeister, Editor-in-Chief: Stevens Professor Emeritus of Mechanical
Engineering, Columbia University in the City of New York
Eugene A. Avallone, Associate Editor: Consulting Engineer: Professor of
Mechanical Engineering, The City College of the City University of New York.
Theodore Baumeister III, Associate Editor, Consultant, Information Systems
Department, E. I. du Pont d Nemours & Co.
And about 100 other contributors which in this quote is C. C. Ward, Retired
Chemical Engineer, Bartlesville Energy Research Center, U.S. Bureau of Mines.
Ethyl alcohol is an oxygenate, in other words it gives off more oxygen molecules
that it uses for combustion. This extra oxygen is used by the other fuel(s)
during combustion. This extra oxygen increases the amount of fuel being burned
per charge: i.e. more complete combustion. Less fuel is needed and less material
from incomplete combustion is released via the exhaust. If this increased
efficiency more than offsets the diluted nature of the gasoline, it stands to
that the ethanol will give more power with less consumption. And if you want,
it will also do it on a leaner mixture as the oxygen is in the fuel and not in
the air ingested. Perhaps the author should have used "higher fuel oxygen
ratio" instead of "higher fuel air ratio" but would that have been understood