Charlie Springer wrote:

On Sat, 24 Sep 2005 23:45:43 -0700, Roger wrote
(in article ):

Alcohol which has a low octane rating although it keeps getting
credit for a high one, when added to gas up to 10% by volume will
increase
the octane rating of the fuel. 10% seems to be the maximum amount
for increasing the octane rating.

Can you explain the octane rating? In my little world octane is a
chain of 8 carbons with 18 hydrogens hooked on.

It's how resistant the fuel is to spontaneous ignition. (Detonation)
Octane Rating really only applies to numbers below 100.
The detonation resistance of a fuel blend is compared to that of a
blend of iso-octane. An octane number of 100 is equivalent to the
knock resistance of 100% octane.
Strictly speaking, numbers above 100 aren't Octane Numbers, but
Performance Numbers.
It has nothing to do with energy content. The energy content of
petroleum based hydrocarbon fuels is actually fairly constant, at
somewhere around 18,000-19,000 BTU/lb. (Density, of course, varies.
Gasolines are consedered to weigh in at about 6.0 lbs/U.S. gallon,
while Kerosines like Jet-A weigh in at around 6.7 lbs/U.S. gallon.)
In fact, most high octane gasolines have a lower energy content than
low octane fuels. The increased knock resistance allows the engine
to use that energy more efficiently.
Methanols are considered to be around 150 Octane (Well. Performance
Number) - but the energy content is low, so you've got to burn a lot
of it, and it doesn't atomize well, so carburetor jets and injectors
need to be redesigned.

--
Pete Stickney
Java Man knew nothing about coffee.