"Tegger" <tegger@[EMAIL PROTECTED]
> wrote in message
>
> Then MTBE is about twice as efficient as ethanol, so the mixture can be
> leaner?
>
>
> --
> Tegger
"Lean", to me, indicates a mixture which does not have an excess of fuel,
or may
even have an excess of the oxidant.
It requires more oxygen to burn a unit amount of MTBE than it does to burn
the same unit amount of ethanol, and the energy released is consequently
greater.
Most of the energy is derived from the oxidation of the hydrogen atoms in
a
hydrocarbon
to form water. Less energy is derived from oxidation of the carbon to
give
CO2.
The oxygen (in oxygenates such as alcohol and MTBE) just occupies space
and
doesnt
contribute to the energy derived from combustion. So, since the ethanol
has
a higher percentage of oxygen in the molecule, it has a lower amount of
energy that it can contribute
upon combustion.
The "octane rating" takes into account different properties of the fuel,
not
directly related to
the stoichiometry.
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