jim wrote:
>
> HLS wrote:
>
>>"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.
>
>
> Not according to the EPA. They say it contains less energy than ethanol
> per gallon. Density might be different but doesn't matter - no one
> purchases liquid fuel by weight.
>
>
>
>>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.
>
>
> But octane is far more im****tant to fuel economy and performance. That
is
> more im****tant to how much energy goes to the wheels.
>
> According to the EPA Ethanol and MTBE are almost the same for oxygen
> content, octane and energy content. According to the EPA it takes 10
> percent ethanol to get the same oxygen as 11 percent MTBE.
>
> -Jim
>
>
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the amount of oxygen required to stoiciometrically burn a unit of fuel
is not directly related to the energy yielded by that process. those
are two different properties of a fuel.
nate
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