Nate Nagel wrote:
> 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.
Jim,
Octane rating has very little to do with fuel economy. Performance, yes.
>>
>> 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
>
You probably meant the amount of energy "liberated" when burning; it's
an exothermic reaction after all.
LHV - Gasoline: 42 MJ/Kg
LHV - Ethanol: 26.68 MJ/Kg
LHV - Methanol: 19.95 MJ/Kg
LHV - MBTE: 35.12 MJ/Kg
For 1 kg of air here are some interesting data.
Terms: LHV - lower heating value (liquid fuel into reaction, uncondensed
water va**** in exhaust). The blend energy@[EMAIL PROTECTED]
is the theoretical yield
from a reaction using one kg of air and stoichiometric amount of fuel.
Blend Blend Blend
EtOH % Stoic LHV energy@[EMAIL PROTECTED]
% Stoic LHV energy@[EMAIL PROTECTED]
not shown above, in all cases if the amount of air is reduced to
maintain constant energy@[EMAIL PROTECTED]
more fuel is still needed for all three
oxygenates as the percentage increases.
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