From: jgd@dixie.com (John De Armond)
Subject: Re: Oxygenated Compounds in Gasoline
Date: Sun, 10 Jan 93 19:58:17 GMT
Organization: Dixie Communications Public Access.  The Mouth of the South.

srgxbhh@grace.cri.nz writes:

>Well I do think that ALL of these fuels can burn without oxygen.
>Clue - Another element starting with F can replace Oxygen as the
>oxidant. I am not saying it is used today as a transportation
>fuel oxidant, but that these fuels " can burn without oxygen ".

Chlorine and Bromine will also oxidize hydrocarbons too but that's
not called "burning" is is?

>In general , if people would realise that the oxygenated fuel
>additives are really just partially burned hydrocarbons, they
>would realise they are paying for oxygen that can not provide
>energy. On a mass basis one molecule of oxygen is equivalent
>to 1.33 carbons or 16 hydrogens, so significant amounts of
>potential fuel energy are lost.

Then you would assert that nitromethane (4CH3NO2) is oxygen paid 
for that can not provide energy?  After all, it carries TWO oxygen
atoms.

>However the oxygenates can help manufacturers utilise
>hydrocarbon feedstocks with inferior combustion characteristics
>(eg low octane numbers ) as gasolines. 

Octane rating has NOTHING to do with combustion characteristics.  Period.
Octane rating is the measure of a very specific parameter, the ability
of a fuel to resist explosive combustion.  This characteristic has to
do with how slow the combustion precursor reactions proceed.  When
they are kept sufficiently slow either from "strong" molecules or
the catalytic action of TEL, no knock occurs.

As far as using oxygenates for improving octane of "inferior stock", no.  
It is cheaper to reform or isomerize low quality feedstocks to higher octane 
components than it is to synthesize ethers and blend.  Ether IS used to push 
the octane above that reasonably possible through reforming but the 
base stock surely is NOT inferior.

>The oxygenates have
>significantly different combustion characteristics to the
>common components of gasoline. Consequently, if correctly
>formulated into gasolines the overall emissions may be reduced
>for the targetted engines. 

The only "combustion characteristic" that differs is the stoichoimetric
point is richer, thus causing the overall mix to be leaner.  

>>Specific energy is almost the same for alcohol and gasoline:
>>
>>Gasoline    2.92
>>methanol    3.08
>>Ethanol     3.00

>I'm not certain of the US definition of "specific energy" but here
>it's defined in MJ/kg of the fuel. Typical values for fuels are

Then you are misusing the term.  The definition of specific energy
according to SAE and API is the actual fuel energy delivered to the 
combustion chamber per unit mass of air.  The theoretical specific
energy is computed by dividing the lower heating value by the stoich
air/fuel ratio.  The actual SE is computed from the actual heat of
combustion and the actual air/fuel ratio.  Indeed this terminology
is used throughout the literature in my library. 

Specific Energy Rato, the specific energy of a fuel ratioed to that
of a standard, usually isooctane, is the best indicator of how
much power a fuel will make relative to another.  Consider:

Nitromethane	2.3
Methanol		1.06
Isooctane		1.00

>However these are only a few of the issues, as many other factors
>also come into play when fuels are used in existing internal
>combustion engines, eg Heat of vapourisation, Research Octane Number,
>Motor Octane Number, Boiling Range, Road Octane Number etc. etc.

Cmon guy, quit pitching out empty buzz words.  Of course these things
are important but they are also fairly tightly regulated, at least
in the US and EC markets so that whatever fuel blend is available at
the pump, the characteristics will be similar.  

John
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