[W126 Coupe] gasoline chemistry, it ain't simple

[Mark Clemence]

Don't forget that the specific mixture will change in
warm weather if you are located in an area which is
required (by our beloved EPA) to have RFG
(reformulated gasoline).   

--- Richard Hogarth <R_Hogarth at Foundrycove.com> wrote:

> Hey there guys,
> 
>   I'm sure that this is more than we all wanted to
> know about octane,
> tri-flouro pentane (octane) and it's cousins:
> toluene, hexane, butane, and
> all of the other cyclic carbon compounds that we
> crave to fuel our cars and
> our egos. . Although I do find it a particularly
> interesting challenge to
> try and understand things at a more fundamental
> level, this stuff pushes my
> college freshman organic chem  beyond   all  limit s
>   .
> 
> 
> -Richard Hogarth
> 
> 
>  
> 
> 
> Emission of alcohols and carbonyl compounds from a
> spark ignition engine.
> Influence of fuel and air/fuel equivalence ratio.
> 
>  
>
<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&itool=Pu
> bMed_Abstract&term=%22Zervas+E%22%5BAuthor%5D>
> Zervas E,
>
<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&itool=Pu
> bMed_Abstract&term=%22Montagne+X%22%5BAuthor%5D>
> Montagne X,
>
<http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&itool=Pu
> bMed_Abstract&term=%22Lahaye+J%22%5BAuthor%5D>
> Lahaye J.
> 
> Institut Francais du Petrole, Rueil-Malmaison,
> France.
> efthimios.zervas at renault.com
> 
> A spark ignition engine was used to study the impact
> of fuel composition and
> of the air/fuel equivalence (lambda) ratio on
> exhaust emissions of alcohols
> and aldehydes/ketones. Fuel blends contained eight
> hydrocarbons (n-hexane,
> 1-hexene, cyclohexane, n-octane, isooctane, toluene,
> o-xylene, and
> ethylbenzene (ETB)) and four oxygenated compounds
> (methanol, ethanol,
> 2-propanol, and methyl tert butyl ether (MTBE)).
> Exhaust methanol is
> principally produced from fuel methanol and MTBE but
> also from ethanol,
> 2-propanol, isooctane, and hexane. Exhaust ethanol
> and 2-propanol are
> produced only from the respective fuel compounds.
> Exhaust formaldehyde is
> mainly produced from fuel methanol, acetaldehyde
> from fuel ethanol, and
> propionaldehyde from straight-chain hydrocarbons.
> Exhaust acroleine comes
> from fuel 1-hexene, acetone from 2-propanol,
> n-hexane, n-octane, isooctane,
> and MTBE. Exhaust crotonaldehyde comes from fuel
> 1-hexene, cyclohexane,
> n-hexane, and n-octane, methacroleine from fuel
> isooctane, and benzaldehyde
> from fuel aromatics. Light pollutants (C1-C2) are
> most likely formed from
> intermediate species which are quite independent of
> the fuel composition. An
> increase in A increases the exhaust concentration of
> acroleine,
> crotonaldehyde, methacroleine, and decreases these
> of the three alcohols for
> the alcohol-blended fuels. The concentration of
> methanol, formaldehyde,
> propionaldehyde, and benzaldehyde is a maximum
> atstoichiometry. The exhaust
> concentration of acetaldehyde and acetone presents a
> complex behavior: it
> increases in some cases, decreases in others, or
> presents a maximum at
> stoichiometry. The concentration of four aldehydes
> (formaldehyde,
> acetaldehyde, propionaldehyde, and benzaldehyde) is
> also linked with the
> exhaust temperature and fuel H/C ratio.
> 
> 
> 
> Isooctane versus n-octane 
> 
> 
> 
> 3/31/2005 
> 
> name         Wasan
> 
> status       student
> 
> grade        9-12
> 
> location     N/A
> 
> 
> 
> Question -   Why does the combustion of isooctane
> provides more energy 
> 
> than the combustion of n-octane?
> 
> --------------------------------------
> 
> If we compare the number of C-C bonds and C-H bonds
> in both molecules, we 
> 
> would conclude that the total bond energy of the two
> molecules should be 
> 
> the same. But the bond energy in iso-octane is
> higher at the branched end 
> 
> because the two Cs (and the three Hs attached to
> those Cs) are actually 
> 
> going to bump into each other a bit more than if
> they were in a straight 
> 
> chain as in n-octane. This "bumping" causes the bond
> energy of the 
> 
> iso-octane to be higher (it is less stable). Thus,
> when the compounds are 
> 
> completely combusted and both compounds form the
> same number of CO2 and 
> 
> H2O, not only are the bond energies released, but
> the additional energy 
> 
> ofsetting the "bumping" is released as well. Thus,
> iso-octane gives off 
> 
> more energy than n-octane.
> 
> 
> 
> This is especially seen in molecules like cubane
> (look up the structure) 
> 
> where the idea of steric strain is very clearly
> visible.
> 
> 
> 
> Greg (Roberto Gregorius)
> 
>
====================================================================\
> 
> Branched hydrocarbons tend to be slightly more
> stable than un-branched
> 
> hydrocarbons of the same composition: CnH(2n+2)
> primarily due to their more
> 
> compact structure. However, the differences are of
> the order of 2-4 %. For
> 
> example the heat of formation from the elements
> carbon and hydrogen of
> 
> n-octane is -49.82 kcal/mol and for
> 2,2,3,3-tetramethyl butane (very
> 
> branched) the heat of formation is -53.99 kcal/mol.
> The net effect on the
> 
> heat of combustion is of course a much smaller
> percentage due to the large
> 
> heats of formation of the combustion products
> CO2(gas) and H2O(liq), -94.05
> 
> and -68.31 kcal/mol, respectively.
> 
> 
> 
> Vince Calder
> 
> 
> > The MB Coupes Website!
> W126 SEC Mailing List
> Postings remain property of MB Coupes, L.L.C.


If you have any questions regarding the content of this message, please contact me at: snarfone054 at yahoo.com

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