Ethanol/gas mixes--gasoline composition (Audi content=0.1%)

[Achille Riviello <acriviel@mailhost.ecn.uoknor.edu>]

At 10:03 PM 11/13/96 -0600, Psycho Bob wrote:
>On Wed, 13 Nov 1996, Achille Riviello wrote:
>
>>No responses on the first try, so here goes again:
>
>>Believe it or not, here in the oil patch (Oklahoma), it is very hard to find
>>gas with an octane rating above 91.  In Virginia, I used to get 93 at the
>>7-11--go figure...  Now, I normally use a 10% ethanol/gas mixture that rates
>>at 91 octane.  I can't seem to see a difference in performance when I switch
>>from a 91 pure hydrocarbon gas to the 10% ocatane.  Is there any potential
>>problem associated with the ethanol/hydrocarbon mixture with respect to
>>engine performance/reliability in my A4Q?  Thanks in advance.
>
>Well, for one thing, you have a very confusing post here. What's "pure
>hydrocarbon?" (: Both gasoline and ethanol are hydrocarbon-bases stuff.
>What's "10% octane?"
>
>As far as I know, most manuals that come with most current autos have
>figures as to the permissible mixture of partial-ethanol gas. Methanol is
>a no-no as far as I know.
>
>------------- clipped here with virtual scissors --------------
>

Being a chemical engineer, I do know that "pure hydrocarbon" is a
misnomer--however, that is the most simplistic way to distinguish between
dino-fuel and ethanol/dino mix.  Most gasolines are composed of primaily
straight and branched chain aliphatic hydrogen-carbon molecules
("hydrocarbons").  Some ringed (aromatic) products of the
cracking/distillation do exist but are kept low for maximization of heating
value (chemical energy change of combustion, reactants to products) and
minimization of health concerns.  Oxygen in the molecule can tend to cause
inefficient combustion with products including the partially oxidized CO
instead the fully oxidized CO2.  In fact, according to Perry's Chemical
Engineering Handbook, "the composition of an average gasoline is carbon,
83.5 to 85%; hydrogen, 15.0 to 15.8%; nitrogen plus sulfur plus oxygen, 0 to
1.0%."  Hence, "pure hydrocarbon".

Ethanol is a derivative of hydrocarbon, but is not actually defined as a
hydrocarbon.  An alcohol is organic but is not a hydrocarbon.  Hope this
clears up any confusion due to my original post.

Thanks for your reference to the manual, but will it cause significant
performance losses in the A4Q?

Achille Riviello
acriviel@mailhost.ecn.uoknor.edu
83 4000s, 200+k miles
96 A4Q, 698 miles
HK USP 45
HK P7M13
HK P7 PSP
"In a world of compromise, some don't." --HK