snip.......
> It's entirely plausible, Ed.
>
> First consider gasoline. Being a organic substance, it is not a nice
> even mixture of identical molecules. It is a random and often chaotic
> mixture of carbon compounds. These compounds are mostly chains of
> carbon atoms with hydrogen hanging off the unused bonds. Sometimes the
> chains hook back on themselves, but mostly they just intertwine like
> strands in a cotton ball. The shorter strands evaporate and burn easier
> and faster. If I can get the order correct, the number of carbon atoms
> in each molecule goes:
>
> 1)methane
> 2)butane
> 3)propane
> .
> .
> 8)octane (this one's important)
> 12)hexane
>
> Now the way organic material burns is important. When exposed to oxygen
> and energy (we usually use heat, but other methods are possible), the
> oxidation process removes a carborn from the END of the chain, reacts it
> with the oxygen to give up carbon dioxide and water. It's very
> important to consider that the center carbons are safe till all the ends
> are burned off, and none will burn till the ends are exposed to oxygen.
>
> Now, how does that apply to us.
>
> First, liquid gas does not burn except for the very surface...the part
> exposed to oxygen. In the few milliseconds that a molecule will be in
> the combustion chamber of an engine, it has to be exposed to air and
> burn completely. If it has to wait for 1000 neighboring molecules to
> burn away first, it will be halfway down the exhaust before it can even
> get started.
>
> Second, if you let the gas distill, you seperate out the short chains
> from the long chains. Think of dried wheat chaff, stick, and logs. The
> chaff will flash and be gone. The sticks will keep an nice fire going,
> and the logs will burn all night...IF you can get them lit. For a nice
> campfire, you'd want some of all of it. What Mistral experienced was
> the chaff getting sucked in quickly and being burned off with some of
> the sticks, and then the logs clumping up and being sucked in as a tree
> trunk.
>
> Third, the magical 'octane'. The original test for octane was to
> compare the burning of a sample of a fuel in a calibrated engine. The
> engine was calibrate with pure OCTANE, exactly 8 carbon atoms in every
> molecule. You can burn any fuel in an internal combustion engine, you
> just have to get the mixture and spark timing correct. If the fuel
> burns fast like propane, you want to spark later. You'd want to spark
> diesel earlier. A mixture that is either lean or rich of peak will want
> an earlier spark. Higher compression calls for a later spark. In all
> cases, what you're doing is compensating for how quickly the fuel burns
> so that you can get maximum pressure in the cylinder at the right time.
> The problem that was found with the long runners was that it screwed the
> mixture up. Instead of a nice clean flame front that could be
> compensated for, you got a hodgepodge mixture of wheat chaff and oak
> tree trunks.
>
> This is courtesy of an overzealous organic chemistry professor from
> 1987. I may have forgotten a thing or two since then.
>
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