Alex,
Good information, Thanks.
The burn rate is the same, but the lower octane fuel is less
resistant to pre ignition and denotation. Also the fuels will
be blended differently for summer and winter formula's.
The Octane numbers are actually generated by empirical methods.
Research Octane Number (RON) & Motor Octane Number (MON). They
are tested at different air intake temperature, and different
operating conditions. So in the USA we have an average number
posted (RON+MON)/2. With an lead additive you will not change
the fuel itself, but will increase the Octane numbers.
I used to be able to buy Toulene in a 5 gallon drum, industrial
cleaning fluid. It is also a nice octane booster.
Anyone know any Chemical - Petroluem Engineers? We need for him/her
to buy a Roadster and join the list! <grin>. Of humor My mom
laughs about her six kids, we all went into different fields.
Nursing, Legal, Chemical, Industrial, CPA-accounting, Engineering.
She loves it as when she has a question, she knows who to call!
My brother who has his degree in Organic Chemistry soon realized
most organic chemist had a life span of 45 years... and changed
to electronics. ;-)
Cheers,
Tom
Alex Avery wrote:
>
> My understanding is the reason that lower octane fuels are more prone to
> detonation is not due to faster burn, but due to a more precise light-off.
> That is, detonation is premature light-off, say from a "hot spot" in the
> combustion chamber, etc. as the fuel/air mixture heats from compression
> during the compression stroke. With lower octane, ie. less refined, fuels,
> there is a higher fraction of lower and higher molecular weight carbon
> compounds--such as pentane (5 carbons) and hexane (six carbons) and 11 and
> 12 carbon compounds. Not only do the lower weight compounds light-off at
> lower temperatures, but the more heterogenous the fuel mixture, the more
> unstable it will be. *(octane ratings are, as most know, just measures of
> the percentage of lower and higher carbon compounds in the gas mixture,
> with the eight carbon molecule "octane" being ideal for gasoline engines.)
>
> The reason higher octane, more refined fuels are more detonation-resistant
> is they have more heptane (7 carbons), octane, nonane (nine carbons), and
> less of the smaller and larger carbon molecules and are therefore more
> stable at higher temperatures--therefore, they only ignite when initiated
> by a spark and the whole process is much more predictable with the more
> uniform the fuel mixture.
>
> Alex Avery (a guy who still remembers his high school and college chemistry
> factoids).
>
> At 12:29 AM 9/23/00 -0400, CarterCM@aol.com wrote:
> >Tom,
> >I've scratched my head on this a few times myself. Question...Gas CAN be
> >refined to a higher octane (anti knock) without additives. So, isn't
> >detonation (explosion) just a degree of the same process of rapid burn? So
> >wouldn't the higher octane 'resist' the increase in rate of burn (burn
> >slower) compared to a non-additive standard, as the ignition advances and
> >pressure goes up?
> >
> >Craig Carter
> >
> >In a message dated 9/22/00 7:53:20 PM Pacific Daylight Time,
> >ra0618@email.sps.mot.com writes:
> ><< I have to admit some old myth's die hard. I had for ages believed that
> >premium
> >fuel burned slower. Not so, all the grades burned the same. Premium just had
> >the additives to prevent knock, so you can run a higher spark advance (which
> >creates a higher pressure, hence better performance). Of course you need
> >higher compression to take advantage of the advanced spark to gain the higher
> >combustion pressure. >>
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