Alex,
When did you graduate????? Last year?????? I remember nothing from high
school chemistry!!
Mike
----- Original Message -----
From: Alex Avery <aavery@rica.net>
To: <CarterCM@aol.com>; <ra0618@email.sps.mot.com>
Cc: <datsun-roadsters@autox.team.net>
Sent: Monday, September 25, 2000 10:28 AM
Subject: Re: PING PING
> 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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