--part1_bd.7501a00.2700d3cc_boundary
Alex,
Thanks for nicely clarifying the point of the question I tried to raise
(without digging out my old organic chem books). While as Tom pointed out,
gas (or the cocktail of compounds within the range of what refiners are
allowed to call *gasoline*) may all burn at the same rate under controlled
conditions but lower and higher refined grades do perform differently in an
engine. Of course this is muddied by the fact that additives modify the way
gas burns or resists detonation, and also allows refiners to sell a
lower-refined (cheaper-to-produce) product that achieves a higher octane
rating.
An interesting side note. In the early days when unleaded fuel was first
introduced, unleaded was more expensive because it had to be more highly
refined to achieve the octane rating required by the engines of the day,
without adding tetra-ethyl lead (remember Premium used to be called Ethyl).
Most cars didn't have catalytic converters yet but removing the lead cleaned
up emissions. Anyway, back then you could create a *super* fuel of higher
octane than Premium by adding a few gallons of Premium into a tank of
unleaded. The lead in the Premium boosted the octane of the highly-refined
unleaded above Premium levels.
Craig Carter
>>
--part1_bd.7501a00.2700d3cc_boundary
Content-Disposition: inline
Return-path: <CarterCM@aol.com>
From: CarterCM@aol.com
Full-name: CarterCM
Message-ID: <9c.791bc07.2700d109@aol.com>
Date: Mon, 25 Sep 2000 12:02:17 EDT
Subject: Re: PING PING
To: aavery@rica.net
MIME-Version: 1.0
X-Mailer: AOL 5.0 for Windows sub 118
In a message dated 9/25/00 7:31:36 AM Pacific Daylight Time, aavery@rica.net
writes:
<< With lower octane, i.e. 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,
Thanks for nicely clarifying the point of the question I tried to raise
(without digging out my old organic chem books). While as Tom pointed out,
gas (or the cocktail of compounds within the range of what refiners are
allowed to call *gasoline*) may all burn at the same rate under controlled
conditions but lower and higher refined grades do perform differently in an
engine. Of course this is muddied by the fact that additives modify the way
gas burns or resists detonation, and also allows refiners to sell a
lower-refined (cheaper-to-produce) product that achieves a higher octane
rating.
An interesting side note. In the early days when unleaded fuel was first
introduced, unleaded was more expensive because it had to be more highly
refined to achieve the octane rating required by the engines of the day,
without adding tetra-ethyl lead (remember Premium used to be called Ethyl).
Most cars didn't have catalytic converters yet but removing the lead cleaned
up emissions. Anyway, back then you could create a *super* fuel of higher
octane than Premium by adding a few gallons of Premium into a tank of
unleaded. The lead in the Premium boosted the octane of the highly-refined
unleaded above Premium levels.
Craig Carter
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