[Cortina-list] We're getting sloppy around here

Peter Pentz peter.pentz at gmail.com
Sat Jan 14 14:29:24 UTC 2012


Norm,
Bryan beat me to it - you are dead wrong on this !  Octane rating is a 
measure of the fuels point of detonation at certain pressures and 
temperatures, and has absolutely nothing to do with the calorific value of 
the fuel, or the flame spread speed. The latter is based on the mix of 
hydrocarbons in the fuel.
Peter

-----Original Message----- 
From: Bryan Engquist
Sent: Friday, January 13, 2012 2:46 PM
To: cortina-list at lotus-cortina.com
Subject: Re: [Cortina-list] We're getting sloppy around here

I think we have discovered "Team Blitz's" Blitz on Engine terms and
terminology!

I was going to write up a "Lesson in Octane Ratings", but I decided to just
say, No Blitz, you are wrong, do your homework, go here for a quick
reference and lesson:
http://en.wikipedia.org/wiki/Octane_rating#Effects_of_octane_rating

If you have any questions, I can answer for you. But in short, as you will
hopefully read and understand, the higher the Octane number (Octane only
goes to 100, high than that has other additives) the less an engine is
likely to knock, or pre-combust which is why it is important for race
engines / engines with high compression. The higher your compression etc ,
the more likely you are to have pre-combustion which is a knock. You can
fix that with timing....but there is a point at which that is bad..

A snippet in case you don't go read the whole lesson so you know the
correct answer: "A common misconception is that power output or fuel
efficiency can be improved by burning fuel of higher octane than that
specified by the engine manufacturer. The power output of an engine depends
in part on the energy density of the fuel being burnt. Fuels of different
octane ratings may have similar densities, but because switching to a
higher octane fuel does not add more hydrocarbon content or oxygen, the
engine cannot develop more power."

"Higher octane ratings correlate to higher activation
energies<http://en.wikipedia.org/wiki/Activation_energy>:
This being the amount of applied energy required to initiate combustion.
Since higher octane fuels have higher activation energy requirements, it is
less likely that a given compression will cause uncontrolled ignition,
otherwise known as autoignition or detonation.

*It might seem odd that fuels with higher octane ratings are used in more
powerful engines, since such fuels ignite less easily. However, detonation
is undesirable in a spark ignition engine, and is signified by audible
"pinging" or in more extreme cases "knock"."*


I suppose it could be worse, talking about Football or Nascrap or something


> Message: 5
> Date: Fri, 13 Jan 2012 13:04:24 -0500
> From: "Team Blitz" <blitz at teamblitz.com>
> Subject: Re: [Cortina-list] We're getting sloppy around here
> To: cortina-list at lotus-cortina.com
> Message-ID:
>        <901880563c8afcc12490314d160fd8c4.squirrel at host155.hostmonster.com>
> Content-Type: text/plain;charset=iso-8859-1
>
> Bryan, exactly wrong.
>
>
>
>
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