Re: low-octane gas

[brian whatcott <inet@INTELLISYS.NET>]

At 09:25 6/27/00 -0700, you wrote:
>        You should use the lowest octane rating gasoline that your vehicle
> can tolerate without knocking or pinging under heavy loads or on upgrades.
> Using any higher octane rating fuel is just a waste of money.
>
> Mark Shapiro
>
> http://www.IrascibleProfessor.com

This was certainly the classical advice. These days, many engines have
electronic engine controls which actively sense pinging, and they have the
curious property that they can tolerate to a certain degree, the use of
lower octane gas. At the onset of pinging, they retard the ignition point.
   This adds further strength to Mark's point.

 Another curious feature of gasoline engines is that the lower octane fuel
tends to have a somewhat higher energy density, so there is a second virtue
(besides cost-saving), associated with minimizing octane ratings.

 On this topic, it is sometimes thought that auto engine thermodynamic
efficiency is controlled by a flame temp to ambient temp ratio.

Strictly, the ratio uses a high temperature to derive a temperature range
of interest, and it is that temperature at which heating is 'added'.
This is strongly influenced by the compression ratio of course, whereas
 flame temperature is relatively insensitive to compression.
   Nevertheless, if the compressive heating and the flame heating together
approach a material limit, one is in trouble all the same!


brian whatcott <inet@intellisys.net>
Altus OK