Dieseling

[Ted Borck <tborck@domain.elided>]

> From: M Edler <m.m.adler@domain.elided>
> Subject: Dieseling
> 
> Okay here is my report on my engine dieseling.  I first put some fuel
> cleaner and that did help some and filled up with 89 octane.  Next I
> filled my tank up again with 92 octane.  It stopped!  This is going to
> suck if I have to run 92 octane all the time (Gas is really expensive
> out here in SF)

Matt,

You're right.  Your engine is dieseling, i.e. the gas/vapor is self
igniting in your engine without benefit of an electrical spark.

But - consider this - the reason that your dieseling stops when using
high(er) octane gas is that high octane gas is formulated to be *less*
likely to self ignite, *less* likely to burn too fast and out of control
(in the engine combustion chamber).  Good combustion means a smooth
controlled burn.  Thus low octane - easy self ignition.

The common fallacy is that high octane gasoline burns hotter and with more
power than low octane.  For the most part this is not true.

By being formulated to be *less* to pre-ignite, and cause "knock" while
running, high octane gasoline allows use of high(er) compresion ratios and
more spark advance, thus more power.  

Older engines' combustion chambers weren't designed for efficient
combustion especially when using compresion ratios higher than 9:1.  

Engineers of that time didn't understand combustion like they do today,
didn't have computer engine controls, and the bean counters didn't have
the gov or racing regulations on their ass to improve gas mileage.

No-one designs engines with hemi-heads any more.  And engines of that time
did not have knock sensors with controls to retard the ignition while
running.

Thus older engines tended to need a lot of spark advance to get the
combustion started early enough to burn at the correct time for maximum
(obtainable) power. 

And as some of you may remember, you use to be able to purchase 103 octane
gasoline (although the way octane is figured today is also different than
when you could purchase 103 octane).

In any event, you could alway do what some of us use to do in Georgia
while running (air/oil cooled) Porsches w/10:1 compresion and over bored
engines in the 1960's. We just poured in a coke bottle (12 oz) of mineral
spirits (12.5 gallon gas tanks) while filling up with high test.  No
pinging - no problem.

Ted Borck	tborck@domain.elided