[Diy_efi] Rich detonation?

[Charles Woock]

If you want to see a graph of the ignition timing to AFR relationship, 
download Tunerpro (EFI tuning software) and just look at the spark tables 
for... say... AUJP which is a Chevy 350.  If you study the VE (fuel) and 
spark tables you'll see that at cruising speed, part throttle with 
relatively high manifold vacuum (leaner) the timing is significantly higher 
than at full throttle (richer).  GM also had, but never implemented, a 
"highway mode" which leaned out the fuel.  (to increase economy but 
unfortunately this would have violated some emissions laws).  Highway mode 
required more spark advance.

In the field of race engines, applied science and testing has clearly shown 
that a richer mixture (within limits) burns slower (flame propagation is 
slower).  This is a very generalized statement.  There is of course much 
more to it and every engine/combustion chamber is different.

This is just one link out of hundreds on the net that talk about it.  This 
one isn't the best at describing "why" but it proves the point.  Keep 
looking and you'll uncover many very technical articles on the subject.

http://www.rodandcustommagazine.com/techarticles/0604rc_ignition_timing/

As far as the specific problem... Knock sensor hits at or below AFR of 10, I 
would have to say that is way too much fuel to be useful for gaining power 
(on gas) and that the ignition timing is too advanced for that much fuel. 
But this is just my opinion.

Charles



----- Original Message ----- 
From: "Becker, Damon (Damon)" <damonb at avaya.com>
To: <diy_efi at diy-efi.org>; <diy_efi at diy-efi.org>
Sent: Tuesday, November 21, 2006 12:51 AM
Subject: RE: [Diy_efi] Rich detonation?


> Sorry for not trimming.
>
> Activation energy is being achieved in each case (rich and lean).  I don't 
> think the answer lies in "which molecules break apart under which 
> conditions" type of analysis.  Combustion Kinematics supports the "richer 
> = faster combustion" theory.  To my surprise, there is a rich limit.  I 
> have my degree in this stuff and I, honestly, don't fully understand why 
> that max velocity exists.
>
> Taking the issue one step further to the subject of the thread, I also am 
> not 100% confident in my answer as to why rich detonation occurs.  I 
> suppose I should have made that clear.
>
> My reason this phonemona exists was what makes sense to me, given the 
> research and experience I have, which both of which I think support my 
> conclusions.