[Diy_efi] Rich detonation?

[Becker, Damon Damon]

I'm not sure what you mean by "shift to use 4:1".  I'm assuming you mean mass ratio, and "shift" means they moved to using that ratio, instead of being associated with gear shifts.  
 
AFR is definitely a thermal management tool, among other things.  What you say does make sense if you are seeing excessive EGT.  If you can infer exhaust valve temp from an integral of the EGT, then that response would definitely make sense.  This doesn't really have much to do with detonation, though.  
 
I'm sure the exact AFR (or lambda) that peak combustion speeds happen differ with fuel.  Although I haven't seen research to this effect, I'm sure it's the case.  I have no idea where 4:1 mass ratio methanol falls on the combustion speed charts, as I haven't played with methanol.  

	-----Original Message----- 
	From: diy_efi-bounces at diy-efi.org on behalf of Mike 
	Sent: Sat 11/18/2006 11:58 PM 
	To: diy_efi at diy-efi.org 
	Cc: 
	Subject: RE: [Diy_efi] Rich detonation?
	
	

	Is the rationale for what you say below, excess fuel, or can you
	articulate just why the detonation occurs. I understand F1 engines
	often shift to  use 4:1 afr (with methanol) and although there is reduced power
	than running at just better than stoich for methanol - that the 4:1 ratio
	still results in combustion but radically reduce stresses on exhaust
	valves - vis a vis cooling the valves immediately after a hard run where the
	integral of EGT over the last few seconds exceeds some maxima ?
	
	Rgds
	
	Mike
	
	At 08:43 AM 11/19/06, you wrote:
	>Hi, Joe!  It's Damon (flyboy) from the MR2 community. 
	>
	>Yes, it's totally possible to get rich detonation.  However, you will usually misfire before you hit this point, unless you are pretty careless with the ignition. 
	>
	>Combustion velocity is what dictates spark timing, and it varies with AFR.  The max velocity is around 11.0 mass air/fuel ratio (the exact value is debatable, but the concept still holds).  Therefore, rich of this value, the combustion velocity increases again, necessitating a reduced spark advance. 
	>
	>If you leave the spark static and add fuel, then very rich mixtures will detonate, assuming the detonation propensity was there to begin with. 
	>
	>        -----Original Message-----
	>        From: diy_efi-bounces at diy-efi.org on behalf of Joseph Obernberger
	>        Sent: Sat 11/18/2006 3:10 PM
	>        To: diy_efi at diy-efi.org
	>        Cc:
	>        Subject: [Diy_efi] Rich detonation?
	>       
	>       
	>
	>        Hi,
	>            I've read in various places that it is possible to run an engine so
	>        rich that detonation can occur - or at least the knock sensor would pick
	>        up what sounded like detonation.  Has anyone ever experienced this?  Any
	>        truth to it?
	>        Thanks!
	>       
	>        -Joe
	>        http://www.lovehorsepower.com
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