[Diy_efi] Rich detonation?
niche at iinet.net.au
Mon Nov 20 00:56:29 CST 2006
At 05:22 AM 11/20/06, you wrote:
>F1 engines dont run on alchool...AFAIK.
ok, I might have been thinking of nascar then, long time ago ~`:o
However, I recall that in respect of F1, the AFR shifted from
just over stoich to 4:1 as that thermal management tool mentioned,
which raises the question - where is this "rich detonation" in that
environment has it been sidestepped, did it exist in the first place ?
Is "rich detonation" a clearly defined effect. Or is it perhaps a consequence
of running very rich, causing huge carbon buildup then when normal stoich
occurs these carbon deposits cause pre-ignition which is interpreted
as if its detonation as it appears to be (closely) caused by the rich
condition - until such time as the preignition or detonation scours most
of the carbon off the various surfaces ?
So what is the mechanism of "rich detonation" ?
>Citando "Becker, Damon \\(Damon\\)" <damonb at avaya.com>:
> 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
> 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
> 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 ?
> 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
> > rich that detonation can occur - or at least the knock sensor would
> > up what sounded like detonation. Has anyone ever experienced this?
> > truth to it?
> > Thanks!
> > -Joe
> > http://www.lovehorsepower.com
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