[Diy_efi] Rich detonation?
Charles Woock
atomic
Mon Nov 20 07:23:10 UTC 2006
The richer the mix the faster the burn. The leaner the mix the slower the
burn. It is all about ignition timing, however the source of detonation
aside from improper timing is from poor quality fuel or fuel not suited for
a specific compression ratio. Poor fuel combined with hot spots in the
combustion chamber results in pre-ignition. I'm not really sure what you
mean by "rich detonation". The whole engine is a system... all the parts
and processes must match.
Good luck
Charles
----- Original Message -----
From: "Mike" <niche at iinet.net.au>
To: <diy_efi at diy-efi.org>
Sent: Monday, November 20, 2006 12:56 AM
Subject: RE: [Diy_efi] Rich detonation?
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" ?
rgds
Mike
>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
> 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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