[Diy_efi] Rich detonation?
Becker, Damon Damon
damonb
Mon Nov 20 16:39:57 UTC 2006
I too am an mechanical engineer, thermo specialty. It was news to me when tuning legends like Ben Strader talked about it.
Combustion velocity increases to a max rich point. That exact point is usually much richer than most cars run. That's why it's usually a non-issue. However, stock turbo cars do actually run richer than this point.
-----Original Message-----
From: diy_efi-bounces at diy-efi.org on behalf of Mike
Sent: Mon 11/20/2006 12:47 AM
To: Charles Woock; diy_efi at diy-efi.org
Cc:
Subject: Re: [Diy_efi] Rich detonation?
At 03:23 PM 11/20/06, you wrote:
>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.
Thats what I want clarified. I've been interested in EFI for 20 years and have
an engineering background in that field since EFI was my subject at uni in 1982,
I appreciate the systems aspect but not heard of this so called "rich detonation"
being any sort of issue, even worth touting as any problem, I also havent heard
of a richer mixture burning that much faster than a lean mixture, well within the bounds of normal range one encounters for road use and in that respect,
although its sensible to conclude it would burn a little faster but I have not heard
of tuning shops advancing the timing by anything significant if at all when
mapping for a richer mixture from say 12.5:1 to 11:1 to squeeze out a bit more
power so in that range I am wondering how much would be gained advancing
the timing by say 1deg if its only for the issue of burn speed vs some other
factor in the system overall such as a richer mixture cooling the charge can
allow for less chance of detonation etc
So in addition to the original post - you have raised another query I'd
like clarified:-
Just how much faster does the mixture burn if it goes from say 14:1 to
11:1 is there a graph that is specific to this relationship which isnt
complicated by average temperature rise in chamber etc *and* why
doesnt it appear that tuning shops advance the timing map (at least a little) when running richer mixtures assuming they are already using the optimum
fuel for that engine configuration.
My post arose as a result of responding to this post by Joseph Obernberger
who started the topic with the same subject line:-
>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!
>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
>> > _______________________________________________
>> > Diy_efi mailing list
>> > Diy_efi at diy-efi.org
>> > Subscribe: http://lists.diy-efi.org/mailman/listinfo/diy_efi
>> > Main WWW page: http://www.diy-efi.org/diy_efi
>> >
>> >
>> >_______________________________________________
>> >Diy_efi mailing list
>> >Diy_efi at diy-efi.org
>> >Subscribe: http://lists.diy-efi.org/mailman/listinfo/diy_efi
>> >Main WWW page: http://www.diy-efi.org/diy_efi
>> _______________________________________________
>> Diy_efi mailing list
>> Diy_efi at diy-efi.org
>> Subscribe: http://lists.diy-efi.org/mailman/listinfo/diy_efi
>> Main WWW page: http://www.diy-efi.org/diy_efi
>>
>>
>>
>>
>>
>>
>>__________________________________________________________
>>Pare de esbanjar dinheiro!
>>Compare o pre?o da sua liga??o ? Internet
>>http://acesso.portugalmail.pt/maisbarato
>>_______________________________________________
>>Diy_efi mailing list
>>Diy_efi at diy-efi.org
>>Subscribe: http://lists.diy-efi.org/mailman/listinfo/diy_efi
>>Main WWW page: http://www.diy-efi.org/diy_efi
>_______________________________________________
>Diy_efi mailing list
>Diy_efi at diy-efi.org
>Subscribe: http://lists.diy-efi.org/mailman/listinfo/diy_efi
>Main WWW page: http://www.diy-efi.org/diy_efi
>
>
>_______________________________________________
>Diy_efi mailing list
>Diy_efi at diy-efi.org
>Subscribe: http://lists.diy-efi.org/mailman/listinfo/diy_efi
>Main WWW page: http://www.diy-efi.org/diy_efi
_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
Subscribe: http://lists.diy-efi.org/mailman/listinfo/diy_efi
Main WWW page: http://www.diy-efi.org/diy_efi
More information about the Diy_efi
mailing list