[Diy_efi] Re: Custom detonation detecting

[Phil Hunter]

Eric B. wrote:

> > My understanding is that the resonant frequency of detonation is
> > a function of bore diameter as the supersonic sound waves bounce
> > back and forth, so a Cavalier knock sensor is probably tuned way
> > off frequency.
> 
> How could this be?  Sound waves are not supersonic.  By definition they
> are "sonic".  They travel at Mach 1, which is however quite higher than
> in the atmosphere due to the heat and the pressure.  Second, how is the
> resonant frequency relevant?  Peak pressure is on the order of 1300 psi
> during combustion, and detonation causes a pressure wave at about 5000
> psi, several degrees of crank angle after the normal pressure peak.
> Anything that will detect that kind of pressure jump will detect a
> detonation, I would think.  Also, I would think the response speed would
> be more important than the frequency the sensor is tuned to.

Yeah, poorly worded on my part, Mach 1 inside, supersonic relative to
outside.

I think you'll find the spike occurs several degrees before the normal
pressure peak rather than after it. Once the pressure and temperature
are falling, detonation should not occur.

For whatever reason, Jon wanted to detect detonation acoustically, so
I was steering him away from his initial choice of a Cavalier(?) knock
sensor as counter-productive. I suspect that after he reads the URLs,
he'll abandon the acoustic approach altogether.

Mike wrote:

> Would you be doing the whole f/back on a PID type controller
> or perhaps multiple parallel PID type threaded segments, I
> was toying with something like this in 82 when I did a thesis on
> using a Z80 for engine control of a Ford escort 1.6L using VW
> K-jetronic parts - back then the PID was a bit too complex for
> me - decisions of transient vs steady-state where a bit of an
> overhead in s/w, these days its run of the mill mostly.
> 
> How much logging memory would you be using ? Would you set it
> up as a rolling fifo type with Kalman filtering for O2 and AFM
> inputs  for rate of change info as well ?

I'm not sure who this is directed to, but for me, I'd be ecstatic
just to get past the physical/mechanical/electronic aspects and see
waveforms on an o'scope. Check out the first URL I listed, and perhaps
contact Ville for the info you're interested in.

Eric F. wrote:
[snip]
> aG9vIG1lZ2Fqb2x0IGxpc3QsIHNvIHNlYXJjaCBvdmVyIHRoZXJlIGluIHRoZSBhcmNoaXZ

Yup.

[snip]
> YXQgaXQgaXMgdHJhbnNtaXR0ZWQgdGhyb3VnaCB0aGF0IGJpZyBtZWNoYW5pY2FsDQphdWR

Nope. ;)

rgds,
philh
(digest)

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