Detonation Monitor

[Bruce]

There is a ton of good info., about this in the archives already.
Bruce



----- Original Message -----
From: "David Hunt" <bamainc at home.com>
To: <diy_efi at diy-efi.org>
Sent: Monday, May 28, 2001 5:40 PM
Subject: Re: Detonation Monitor


> Yeah, you're right (as you knew you were!) since the speed of sound
doesn't
> change with ocean depth. I've seen the waveform for the ping and it was a
> near sine wave that was much higher than the apparent audible frequency.
>
> Maybe it was the measuring device.  Piezo bolted directly to the head.
The
> pinging was caused by increasing the timing.  Increase by 1 or 2 degrees
at
> a time (not a trivial task) and wait for a minute or two.  The pinging
would
> start softly at first and then increase in apparent amplitude.  The scope
> said that the ping was simply more often, but always at the same
amplitude.
> Guessed is was because there was something heating in the combustion
> chamber.
>
> I believe I recall a 30kHz fundamental ping frequency.  Does anyone have
> better data?
>
> dh
>
> ----- Original Message -----
> From: "Greg Hermann" <bearbvd at cmn.net>
> To: <diy_efi at diy-efi.org>
> Sent: Saturday, May 26, 2001 8:10 PM
> Subject: Re: Detonation Monitor
>
>
> > At 6:18 PM 5/26/01, David Hunt wrote:
> > >I have been thinking about the detonation situation and you have
ignited
> > >some further thoughts on that subject.  You have mentioned that the
> > >detonation frequency would be at about the combustion chamber Helmholtz
> > >frequency.  I think you're probably right but it just occurred to me
that
> > >the speed of sound should be quite high due to the compression ratio.
> >
> > Mach 1 (speed of sound) in any gas varies with molecular weight and
square
> > root of absolute temperature. Nothing else. NOT related to pressure!
> > Obviously, Mach 1 will be increasing in the chamber during the
combustion
> > process.
> >
> > Greg
> > >
> > >So, if the volume is (for a 350 small block Chevy)
> > >
> > >350/8 * sine(degrees BTDC) + .125(350/8)
> > >
> > >where:
> > >    The .125 is clearance volume for an 8:1 engine.)
> > >    350/8 is the volume of one cylinder.
> > >    sine(degrees BTDC) is the ratio of volume of the cylinder at that
> position
> > >
> > >And the pressure is:
> > >
> > >14.7PSI * .8 * 8
> > >
> > >Where:
> > >    14.7 is the initial pressure
> > >    .8 is the volumetric efficiency
> > >    8 is the compression ratio
> > >
> > >Then we should have the 'ping' frequency.  That's as far as I can go
> right
> > >now, I'll work more on it later.  I don't know the Helmholtz theorem
> right
> > >now.  But it seems that the ping frequency will increase depending on
> > >where the ping is started in relationship to the cycle
> > >
> >
> >
>
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