Detonation Monitor

[David Hunt]

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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