Detonation Monitor

[Jorgen Karlsson]

This was funny, I just made a diagram showing the speed of sound at
different temperatures today. I wanted it to get a better overview for
header construction.

A quick look at it shows that at 1000oC the speed of sound is 707m/s. More
then twice the speed at room temperature.

But to an other subject, I don't think that the helmholtz frequency has
anything to do with the detonation frequency. I don't even have a clue how
to apply the helmholtz equations in this case.

I have always heard that it is the diameter of the bore that is the only
variable. By doning a quick calculation on my engine that has a 79.5mm bore
and assuming around 1000oC combustion temp I came up with 8949Hz resonance.
I think that only using 1X the diameter is the right way to do it, but I
would probably try to monitor from half of that frequency and up.

After consulting with one of the guys at volvos engine lab I have decided to
glue an electret microphone to a bolt that I then attach to the block. By
listening to the output I should be able to hear detonation very early.


Jorgen Karlsson
Gothenburg, Sweden.

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