Detonation Monitor

[Jorgen Karlsson]

I used 1000oC because I thought that the medium temperature during knock was
somewhere around there, but what you say makes sense.

The pressure in it self does not change speed of sound, it is only
temperature dependent.

I have ordered a bosch knock sensor to try too, but I think that the
electret microphone is a good backup. I would of course like the knock
sensor to work, it is better suited to the enviroment in the engine
compartment.

I wonder if the knock detection systems used on some dragrace cars with dry
sump can be used on an ordinary street car. They measure the pressure in the
crankcase, and pressure peaks indicate detonation. What do you think?

Jorgen

> It's the primary mode of oscillation - being the lowest-energy one
> possible. Typical knock-detection is by listening to frequencies in
> the range of 6kHz to 10kHz. Higher frequencies do exist but their
> magnitude is several dB down on the main one. An infinite number of
> frequencies is possible; the main ones are determined by the longer
> dimensions of the combustion chamber. Near TDC, the bore is the
> longest dimension.

> There's been some recent research on using specialised washers under
> head bolts to determine cylinder pressures during combustion; less
> invasive than a pressure tapping, but subjected to other stresses as
> the head flexes under load.

> That's about all it takes. You can use a typical Bosch knock sensor
> to the same effect. It's just a piezo element bonded to a metal
> structure that's bolted to the block; typically at an anti-node
> location of the block.

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