combustion pressure sensor

[Greg Hermann]

At 2:42 PM 5/8/01, BamaInstrument wrote:
>Don't know that I agree with all this.  It seems to me that the force read
>is the force pushing the spark plug out of the hole.  Therefore, If the
>spark plug is torqued correctly then the force gauge would indicate a
>decrease of the tightening force.  Since the tightening force would be much
>greater than the compression force the transducer would probably be very
>linear.
>
Suggest you learn a bit about the forces in bolted joints and also abotu
vibration theory before offering such an opinion!

Basically, what goes on in this instance, is that the (compressive)
clamping force against the spark plug sealing washer is reduced as the
pressure in the combustion chamber increases. Because the clamped washer is
part of a relatively stiff  assembly, a load cell included in the washer
could read fairly high frequency changes in pressure without filtering them
out, so long as the DAQ circuitry is up to the job.

Whether or not such sensors are used to try to read the "ringing" that
occurs with detonation is another matter.

Greg


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