No Engine Knock
Image from cylinder pressure sensor
See the smooth rise in pressure
and the smooth decline in pressure
This is a normal pressure trace in a combustion
chamber when no knock occurs
Hard Engine Knock
Image from cylinder pressure sensor
See the smooth rise in pressure then
the loss of control with cylinder pressure
The pressure in the combustion chamber almost
doubles when hard engine knock occurs
No Knock at 3000 rpm. 17 degrees
Image generated by high end sound recording equipment
Red trace is engine background noise
Blue trace is no engine knock
Both traces are of similar appearance
Hard Knock at 3000 rpm. 27 degrees
Image generated by high end sound recording equipment
Red trace is engine background noise
Blue trace is hard engine knock
When engine has knock the noise is far
louder than the engine background noise
You will see by the large blue spike that the
engine knock happens in this example at 5.2Khz