Abstract: A spark ignited internal combustion engine includes knock sensing apparatus comprising vibration sensing apparatus having a portion mounted on an engine component for vibration therewith and a tuned response to vibrations of a plurality of the acoustic cavity resonance frequencies of the engine cylinders. A separate signal processing channel is provided for the sensor output at each of the frequencies to indicate significant vibrations at the respective frequency. Coincidence means fed by all channels produce an engine knock signal only when significant vibrations are detected on all channels simultaneously.

Abstract: The bulk temperature of the gas in a piston engine during combustion is determined by detecting the high frequency pressure oscillation in the combustion chamber operating the engine to produce knock and measuring the frequency of the lowest frequency mode of the high frequency knock signal. The frequency or inversely the period of that signal is a function of the gas temperature.