Engine knock has been recognized as a major problem limiting the development of fuel efficient spark-ignition engines. Detection methods employed in current knock control systems for spark ignition engines use a measurement of engine block vibration tuned to one or more resonance frequencies to extract knock-related information from the engine structural vibration. These techniques suffer from poor signal-to-noise ratio (especially at high engine speed), due to background vibration. It is known that the engine knock resonance frequencies vary due to changes in combustion chamber volume and temperature during the expansion phase. Therefore, the authors propose an improved knock detection method using joint, time-frequency analysis of engine block vibration and pressure signals. The experimental results for the proposed detection method, show a significant improvement in signal-to-noise ratio (SNR).
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