Knock Analysis for a Small-Size Two-Stroke Spark-Ignition Marine Engine

The engine knock experiment was conducted on a small-size two-stroke marine engine. Wavelet transform was used to extract the high-frequency noise signals of engine cylinder pressure and block vibration acceleration. Then the characteristic frequency of slight engine knock was obtained by fast Fourier transform. The results show that the combination of wavelet transform and fast Fourier transform can effectively extract the feature of slight knock. Therefore, it can be used for knock fault diagnosis. As the ignition advance angle is 26°CA (crank angle) BTDC (before top dead center), the knock characteristic frequency of the cylinder pressure signal is 4.88 kHz, and the knock characteristic frequency of the block vibration acceleration signal is 16.01 kHz. As the ignition advance angle is 30°CA BTDC, the knock characteristic frequency of the cylinder pressure signal is 4.30 kHz, and the knock characteristic frequency of the block vibration acceleration signal is 15.82 kHz.