In this paper, knock detection and analysis methods of the gasoline engine are applied to a modified kerosene engine. Two kinds of signals, the cylinder pressure signal and the vibration signal, are acquired by a pressure sensor mounted in a spark plug and an accelerometer mounted on the cylinder block separately. Due to the influence of noise, such as cam shocks, piston up-and-down motion, crank rotation and so on, the vibration signal should be processed to extract knock feature. Firstly, FFT, a frequency analysis approach, is used to determine the characteristic frequency range of knock. Then, combining the sampling frequency, the vibration signal is divided into different frequency sub-bands, and the characteristic sub-band of DWT, a time-frequency analysis method, is determined. After that, DWT is applied to extract knock feature from the vibration signal. At last, the knock energy evaluation index is used to judge knock intensity. The reference knock energy is chosen by the researchers, and it is not absolutely suitable for the engine operating condition, so intuitive cylinder pressure signal is applied to supplement for knock judgment.
