Knock detection in SI engines by using the Discrete Wavelet Transform of the engine block vibrational signals

In the present work, the Discrete Wavelet Transform (DWT) has been applied on the vibrational signals acquired by an accelerometer placed on the cylinder block of a Spark Ignition (SI) engine, for detecting knock phenomena. In order to collect both vibrational data and in-cylinder pressures, useful for the analysis, a series of experiments on a four cylinder, four stroke Internal Combustion (IC) engine has been carried out. The obtained results show how the presented knock detection algorithm is able to monitor the goodness of the combustion phase in absence of knock phenomena, and otherwise to determine its intensity. This algorithm uses a Multi-Resolution Analysis (MRA) performed on the vibrational signals of the engine block as acquired. The same kind of analysis has been executed by using the traditional index MAPO, which is widely applied on the pressure data, and the results of the two methods have been compared. The comparison, showing how the results are very similar, confirm that the use of the DWT represents a very valid alternative to the traditional knock detection techniques.