Multi-load knock detection of a marine micro-ignition diesel (DI) -natural gas (PFI) dual-fuel engine based on in-cylinder pressure signals

A new knock definition was proposed to satisfy the unified knock detection under various engine loads based on in-cylinder pressure signals. Knock indices such as maximum amplitude pressure oscillation (MAPO), maximum pressure rise rate (MPRR), peak pressure (Pmax), arithmetic mean, standard deviation and so on were investigated. The standard deviation and arithmetic mean were found to have a high correlation with MAPO. However, these knock indicators cannot use a fixed value to meet the requirements of knock detection under different engine loads. Time-frequency analysis was conducted to investigate the knock characteristics under various engine loads. There is a significant increase in the energy of 8-12 kHz frequency domain when knock occurs, which may use for effective knock detection. Further analysis of the cylinder pressure signal by using Discrete Wavelet Transform (DWT) revealed that the energy proportion of the 8-12 kHz energy segment in the D2 sub-band can well distinguish the knock phenomenon under different engine loads. Therefore, a new definition Pn which clearly distinguishes the knock cycles from normal cycles regardless of engine loads was proposed and validated by comparing it to the MAPO.