In-Cycle Knocking Detection and Feedback Control Based on In-Cylinder Pressure and Ion Current Signal in a GDI Engine 2016-01-0816

Due to much higher pressure and pressure rising rate, knocking is always of potential hazards causing damages in the engine and high NO_X emissions. Therefore, the researchers have focused on knocking diagnosis and control for many years. However, there is still lack of fast response sensor detecting in-cycle knocking. Until now, the feedback control based on knocking sensor normally adjusts the injection and ignition parameters of the following cycles after knocking appears. Thus in-cycle knocking feedback control which requires a predictive combustion signal is still hard to see. Ion current signal is feasible for real-time in-cylinder combustion detection, and can be employed for misfiring and knocking detection. Based on incylinder pressure and ion current signals, the in-cycle knocking feedback control is investigated in this research. The 2^nd-order differential of in-cylinder pressure, which means the response time of pressure rising rate dP_R, is employed for knocking prediction. Compared with the original in-cylinder pressure, the timing of knocking detection with dP_R is advanced, and thus in-cycle feedback control can be achieved. Optimizing the anti-noise performance of ion current signal, the ion current signal is converted into a digital ion current signal (DIC) before input ECU. The results show in-cycle knocking can be predicted by both dP_R and DIC. The diagnosis accuracy reaches 70% with dP_R and 85% with DIC. The in-cycle feedback control is designed based on the prediction. When knocking is detected, ECU operates re-injection immediately reducing incylinder temperature, and thus the knock can be inhibited. After knocking inhibition control, NO_X is 25% lower and the HC is 73% higher. And the success rate of knocking inhibition is 80% with dP_R and 90% with DIC.