Liu, Y., Li, L., Lu, H., Deng, J. et al., "In-Cycle Knocking Detection and Feedback Control Based on In-Cylinder Pressure and Ion Current Signal in a GDI Engine," SAE Technical Paper 2016-01-0816, 2016, doi:10.4271/2016-01-0816.
Due to much higher pressure and pressure rising rate, knocking is always of potential hazards causing damages in the engine and high NOX 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 2nd-order differential of in-cylinder pressure, which means the response time of pressure rising rate dPR, is employed for knocking prediction. Compared with the original in-cylinder pressure, the timing of knocking detection with dPR 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 dPR and DIC. The diagnosis accuracy reaches 70% with dPR 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, NOX is 25% lower and the HC is 73% higher. And the success rate of knocking inhibition is 80% with dPR and 90% with DIC.