Knock Detection and Control in an HCCI Engine Using DWT

Abstract

The novel application of the Discrete Wavelet Transform (DWT) in a real time controller is used to detect and subsequently control knock in a Homogeneous Charge Compression Ignition (HCCI) engine. Classical Fourier techniques for knock detection are discussed and compared to Wavelet Transforms. The Discrete Wavelet Transform filter bank is chosen as the best method for knock detection due to its good time-resolution and low computational requirements. The DWT method is compared with the root mean squared value of the pressure trace as the benchmark method for determining knock and the two methods are linearly correlated. Using the DWT method for knock detection and modulating fuel octane, both a Proportional Integral (PI) and PI with Feed-forward control are implemented. Both of these methods reduce knock intensity for a step increase in engine load. The combination of Feed-forward with PI feedback is found to be slightly more effective than just PI feedback control.