Investigation of Knock and Resonance under Heavy Knocking Conditions in Gasoline Engines Using Continuous Wavelet Transform 03-14-04-0036

The continuously increasing demand for better fuel efficiency, low emissions, and high performance has led to downsizing and down-speeding in gasoline engines. High power density in spark ignition (SI) gasoline engines is impeded by abnormal combustion, namely, knock, megaknock, and pre-ignition. The objective of the present work is the experimental investigation of knock in gasoline engines and the development of a procedure for knock severity quantification and analysis. The methodology relies on several existing techniques such as Maximum Amplitude Pressure Oscillation (MAPO) and digital signal processing to investigate individual cycle knock characteristics. The novelty of the approach is in combining characteristic knock parameters with advanced signal processing tools to identify and analyze outlier cycles. The multi-outlier filtering approach enables the detection of abnormal knocking cycles as well as identifying cycles with distinct combustion behavior. By incorporating a Continuous-Wavelet Transform (CWT) in addition to Fast Fourier Transform (FFT), the amplitude and frequency of the pressure oscillations can be analyzed on a Crank Angle resolved basis. The spark sweep investigation permitted analysis under heavy knocking conditions in which knock occurred very frequently with the most advanced spark timing leading to a 300 cycle-averaged MAPO of 6.9 bar and peak MAPO of 44.2 bar. The analysis led to the detection of numerous peculiar cycles with high MAPO, albeit with low resonance.