Engine block vibrations: An indicator of knocking in the SI engine

Abstract

The factors influencing the onset of knocking have a significant impact on how well a SI engine performs. Hence, the efficacy in determining the onset and controlling of knock is a key factor in improving the SI engine's performance. This paper provides insight into the role of engine block vibrations in determining the occurrence of knock using Empirical Mode Decomposition and Short-Time Fourier Transform. To comprehend the behaviour of vibration amid normal combustion and knocking conditions, the engine block vibration signals are analyzed and compared with the incylinder pressure fluctuations. The features of knock are extracted from the engine block vibration signals using Empirical Mode Decomposition. The first Intrinsic Mode Function (IMF) thus obtained is used to generate the Hilbert spectrum for detecting the occurrence of knock. Similarly, ShortTime Fourier Transform is also performed on the first IMF to obtain the spectrogram. The findings demonstrate unequivocally that higher frequency variations are produced when knock occurs. These results also indicate that the combination of Empirical Mode Decomposition and Short-Time Fourier Transform can be used effectively for determining the occurrence of knock.