The Use of Digital Fourier Transform Methods in Engine Noise Research

Recent developments by the author in the application of digital Fourier transform (DFT) methods, i.e., coherence and transfer function techniques to the investigation of noise from an engine are discussed. The transfer functions are determined empirically and they can be used to determine the mechanism of noise generation of an engine. They can also be used to predict the effect on engine noise of various assumed cylinder pressure wave forms. Among other results, it is demonstrated that the rapid pressure rise in the cylinder pressure has a strong effect on engine noise.