DIESEL ENGINES' VIBROACOUSTIC SIGNATURE EXTRACTION BY WAVELET PACKET TECHNIQUE

Multisource unstable impulsive excitations, time varying transmission path, concentrated mode, dispersion and reverberation that are important characteristics of reciprocating machines such as diesel engines result in wide band non stationary vibroacoustic responses which influence the effective extraction of vibroacoustic signatures and become a key factor to limit diesel engines’ vibration diagnosis. In this paper, a serial theoretical deduction on the unstable dynamic properties of diesel engines was made; the mechanism of non stationary vibroacoustic responses was elucidated. Based upon that, the wavelet packet technique was introduced. The reason for the existence of frequency aliasing in the Paley series from wavelet packets’ decomposition was analyzed, and the wavelet packet frequency shifting algorithm was given. Experiments on 190 serial diesel engines verify the given method’s significant validity in vibroacoustic signature extraction and reciprocating machines’ vibration diagnosis.