Fault diagnosis of diesel engine based on adaptive wavelet packets and EEMD-fractal dimension

摘要

In this paper a novel method for de-noising nonstationary vibration signal and diagnosing diesel engine faults is presented. The method is based on the adaptive wavelet threshold (AWT) de-noising, ensemble empirical mode decomposition (EEMD) and correlation dimension (CD). A new adaptive wavelet packet (WP) thresholding function for vibration signal de-noising is used in this paper. To alleviate the mode mixing problem occurring in EMD, ensemble empirical mode decomposition (EEMD) is presented. With EEMD, the components with truly physical meaning can be extracted from the signal. Utilizing the advantage of EEMD, this paper proposes a new AWT-EEMD-based method for fault diagnosis of diesel engine. A study of correlation dimension in engine condition monitoring is reported also. Some important influencing factors relating directly to the computational precision of correlation dimension are discussed. Industrial engine normal and fault vibration signals measured from different operating conditions are analyzed using the above method. These techniques have integrated with our proposed adaptive wavelet threshold de-noising to form a new AWT-EEMD-CD method. The advantage of combining of EEMD and fractal dimension is that it does not require the classifiers to recognize the diesel engine fault types, also the method can solve the difficulty of recognizing fault states when two or more fractal dimensions are close to each other. To verify the effectiveness of the EEMD-CD in detecting the faults, their induced vibrations are collected from a series of generators under normal and faulty engine conditions after de-noising. The results show that this method is capable of extracting the impact signal features induced by vibrations and is able to determine their types of fault accurately even when the impacts have been overwhelmed by other unrelated vibration signals.