A Diesel Engine Intelligent Fault Diagnosis System Of Signal Filtering

The condition monitoring and fault (CMFD) diagnosis of the diesel engine has become the hotspot in condition monitoring and fault diagnosis recently. The CMFD based on the thermodynamic parameters is developing towards intelligence. Transient speed signal and fuel pressure signal are two important parameters for the CMFD based on the thermodynamic parameters.The regularity of diesel engine transient speed's fluctuation offers a lot of information for analyzing run-parameter. The transient speed's fluctuation which can reflects the state of cylinder work synthetically corresponds with the energy producing process of every cylinder. The cylinder's compress pressure, cylinder uniformity, combustion pressure distinction can all be detected by the transient speed. The factors that effecting the transient speed are analyzed. The theoretic reason of measured error has been analyzed and the applied method to lessen this error has been put forward.But, the measured signal was disturbed by impulse noise. A two-pass method is used to do denoising in this paper. First, impulse noise is reduced, although the median filter is a good method for impulse noise's denoising, it may make the signal details lost, thus impulse noise was firstly detected and then reduced. Differential rank order impulse detector was improved for the impulse noise's detection. The impulse noise was detected more exactly and signal details were preserved. And the resumed signal shows that the improved method is better. 'Local mean' method is also put forward to reduce impulse noise. This method can reduce part of the low frequency noise while reduce the impulse noise, so it was the best one in these four methods.After the impulse noise is reduced, low pass filter is used to denoise the low frequency noise. Because the diesel engine transient speed signal is a non-stationary signal, the wavelet transform with multi-resolusion analysis is used to do denoising. Experiments show this method is good for transient speed signal's denoising. FIR low pass filter, IIR low pass filter, zero angle digital filter and wavelet method have been compared for transient speed signal's filtering. Experiments show that if the workequality of the transient speed is better, the wave crest and trough will correspond the crankshaft angle better.Spary system is one of the most important facilities of the diesel engine. It has crucial influence on the fuel sparying and the burning course. The fuel pressure signal of the diesel engine is an important parameter for the oil spary system's CMFD. This signal is also disturbed by impulse noise, and two-pass method is also used to reduce the noise. Impulse noise was detected based on the pressure increasing while oil spraying, and then low pass filter was used to resume the signal.