Study On The Intelligent Fault Diagnosis Techniques Of Diesel Engine

The fault diagnosis technology of diesel engine is a comprehensive technology built upon many subjects. It can be quantificationally identified the technical state of real time of diesel engine, and the future technical states of abnormal fault are forecasted with the status messages and history status of diesel engine through analysis and handling. This paper attempts to research profoundly fault mechanism, fault feature extraction and fault diagnosis method of diesel engine from the view of project application. Its research object is diesel-dynamotor unit and its academic foundation is test technology, signal processing, wavelet analysis, fuzzy clustering, artificial neural network and rough sets theory, etc.This paper consists of eight parts: i) The meaning and research purpose of this paper is described briefly, the research present situation of fault diagnosis technology and the various state inspection methods of diesel engine are summarized. The suitable scope and the characteristic of various diagnosis methods are analyzed. The future development and the existed problems are pointed out. ii) To raise the precision of frequency spectrum analysis of FFT, the leakage error reasons of the window spectrum analytic method are analyzed. Aimed at the fence effect of window Fourier transform, the various methods of window spectrum emendation and frequency subdivision are studied, and the influence of the sample's length for window spectrum calibration accuracy is analyzed. iii) From the point of view of fault diagnosis, the information model is given and the frequency domain, time domain and circular fluctuation characteristic of the cylinder cap vibration signal of diesel engine are analyzed. A method of combining sampling analysis by means of section and parameter average is put forward, the measure method and realization of the cylinder cap surface vibration signal of diesel engine are studied. On this foundation, the vibration diagnosis mechanism and diagnosis methods of some typical fault, such as an abnormal valve gap and gas leakage from exhaust valve, are also studied, and the essential connection between these faults and the cylinder cap vibration signal of diesel engine is revealed. iv) On the foundation of introducing the composition of fuel injection system and the fuel injection process of diesel engine, the fault mechanism of 3 coupling parts abrasion and fuel injection process is analyzed deeply, and its influence is discussed in the same time. According to the working characteristic of fuel injection system, its fuel pressure wave that various typical fault states are discussed, and the corresponding relation between fuel pressure waveform and faults is analyzed. v) Many kinds of methodsfor the feature extraction of fault diagnosis to diesel engine, including the methods based on short time signal AR analysis and the methods based on wavelet multi-distinguish rate analysis, are studied. Using short time signal AR analysis, the realization method of full circulating feature extraction from the cylinder cap vibration signal of diesel engine is given. After introducing some basic theoretical foundation such as continuous wavelet transform, binary discrete wavelet transform and wavelet packet transform, a most important algorithm in wavelet analysis－Mallat fast algorithm is given. The mixed-frequency phenomenon existed in the result of wavelet packet decomposition is studied. An improved algorithm of wavelet packet transform that can prevent frequency alias is put forward. After using wavelet decomposition for the surface vibration signal of diesel engine, the characteristic frequency band of each fault state can be confirmed with the use of multi-resolution wavelet analysis or wavelet packet decomposition as well as least Kllback-Leibler information. Using its AR model parameter as characteristic vector, the fault diagnosis of diesel engine can be realized. It is expounded that fuel pressure waveform carried out in wavelet decomposition can remove noise interference and enhance S/N ratio. S...