Research On Fault Diagnosis Technique Of The High Speed V-engine With High Number Of Cylinders

As the prime mover in many industrial applications,diesel engines are so important to ensure reliability of their service that a lot of condition-monitoring and diagnosis techniques have been developed.Compared with the others,IAS(instantaneous angular speed)based method has the advantages of less noise contamination,easy installation,economical price,which make this method practical and useful.Most methods are aimed at small engines with low speed and have achieved a very good performance on many engines.However,their applicability to large diesel engine is strongly contested due to the high number of cylinders and the complex load and crankshaft which complicate the IAS.In order to solve the problems,further researches have been done in this paper.First,the crankshaft dynamic model of a V12 diesel engine is built.Combined with simulating calculation and experimental analysis,combustion fault is then studied to diagnose and locate.At last,the EEMD(Ensemble Empirical Mode Decomposition)based method and VMD(Variational Mode Decomposition)based method are used to improve the discrimination of faulty features.All the research are as follows:(1)In order to compare the filtering characteristics of two data mode decomposition method,the theory of the Empirical Mode Decomposition(EMD)and VMD has been studied by calculating the average white noise power spectrum.(2)The zero crossing method and the demodulation method are both used to extract the instantaneous speed;the effects of different factors on the instantaneous speed measurement accuracy are discussed;data mode decomposition method are also applied to filter IAS.(3)The harmonic order of IAS is analysed in theory.Misfire fault is conducted relying on a V12 diesel engine dynamics model.Compared the test results with the simulating calculation,the diagnosis of misfire has been studied.On this basis,the power shortage fault in one cylinder is also studied.The influence of firing angle is researched.(4)IAS are decomposed by EEMD and VMD,respectively.The decomposition characteristics of two data mode decomposition method are compared.The possibe physical meaning of each Intrinsic Mode Function(IMF)component has been explained.Comparison with the normal decomposition fault condition and combined with Hilbert-Huang Transform(HHT)time-frequency diagram and Fast Fourier Transform(FFT)analysis,the diagnosis of diesel engine misfire fault is diagnosed.On this basis,the EEMD-based method is applied to diagnose the simulation power shortage in one cylinder.