Fault Diagnosis Study On Combustion Chamber Components Of Diesel Engines Using Acoustic Emission Technology

Economy,high efficiency,long life and intelligence are always the consistent pursuits of modern marine diesel engines.The worst working environment of the combustion chamber components has led to the largest probability of failure among the engines.Therefore,the condition monitoring of the combustion chamber components has been regarded as the prerequisite for the development of the diesel engines.The acoustic emission(AE)technique has been expected to hold promise in marine diesel engines monitoring and diagnosis due to its unique advantages of non-destructivity and high signal-to-noise ratio(SNR).Besides,the AE signal of marine diesel engines contains a lot of information about the faults of the engines.However,it still needs more studies about how to determine the fault location and severity of the combustion chamber components fault through a small number of sensors by selecting the appropriate sensor installation positions.According to the faults owning various degrees that are likely to occur in the combustion chamber,relevant research has been carried out on a 6-cylinder four-stroke turbocharged marine diesel engine to realize the monitoring and diagnosis of different faults of the diesel engine combustion chamber components by using acoustic emission signals.The main research contents and results of the paper as following:(1)The different sensor positions correspond to different influence on the AE signal acquired by sensors and the diagnostic effect.To determine the optimal sensor position of the cylinder head,a standard Hsu–Neilson(pencil breaking)source was applied at seven different AE sources at the bottom of the cylinder head.The AE signal of ten available sensor installation positions of the cylinder head has been acquired and analyzed.As the product of AE energy attenuation factor k by distance x between the sensor installation positions and the AE source,the kx has been selected as the parameter to evaluate the goodness of the position of a sensor.The position P5 that owns most sensitivity to the main AE sources amongst the combustion chamber has been determined by static test.(2)To verify the results of static test,the fault simulation experiments of injector clogging fault and exhaust valve leakage fault have been carried out in the first cylinder(starts from the flywheel end).It was found that the AE signal of P5 owns higher SNR,and P5’s AE signal is suitable for the identification and diagnosis of various combustion chamber components faults.At low degree fault conditions,even if the has not changed much from the normal value,the characteristic values of the AE signal of the P5 have changed significantly.As for the friction and impact process between the piston ring and the cylinder liner,the position Pw outside the engine block owns stronger sensitivity.(3)A series of simulation schemes for different fault levels have been designed for the injection pressure reduction,misfire,nozzle clogging,needle valve wear,exhaust valve leakage and piston ring wear failure,which are easy to occur among the combustion chamber components of marine diesel engines.The data acquisition program has been programmed based on LabVIEW software and the test system for the diesel engine combustion chamber component failure simulation experiments was also constructed.(4)The characteristics of fault simulation experiments signals have been analyzed.At the same time,the characteristic parameters of the injection pressure reduction,misfire,nozzle clogging,needle valve wear,exhaust valve leakage and piston ring wear failure have been extracted correspond to the signal energy sum of 340~355°and 370~420°CA ranges,signal energy of 340~380°CA,signal power of the whole working cycle 25.8~31.7kHz frequency band,signal power ratio 9)of 23.3~28.3kHz and 28.3~32.3kHz frequency bands of 340~380°CA range,signal power of 340~380°CA range 8~41kHz frequency band and signal power of 425~500°CA range 8~39.7kHz frequency band,the method of monitoring and diagnosis of various combustion chamber components faults using AE technology has also been proposed.This paper has carried out related studies focusing on the selection of sensor positions,the feasibility of fault diagnosis by AE signal from the sensor positions,the characteristics of AE signal when the faults occur and the extraction of fault characteristic parameters during process that AE technology is applied to the monitoring and diagnosis of combustion chamber components.This paper has provided a technical reference for the comprehensive diagnosis of the marine engines and the realization of the intelligent engine rooms.