Research On Thermo-economics Fault Diagnosis For Marine Low Speed Two Stroke Diesel Engine

Marine diesel engine is the key equipment of marine power plant.If it breaks down,it will affect the operation of the ship,and may directly or indirectly cause huge economic losses,even lead to the damage of key equipment.The traditional maintenance support of diesel engine often depends on the scheduled maintenance in advance or the post maintenance after the occurrence of serious faults,which lacks the ability of pre diagnosis.Thermoeconomic fault diagnosis is a kind of generalized diagnosis.Based on exergy cost,it quantifies the cost impact caused by various abnormalities.It has the advantages of simple calculation,sensitive response,high accuracy,and is of great significance for diesel engine fault diagnosis.Take 6S50 MC marine low-speed two-stroke diesel engine as research object,the zero dimensional mathematical model of the working process of the diesel engine is established,and the simulation model of the diesel engine is built with AVL-BOOST software.The main performance parameters obtained from the simulation are compared with the experimental data,and the error is within 5%.On this basis,the physical structure diagram of marine diesel engine is established,which is divided into six components: cylinder,intercooler,compressor,turbine and cylinder liner water cooler.Through exergy analysis,the production structure diagram of diesel engine is established,and the "fuel" and "product" of each component are determined.Based on the theory of thermoeconomics,the failure cost of components and the internal irreversible loss are determined as the fault location index,and the fault diagnosis model of thermoeconomics is established.The simulation model is used to simulate the typical single fault of four kinds of diesel engines,and then the single fault of each component is superposed to further simulate the multiple faults of four kinds of diesel engines,and the applicability of the fault diagnosis model is verified by the fault data obtained from simulation.The results show that the thermo-economic fault diagnosis model is very accurate for the single fault of diesel engine,and the four single faults can be diagnosed accurately.In particular,when the intercooler has a slight fault,the power of the main engine drops only about 66 k W,but the fault can still be accurately located and judged,indicating that the thermo-economic fault diagnosis model has a high sensitivity to a single fault.The diagnosis model can still locate the fault component accurately when the two fault occurs simultaneously.When three components fail at the same time,the failure cost of one component may be overshadowed by the other two components.For example,the compressor fuel impact in the study case is only 1/16 of the intercooler element,but the compressor failure can still be judged by the second indicator--the internal irreversible loss.Therefore,it is necessary to use a combination of two fault location indicators to diagnose faults in thermoeconomics.The application of thermo-economic fault diagnosis in diesel engine can provide certain technical support for accurate location of diesel engine fault.