Research On Fault Diagnosis And Management Strategy Of Urea-SCR For Diesel Engine

Environment pollution exacerbates with the rapid growth of automobile industry and car ownership,which leads to rigorous emission laws across the world.For heavy diesel engine,a post-processing system is necessary and being equipped with OBD was written in the regulation.This paper in combination with the international technology corporation special project,the unite research of control technology in vehicle emission post-processing system,and the Natural Scientific Fund youth project,Research on Urea-SCR Catalyst Fault Diagnosis,Mechanisms of Deactivation and Fault-tolerant Control Method,researched on malfunction diagnosis and manage strategy of crucial parts in diesel Urea-SCR system.Firstly,the fault diagnosis strategy of Urea-SCR urea supply system is studied.The urea supply system being simplified to the structure of the pump tube nozzle and the hydraulic model of urea supply system being designed by using AMEsim software,which is used to simulate the dynamic characteristics of construction stage and stable stage of the injection pressure of the urea supply system.The failure factor being acted on the basis of the model and the system fault model being established.The simulation of typical faults the system is realized,and the rule of supply line pressure fluctuations of typical fault state under different failure degree is obtained.The pipeline pressure fluctuation signal is supplied as the characteristic parameter of fault diagnosis.The residual pressure under fault condition is obtained by combing the characteristic parameter with the predictive observer value.The judgement of system fault and failure degree is based on the residual pressure.Secondly,the fault diagnosis strategy of performance of Urea-SCR catalyst for diesel engine is studied.According to the catalytic converter failure factors and catalytic chemical theory on the catalytic converter,combining the Eley-Rideal mechanism and Langmuir isothermal adsorption equation,the performance diagnosis model of catalytic converter is built by using Simulink software.The model is solved for the problem of the decreasing of transformation efficiency and the NH₃ leakage.The diagnosis strategy is designed according to the laws of the emission limit.The validity of diagnosis model and strategy is tested by the simulation under ETC cycle condition.The effective measures should be taken when the NOx emissions and the leak of ammonia exceeded the amount.Finally,the faults management strategy of Urea-SCR is studied and divided the faults management system into three functional units:faults monitoring function,faults processing function and diagnosis communication function.Faults monitoring function can present real-time monitoring to the possible abnormal condition of Urea-SCR system and take pre-treatment to the faults by faults elimination.Faults processing function can process problems by storing and deleting the faults and taking corresponding measures according to check the change of faults state.Diagnosis communication function was developed based on the ISO15765 communication protocols,which achieve the control of the fault indicator light and diagnostic communication function.The above research content is tested and verified through bench test of the engine.The final results show that all functions can meet the desired objectives and requirements.