Research And Development Of SCR System Based On The Control Strategy Of Ammonia Storage

As one of common vehicle power sources,diesel engine is widely used due to strong power and lower fuel consumption.Yet it has greater impact on the atmospheric environment because of the far exceeding emissions of NO_x and PM compared with other types of engines.In order to reduce air pollution and meet increasingly strict standards,it's essential to develop advanced external emission treatment technology except optimization of internal reaction control technology for diesel engine.Currently,SCR is one of the main methods for domestic diesel engine exhaust treatment.It converts NO_x into NH₃ and H₂O through the formation of ammonia from injected urea,then purify off-gas.Therefore,the ammonia storage,which affects the SCR system efficiency,is one of the key factors.The paper takes the aftertreatment system of a certain diesel engine as research object,describes the reaction process of ammonia storage based on the principle of chemical reaction dynamics.According to V-type process of automotive electronic,build models of ammonia storage process and analyze them for forming the strategy.Then do the work of model calibration,equivalent tests,parameters identification,comparison validation.Subsequently,design hardware circuits for SCR controller and softwares about additional functions.Ultimately,inspect effects combined with bench tests.The details are as follows:Firstly,the model-based design method is used to model and analyze the process of ammonia storage control,finish fixed-point and obtain calculation accuracy by equivalent tests,explain the process of genreating embedded codes from the models.Then carry out catalyst experiment for observing ammonia adsorption and desorption processes and identify the key characteristic parameters of them.Establish simulation environment by Boost,the processes of adsorption and desorption are simulated with the identification parameters as boundary conditions.The results of model simulation and experiment are used to confirm the simulation effects of corresponding strategy.Secondly,choose MPC5634M chip as core processor.Design hardware circuits of SCR controller like power detection,voltage conversion,signals input,power supply,CAN transceiver.Compile the host computer software by LabVIEW in order to realize serial communication functions such as mode selection,transmission simulation and bytes statistics.For simulating data reading process of engine bench and management,a simple signal generator and database management software are developed with Delphi.Finally,carry out the bench emission tests by following the WHTC and WHSC.The bench systems consists of the SCR control system and the diesel engine,which is used to verify whether the strategy meets the requirements of latest emission limit.The test results show that the SCR system can greatly reduce the emission of NO_x and NH₃leakage,reach the standards in new pollutant discharge of vehicle exhausts in the future.