Developing And Simulation Research Of Urea-SCR System Control Model Of Diesel Engine

With the continued growth of motor vehicles and the subsequent shortage of energy, develop and perfect the NOx control technology for vehicles has a great significance to reduce the global NOx emission. Facing the daily stricter emission regulation, the Urea-SCR technology is generally acknowledged as the favorable choice among various exhaust aftertreatment technologies for meeting the current automotive diesel engine emission standards. In order to handle the different diesel engines with discrepant NOx emissions levels, exert great efforts in developing suitable SCR aftertreatment systems has become an urgent task.After the urea injection flow control strategy of SCR system is determined, obtaining the precise control parameters through effective calibration is indispensable. It is aimed to ensure that during the SCR system's usual service conditions the diesel engine emissions correspond to the regulations and standards. This paper established the SCR system simulation model for diesel engines, which was based on MATLAB/Simulink software platform. According to the diesel engine's ETC test NOx emission and the NH3 slip simulation prediction, improved and optimized the diesel engine's SCR control strategy. The main contents in the paper are as follows:(1) Established the catalyst's one-dimensional transient model under certain hypothetical terms, based on the AVL BOOST software platform, and introduced the model's solution plan and the optimization method for the parameters calculation; With the aid of AVL Design Explorer platform, adopted genetic algorithm to optimize the SCR chemical reaction kinetics parameters, Through the comparison of optimized calculation results and experimental data, it indicated that the optimized parameters improved the simulation performance of catalyst.(2) Established the urea injection flow controlling model in SCR system based on MATLAB/Simulink software platform, provided the function of modifying the model controlling parameters and adjusting the urea injection flow on-line. Through the calculation of urea solution's theory demand in NOx exhaust, and the logical computation of urea injection flow demand, combined the original engine's NOx emission map, the exhaust flow map and conversion efficiency map of the catalytic converter, established urea injection flow control model in SCR system on MATLAB/Simulink software platform.(3) By using the MATLAB/Simulink software, based on the urea injection flow control model in SCR system, through the coupling calculating with AVL BOOST software, it embedded the real-time SCR catalytic chemical reaction model and structured a diesel engine's NOx emission prediction model, which included signal input system, urea injection flow control system, catalytic reaction calculation system and NOx emission output system. This paper propounded and carried out an advanced and matched diesel engine emission calibration method. According to the diesel engine's ETC circular NOx emission test and the results of NH3 slip simulation prediction, this paper improved and optimized the diesel engine's SCR control strategy based on established simulation model. Finally, the experiment results testified the validity and practicability of the simulation model.