Modeling And Simulation Optimization Of Emission Control SCR System For Diesel Engine In Use

Diesel engines are widely used in transportation,industry,production and other fields because of their excellent power and fuel economy.For diesel engines,the emission of nitrogen oxides is the most important part of diesel engine emission control.SCR system is optimized from two aspects of system structure and control strategy.The main contents of this paper are as follows:(1)Research background and significance of SCR system optimization.Firstly,China's current emission regulations and pollutant control forms are briefly introduced,and then several industrial treatment methods of diesel engine main pollutants are listed from the point of view of In-engine purification and exhaust after-treatment.In addition,the structure optimization and control of SCR system at home and abroad are summarized.The research background and current situation of control strategy optimization lead to the purpose and research content of this paper,which optimize the SCR system by numerical simulation and control simulation respectively to improve the system performance.(2)Research methods and simulation software are introduced.Firstly,the research method of SCR system structure optimization is introduced.A three-dimensional geometric model of diesel engine SCR system is established.Based on the physical and chemical process of urea solution,five sub-models of turbulent diffusion,droplet evaporation,pyrolysis,fragmentation and wall-impact are established to simulate the whole SCR system.Secondly,the paper introduces the strategy framework of urea injection in SCR system,and builds the chemical reaction dynamics model of SCR system based on MATLAB/Simulink,and the fuzzy logic control method of urea injection quantity.(3)Research on SCR system structure optimization.The SCR reactor was simulated and validated by AVL FIRE software,and the structural parameters of SCR system were optimized by response surface optimization method.The optimum injection parameters were obtained as follows: the number of nozzle holes was 8,the distance from the front end of the reactor was0.29 m,the injection velocity was 69.65 m/s,and the spray cone angle was 117.4 degrees.The optimum parameters for the structure design of SCR catalyst were obtained.(4)The optimization of control strategy for SCR system is studied.The urea injection enabling control strategy of SCR system and the calculation method of urea injection quantity ofSCR system are studied.The control effect of fuzzy control system on NOx concentration at outlet is analyzed by simulation.Finally,the ESC cycle and ETC cycle are simulated offline,and the ESC cycle is calculated respectively.The results show that the SCR fuzzy logic control strategy meets the emission regulation standards.