Modeling And Research Of Urea-SCR Exhaust System

In the modern era, the auto industry is undergoing a fundamental transformation due to the energy crisis and the air pollution issue. High efficiency and eco-friendly orientated innovations have become the biggest focus for all the auto makers and related practitioners. Engine NOx control is a critical technique and contributes significantly to the NOx emission reduction. In this paper, two engine NOx emission routes had been compared, from which a conclusion can be drawn that Selective Catalytic Reduction(SCR) is currently the most effective NOx control technique and suitable to Chinese condition. Rapid designing and developing specific SCR systems for engines with particular NOx emission level has become one of the most urgent tasks.This paper based on a deep understanding of Urea-SCR catalytic converter system, developed a numerical model for calculating NOx converting rate of the system and obtained the law of internal motion for the SCR catalytic converter system. A series of conclusions had been reached including the movement direction of exhaust inside the converter and a series of changes of Urea aqueous solution from evaporation decomposition, mixing with exhaust, to catalytic reduction reaction. The main research content included:1. Conducted a comprehensive literature review of the work principle of catalytic converter system and the timeline and summarized a variety of theories and mathematical models involved in the SCR catalytic converter modeling process.2.Established a full auto-use SCR Catalytic Converter system model and developed an ideal SCR catalytic muffler3D model in AVL FIRE platform based on a modified computational hydrodynamic model that was integrated with SCR reaction dynamic model and urea aqueous solution decomposition reaction model.3. Analyzed the distribution of critical parameters such as flow rate and component concentration in one injection cycle; revealed the urea aqueous solution-to-ammonia conversion and mixing process; proposed structural performance evaluation metric for SCR catalytic muffler system.4. Studied the influence of temperature, excess coefficient of ammonia, and air speed ratio on the efficiency of the catalytic converter, which provided a basis for urea supply and converter selection.