Numerical Simulation Study Of Urea-SCR System For Vehicle Diesel Engines

In recent years, the diesel engine has been widely used because of its advantages in good economy,power and reliability. However, the emissions of main pollutants nitrogen oxides(NOx) and particulate matter(PM) are more serious. With the development of low emission law, simply reduce diesel emissions of pollutants by diesel machine measures do not meet emissions regulations, and the use of selective catalytic reduction(SCR) after-treatment technology to reduce nitrogen oxide emissions of diesel engine is one of the most effective methods.Taking a type of six-cylinder diesel engine exhaust system as the research object, on the basis of understanding about working and main chemical reaction mechanism, completed the following work:1) In order to improve the velocity uniformity of the front end of the SCR catalytic converter, the DOE(Design of Experiments)was used to optimize the structure parameters of SCR pipeline, which is obtained by combining the Latin Hypercube Design and Nelder-Mead algorithm.2) Based on computational fluid dynamics, three dimensional numerical simulation of SCR system of diesel engine was carried out by using AVL Fire software, and analysis of the distribution of the urea droplet and gas component of SCR system under different working conditions. At the same time, the influence of different nozzle jet direction, different nozzle offset angle and different nozzle offset position on the conversion efficiency of SCR system was studied.3) The paper selected three important factors what the nozzle jet direction, nozzle offset angle and nozzle offset position, and each factor selects five levels to orthogonal test analysis. It works out that each factor the order of affect NOx conversion efficiency, and we ascertain the best matching scheme about nozzle arrangement in B50 condition.4) The effect of the mixer on the SCR system is studied, and optimizing the structure of the mixer to improve the NOx conversion efficiency and reduce pressure loss of the system.5) The influence of SCR system on engine performance is analyzed with AVL Boost software.