Structural Optimization And Experimental Study For Diesel Engine SCR System Based On China-6 Standard

Diesel engines have inherent advantages such as high power,high torque,and strong power.They play an irreplaceable role in machinery,transportation,aerospace,military and other important fields,but their exhaust emissions are the source of many air pollution problems.China-Ⅵheavy diesel engine emission regulations were officially implemented on July 1,2019,which indicates that China’s restrictions on diesel engine exhaust pollutants will be tightened further.With the continuous updating of emission control methods,more and more effective technologies have emerged.Among them,Selective Catalytic Reduction is a high-efficiency technology that is widely used to deal with NO_xpollution.In this paper,the CFD fluid simulation method is used to optimize the structure of the SCR catalyst,and the related experiments verify that the optimization scheme can effectively improve the catalytic reduction reaction rate of the system,which has certain theoretical value and practical significance.This article takes the H20 diesel engine of a domestic main engine factory as the research object,and relies on the China-Ⅵaftertreatment development project.Starting from the theoretical method,the development process of domestic and foreign emission regulations is explored,and the current mainstream post-processing technology route is introduced.Then combined with the structure and working principle of the SCR catalytic converter,a numerical model was established,and a new grid mixer was designed.Use modeling software to build the SCR system and three-dimensional models of different mixers,and then mesh the mesh.Import the divided models into the simulation software AVL FIRE for CFD fluid simulation.The SCR system of the scheme is used to analyze the flow field,and the pressure loss,turbulent kinetic energy,NH3 distribution,NO_xconversion efficiency and other factors are used as the evaluation indicators to select the best scheme and verify the bench test.During the test,the effect of the new mixer on mixing uniformity and NO_xconversion efficiency was studied,and the reliability of the model was verified;the SCR shell structure was optimized to investigate the changes in the speed distribution,The influence of flow field distribution and pressure distribution is the best transformation plan.The design test explored the factors influencing the NO_xconversion efficiency of the optimized SCR system.The analysis and test results showed that the conversion efficiency of the SCR system equipped with the new mixer was higher,and the urea crystallization condition was better,which met the requirements of the China-VI emission pollutant limit.Finally,the WHTC emission cycle test was used to verify the suppression effect of the conversion performance of the aftertreatment system equipped with the new mixer on NH₃leakage.During the test,the following conclusions were obtained:the pressure loss of different mixer schemes varies greatly,and the mixer with larger pressure difference is more prone to urea crystallization problems,which affects the catalytic conversion effect;under different working conditions,the two scheme mixers can effectively improve NH3 mixing uniformity;transform the expansion cone angle of the inlet expansion tube,the larger the angle,the greater the pressure loss,and the catalyst is easy to accelerate aging,affecting the catalytic conversion rate;the change of the shrink cone angle of the outlet shrink tube affects the mixing uniformity and catalysis The reduction reaction rate has no obvious effect.The NO_xconversion efficiency of the optimized SCR catalyst is increased by 2.1%-4.6%compared to the original SCR catalyst.And the NO_xconversion efficiency of the optimized SCR system in the temperature range of 210℃-530℃is higher than 95%,which meets the development requirements of the China-VI diesel engine SCR system.