SCR Structure Optimization And Test Validation Based On The CFD Simulation Technology Of Diesel Engine

With the increasing of air pollution,more and more people pay attention to car exhaust emissions.Under the increasingly strict requirements of emission regulations,exhaust after-treatment technology get more and more attention by people.SCR technology can meet the European IV even European V emission standards,become the main direction of present medium-duty truck reduce NOx.The SCR system for impact of six-cylinder heavy diesel engine and its numerical analysis and experimental verification are studied in this paper the main research contents include:(1)Analyzes the route and reduce NOx simulation analysis principle,the dynamics of the original model of one-dimensional simulation parameter calibration and two different conditions of three-dimensional numerical simulation of fluid to the following conclusion: Under two kinds of working points,before and after the spray,the pressure and the flow field change is very small;loss of pressure and velocity variation,working rated condition is significantly higher than the working condition 2.Working condition 2 through distance,sauter mean diameter of stability more easily;the working rated condition of the carrier of a front-end NH3 uniformity and NOx conversion rate below working condition 2.(2)On the basis of the original model,through the CFD simulation comparison of the three types of mixer position(Scheme 1 upstream to join in the nozzle mixer,scheme 2 and scheme 3 in the downstream of the nozzle to join mixer,but plan three position even more)changes affect of SCR,concluded that : three kinds of mixer position can improve the vehicle front velocity uniformity,NH3 distribution uniformity,and scheme 2 more obvious,but scheme 2 mixer internal temperature distribution is more uneven,produce more liquid membrane,increase the risk of urea crystallization at low temperatures.(3)In the above scheme 2,before the taper pipe added three porous pipes(Pipe a add a covered with a diameter of 11 mm at the bottom of the porous pipe 1 and also with the same diameter holes,posous pipe 2 o is on the basis of a porous pipe 1 sealing,perforated porous pipe 3 will be at the bottom of a perforated pipe into a cone),get the following conclusions: three kinds of solution can affect the flow field,raised the speed of the vehicle front-end uniformity,NH3 distribution uniformity,NOx conversion rate,the uniformity of temperature field distribution,and porous pipe 2 more apparent.(4)The standard test bench show: One-dimension calculation model and the threedimensional calculation model test values and the calculated values are less than 5% error,the models are reasonable.Use porous pipe 2 Urea-SCR system to test the ESC steady-state cycle as an example,and study the 13 conditions of NOx,CO and THC emissions,the Urea-SCR system can achieve the china stage IV emission regulations,and has the potential to upgrade to the china stage V emission regulations.And explores the SCR system for the whole engine performance and fuel economy,the influence of both shows different degrees of decline.