Numerical Study On Spray Characteristics For Urea-SCR Diesel Nozzles And Test Research

With the reducing of the non-recycling energy and the strengthening of public awareness of environmental protection, the automotive engine emission problem, especially NOx emission problem, has become pay attention to. Based on reading a lot of literature, we found that the urea selective reduction technology (Urea-SCR), one of the diesel engine after-treatment technologies, has been considered to be the most effective one to reduce the global nitrogen oxide emissions, which would be very significance. China started relatively late on the SCR technology. But with further research, many domestic enterprises also began to produce SCR products.This paper summarizes the chemical reaction principle of the Urea-SCR after-processing system, analyzing the influencing factors of the process of the reaction, and studying the urea nozzle and the catalytic reduction reactor through the market survey. Based on the FLUENT software, it summarizes the simulation test method and analysis the spray model and the porous medium model by the mathematical and modeling methods.Apply the SOLID WORKS software to build a three-dimensional model of the SCR system, and then import the model to the GAMBIT for meshing. To verify the spray model with the parameter of the test spray pattern. Measure the loss of the pressure of the model. The pressure loss of the catalytic converters accounted for30%-40%of the engine exhaust system pressure loss, which can verify the rationality of the model.Based on the flow uniformity criteria to compare different number of nozzles, different jet positions and jet directions, different nozzle diameters, which will have an effect on the system. The results show that:at the center of the pipe, the arrangement of the four-hole radial jet can help to improve the mixing uniformity of NOx and NH3at the entrance of the catalyst carrier to ensure the adequacy of the catalytic reduction reaction, slowing the aging of catalytic converters, improving NOx conversion efficiency and reducing the NH3leak. The nozzle pressure loss of carrier of the catalytic converter with different jet positions and jet directions is in the normal range.According to the conclusion reached by the simulations, we could choose the form of a four-hole nozzle with radial injection at the center of the pipe to test the Urea-SCR system. The results showed that:this form made NOx conversion rate reach above95%, improving the conversion rates with higher urea injection. But too much urea injection would cause the NH3to leak. The best ratio of the exhaust gas mixed with NH3is1.2.