Experimental and numerical investigation on the urea SCR dosing system to improve NOx reduction efficiency

Urea SCR system is widely used for heavy duty commercial vehicle to meet the stringent NOx emission standards. However, urea SCR system has some problems such as ammonia slip and urea deposition in the exhaust pipe. Therefore, systematic optimization on the urea dosing components including SCR catalyst is absolutely required to confirm the high purification performance. In this research, urea injection spray patterns were investigated with various injection nozzle holes and geometries using PMAS (Particle Motion Analysis System). Micro thermal reactor which could control the mass flow rate and temperature of modal gases was designed to determine the optimal urea dosing location, spray cone angle and injection control strategy for minimizing ammonia slip. To verify the high purification ratio of SCR catalyst, catalyst volume and inlet diffuser geometry were evaluated. Finally, numerical analysis based on the modal test results was performed to decide the optimal urea injection location which enhanced the mixing uniformity at frontal reacting zone of SCR catalyst.