Simulation Study on Prediction of Urea Crystallization of a Diesel Engine Integrated after-Treatment Device

An integrated after-treatment device model was established for our target engine based on the fluid simulation software (Converge), and simulation was performed to determine the NH₃, temperature, and velocity uniformity at the front-end cross section of its SCR catalyst, urea deposition rate, liquid film mass of the mixer, and its positions under a low-load condition. Moreover, the structure of the mixer and injection pressure were optimized to improve the uniformity and reduce the liquid film mass. Our simulation results show the following facts: the liquid film is easily accumulated under a low-load condition and the structure of the mixer and the injection pressure significantly affect the urea deposition rate and uniformities and accumulation masses of the liquid film. As a result, our final optimization results indicate that the mass of the NH₃ and the NH₃ uniformity at the front-end cross section of the SCR catalyst increase by 2.83 times and 5.65%. The urea deposition rate and the cumulative mass of the liquid film fall by 4.82 and 10.4%, respectively. This study has certain theoretical guiding significance for the optimal design of this type of after-treatment devices.