Abstract: The prediction and control of ammonia slip are the key issues of selective catalytic reduction (SCR) system. A SCR sample test bench was built. The adsorption and desorption characteristics of ammonia in V₂O₅-WO₃/TiO₂ catalyst are studied, and the effects of NH₃/NO_x ratio and catalyst temperature on ammonia slip are analyzed. The results show that the ammonia slip increases rapidly once ammonia leaks. The prediction of critical point of ammonia slip is very crucial for the control of ammonia slip. When the ammonia slip reachs to a critical point, the ammonia storage saturation level is not changed with the change in NH₃/NO_x ratio and catalyst temperature. When NH₃/NO_x ratio is set to 0.7, 1.0 and 1.4, the ammonia storage saturation level is 79%, 75% and 76%. The value of ammonia storage saturation level maintains fluctuations in the rangg of about 76.7% when the ammonia slip reachs to the critical point. The ammonia storage saturation level is related to the ammonia slip critical point. The control method of ammonia slip is designed based on the correlation between ammonia saturation level and ammonia slip critical point. The control method was used for SCR, and the European transient cycle (ETC) test of engine was performed. The ETC test results show that the brake specific emission of outlet NO_x is reduced to 2.45 g/(kW·h), the average ammonia slip is 3.7 ×10^-6, and the peak ammonia slip is 12.8×10^-6, which meet the requirements of national IV emission regulations. Key

Key words: powermachineryengineering, dieselengine, selectivecatalyticreduction, ammoniaslip, emission