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  • Title: Experimental demonstration of NOx reduction and ammonia slip for diesel engine SCR system.
    Author: Yue G, Qiu T, Lei Y.
    Journal: Environ Sci Pollut Res Int; 2022 Jan; 29(1):1118-1133. PubMed ID: 34350573.
    Abstract:
    This paper investigates the characteristics of selective catalytic reduction (SCR) with a V2O5-WO3/TiO2 catalyst by studying the key parameters and determining a method for controlling ammonia injection with a sample test bench. Four parameters are defined and adopted to represent the characteristics of nitrogen oxides (NOx) and the ammonia reaction. The effects of NH3/NOx ratio (NSR), catalyst temperature, and ammonia injection period on NOx conversion efficiency and ammonia slip are investigated. The correlation between ammonia slip and ammonia saturation storage level is studied. The experimental results show that the ammonia saturation storage level has a great impact on NOx reduction and ammonia slip. The NOx conversion efficiency and ammonia slip strongly depend on the ammonia saturation storage level. Under such conditions, the NOx conversion efficiency is best when the ammonia saturation storage level is 68.2~73%, and the value reaches 75% before ammonia slip. Pulse injection improves the NOx conversion efficiency and limits ammonia slip. Comprehensive comparison shows that the injected ratio of NH3/NOx is first larger and then smaller than is beneficial for the rapid improvement of NOx conversion efficiency; the appropriate NH3/NOx ratio and continuous injection time must be controlled, or it is easy to cause ammonia slip. Therefore, a control algorithm based on ammonia storage saturation level has been proposed. According to the difference between the actual value of ammonia storage saturation and the target value, the controller corrects the injection of urea to achieve control of ammonia storage saturation level. The period of pulse injection has little influence on the mean value of NOx at the outlet; however, it affects the peak level of NOx and ammonia slip. Using varied period pulse injection further improves the NOx conversion efficiency and restrains ammonia slip. The outlet level of NOx can be reduced by adopting a suitable ammonia pulse injection interval.
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