双级SCR系统N_(2)O排放特性试验研究

Experimental Study on N_(2)O Emission Characteristics of a Two-Stage SCR System

以1台国六重型柴油机为研究对象,搭建了双级选择性催化还原(SCR)后处理系统,对冷态和热态全球统一瞬态(WHTC)循环的N_(2)O排放特性进行试验研究。结果表明:采用双级SCR系统后,柴油机在冷态和热态WHTC循环均产生大量的N_(2)O,且出现明显的排放峰值,冷态循环N_(2)O平均体积分数为22.3×10^(-6),热态循环N_(2)O平均体积分数为24.4×10^(-6)。前置SCR单独工作时,其出口处N_(2)O排放较低,但由于尿素过量喷射,导致尾排处N_(2)O排放峰值较大,热态循环N_(2)O平均体积分数达到13.5×10^(-6)。主SCR单独工作时产生的N_(2)O排放峰值较小,冷、热态循环N_(2)O平均体积分数分别为5.5×10^(-6)和11.2×10^(-6)。通过减少前置SCR的尿素喷射量以控制NH3泄露,同时优化主SCR尿素喷射策略可以有效降低N_(2)O排放。

A two-stage SCR aftertreatment system was built for a heavy-duty diesel engine of China 6.The N_(2)O emission characteristics of cold and hot WHTC cycles were studied.The results show that a large amount of N_(2)O emission is produced in both cold and hot WHTC cycles with an obvious peak value of N_(2)0 emission.The mean volume fraction of N_(2)0 in cold cycle is 22.3×10^(-6).The mean volume fraction of N_(2)0 in hot cycle is 24.4×10^(-6).When the front SCR works alone,the N_(2)0 emission is lower at the exit.Because of the excessive urea injection,the peak N_(2)O emission is larger at the tail end,and the average volume fraction of N_(2)O in the hot cycle reaches 13.5×10^(-6).The peak value of N_(2)0 emission is small when the main SCR works alone.The mean volume fraction of N_(2)0 in cold and hot cycles are 5.5×10^(-6)and 11.2×10^(-6),respectively.N_(2)0 emissions can be effectively reduced by reducing the amount of urea injection of the front SCR to control NH,leakage and optimizing urea injection strategy of the main SCR.