柴油机SCR载体SOF覆盖试验研究

Experimental Study on the SOF Coverage of SCR Carrier of Diesel Engine

针对柴油机选择性催化还原(SCR)载体因可溶性有机物(SOF)覆盖而导致SCR系统NO_(x)转化效率低的问题,首先通过试验确定发动机颗粒物(PM)原始排放成分(典型稳态工况)中soot和SOF平均质量占比分别约为24.9%和75.1%;其次,进行PM成分的捕集效率试验(典型稳态工况),SCR载体对SOF具有较高的捕集效率,且与SOF沉积量有关,soot会伴随SOF被SCR载体捕集,对PM的捕集效率为两者的叠加,基于笔者设计的稳态15工况点,新鲜态SCR载体对SOF、soot和PM的捕集效率平均值分别为73.3%、-0.7%和56.9%左右;然后进行SCR载体的SOF沉积量试验,24 h稳态试验后SOF沉积量约为30 g时,NO_(x)转化效率下降36%左右;最后进行基于台架的SOF热解去除试验,控制SCR上游排气温度约为300℃,持续1 h,NO_(x)转化效率可以完全恢复.相同质量的SOF,台架热解的时间比热重(TG)分析热解的长,台架热解的活化能与TG热解的相当,台架热解指前因子自然对数仅为TG热解的36%左右.

Effects of soluble organic fraction(SOF)coverage on NO_(x) conversion efficiency of the selective catalytic reduction(SCR)were studied by engine bench tests on a diesel engine with SCR system.Firstly,results show that soot and SOF average mass take up about 24.9%and 75.1%of engine PM raw emission in typical steady-state condition.Secondly,the experimental study on the capture efficiency of PM under typical steady-state conditions proves that SCR carrier has a comparable capture efficiency to SOF and is related to the amount of SOF deposition.Soot will be collected together with SOF by SCR carrier,and PM collecting efficiency is the superposition of both.Based on the 15 steady-state working points,the capture efficiency of SCR carrier to SOF,soot and PM are about 73.3%,-0.7%and 56.9%on average in fresh state.Then SOF deposition test measures that the NO_(x) conversion efficiency decreased by about 36%when the SOF deposition is about 30 g after the 24h steady-state test.Finally,SOF pyroly-sis test based on the bench show that the NO_(x) conversion efficiency can be completely recovered with 300℃of SCR upstream temperature for 1 h.For the same mass SOF,the pyrolysis time of bench is longer than that of thermogravimetry(TG)analysis,the activation energy of the bench pyrolysis is equivalent to that of TG pyrolysis,and the natural logarithm of the pre-exponential factor is only about 36%of TG.