中文摘要：

采用1台满足国Ⅳ标准的高压共轨、涡轮增压中冷柴油机，研究了在加装尿素选择催化还原器（urea—SCR）前后的NOz排放特性。通过测量urea—SCR前后排气温度、压力、氮氧化物（NO2）和二氧化氮（NO2）排放量等参数，研究了NOz对柴油机urea—SCR性能的影响。分析结果表明：随着urea—SCR前排气温度上升，NOx中NO2百分比降低；当发动机转速一定时，NO2比例随扭矩的增大而降低；当发动机扭矩一定时，NO2比例随转速的上升呈现“V”形变化趋势；当urea—SCR前排气温度为255℃时，urea-SCR转化效率受NO2比例的影响波动性较大；在335℃时转化效率和NO2比例的变化趋势一致性最大。

英文摘要：

For a turbocharged and intercooled State IV diesel engine with high-pressure common rail, the NO2 emission before and after the urea-SCR was researched. Based on the measured exhaust temperature, exhaust pressure, NO~ and NO2, the in- fluence of NO2 on urea-SCR performance was studied. The results show that the NO2/NOx ratio decreases with the increase of temperature before the urea-SCR. For the constant speed, the NO2/NOx ratio decreases with the increase of engine torque. For the constant torque, the NO2/NOx ratio shows the V-typed trend with the increase of engine speed. When the temperature be- fore the urea-SCR is 255 ℃ , the influence of NO2 on SCR efficiency fluctuates. At 335℃ , the trends of SCR efficiency and NO2 fraction have the best consistency.