重型柴油机主要含氮化合物的排放特性

Emission of nitrogen-containing compound from a heavy duty diesel engine

采用傅里叶变换红外光谱(FTIR)技术,研究了加装选择性催化还原SCR装置的重型柴油机主要含氮化合物排放,重点探索了不同工况下主要含氮化合物NO、NO2和N2O的排放特性。结果表明:未加装SCR的原机,随负荷的增加,柴油机NO排放持续上升,NO2排放先升后降,N2O排放很少。加装SCR后该柴油机NO与NO2排放均明显下降,标定转速下NO2排放降幅较大,主要是其NO2/NO值稍高导致快速SCR反应较多的原因。由于存在SCR副反应,与原机相比,柴油机N2O排放比原机平均增加2倍以上,最大转矩转速下N2O排放升幅更高。N2O排放随负荷的增加而上升,主要是排温升高导致NH3氧化生成N2O反应速率增加的原因。加装SCR后,该机排气中的NO/NOx值要明显低于原机状态,而外特性的NO2/NOx值和N2O/NOx值高达12.8%和20.7%,均远高于原机的3.0%和0.5%。

The emission of nitrogen-containing compound from a heavy-duty diesel engine with selective catalytic reduction（SCR） was studied by using Fourier transform infrared spectrum（FTIR） technology. The main emitted nitrogen-containing compounds including NO, NO2 and N2O under different operating conditions were analyzed. The results showed that the NO emission from the engine without SCR ascended with increasing engine load. The NO2 emission ascended firstly and then declined, while the N2O emission was very low. Compared to the engine without SCR, the NO and NO2 emissions from the engine with SCR significantly descend, and the NO2 emission decreased remarkably at rated engine speed, which was because the rapid SCR reaction rate increased with increasing NO2/NO ratio. The N2O emission from the engine with SCR was more than twice from the engine without SCR, particularly higher at full load, which was due to the existed SCR side reaction. The N2O emission ascended with increasing engine load since that increasing exhaust temperature led to higher oxidation reaction rate of NH3 to N2O. The NO/NOx ratio of the engine with SCR was obviously lower than that of the engine without SCR, while the NO2/NOx ratio and N2O/NOx ratio were 12.8% and 20.7%, respectively, which were much higher than those of the engine without SCR.