重型柴油机主要含氮化合物的排放特性

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/NO_x值要明显低于原机状态,而外特性的NO₂/NO_x值和N₂O/NO_x值高达12.8%和20.7%,均远高于原机的3.0%和0.5%。

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

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/NO_x ratio of the engine with SCR was obviously lower than that of the engine without SCR, while the NO₂/NO_x ratio and N₂O/NO_x ratio were 12.8% and 20.7%, respectively, which were much higher than those of the engine without SCR.