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.