A simulation model for selective catalytic reduction (SCR) of exhaust gas from diesel engine is established

and a concept of urea decomposition efficiency is proposed. Effects of exhaust gas temperature

NH3 storage

NO2/NOx ratio and NH3/NOx ratio on the NOx conversion efficiency are studied. The results show that the urea decomposition efficiency increases with decreasing exhaust gas flow rate and rising exhaust gas temperature. Special evaluating experiments for NOx conversion efficiency under various temperatures were performed. The data obtained by simulation show good agreement with the experimental results. The results show that the NOx conversion efficiency increases with the NH3 storage capacity rising. Similarly

the NOx conversion efficiency increases with rising exhaust gas temperature

and it gets stable when the exhaust gas temperature reaches a certain value. Increasing NO2/NOx ratio can also improve the NOx conversion efficiency

but the opposite phenomenon occurs when the NO2/NOx ratio is greater than 50%. With increase of NH3/NOx ratio

the NOx conversion efficiency ascends

and the influence is obvious when the exhaust gas temperature is high.