DOC系统催化性能的仿真和分析

Numerical simulation and analysis of catalytic performance of DOC system

以Langmuire Hinshelwood机理为理论依据,基于MATLAB/Simulink建立DOC系统的数值计算模型,研究不同参数(如空速、氧气浓度、NO2/NOx比例)对氮氧化物(NOx)、一氧化碳(CO)、碳氢化合物(HC)转化效率的影响,并对部分工况进行了实验研究,从而验证数值模型的准确性。结果表明,空速的降低可以增大DOC对CO、HC、NO的氧化性能,这是由于排气在催化器内的反应时间增长。当排气温度为225~300℃时,减小空速对增大HC的氧化效率效果明显,当排气温度在175~450℃范围内,减小空速对增大NO的氧化效率影响明显;当O2浓度低于1%,排气温度在175~250℃时,CO转化效率增大,在250℃之后均接近100%。当O2浓度为10%时,温度的变化对CO的转化效率影响很小。当O2浓度大于1%时,温度的变化对NO的氧化效率影响较大;当排气温度在300~550℃时,NO2/NOx比例的变化对NO的转化效率影响较大。降低排气中NO2/NOx比例,能够在排气温度高于300℃时,明显提高NO的转化效率。

Based on Langmuire Hinshelwood mechanism, a numerical simulation model of DOC was established under the environmental of the MATLAB/Simulink. After introducing mathematical models for the DOC reaction,the effects of various parameters such as gas hourly space velocity, the O2 concentrations and the ratio of NO2/NOx on the CO,HC,NO conversion efficiencies are thoroughly studied and validated by comparing with the experimental data. The results show that lowering the space velocity can improve the DOC performance due to the residence time of the exhaust gas increases. The HC conversion efficiency depends strongly on the space velocity in the range of225 ℃ and 300 ℃. The NO conversion efficiency depends strongly on the space velocity in the range of 175 ℃and 450 ℃. The CO conversion efficiency increase with temperature and reaches nearly 100% in the range 250 ℃and 550 ℃ when the O2 concentration lower than 10%. The O2 concentration greater than 10% have no significant effects on the CO conversion efficiency. The NO conversion efficiency depends strongly on the temperature when the O2 concentration greater than 1%. The NO conversion efficiency depends strongly on the NO2/NOxratio in the range of 300 ℃ and 550 ℃. Lowing the NO2/NOxratio can improve the NO conversion efficiency when the temperature greater than 300 ℃.