Study On The Catalyse Simulation And Control Strategy Of Urea-SCR System

Through injecting the 32.5% urea solution into the exhaust and with the effect of catalyst,the technology of Urea-SCR applied in diesel engine can make the NOx reacted with the NH3 into nitrogen and water.This technology is the best promising way for the heavy-duty diesel engines to meet the ChinaⅣandⅤemission standards. This paper did a detailed analaysis of the Urea-SCR system,the main content includes:（1）According to the assumptions of porous media, the one dimensionl model of an advanced catalytic converter-HSO was built.And the model was verified by comparing with the experimental data in related literatures,and the simulation results were well agreed with the experimental data.It indicates that the HSO model can simulate the process of the reaction in the catalytic converter.（2）The factors influencing the efficiency about DeNOx and other features of the systerm were studied .The results suggest that when the content of NO₂ gets 50% of the NOx,the DeNOx of the system, especially under the lower tempreture, can reach the best.The preoxidation catalyst has a positive effect on improving the activeness of the catalyst under the lower temperature,but less or negative effect when the temperature is high;The DeNOx is not the only target when we consider the amont of the NH3,but the slip and the efficiency of NH3;The study of the O₂ content suggest that:The DeNOx increase with the increasing of O₂ when the content stay at a low level,and when the O₂ content is higher than a value,the DeNOx can hardly change; The system has a higher DeNOx when the GHSV become lower.Both of the experimental and simulation research show that:at the lower temperature,the H2O has a inhibition effect and the SO₂ has a little positive effect on the system.（3）This paper did a research on the control strategy. The urea dosing and correction strategy were detaily studied.The closed-loop control strategy based on NOx and NH3 sensor are studied and setup;To solve the urea frozen problem when the temperature comes below -11℃,the control and judging strategy experimental were studied. The cold chamber experimental indicates that:By setting up and spying the pressure of the pump,we can successfully kown the situation of the deforsting;And the way of heating the tank and dosing module with the cirlculating water ,and heating the pipe with the electricity is effective.The experimental data shows that:when the environment tempreture is -20℃,to defrost the system need 30 minutes ;And when the the environment tempreture is lower than -30℃,the deforsting time is about 50 minutes.