The Model Based Control Strategy for an Advanced UREA-SCR System
Currently the advanced UREA-SCR system is one of the most popular technology to meet the strict emission standards as Euro IV or above. In order to reach high NOx conversion and low NH3 slip, the urea dosing rate needs to be calculated and controlled prec
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Abstract Currently the advanced UREA-SCR system is one of the most popular technology to meet the strict emission standards as Euro IV or above. In order to reach high NOx conversion and low NH3 slip, the urea dosing rate needs to be calculated and controlled precisely. This paper describes an advanced UREA-SCR system based on model based control strategy and advanced diaphragm urea dosing pump. The strategy can be seen as a virtual closed-loop control method for the dosing rate calculation, and it was integrated with the advanced diaphragm urea dosing pump for the tailpipe urea dosing. A SCR chemical reaction model was developed to describe the concentration of different spices inside the SCR catalyst. Three different reactions were taken as the foundation of the model, including fast reaction, normal reaction and slow reaction. To simplify the process of calculation, the catalyst model was divided to three cells. In each cell, the NH3 storage ability was estimated and the results were taken as the feedback signals for the controller. A virtual closed-loop control method was developed to calculate the dosing rate. The model was tuned under different engine running conditions, the exhaust gas temperature was controlled between 250 and 400 °C and the NH3/ NOx molar ratio was controlled between 0.8 and 1.1. An advanced-diaphragm urea dosing pump was developed to finish the urea dosing activity. The results of transient engine running experiment show that the NOx conversion efficiency can reach 85 % while keeping the average NH3 slip under 15 ppm, the peak average NH3 slip under 30 ppm. And the dosing rate error can be controlled less than 3 %. Keywords Diesel engine
UREA-SCR Model based control NOx SCR
F2012-A04-036 Z. Liu (&) H. Wang Y. Wang China Automotive Engineering Research Institute, Chongqing, China e-mail: [email protected]
SAE-China and FISITA (eds.), Proceedings of the FISITA 2012 World Automotive Congress, Lecture Notes in Electrical Engineering 189, DOI: 10.1007/978-3-642-33841-0_61, Ó Springer-Verlag Berlin Heidelberg 2013
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1 Introduction As one of the main technology method to meet the Euro IV or more strict emission regulation, SCR technology has been widely used all over the world. Compared with another main technology-EGR, SCR has the advantage of simple structure, obvious effect to reduce NOx emission and has low fuel consumption. To control the dosing rate of UREA, the system needs to take the balance of NOx conversion efficiency and ammonia slip into account. That means if the system has a smaller UREA dosing rate than requested, the NOx conversion efficiency will be affected, and the ammonia slip will be reduced. And if the system has a larger UREA dosing rate than requested, though the NOx conversion efficiency can reach a higher level, the ammonia slip will exceed the standard. When the engine runs in a steady state, it is easy to adjust the dosing rate to balance the NOx conversion efficiency and ammonia slip. But when the engine runs in transient
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