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Development of a variable resistance-capacitance model with time delay for urea-SCR system

  • Feng, Tan (Key Laboratory of High Performance Ship Technology of Ministry of Education, Wuhan University of Technology) ;
  • Lu, Lin (Key Laboratory of High Performance Ship Technology of Ministry of Education, Wuhan University of Technology)
  • Received : 2014.06.15
  • Accepted : 2015.04.14
  • Published : 2015.06.30

Abstract

Experimental research shows that the nitric oxides ($NO_X$) concentration track at the outlet of selective catalytic reduction (SCR) catalyst with a transient variation of Adblue dosage has a time delay and it features a characteristic of resistance-capacitance (RC). The phenomenon brings obstacles to get the simultaneously $NO_X$ expected to be reduced and equi-molar ammonia available to SCR reaction, which finally inhibits $NO_X$ conversion efficiency. Generally, engine loads change frequently, which triggers a rapid changing of Adblue dosage, and it aggravates the air quality that are caused by $NO_X$ emission and ammonia slip. In order to increase the conversion efficiency of $NO_X$ and avoid secondary pollution, the paper gives a comprehensive analysis of the SCR system and tells readers the key factors that affect time delay and RC characteristics. Accordingly, a map of time delay is established and a solution method for time constant and proportional constant is carried out. Finally, the paper accurately describes the input-output state relation of SCR system by using "variable RC model with time delay". The model can be used for a real-time correction of Adblue dosage, which can increase the conversion efficiency of $NO_X$ in SCR system and avoid secondary pollution forming. Obviously, the results of the work discover an avenue for the SCR control strategy.

Keywords

Diesel engine;Urea-SCR;Weight analysis;Time delay;Resistance-capacitance

Acknowledgement

Supported by : National Natural Science Foundation of China

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