Experimental studies on the diesel engine urea-SCR system using a double NOx sensor system

  • Tang, Wei (School of Automotive and Traffic Engineering, Jiangsu University) ;
  • Cai, Yixi (School of Automotive and Traffic Engineering, Jiangsu University) ;
  • Wang, Jun (School of Automotive and Traffic Engineering, Jiangsu University)
  • Received : 2015.08.19
  • Accepted : 2015.11.06
  • Published : 2015.12.31


SCR has been popularly approved as one of the most effective means for NOx emission control in heavy-duty and medium-duty vehicles currently. However, high urea dosing would lead to ammonia slip. And $NH_3$ sensor for vehicle emission applications has not been popularly used in real applications. This paper presents experimental studies on the diesel engine urea-SCR system by using a double NOx sensor system that is arranged in the downstream of the SCR catalyst based on ammonia cross-sensitivity. It was shown that the NOx conversion efficiency rised as $NH_3/NOx$ increases and the ammonia slip started from the $NH_3/NOx$ equal to 1.4. The increase of temperature caused high improvement of the SCR reaction rate while the space velocity had no obvious change. The ammonia slip was in advance as catalyst temperature or space velocity increase and the ammonia storage reduced as catalyst temperature or space velocity increase. The NOx real-time conversion efficiency rised as the ammonia accumulative storage increase and reached the maximum value gradually.


Supported by : National Natural Science Foundation of China


  1. Knecht W. Diesel engine development in view of reduced emission standards. Energy 2008;33:264-271.
  2. Sarlashkar J, Sasaki S, Neely GD, Wang J, Sono H. An airflow-dominant control system for future diesel engines. SAE Technical Paper 2007;116:753-765.
  3. Guo JD, Ge YS, Hao LJ, Tan JW, Li JQ, Feng XY. On-road measurement of regulated pollutants from diesel and CNG buses with urea selective catalytic reduction systems. Atmos. Environ. 2014;99:1-9.
  4. Sasaki S, Sarlashkar J, Neely GD, Wang J, Lu Q, Sono H. Investigation of alternative combustion, airflow-dominant control and aftertreatment system for clean diesel vehicles. SAE Technical Paper 2007;116:486-495.
  5. Wang J. Smooth in-cylinder lean-rich combustion switching control for diesel engine exhaust-treatment system regenerations. SAE Int. J. Passeng. Cars - Electron. Electr. Syst. 2009;1:340-348.
  6. Sullivan JA, Keane O. A combination of NOx trapping materials and urea-SCR catalysts for use in the removal of NOx from mobile diesel engines. Appl. Catal. B-Environ. 2007;70:205-214.
  7. Colombo M, Nova I, Tronconi E, Schmeisser V, Weibel M. Mathematical modelling of cold start effects over zeolite SCR catalysts for exhaust gas aftertreatment. Catal. Today 2014;231:99-104.
  8. Sebelius S, Le TT, Pettersson LJ, Lind H. Identification of urea decomposition from an SCR perspective; A combination of experimental work and molecular modeling. Chem. Eng. J. 2013;231:220-226.
  9. Youn S, Jeong S, Kim DH. Effect of oxidation states of vanadium precursor solution in $V_2O_5$/$TiO_2$ catalysts for low temperature $NH_3$ selective catalytic reduction. Catal. Today 2014;232:185-191.
  10. Choi BC, Kim YK, Jhung WN, Lee CH, Hwang CY. Experimental investigation on melting characteristics of frozen urea-water-solutions for a diesel SCR de-NOx-system. Appl. Therm. Eng. 2013;50:1235-1245.
  11. Song Q, Zhu G. Model-based closed-loop control of urea SCR exhaust aftertreatment system for diesel engine. SAE Technical Paper 2002.
  12. Qiu T, Li XC, Liang H, Liu XH, Lei Y. A method for estimating the temperature downstream of the SCR (selective catalytic reduction) catalyst in diesel engines. Energy 2014;68:311-317.
  13. Canova M, Midlam-Mohler S, Pisu P, Soliman A. Model-based fault detection and isolation for a diesel lean NOx trap aftertreatment system. Control Eng. Pract. 2010;18:1307-1317.
  14. Strom H, Lundstrom A, Andersson B. Choice of urea-spray models in CFD simulations of urea-SCR systems. Chem. Eng. J. 2009;150:69-82.
  15. Hsieh MF, Wang JM. Development and experimental studies of a control-oriented SCR model for a two-catalyst urea-SCR system. Control Eng. Pract. 2011;19:409-422.
  16. Lee SI, Park SY. Numerical analysis of internal flow characteristics of urea injectors for SCR dosing system. Fuel 2014;129:54-60.
  17. Shan WP, Liu FD, Yu YB, He H. The use of ceria for the selective catalytic reduction of NOx with $NH_3$. Chinese J. Catal. 2014;35:1251-1259.
  18. Hsieh MF, Wang JM. Design and experimental validation of an extended Kalman filter-based NOx concentration estimator in selective catalytic reduction system applications. Control Eng. Pract. 2011;19:346-353.
  19. Hou J, Yan FW, Hu J, Wang TT, Liu CB. Ammonia cross-sensitivity of NOx sensor for urea-SCR system. Transactions of CSICE. 2014;32:249-523.
  20. Chou CC, Chiang CJ, Su YH, Ku YY. Interpretation of the Oscillating Signals of the Smart NOx Sensors Used in Urea Selective Catalyst Reduction Systems via Spectral Analysis. Applied Mechanics and Materials, 2014;479-480:719-723.

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