The Development and Implementation of Model-based Control Algorithm of Urea-SCR Dosing System for Improving De-NOx Performance and Reducing NH₃-slip

Abstract

: The selective catalytic reduction (SCR) system is a highly-effective aftertreatment device for NOx reduction of diesel engines. Generally, the ammonia (NH3) was generated from reaction mechanism of SCR in the SCR system using the liquid urea as the reluctant. Therefore, the precise urea dosing control is a very important key for NOx and NH3 slip reduction in the SCR system. This paper investigated NOx and NH3 emission characteristics of urea-SCR dosing system based on model-based control algorithm in order to reduce NOx. In the map-based control algorithm, target amount of urea solution was determined by mass flow rate of exhaust gas obtained from engine rpm, torque and O2 for feed-back control NOx concentration should be measured by NOx sensor. Moreover, this algorithm can not estimate NH3 absorbed on the catalyst. Hence, the urea injection can be too rich or too lean. In this study, the model-based control algorithm was developed and evaluated on the numerical model describing physical and chemical phenomena in SCR system. One channel thermo-fluid model coupled with finely tuned chemical reaction model was applied to this control algorithm. The vehicle test was carried out by using map-based and model-based control algorithms in the NEDC mode in order to evaluate the performance of the model based control algorithm.

Study on the flow effects of an exhaust system by mixer modeling

“…However, for LNT, total fuel efficiency of a vehicle tends to drop since it uses the fuel as a reducing agent. [4][5][6] Components of the SCR system includes an injector to spray urea solution, urea tank, urea pump module, SCR Catalyst, and mixer. Even though the cost of automobiles increases when utilizing the SCR system, due to a large number of components needed, it clearly presents advantages in better fuel efficiency compared to vehicles with LNT since it does not use fuel as a reducing agent.…”