제어알고리즘에 따른 Urea SCR 분사 시스템의 NOx 및 NH₃ 배출 특성

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 urea solution in the SCR system using the liquid urea as the reductant. Therefore, the precise urea dosing control is a very important factor for reducing NOx and NH₃ slip in the SCR system. This paper investigated that the effect of urea dosing control algorithms on NOx and NH₃ emission characteristics in order to minimize NOx emission and NH₃ slip. In the map-based control algorithm, the urea injection was determined by mass flow rate of exhaust gas based on engine rpm, torque and O₂, NOx concentration measured by NOx sensor. However, this algorithm cannot consider the effect of adsorption and desorption of NH₃ so that the amount of urea injection may be over- and under-estimated, which leads to NH₃ slip and deterioration of deNOx performance. Therefore, the model-based control algorithm based on physics of chemistry and mechanics has been developed in this study. The mass flow rate map obtained from engine test and NO, NO₂ and O₂ concentration measured by NOx sensor during engine test were used. A comparison of map-based and model-based control algorithms has been performed in terms of NOx emission and NH₃ slip