MODEL-BASED NH3 ADAPTATION METHOD FOR SCR CONTROL |
Tiantian Wang 1,2, Zhichao Huang 1, Xuwei Luo 2, Jie Hu 3, Zhi Wang 4, Yayu Cheng 3 |
1Key Laboratory of Conveyance and Equipment, Ministry of Education, East China Jiaotong University 2Power Transmission Development Department, Jiangling Automobile Co., Ltd. 3School of Automotive Engineering, Wuhan University of Technology 4AVL List Technical Center (Shanghai) Co., Ltd. |
|
|
|
|
ABSTRACT |
Selective Catalytic Reduction (SCR) system is widely used for diesel nitrogen oxide (NOx) control, but the
closed-loop control and adaptive correction method which based on NOx sensor signal will be affected by the working
characteristics of NOx sensor, such as the cross-sensitivity of ammonia (NH3). Based on the highly linear correlation between
conversion efficiency and ammonia to NOx ratio (ANR) at insufficient supply level, a model-based adaptive correction method
for urea injection quantity is proposed to eliminate this effect, which can effectively correct the deviation caused by multiple
sources when using accurate models. The difference between the conversion efficiency of current SCR system and which
generated from model is calculated by stopping injection and under injection actions to obtain an accurate adaptation factor,
and the basic injection quantity can be modified by this factor. The maximum error of the 18 calculated correction factors from
18 WHTC cycles is only 1.1 % when using standard AdBlue; After urea solution concentration changed, the calculated
correction factor error is within 5 % when comparing with the theoretical correction factor after 2 ~ 3 rounds adaptation function
running. The adaptation function keeps the reductant supply to adapt the deviation caused by catalyst aging, reductant
concentration drift and supply accuracy variation only with slightly influence of tailpipe NOx emission (less than 2 % in average),
which ensure SCR system always stay in appropriate dosing control state, make best for NOx emissions and NH3 emissions
control. |
Key Words:
SCR system, Model, Adaptation, Special maneuver |
|