Model-based NH 3 Adaptation Method for SCR Control

Selective Catalytic Reduction (SCR) system is widely used for diesel nitrogen oxide (NO x ) control, but the closed-loop control and adaptive correction method which based on NO x sensor signal will be affected by the working characteristics of NO x sensor, such as the cross-sensitivity of ammonia (NH 3 ). Based on the highly linear correlation between conversion efficiency and ammonia to NO x 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 NO x emission (less than 2 % in average), which ensure SCR system always stay in appropriate dosing control state, make best for NO x emissions and NH 3 emissions control.