Is Closed-Loop SCR Control Required to Meet Future Emission Targets?

<div class="htmlview paragraph">To meet 2010 emission targets, optimal SCR system performance is required. In addition, attention has to be paid to in-use compliance requirements. Closed-loop control seems an attractive option to meet the formulated goals. This study deals with the potential and limitations of closed-loop SCR control.</div> <div class="htmlview paragraph">High NO_x conversion in combination with acceptable NH₃ slip can be realized with an open-loop control strategy. However, closed-loop control is needed to make the SCR system robust for urea dosage inaccuracy, catalyst ageing and NO_x engine-out variations. Then, the system meets conformity of production and in-use compliance norms.</div> <div class="htmlview paragraph">To demonstrate the potential of closed-loop SCR control, a NO_x sensor based control strategy with cross-sensitivity compensation is compared with an adaptive surface coverage/NH₃ slip control strategy and an open-loop strategy. The adaptive surface coverage/NH₃ slip control strategy shows best performance over simulated ESC and ETC cycles.</div> <div class="htmlview paragraph">SCR catalyst dynamics, time delay in the urea injection and maximum NH₃ slip targets limit the performance of closed-loop SCR control. If new reagent dosage systems and future catalyst technology are able to relieve these limitations, closed-loop control has the potential to reduce the calibration effort and to improve the transient control performance.</div>