Adaptive and Efficient Ammonia Storage Distribution Control for a Two-Catalyst Selective Catalytic Reduction System

Abstract

This paper presents an adaptive urea-SCR dosing control design for a two-catalyst SCR system. A novel SCR ammonia storage distribution control (ASDC) approach aiming to simultaneously increase the SCR NOx conversion efficiency and reduce the tailpipe ammonia slip was proposed and experimentally validated. Based on the insight into SCR operational principles, a high ammonia storage level at the upstream part of the catalyst can generally yield a higher NOx reduction efficiency while a low ammonia storage level at the downstream part of the catalyst can reduce the undesired tailpipe ammonia slip. To achieve such an ammonia storage distribution control, a two-catalyst (in series) SCR system with NOx and NH3 sensors was devised. Grounded in a newly developed SCR control-oriented model, an adaptive (with respect to the SCR ammonia storage capacity) controller was designed to control the urea injection rate for achieving different ammonia storages in the two catalysts. Experimental data from a US06 test cycle conducted on a medium-duty Diesel engine system showed that, with the similar total engine-out NOx emissions and NH3 (AdBlue) consumptions, the proposed ASDC strategy simultaneously reduced the tailpipe NOx emissions by 57% and the ammonia slip by 74% in comparison to those from a conventional controller.