Control of diesel engine urea selective catalytic reduction systems

A systematic nonlinear control methodology for urea-SCR systems applicable for light-to-heavy-duty Diesel engine platforms in a variety of on-road, off-road, and marine applications is developed and experimentally validated in this dissertation. Urea selective catalytic reduction (urea-SCR) systems have been proved of being able to reduce more than 90% of Diesel engine-out NOx emissions and have been favored by the automotive industry in recent years. Urea-SCR systems utilize ammonia, converted from 32.5% aqueous urea solution (AdBlue) injected at upstream of the SCR catalyst, as the reductant for NOx reductions. Because ammonia is considered a hazardous material, urea injection should be systematically controlled to avoid undesired tailpipe ammonia slip while achieving a sufficient level of SCR NOx reduction.;The novelty of the control methodology is to regulate the ammonia storage distribution along the axial direction of a SCR catalyst to a staircase profile and thus to simultaneously realize high NOx reduction efficiency and low ammonia emissions. To achieve this control objective, several relevant subjects are studied, including: (1) aftertreatment system control-oriented modeling, (2) online NOx sensor ammonia cross-sensitivity correction, (3) SCR catalyst ammonia coverage ratio estimation, as well as (4) adaptive urea dosing controller design. A unique SCR system which consists of a urea injector and two SCR catalysts connected in-series with several NOx and NH3 sensors is used for the study of the proposed urea-SCR control methodology. Such a SCR system is integrated with a state-of-the-art Diesel engine and aftertreatment system (DOC-DPF). The US06 test cycle experimental results show the proposed control methodology, in comparison to a conventional control strategy, is capable of improving the SCR NOx reduction by 63% and reducing the tailpipe ammonia slip amount by 74%.;The contributions of this research to the art include: (1) A novel, efficient, and generalizable urea-SCR dosing control methodology; (2) Diesel engine-DOC-DPF NO/NO2 ratio control-oriented models and observer-based estimations; (3) SCR catalyst ammonia coverage ratio estimation methods; (4) An online correction approach for NOx sensor ammonia cross-sensitivity elimination; and (5) An improved SCR control-oriented model.