A Controls Overview on Achieving Ultra-Low NOx

The California Air Resources Board (CARB)-funded Stage 3 Heavy-Duty Low NO_X program focusses on evaluating different engine and after-treatment technologies to achieve 0.02g/bhp-hr of NO_X emission over certification cycles. This paper highlights the controls architecture of the engine and after-treatment systems and discusses the effects of various strategies implemented and tested in an engine test cell over various heavy-duty drive cycles. A Cylinder De-Activation (CDA) system enabled engine was integrated with an advanced after-treatment controller and system package. Southwest Research Institute (SwRI) had implemented a model-based controller for the Selective Catalytic Reduction (SCR) system in the CARB Stage 1 Low-NO_X program. The chemical kinetics for the model-based controller were further tuned and implemented in order to accurately represent the reactions for the catalysts used in this program. Novel dosing, and ammonia storage management strategies augmented with the model-based controls was critical in achieving the objectives of this program. Results for Heavy-Duty-Federal Test Procedure (HD-FTP), Ramp Mode Cycle (RMC) and Low Load Cycle (LLC) are presented with a focus on controller features and characteristics that enabled to meet the desired targets. It is important to note that the model-based controller did not require specific calibration for each cycle. The controller gains and calibration were untouched across the various test cycles described in this paper.