A controls overview on achieving ultra-low NOx 2020-01-1404
The California Air Resources Board (CARB) funded Stage 3 Heavy-Duty Low NOx program focusses on evaluating different engine and after-treatment technologies to achieve 0.02g/bhp-hr of NOx emission over certification and low load 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 heavy-duty drive cycles. A cylinder deactivation enabled engine was integrated with an after-treatment system consisting of a Light-Off Selective Catalytic Reduction (LO-SCR) system with a heated urea dosing system which was located close to the turbine outlet, a Catalyzed Soot Filter (CSF), and a main SCR system with single point urea dosing. Southwest Research Institute (SwRI) had developed a model-based controller for the main SCR system in the Stage 1 Low-NOx program. The chemical kinetics for the model-based controller were further tuned and implemented in this program to better simulate the reactions in the Stage 3 SCR system. Novel dosing, and ammonia storage management strategies created along with the model-based controls were 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 us to meet the desired targets.
Sandesh Rao, Jayant Sarlashkar, Sankar Rengarajan, Christopher Sharp, Gary Neely