CARB Low NOx Stage 3 Program - Modified Engine Calibration and Hardware Evaluations

With the conclusion of the California Air Resources Board (CARB) Stage 1 Ultra-Low NO_X (ULN) program, there continues to be a commitment for identifying potential pathways to demonstrate 0.02 g/bhp-hr NO_X emissions. The Stage 1 program focused on achieving the ULN levels on the heavy-duty regulatory cycles utilizing a turbo-compound engine which required the integration of novel catalyst technologies and a supplemental heat source. While the aftertreatment configuration provided a potential solution to meet the ULN target, a complicated approach with a greenhouse gas (GHG) penalty was required to overcome challenges from low temperature exhaust. A subsequent Stage 2 program was concerned with the development of a new low load test cycle and evaluating the trade-off between GHG and tailpipe NO_X on the Stage 1 ULN solution. The current Stage 3 program focuses on both the regulatory cycles and the new low load cycle, but leverages a different engine architecture that is more representative of the broader heavy-duty industry to meet the Phase 2 GHG regulations and to simplify the ULN aftertreatment solution. Aftertreatment thermal management is a key aspect of achieving ULN on both the regulatory cycles and the low load cycle. Therefore, a more aggressive engine calibration was developed on the Stage 3 platform using the available engine actuators for aftertreatment heat up and thermal management. This modified calibration was then used to evaluate additional hardware technologies under steady-state and transient operation to assess the trade-offs between exhaust gas characteristics, emissions, and fuel consumption. A simple ranking system was applied to the transient results and with cylinder deactivation being selected to carry forward into the subsequent tasks of the Stage 3 ULN program.