Meeting Phase-2 GHG and Ultra-Low NOx Emissions with Conventional Engine Design for Light Heavy-Duty Applications

Increasing concerns due to global warming have led to stringent regulation of greenhouse gas (GHG) emissions from diesel engines. Specifically, for GHG phase-2 regulation (2027), more than 4% improvement is needed when compared to phase-1 regulation (2017) in the light heavy-duty (LHD) diesel engine category. At the same time, California Air Resources Board (CARB) and Environmental Protection Agency (EPA) have proposed the new Low NOx standards that require up to 90% reduction in tailpipe (TP) NOx emissions in comparison to the current TP NOx standards that were implemented in 2010. In addition, CARB and EPA have proposed new certification requirements – Low Load Cycle (LLC) and revised heavy-duty in-use testing (HDIUT) based on the moving average window (MAW) method that would require rigorous thermal management. Hence, strategies for simultaneous reduction in GHG and TP NOx emissions are required to meet future regulations.

This paper presents potential pathways to achieve the GHG phase-2 and the ultra-low NOx (ULN) regulations with minimum changes in engine design, while meeting the constraints that need to be considered for engine performance stability, component durability, and vehicle drivability. Experimental evaluations were performed focusing on transient cycles such as heavy-duty Federal Test Procedure (hereafter referred as FTP), LLC, and custom transient cycles for HDIUT assessment. We used a model-year (MY) 2021 production Isuzu diesel engine and an advanced dual-dosing aftertreatment system comprising of a close-coupled SCR (ccSCR), diesel oxidation catalyst (DOC), diesel particulate filter (DPF), selective catalytic reduction (SCR), and Ammonia Slip Catalyst (ASC). Conventional thermal management techniques such as multi-injection, intake, and exhaust throttling were implemented to achieve the emissions targets. In addition to the proposed system design, this paper presents following test results from a full-scale system evaluation:

1. 1
   Achieve rapid and sustained turbine-out exhaust temperatures (>200°C) while meeting the engine-out emissions constraints for soot and total hydrocarbon (THC) emissions.
2. 2
   A summary of TP NOx, TP N2O and GHG emissions over a composite FTP and LLC.
3. 3
   HDIUT assessment results and observations for LLC and custom transient cycles.
4. 4
   Robustness evaluation of TP NOx emissions for composite HDT, LLC and custom transient cycles by imposing component variations.