Further Advances in Demonstration of a Heavy-Duty Low NOX System for 2027 and Beyond

Multiple areas in the U.S. continue to struggle with achieving National Ambient Air Quality Standards for ozone. These continued issues highlight the need for further reductions in NO_X emission standards in multiple industry sectors, with heavy-duty on-highway engines being one of the most important areas to be addressed. Starting in 2014, CARB initiated a series of technical demonstration programs aimed at examining the feasibility of achieving up to a 90% reduction in tailpipe NO_X, while at the same time maintaining a path towards GHG reductions that will be required as part of the Heavy-Duty Phase 2 GHG program. These programs culminated in the Stage 3 Low NO_X program, which demonstrated low NO_X emissions while maintaining GHG emissions at levels comparable to the baseline engine. Building on that prior program effort, EPA continued to support further Low NO_X demonstration efforts in support of the development of new Federal Emissions Standards for heavy-duty highway vehicles and engines as part of the Clean Trucks Plan.

Some of these efforts have been reported in previous publications, which focused on the evaluation of a modified Stage 3 architecture to extended useful life, as well as examination of various challenges related to field duty cycles, in-use measurements, sensors, and fuel. Beyond these efforts, EPA also undertook a redesign effort to produce an updated Low NO_X aftertreatment system. The updated system incorporated many lessons learned from previous efforts, as well as recent catalyst process and formulation updates to improve performance and durability in key areas. This updated system was evaluated for emission control performance and durability using the Stage 3 Low NO_X test engine. The updated system was aged to 800,000 equivalent miles using DAAAC accelerated aging techniques, and it was evaluated over both regulatory and field duty cycles. The results of these evaluations are presented within this paper.