CARB Off-Road Low NOx Demonstration Program - Engine Calibration and Initial Test Results

Off-road diesel engines remain one of the most significant contributors to the overall oxides of nitrogen (NO_X) inventory and the California Air Resources Board (CARB) has indicated that reductions of up to 90% from current standards may be necessary to achieve its air quality goals. In recognition of this, CARB has funded a program aimed at demonstrating emission control technologies for off-road engines. This program builds on previous efforts to demonstrate Low NO_X technologies for on-road engines. The objective was to demonstrate technologies to reduce tailpipe NO_X and particulate matter (PM) emissions by 90 and 75%, respectively, from the current Tier 4 Final standards. In addition, the emission reductions were to be achieved while also demonstrating a 5 to 8.6% carbon dioxide (CO₂) reduction and remaining Greenhouse Gas (GHG) neutral with respect to nitrous oxide (N₂O) and methane (CH₄). This paper focuses on the engine calibration efforts for aftertreatment (AT) thermal management and improved fuel economy which included a diesel Dynamic Skip Fire (dDSF™) calibration. Test results obtained with a development-aged (hydrothermal aging only) AT system over the applicable off-road test cycles and a low load cycle are presented. The emission control system and modified calibrations could achieve internal tailpipe (TP) NO_X development targets with technologies suitable for production, allowing for a significant potential compliance margin. The level of CO₂ reduction was dependent on the test cycle with the target achievable without dDSF for all cycles except for the RMC where a 4% reduction was observed. The addition of dDSF reduced cycle CO₂ by an additional 0.5 to 3%, depending on the test cycle, and maintained higher AT temperatures which reduced the use of AT thermal management modes.