On Road vs. Off Road Low Load Cycle Comparison 2024-01-2134

Reducing criteria pollutants while reducing greenhouse gases is an active area of research for commercial on-road vehicles as well as for off-road machines. The heavy duty on-road sector has moved to reducing NOx by 82.5% compared to 2010 regulations while increasing the engine useful life from 435,000 to 650,000 miles by 2027 in the United States (US). An additional certification cycle, the Low Load Cycle (LLC), has been added focusing on part load operation having tight NOx emissions levels. In addition to NOx, the total CO₂ emissions from the vehicle will also be reduced for various model years. The off-road market is following with a 90% NOx reduction target compared to Tier 4 Final for 130-560 kW engines along with greenhouse gas targets that are still being established. The off-road market will also need to certify with a Low Load Application Cycle (LLAC), a version of which was proposed for evaluation in 2021. Since the LLAC has not been finalized, this study is being conducted to compare and contrast the LLC for on-road with the LLAC for off-road as there might be some shared learnings. A US off-road production 2023 Fiat Powertrain 13L engine and aftertreatment system was chosen for this work. This engine is used in production for both off-road and on-road products, so it is a good choice for this study. The associated off-road aftertreatment system was aged for more relevant comparisons. The engine calibration was not altered for either of the low load cycles. This study shows that the cycles are quite different in nature as the market needs are different. The LLC includes a large fraction of operation at idle and lower speeds, representing products that use the engine primarily for motive power, where lower vehicle speed means a lower engine speed and load. The LLAC has more time and load spent at high speeds and slightly higher loads. The off-road products represented by this cycle often use the engine to drive auxiliary equipment which means higher parasitic loads and hand/fixed throttle. The comparison will include the use profiles, tailpipe NOx and greenhouse gas emissions (CO₂, N₂O).