Diesel Cold Start Emission Control Research for 2015-2025 LEV III Emissions,
Gary D. Neely
Dr. Jayant Sarlashkar
Inclusive Dates: 04/01/12 – 03/31/13
Background — The diesel engine can be an effective solution to help OEMs meet the 2017-2025 U.S. EPA and National Highway Traffic Safety Administration light-duty greenhouse gas and fuel economy standards, especially for larger segment vehicles. However, in this same timeframe, very stringent emission standards will be phased-in (EPA Tier 3 and CARB LEV III), which pose a significant challenge for the diesel engine due to the difficulty in obtaining rapid emissions control with aftertreatment following a cold-start. Therefore, a cost-effective approach is needed for a diesel to obtain rapid emission control following a cold-start to meet future emission regulations.
Approach — The goal of this project was to develop and evaluate a novel diesel cold-start emissions control strategy. The strategy comprises multiple engine tuning improvements to increase exhaust gas temperature without increasing hydrocarbon (HC) emissions and replacing the standard close-coupled diesel oxidation catalyst (DOC) with a state-of-the-art Lean NOx Trap (LNT). The goal of the strategy was to achieve rapid HC and NOx control during the first hill of the FTP75, which is necessary to meet future emission standards. An illustration of the various technologies that comprised this strategy is shown in Figure 1.
Accomplishments — The engine tuning technologies were found to be quite effective in increasing exhaust temperature while maintaining low HC emissions. When the engine tuning technologies were combined with the state-of-the-art LNT, simultaneous NOx and HC control was achieved within 50 seconds from the start of the FTP75. Cumulative NOx + HC emissions obtained during the first 160 seconds of the FTP75 are shown in Figure 2. In addition to the SwRI test results, emissions obtained from a production Tier 2 Bin 5 vehicle are shown for comparison purposes. FTP75 Bag 1 weighting factors were applied to both results. Using the SwRI approach, a 52 percent emission margin remained for meeting the future EPA Tier 3/CARB LEV III fleet-average emission requirement compared to only 9 percent for the production vehicle. The potential of achieving the target emission level with the SwRI-developed strategy was confirmed by combining the SwRI results obtained for the first 160 seconds with the production Bin 5 diesel results for the remainder of the test cycle.