Diesel Cold-Start Emission Control Research for 2015-2025 LEV III Emissions

The diesel engine can be an effective solution to meet future greenhouse gas and fuel economy standards, especially for larger segment vehicles. However, a key challenge facing the diesel is the upcoming LEV III emissions standard which will require significant reductions of hydrocarbon (HC) and oxides of nitrogen (NO_x) from current levels. The challenge stems from the fact that diesel exhaust temperatures are much lower than gasoline engines so the time required to achieve effective emissions control with current aftertreatment devices is considerably longer.

The objective of this study was to determine the potential of a novel diesel cold-start emissions control strategy for achieving LEV III emissions. The strategy combines several technologies to reduce HC and NO_x emissions before the start of the second hill of the FTP75. The technologies include: 1) intake throttling, 2) high temperature glow plugs with model-based temperature control, 3) multiple fuel injections, 4) high EGR idle operation after the first hill, 5) improved diesel particulate filter (DPF) catalyst formulation, and 6) a small close-coupled LNT with improved an formulation. For the overall emissions control strategy, an underfloor SCR would provide the main NO_x control starting in the second hill.

This paper describes the benefits of the engine tuning technologies (1-4) and evaluates the strategy during transient engine dynamometer investigations that simulate the first 162 seconds of the FTP75. Using the combined engine tuning technologies, HC emission reduction of over 80% relative to the baseline calibration was achieved at the tailpipe (or more correctly, at the entrance to the underfloor NO_x control device) with the baseline aftertreatment system. This level of HC reduction is in the range required for LEV III compliance; however, part of the reduction was obtained by moving to higher NO_x on the HC versus NO_x trade-off curve. Additional tests with a closed-coupled LNT and DPF with improved catalyst formulations are planned to investigate if the right balance of engine-out HC and NO_x can be obtained with this strategy for LEV III.