Emission reduction study for meeting new requirements with advanced diesel engine technology

Tier 2 Emission standards enacted by the U.S. Environmental Protection Agency (EPA) require substantial emission reductions for new vehicles, including those with diesel engines. The standards are fuel neutral, and all light duty vehicles must eventually meet a fleet averaged emission level of Bin 5. To improve the emission capability for diesel engines, several advanced technologies have been investigated. These technologies include: common rail FIE with multi-injection capability, enhanced cooled EGR system with increased flow capability, variable geometry turbo charger, and a lower compression ratio piston. A new combustion approach using premixed diesel combustion was applied in the low load area for improving NO_x and soot emissions significantly in the FTP-75 test cycle. Applying these technologies, engine out NO_x was substantially reduced while maintaining similar soot levels.

An aftertreatment system with lean NO_x trap (LNT) catalysts and a catalyzed soot filter was studied on a demonstration vehicle. The aftertreatment system was prepared for evaluation by thermal aging to useful vehicle life. A regeneration strategy for the LNT has been developed which provides NO_x reduction efficiency, while minimizing the fuel penalty and HC slip to the tail pipe. A new combustion approach using premixed diesel combustion was also applied to the rich composition in order to reduce HC slip and soot emission. After aging with a simulated 120kmile aging cycle, this system showed greater than 90% reduction for PM and 60% reduction for NO_x emission in the FTP-75 test cycle.