Development of Diesel Exhaust Aftertreatment System for Tier II Emissions 2002-01-1867

Due to their excellent fuel efficiency, reliability, and durability, compression ignition direct injection (CIDI) engines have been used extensively to power almost all highway trucks, urban buses, off-road vehicles, marine carriers, and industrial equipment. CIDI engines burn 35 to 50% less fuel than gasoline engines of comparable size, and they emit far less greenhouse gases (Carbon Dioxides), which have been implicated in global warming. Although the emissions of CIDI engines have been reduced significantly over the last decade, there remains concern with the Nitrogen Oxides (NO_X) and Particulate Matter (PM) emission levels. In 2000, the US EPA proposed very stringent emissions standards to be introduced in 2007 along with low sulfur (< 15ppm) diesel fuel. The California Air Resource Board (CARB) has also established the principle that future diesel fueled vehicles should meet the same emissions standards as gasoline fueled vehicles and the EPA followed suit with its Tier II emissions regulations.

Meeting the Tier II standards requires NO_X and PM emissions to be reduced dramatically. Achieving such low emissions while minimizing fuel economy penalty cannot be done through engine development and fuel reformulation alone, and requires application of NO_X and PM aftertreatment control devices. A joint effort was made between Cummins Inc. and the Department of Energy to develop the generic aftertreatment subsystem technologies applicable for Light-Duty Vehicle (LDV) and Light-Duty Truck (LDT) engines. This paper provides an update on the progress of this joint development program.

Three NO_X reduction technologies including plasma-assisted catalytic NO_X reduction (PACR), active lean NO_X catalyst (LNC), and adsorber catalyst (AC) technology using intermittent rich conditions for NO_X reduction were investigated in parallel in an attempt to select the best NO_X control approach for light-duty aftertreatment subsystem integration and development. Investigations included system design and analysis, critical lab/engine experiments, and ranking then selection of NO_X control technologies against reliability, up-front cost, fuel economy, service interval/serviceability, and size/weight. The results of the investigations indicate that the best NO_X control approach for LDV and LDT applications is a NO_X adsorber system. A greater than 83% NO_X reduction efficiency is required to achieve 0.07g/mile NO_X Tier II vehicle-out emissions. Both active lean NO_X and PACR technology are currently not capable of achieving the high conversion efficiency required for Tier II, Bin 5 emissions standards.

In this paper, the NO_X technology assessment and selection is first reviewed and discussed. Development of the selected NO_X technology (NO_X adsorber) and PM control are then discussed in more detail. Discussion includes exhaust sulfur management, further adsorber formulation development, reductant screening, diesel particulate filter development & active regeneration, and preliminary test results on the selected integrated SO_X trap, NO_X adsorber, and diesel particulate filter system over an FTP-75 emissions cycle, and its impact on fuel economy. Finally, the direction of future work for continued advanced aftertreatment technology development is discussed.