Development of Diesel Exhaust Aftertreatment System for Tier II Emissions

Abstract

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 plasmaassisted 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...

Spatially resolved in situ measurements of transient species breakthrough during cyclic, low-temperature regeneration of a monolithic Pt/K/Al2O3 NOx storage-reduction catalyst

“…This suggests that NO x release and reduction are similarly effective for all H 2 /CO combinations at 300 8C. This also seems to imply that the Pt/ K/Al 2 O 3 catalyst studied here behaves consistently with many other NSR catalysts in responding to H 2 and CO at temperatures greater than 250 8C [4][5][6]18,21].…”

“…Several technologies have been proposed for lean NO x removal, and one of these, the NO x storage-reduction (NSR) catalyst, is now considered a promising candidate [4]. Also known as lean NO x traps (LNTs) or NO x adsorber catalysts (NACs), NSR catalysts combine NO x storage components (in general, alkali-or alkaline-earth metal) with more conventional-supported precious metals [5,6].…”

Thermal decomposition of bulk and supported barium nitrate

“…Though first developed for lean burn gasoline engines [3][4][5][6][7] NSR catalysts are now more widely investigated for NO x control in diesel vehicles [8,9]. The operating mechanism of NSR catalysts has attracted considerable attention (see for example [10][11][12][13]) and involves the interaction of NO 2 with an adsorber component under oxidising conditions with a periodic rich excursion to decompose and reduce the stored NO x species.…”

Intra-channel evolution of carbon monoxide and its implication on the regeneration of a monolithic Pt/K/Al2O3 NOx storage-reduction catalyst

“…Among multiple technical options being explored is NO x storage-reduction (NSR) catalysts which have shown potential in meeting future NO x emission standards [2]. Also known as lean NO x traps (LNTs) or NO x adsorber catalysts (NACs), NSR catalysts combine NO x storage components (in general, alkali or alkaline-earth metal) with supported precious metals (similar to 3-way catalysts) [3][4][5][6][7].…”