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The regulative environment is poised for ultra-low emissions in the 2024+ time frame with ultra-low NOx proposals from CARB and PN PEMS testing requirements from EU. GHG emissions limits are getting tighter in the next few years along with extended full useful life (FUL) requirements. Diesel Particulate Filters (DPF) will be an integral part of all diesel exhaust aftertreatment systems for the next several years and will need advanced technology solutions to meet the challenges above, without compromising on high performance requirements, namely, low lifetime pressure drop, high filtration efficiency, high durability (extended FUL), increased service intervals or lifetime filter solutions (high ash storage capacity). This paper discusses the primary challenges associated with meeting these future demands and possible technological solutions to address them.

Ceramic preconverters have become a viable strategy to meet the California LEV and ULEV standards. To minimize cold start emissions the preconverter must light-off quickly and be catalytically efficient. In addition, it must also survive the more severe thermomechanical requirements posed by its close proximity to the engine. The viability of the ceramic preconverter system to meet both emissions and durability requirements has also been reported recently(1,2). This paper further investigates the impact preconverter design parameters such as cell density, composition, volume, and catalyst technology have on emissions and pressure drop. In addition, different preconverter/main converter configurations in conjunction with electrically heated catalyst systems are evaluated. The results demonstrate that ceramic preconverters substantially reduce cold start emissions. Their effectiveness depends on preconverter design and volume, catalyst technology, and the system configuration.

The stringent emissions legislation has necessitated advances in the catalytic converter system comprising the substrate, washcoat technology, catalyst formulation and packaging design. These advances are focused on reducing light-off emissions at lower temperature or shorter time, increasing FTP efficiency, reducing back pressure and meeting the mechanical and thermal durability requirements over 100,000 vehicle miles. This paper reviews the role of cordierite ceramic substrate and how its design can help meet the stringent emissions legislation. In particular, it compares the effect of cell geometry and size on performance parameters like geometric surface area, open frontal area, hydraulic diameter, thermal mass, heat transfer factor, mechanical integrity factor and thermal integrity factor - all of which have a bearing on emissions, back pressure and durability. The properties of advanced cell configurations like hexagon are compared with those of standard square cell.

The 290,000 vehicle-mile durability requirement for diesel/natural gas oxidation catalysts calls for robust packaging systems which ensure a positive mounting pressure on the ceramic flow-through converter under all operating conditions. New data for substrate/washcoat interaction, intumescent mat performance in dry and wet states, and high temperature strength and oxidation resistance of stainless steels, and canning techniques insensitive to tolerance stack-up are reviewed which help optimize packaging durability. Factors contributing to robustness of converter components are identified and methods to quantify their impact on design optimization are described. CERAMIC FLOW-THROUGH catalysts for diesel exhaust aftertreatment have met with much success since their introduction in 1993.