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Technical Paper

Design Considerations for Advanced Ceramic Catalyst Supports

Stringent emissions standards with 95+% conversion efficiency requirements call for advanced ceramic catalyst supports with thinner walls, higher cell density and optimum cell shape. The extrusion technology for cellular ceramics has also made significant progress which permits the manufacture of advanced catalyst supports. Similarly, modifications in cordierite chemistry and the manufacturing process have led to improved microstructure from coatability and thermal shock points of view. The design of these supports, however, requires a systems approach to balance both the performance and durability requirements. Indeed as the wall gets thinner, the contribution of washcoat becomes more significant in terms of thermal mass, heat transfer, thermal expansion, hydraulic diameter and structural stiffness - all of which have an impact on performance and durability. For example, the thinner the wall is, the better the light-off performance will be.
Journal Article

Diesel Emission Control in Review

This summary covers the developments from 2007 in diesel regulations, engine technology, and NOx and PM control. Regulatory developments are now focused on Europe, where heavy-duty regulations have been proposed for 2013. The regulations are similar in technology needs to US2010. Also, the European Commission proposed the first CO2 emission limits of 130 g/km, which are nearly at parity to the Japanese fuel economy standards. Engines are making very impressive progress, with clean combustion strategies in active development mainly for US light-duty application. Heavy-duty research engines are more focused on traditional approaches, and will provide numerous engine/aftertreatment options for hitting the tight US 2010 regulations. NOx control is centered on SCR (selective catalytic reduction) for diverse applications. Focus is on cold operation and system optimization. LNT (lean NOx traps) durability is quantified, and performance enhanced with a sulfur trap.
Technical Paper

Effect of Thermal Mass and Aging on CO-NOx Crossover and Light Off Behavior

The tightening of emissions regulations has required changes in many areas of vehicle systems, including calibration strategies, catalytic converter strategies and exhaust configurations. Engine calibration strategies can be engineered to complement the performance parameters of the converter. Knowledge of the precise window of converter performance for different substrates can therefore provide guidance in targeting engine calibration strategies as well as selecting compatible converter systems within calibration constraints. In a previous paper [5], we explored the effect of thermal mass on emissions performance in the context of the FTP. This paper expands on the previous work and explores the effect of the aging cycle and thermal mass differences on CO-NOx crossover and light-off profiles. This analysis provides a tool to assist in design by defining a window of performance in the converter to be used in matching to a window of operation in the calibration.
Technical Paper

Erosion Mechanisms and Performance of Cellular Ceramic Substrates

High emission performance standards and precious metals costs have pushed the catalytic substrate toward high cell density and thin wall, such as the 600/4, 600/3 and 900/2 products. Due to the inherently lower mechanical strength of these products, coupled with a shift from underbody to close-coupled placement, a concern was expressed that the severe thermal and mechanical conditions may cause structural damage to the substrate, which in turn could impact the catalyst performance. One source of reduced performance during use is the loss of catalyst due to erosion. A previous study1 indicated that the existence of particulate in an air-stream could cause substrate erosion. However, it was not clear if other factors could contribute to or accelerate the erosion process. In order to address this question, experiments were performed to examine the influence of high velocity flow, temperature, impingement angle, particulate characteristics, and coating effect on erosion.
Technical Paper

Evaluation of In-Line Adsorber Technology

To meet tightening emissions standards, alternate pollution abatement technologies are necessary, such as an In-Line Adsorber (ILA) system. The ILA has a first catalyst, an adsorber, and a second catalyst. A diverter directs exhaust gas through the adsorber to capture unconverted hydrocarbons until the first catalyst reaches light-off temperature. The ILA system was designed so that the second catalyst becomes active concurrent with the adsorber hydrocarbon desorption. The system was evaluated using the FTP test with two different secondary air strategies on 3.8 liter V6 and 4.0 liter V8 vehicles. The ILA system performance consistently reduced ∼50-60% of cold start hydrocarbon emissions. This study examined a simplified ILA system designed to operate with a commercial secondary air pump powered by the engine.
Technical Paper

Next Generation Cordierite Thin Wall DPF for Improved Pressure Drop and Lifetime Pressure Drop Solution

Diesel particulate filters (DPF) have become a standard aftertreatment component for a majority of current on-road/non-road diesel engines used in the US and Europe. The upcoming Stage V emissions regulations in Europe will make DPFs a standard component for emissions reductions for non-road engines. The tightening in NOx emissions standard has resulted in the use of selective catalytic reduction (SCR) technology for NOx reduction and as a result the general trend in engine technology as of today is towards a higher engine-out NOx/PM ratio enabling passive regeneration of the DPF. The novel filter concept discussed in this paper is optimized for low pressure drop, high filtration efficiency, and low thermal mass for optimized regeneration and fast heat-up, therefore reducing CO2 implications for the DPF operation.
Journal Article

Regeneration Strategies for an Enhanced Thermal Management of Oxide Diesel Particulate Filters

Diesel particulate filters are expected to be used on most passenger car applications designed to meet coming European emission standards, EU5 and EU6. Similar expectations hold for systems designed to meet US Tier 2 Bin 5 standards. Among the various products oxide filter materials, such as cordierite and aluminum titanate, are gaining growing interest due to their unique properties. Besides the intrinsic robustness of the filter products a well designed operating strategy is required for the successful use of filters. The operating strategy is comprised of two elements: the soot estimation and the regeneration strategy. In this paper the second element is discussed in detail by means of theoretical considerations as well as dedicated engine bench experiments. The impact the key operating variables, soot load, exhaust mass flow, oxygen content and temperature, have on the conditions inside the filter are discussed.
Technical Paper

Review of Development, Properties and Packaging of Thinwall and Ultrathinwall Ceramic Substrates

Driven by the worldwide automotive emission regulations, ceramic substrates were developed to serve as catalyst support. Since the introduction of Standard wall substrates in 1974, substrates with thinner walls and higher cell densities have been developed to meet the tighter emission requirements; Worldwide, the amount of Thinwall and Ultrathinwall substrates in series applications is increasing continuously. The properties of the substrates determine their performance regarding pressure drop, heat-up and conversion efficiency. These properties are analyzed, as well as the packaging process for Thinwall and Ultrathinwall substrates; A new packaging technique with lower pressure load is described.
Journal Article

Vehicular Emissions in Review

This review paper summarizes major developments in vehicular emissions regulations and technologies (light-duty, heavy-duty, gasoline, diesel) in 2012. First, the paper covers the key regulatory developments in the field, including finalized criteria pollutant tightening in California; and in Europe, the development of real-world driving emissions (RDE) standards. The US finalized LD (light-duty) greenhouse gas (GHG) regulation for 2017-25. The paper then gives a brief, high-level overview of key developments in LD and HD engine technology, covering both gasoline and diesel. Marked improvements in engine efficiency are summarized for gasoline and diesel engines to meet both the emerging NOx and GHG regulations. HD engines are just starting to demonstrate 50% brake thermal efficiency. NOx control technologies are then summarized, including SCR (selective catalytic reduction) with ammonia, and hydrocarbon-based approaches.