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Technical Paper

Performance of Different Cell Structure Converters A Total Systems Perspective

The objective of this effort was to develop an understanding of how different converter substrate cell structures impact tailpipe emissions and pressure drop from a total systems perspective. The cell structures studied were the following: The catalyst technologies utilized were a new technology palladium only catalyst in combination with a palladium/rhodium catalyst. A 4.0-liter, 1997 Jeep Cherokee with a modified calibration was chosen as the test platform for performing the FTP test. The experimental design focused on quantifying emissions performance as a function of converter volume for the different cell structures. The results from this study demonstrate that the 93 square cell/cm2 structure has superior performance versus the 62 square cell/cm2 structure and the 46 triangle cell/cm2 structure when the converter volumes were relatively small. However, as converter volume increases the emissions differences diminish.
Technical Paper

Impacts of B20 Biodiesel on Cordierite Diesel Particulate Filter Performance

Engine laboratory tests were conducted to assess the impact of B20 biodiesel on the performance of cordierite diesel particulate filters (DPFs). Test fuels included 20% soy based methyl ester blended into ultra low sulfur diesel fuel, and two ULSD on-road market fuels. B20 has a higher cetane number, boiling point and oxygen content than typical on-road diesel fuels. A comparative study was performed using a model year 2007 medium duty diesel truck engine. The aftertreatment system included a diesel oxidation catalyst (DOC) followed by a cordierite wall flow DPF. A laboratory-grade supplemental fuel doser was used in the exhaust stream for precise regeneration of the DPF. Tests revealed that the fuel dosing rate was higher and DOC fuel conversion efficiency was poorer for the B20 fuel during low exhaust temperature regenerations. The slip of B20 fuel past the DOC was shown to produce significantly higher exotherms in the DPF during regeneration.
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.
Technical Paper

Relative Benefits of Various Cell Density Ceramic Substrates in Different Regions of the FTP Cycle

Continuous improvement in vehicle emissions is necessary to meet ever tightening regulations. These regulations are advancing in both passenger and light truck vehicle markets, currently at different rates. Divergent design requirements and target markets for these platforms create unique conditions for aftertreatment needs. To understand the performance of various products in these categories and the potential for optimization, we examine various ultrathin-wall products in the context of a close-coupled configuration in a SULEV vehicle. In addition, these comparisons are carried over to a larger platform to show the performance trends in the context of the sport utility vehicle category. This study considers converter performance in FTP tests, examining bag data, light-off behavior, pressure drop comparisons and front and rear converter contributions. Conclusions are drawn regarding the optimization of converter substrate selection for various target design criteria
Technical Paper

New Catalyzed Cordierite Diesel Particulate Filters for Heavy Duty Engine Applications

A family of cordierite DPF filters were developed and studied for their efficacy for catalyzed soot filter applications. In addition to porosity and median pore size of DPF filters, breadth of pore size distribution, microstructure, and pore connectivity have a profound influence not only in filter performance (pressure drop, catalyst coatability, and filtration efficiency) but also on mechanical and physical properties. Through filter material composition development, optimum values for the %porosity, median pore diameter, and breadth of the pore size distribution for minimizing pressure drop have been identified, leading to the development of a new family of high-porosity cordierite diesel particulate filters that possess a unique combination of high filtration efficiency, high strength, and very low clean and soot-loaded pressure drop in both the catalyzed and non-catalyzed states. By controlling the microstructure, the impact of the catalyst on pressure drop has been minimized.
Technical Paper

Comparative Analysis of Different Heavy Duty Diesel Oxidation Catalysts Configurations

Diesel Oxidation Catalyst in conjunction with large frontal area substrates is a key element in HDV Diesel emission control systems. This paper describes and reviews tests on a set of various Diesel Oxidation Catalyst configurations (for example cell densities), all with the same catalyst coating. The Diesel Oxidation Catalyst specimens were subjected to the European Stationary Cycle (ESC), the European Transient Cycle (ETC), and the US heavy duty Federal Test Procedure (US FTP). The focus was to study relative emissions, pressure drop, and light-off performance. All tests were conducted using the same Detroit Diesel Series 60 engine operating on ultra low sulfur diesel fuel. In addition to this, the exhaust was regulated so that the backpressure on the engine, upstream of the catalyst was also the same for all catalysts.
Technical Paper

Diesel Emission Control Technology 2003 in Review

This paper will review the field of diesel emission control with the intent of highlighting representative studies that illustrate the state-of-the-art. First, the author reviews general technology approaches for heavy and light duty applications. Given the emerging significance of ultrafines to health, and to emission control technologies, an overview of the significant developments in ultrafine particulate science is provided, followed by an assessment of filter technology. Regarding NOx control, SCR (selective catalytic reduction) and LNT (lean NOx traps) progress is described. Finally, system integration examples are provided. In general, progress is impressive and studies demonstrate that high-efficiency systems are within reach in all highway vehicle sectors. Engines are making impressive gains, and will increase the options for emission control.
Technical Paper

A CFD Study of Diesel Substrate Channels with Differing Wall Geometries

This paper describes efforts to use computational fluid dynamics (CFD) to provide some general insights on how wall-based protuberances affect the flow and thermal fields in substrates exposed to typical diesel engine exhaust conditions. The channel geometries examined included both square and round bumps as well as an extreme tortuous path design. Three different 2d CFD laminar-flow analyses were performed: (1) a transient fluid analysis to identify the existence of any vortex shedding in the vicinity of the bumps, (2) a steady-state fluid analysis to examine the velocity and pressure fields as well as momentum transport characteristics, and (3) a thermal analysis to examine the heat transport characteristics. The model predicts no vortex shedding behind the bumps for the conditions and geometries examined, confirming the validity of a steady state approach and eliminating this possible transport mechanism.
Technical Paper

Principles for the Design of Diesel Oxidation Catalysts

The diesel oxidation catalyst is required to remove hydrocarbons and carbon monoxide from the diesel engine exhaust stream while minimizing the impact of all other features such as cost, space, pressure drop, weight, fuel consumption, etc. The challenge of designing a catalytic converter for a particular application then becomes to: first, understand the emissions and other performance targets and requirements for the engine; second, understand the influence each of the converter parameters has on the overall system performance and; third, optimize the system using these relationships. This paper will explore some of the considerations with respect to the second of the above challenges.
Technical Paper

DPF Regeneration-Concept to Avoid Uncontrolled Regeneration During Idle

Significant particulate emission reductions of diesel engines can be achieved using diesel particulate filters (DPFs). Ceramic wall flow filters with a PM efficiency of >90% have proven to be effective components in emission control. The challenge for the application lies with the development and adaptation of a reliable regeneration strategy. The main focus is emission efficiency over the legally required durability periods, as well as over the useful vehicle life. It will be shown, that new DPF systems are characterized by a high degree of integration with the engine management system, to allow for initiation of the regeneration and its control for optimum DPF protection. Using selected cases, the optimum combination and tuning will be demonstrated for successful regenerations, taking into account DPF properties.
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.
Technical Paper

Diesel Emission Control in Review – The Last 12 Months

Driven mainly by tightening of regulations, advance diesel emission control technologies are rapidly advancing. This paper will review the field with the intent of highlighting representative studies that illustrate the state-of-the-art. First, the author makes estimates of the emission control efficiency targets for heavy and light duty applications. Given the emerging significance of ultrafines to health, and to emission control technologies, an overview of the significant developments in ultrafine particulate science is provided, followed by an assessment of filter technology. Major deNOx catalyst developments, in addition to SCR and LNT progress is described. Finally, system integration examples are provided. In general, progress is impressive and studies have demonstrated that high-efficiency systems are within reach in all sectors highway vehicle sectors. Engines are making impressive gains, and will increase the options for emission control.
Technical Paper

Impact of Ultra Thinwall Catalyst Substrates for TIER2 Emission Standards

The impact of ultra thinwall catalysts on TIER2 emission performance, packaging and total system cost was evaluated. The primary focus was to compare ultra-thinwall and thinwall cell configurations (400/3, 400/4, 600/2, 600/3, 600/3 hex, 900/2, and 1200/2) with a baseline 600/4 at constant substrate volume, washcoat and PGM loading. Other areas investigated included the evaluation of decreasing catalyst volume while maintaining constant or increased mass transfer capabilities while holding washcoat and PGM loadings constant. The emissions impact of varying washcoat and PGM loading was measured on specific substrates, including a comparison of square to hex cell. Backpressure for each configuration was calculated with the Corning substrate pressure drop modeling tool. Converters were rapid aged on dynamometers reflecting approximately a 50,000 mile aged performance. Emission testing was completed using the FTP test cycle.
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

Impact of Ceramic Substrate Web Thickness on Emission Light-Off, Pressure Drop, and Strength

The effect of web thickness on emission performance, pressure drop, and mechanical properties was investigated for a series of catalyzed ceramic monolith substrates having cell densities of 900, 600 and 400 cpsi. As expected, thinner webs provide better catalyst light off performance and lower pressure drop, but mechanical strength generally decreases as web thickness is reduced. Good correlations were found between emission performance and geometric parameters based on bare and coated parts. An improved method for estimating the effects of cell density and web thickness on bare substrate strength is described, and the effect of porosity on material strength is also examined. New mechanical strength correlations for ceramic honeycombs are presented. The availability of a range of ceramic product geometries provides options for gasoline exhaust emission design and optimization, especially where increased levels of performance are desired.
Technical Paper

Predicting Pressure Drop of Wall-Flow Diesel Particulate Filters - Theory and Experiment

Information on transport mechanisms in a Diesel Particulate Filter (DPF) provides crucial insight into the filter performance. Extensive experimental work has been pursued to modify, customize and validate a model yielding accurate predictions of a ceramic wall-flow DPF pressure drop. The model accounts, not only for the major pressure drop components due to flow through porous walls but also, for viscous losses due to channel plugs, flow contraction and expansion due to flow entering and exiting the trap and also for flow secondary inertial effects near the porous walls. Experimental data were collected on a matrix of filters covering change in filter diameter and length, cell density and wall thickness and for a wide range of flow rates. The model yields accurate predictions of DPF pressure drop with no particulate loading and, with adequate adjustment, it is also capable of making predictions of pressure drop for filters lightly-loaded with particulates.