Filters & Substrates

Oxide Based Particulate Filters for Light-Duty Diesel Applications – Impact of the Filter Length on the Regeneration and Pressure Drop Behavior
SAE #: 2008-01-0485 | View PDF

AUTHORS:
Thorsten Boger and Ingo-C. Tilgner - Corning GmbH
Min Shen and Yi Jiang - Corning Incorporated

ABSTRACT:
Diesel particulate filters are becoming a standard for most light duty diesel applications designed for European EU5 and EU6 regulations. Oxide based filter materials are continuing to gain significant interest and have been in high volume serial application since 2005. Compared to carbide materials they show some unique properties.

With respect to the design, the length of a filter is a key variable. Usually the prime design consideration is the desired filter volume. The diameter or frontal area is then usually defined by packaging constraints. Finally, the length is adapted. The paper provides experimental data on the impact this key design parameter has on the pressure drop and the thermal behavior under “worst case” regeneration conditions. A wide range of soot loads (from 4 g/dm³ to 9 g/dm³) as well as filter lengths from 6” to 12” is considered and evaluated under comparable experimental conditions.

The discussion is based on experimental data as well as numerical simulations with a 2D simulator. The simulator is shown to be in good agreement with the experimental observations. In general shorter filters are found to be of advantage. They provide for lower pressure drop and yield lower temperatures and gradients during worst case regeneration conditions. Data are provided that can help to estimate the impact of the filter length on the soot mass limit.

Regeneration Strategies for an Enhanced Thermal Management of Oxide Diesel Particulate Filters
SAE #: 2008-01-0328 | View PDF

AUTHORS:
Thorsten Boger, Dominik Rose and Ingo-C. Tilgner - Corning GmbH
Achim K. Heibel -Corning Incorporated

ABSTRACT:
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. Their practical relevance and the ability to use them for control purposes is analyzed. Guidelines are presented that should be considered when applying oxide diesel particulate filters. The differences between oxides and materials with higher thermal conductivity are discussed with respect to the relationship between regeneration conditions and the achievable regeneration efficiency. Experimental data show benefits for oxide materials vs. SiC, expected to come from their low conductivity.For the regeneration strategy a simple approach is proposed and illustrated by means of examples. The benefits of a staged regeneration approach are discussed, using two temperature levels during the regeneration.

Diesel Emission Control in Review
SAE #: 2008-01-0069 | View PDF

AUTHOR:
Timothy V. Johnson - Corning Incorporated

ABSTRACT:
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.

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. LNCs developments are updated.

Diesel particulate filter (DPF) technology is in a state of optimization and cost reduction. New DPF regeneration strategies are described as well as the new learnings on the fundamentals of soot/catalyst interaction and the impact of DPF pore structure.

Finally an update on diesel oxidation catalysts (DOCs) is provided showing potential issues with advanced combustion strategies, important interactions on NO2 formation, and new formulations for enhanced durability.

Performance Aspects of New Catalyzed Diesel Soot Filters Based on Advanced Oxide Filter Materials
SAE #: 2007-01-1268 | View PDF

AUTHORS:
W. A. Cutler and T. Boger - Corning GmbH
A. F. Chiffey, P. R. Phillips, D. Swallow and M. V. Twigg - Johnson Matthey PLC

ABSTRACT:
Catalyzed soot filters are being fitted to an increasing range of diesel-powered passenger cars in Europe. While the initial applications used silicon carbide wallflow filters, oxide-based filters are now being successfully applied. Oxide-based filters can offer performance and system cost advantages for applications involving both a catalyzed filter with a separate oxidation catalyst, and a catalyzed filter-only that incorporates all necessary catalytic oxidation functions. Advanced diesel catalyst technologies have been developed for alternative advanced oxide filter materials, including aluminum titanate and advanced cordierite. In the development of the advanced catalyzed filters, improvements were made to the filter material microstructures that were coupled with new catalyst formulations and novel coating processes that had synergistic effects to give enhanced overall performance. This paper discusses relevant system performance criteria including pressure-drop, emissions, thermalmechanical influences and the overall system durability in tests under certain controlled test conditions.

Improved Lifetime Pressure Drop Management for Robust Cordierite (RC) Filters with Asymmetric Cell Technology (ACT)
SAE #: 2007-01-0920 | View PDF

AUTHORS:
Krishna Aravelli and Achim Heibel - Corning Incorporated, Diesel Technologies Development

ABSTRACT:
The stricter emissions legislation in the US, require the implementation of Diesel Particulate Filters (DPF) for Heavy Duty Diesel engines to meet the 2007 PM emissions targets. Cordierite based wall-flow filters with high filtration efficiency, low op and good thermal durability are the product of choice for these applications. Continuous passive oxidation of the soot by NO2 is desired, however under certain operating and ambient conditions periodic active oxidation of the soot at elevated temperatures (>550ºC) is required. A part of the PM emissions of the engine contains noncombustible contributions (ashes). These materials accumulate in the filter over lifetime, resulting in an increase in pressure drop as well as a reduction of the filter volume available for soot accumulation. As the pressure drop rises above manageable levels from a performance perspective, ash cleaning of the filter is required. The ash storage capacity of the filter determines the service interval for the filter. Long service intervals are desired by the end customer. To mitigate the impact of the ash accumulation in the filter, Corning Incorporated has developed filters with the proprietary asymmetric cell technology (ACT), providing high ash capacity with good strength attributes. These filters have larger inlet and smaller outlet channels and therefore a higher volume available for ash storage.

The present work summarizes the results of on-engine (HD) ash testing on uncoated Robust Cordierite (RC) filters – Ø267mmX305mm (Ø10.5”x12”) in both Standard (200/19) and ACT (270/16) design configurations. The work demonstrates, for an equal size filter a 30% improved ash storage capacity and therefore longer service interval for the ACT design over the standard filter. Good durability of the filters for a long operation timeframe (up to 2700h) was demonstrated. Furthermore the paper summarizes a wide set of post testing evaluations, both non-destructive and destructive to understand the ash distribution and interactions in the filter.

Performance Evaluations of Aluminum Titanate Diesel Particulate Filters
SAE #: 2007-01-0656 | View PDF

AUTHORS:
R. S. Ingram-Ogunwumi, Q. Dong, T. A. Murrin, R. Y. Bhargava, J. L. Warkins and A. K. Heibel - Corning Incorporated

ABSTRACT:
Over the past decade, regulations for mobile source emissions have become more stringent thus, requiring advances in emissions systems to comply with the new standards. For the popular diesel powered passenger cars particularly in Europe, diesel particulate filters (DPFs) have been integrated to control particulate matter (PM) emissions. Corning Incorporated has developed a new proprietary aluminum titanate-based material for filter use in passenger car diesel applications. Aluminum titanate (hereafter referred to as AT) filters were launched commercially in the fall of 2005 and have been equipped on more than several hundred thousand European passenger vehicles. Due to their outstanding durability, filtration efficiency and pressure drop attributes, AT filters are an excellent fit for demanding applications in passenger cars.

Extensive testing was conducted on engine to evaluate the survivability and long-term thermo-mechanical durability of AT filters. Catalyzed filters were first tested to failure under severe uncontrolled regenerations to define filter survivability limits by means of filter maximum temperatures and thermal gradients. In the second phase filter durability was evaluated, exposing the AT filter to hundreds of high temperature regenerations. This paper demonstrates a broad window of operation for AT filters under extreme exposures. Furthermore the pressure drop as well as the filtration performance of the filters was investigated and compared to commercially available filter alternatives.

Advanced Mounting System for Light Duty Diesel Filter
SAE #: 2007-01-0471 | View PDF

AUTHORS:
S. T. Nickerson, C. B. Sawyer and S. T. Gulati - Corning Incorporated
S. D. Fernandes, Jr. and J. R. Olson - Unifrax Corporation

ABSTRACT:
This paper employs a systematic approach to packaging design and testing of a system and its components in order to determine the long term durability of light duty diesel filters. This effort has utilized a relatively new aluminum titanate filter technology as well as an advanced support mat technology engineered to provide superior holding force at lower temperatures while maintaining its high temperature performance. Together, these two new technologies form a system that addresses the unique operating conditions of diesel engines. Key physical properties of both the filter and the mat are demonstrated through laboratory testing. The system behavior is characterized by various laboratory techniques and validation procedures.

Diesel Emission Control in Review
SAE #: 2007-01-0233 | View PDF

AUTHORS:
Timothy V. Johnson - Corning Incorporated

ABSTRACT:
This summary covers the developments from 2006 in diesel regulations, engine combustion, and NOx and PM remediation.

Regulatory developments are now focused on Europe, where light-duty Euro 5 and 6 regulations have been proposed for 2009 and 2014, respectively. The regulations are lass stringent than those in the US, but options exist for adopting European vehicles for the US market. Europe is just beginning to look at heavy-duty regulations for 2012 and beyond.

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 focusing on SCR (selective catalytic reduction) for diverse applications. Focus is on cold operation, durability, secondary emissions, and system optimization. Aged LNTs (lean NOx traps) are effective up to about 60-70% deNOx efficiency, and are being considered for light-duty and some light heavy-duty applications. There is growing interest in supplementing LNT performance with integrated SCR, which utilizes ammonia generated in the LNT during rich regenerations.

Diesel particulate filter technology is in a state of optimization and cost reduction. Very sophisticated management strategies are being utilized, which open up options for new filter materials and alternative system architectures. Secondary emissions issues are emerging and are being addressed.

Relative Benefits of Various Cell Density Ceramic Substrates in Different Regions of the FTP Cycle
SAE #: 2006-01-1065 | View PDF

AUTHORS:
Katherine W. Hughes - Corning Incorporated
David Gian and Jason Calleja - FEV Engine Technology, Inc.

ABSTRACT:
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.

Diesel Emission Control in Review
SAE #: 2006-01-0030 | View PDF

AUTHORS:
Timothy V. Johnson - Corning Incorporated

ABSTRACT:
The paper summarizes the key developments in diesel emission control, generally for 2005. Regulatory targets for the next 10 years and projected advancements in engine technology are used to estimate future emission control needs. Recent NOx control developments on selective catalytic reduction (SCR), lean NOx traps (LNT) and lean NOx catalysts (LNC) are then summarized. Likewise, the paper covers important recent developments on diesel particulate filters (DPFs), summarizing regeneration strategies, new filter and catalyst materials, ash management, and PM measurement. Recent developments in diesel oxidation catalysts are also briefly summarized. Finally, the paper discusses examples of how it is all pulled together to meet the tightest future regulations.

Aluminum Titanate Compositions for Diesel Particulate Filters
SAE #: 2005-01-0583 | View PDF

AUTHORS:
S. B. Ogunwumi, P. D. Tepesch, T. Chapman, C. J. Warren, I. M. Melscoet-Chauvel and D. L. Tennent - Corning Incorporated

ABSTRACT:
Compositions in the mixed strontium/calcium feldspar ([Sr/Ca]O.Al2O3.2SiO2) - aluminum titanate (Al2O3.TiO2) system were investigated as alternative materials for diesel particulate filter application. A key attribute of these compositions is their low coefficient of thermal expansion. Samples were prepared with porosities of >50% and with average pore sizes of between 12 and 16um. Coupled with monolithic fabrication, the superior thermal shock resistance, increased resistance to ash attack, and high volumetric heat capacity of these materials provide advantages over other products available today. Testing to date demonstrates that (bare and catalyzed) aluminum titanate-based filters provide excellent chemical durability and pressure drop performance.