7th CLEERS Workshop

Emphasized topic areas:

• Diesel Particle Filters
• Selective Catalytic Reduction
• Lean NOx Traps
• Synergies between these three components in actual systems

Objectives:

• Provide technical updates on the latest developments for these technologies and corresponding simulation tools
• Enhance emissions control collaboration among industry, government and universities
• Improve and update recognition of key research priorities

Purpose

CLEERS workshops are intended as relatively informal but tightly focused forums for sharing recent research results on understanding and simulating lean exhaust emissions control. Joint participation by researchers in government, universities, and industry is encouraged. This is the 7th workshop in a series sponsored by the DOE Office of FreedomCAR and Vehicle Technologies and the DOE Diesel Crosscut Team. The results of the workshop discussions, especially the all-participant discussion at the end, will be documented for the DOE Office of Transportation Technology (OTT) for consideration in improving R&D priorities and technical focus in DOE-supported transportation programs.

About Workshop 7

The 7th CLEERS workshop will be hosted by Detroit Diesel Corporation at their training center in Detroit on June 16th and 17th, 2004. Diesel particulate filters (DPF) and selective catalytic reduction (SCR) will be the major discussion themes, but it is also anticipated that there will be important updates on measurements and modeling for lean NOx traps (LNT’s) and synergies among these components in actual systems. As with the previous CLEERS workshops, this will be a public meeting open to all who are interested in the most recent developments in understanding and simulating the performance of these devices under realistic conditions.

It is expected that the workshop presentations will include invited presentations by internationally prominent researchers in DPF and SCR and updates on the development of standardized characterization procedures for LNT materials. Contributed presentations of 20-30 minutes about DPF, SCR, and LNT technologies are also invited from interested parties. Those who are interested in making such presentations should contact one of the following topical coordinators:

• DPF technology- George Muntean, Pacific Northwest National Laboratory, email George.Muntean@pnl.gov, phone 509-375-2224 or Chris Rutland, University of Wisconsin, email rutland@engr.wisc.edu, phone 608-262-5853
• SCR technology- Darrell Herling, Pacific Northwest National Laboratory, email darrell.herling@pnl.gov, phone 509-375-6905 or Joe Bonadies, Delphi, email joseph.v.bonadies@delphi.com, phone 810-257-2074
• LNT technology and system integration- Stuart Daw, Oak Ridge National Laboratory, email dawcs@ornl.gov, phone 865-946-1341 or Dick Blint, General Motors, email richard.j.blint@gm.com, phone 586-596-4291

This was the seventh in a series of CLEERS public workshops. The meeting was hosted by Detroit Diesel at their Detroit training facility. Target topics for this workshop included the modeling and simulation of Diesel Particulate Filters (DPF’s), Selective Catalytic Reduction (SCR), and Lean NOx Traps. Since the previous workshop had a major emphasis on LNT’s, it was agreed that this workshop would focus more heavily on DPF and SCR.

The specific workshop objectives were:

• Conduct an in-depth technical discussion on aftertreatment modeling, especially concerning DPF and SCR;
• Review the status of development of the standard LNT characterization protocol and how that experience can be adapted for DPF and SCR;
• Update the general CLEERS community on the status of the Focus Groups and generate useful feedback to the Focus Groups from that community; and
• Identify up-to-date research priorities for DPF’s, SCR, and LNT’s and feed that information back to Diesel Crosscut Team and DOE.

There were 90 participants, including representatives from software companies, universities, emission controls suppliers, automotive and engine manufacturers, national laboratories, and consulting companies. Altogether, twenty eight presentations were given, with the following general breakdown:

• DPF (10 talks)
  • Invited
    • Prof. Konstandopoulos (APTL, CERTH/CPERI, Greece )
    • Dr. Merkel (Corning)
    • Dr. Gulati (Corning)
  • 7 contributed
• LNT (8 talks, all contributed)
• SCR (8 talks)
  • Invited
    • Prof. Burch (Queens University, Belfast)
  • 7 contributed

A detailed agenda and downloadable copies of most of the presentations are available on the CLEERS website (www.cleers.org). Detailed notes about the presentations and discussion taken by John Hoard (Ford) are also available on the website.

Highlights from the technical discussions in each technology area included the following:

Diesel Particulate Filters

• Standard characterization and modeling of DPF’s are especially challenging because of the large variability and hysteresis in soot properties;
• Several groups are involved in detailed modeling of soot cake development and filter media pore plugging, including Michigan Tech University, Pacific Northwest National Lab, and Centre for Research and Technology Hellas (Greece);
• Several groups are involved in lower-order/system modeling of DPF performance including University of Wisconsin, University of Michigan, and Michigan Tech University;
• The availability of key global rate parameters needed for performance simulation of DPF’s is notably lacking; and
• There is a widespread belief that although many details of DPF performance are currently hard to quantify in a consistent way, the DPF Focus Group should concentrate on developing some elements of a standard characterization protocol rather than trying to be too comprehensive at the beginning.

In regard to the last point, there was much discussion about the idea for developing a characterization procedure for DPF’s that would be analogous to what is currently done for turbochargers. It was widely agreed that this analogy is useful for starting the discussion, but the process for quantifying DPF functionality is more complex than it is for turbochargers. However, engine companies still have a strong need to simplify the process of defining performance parameters that can be used for prediction and system integration.

Lean NOx Traps

• GM/Chalmers and ORNL are developing and testing global kinetic models that appear to be useful for interpreting and guiding LNT testing;
• Hysteresis is an important factor for LNT’s but is less complex than for DPF’s;
• One of the most complex issues in modeling and simulating LNT’s is the impact of different exhaust reductant species on the NOx regeneration efficiency;
• An appropriate level of degreening is one of the most difficult issues involved in developing a consistent LNT characterization protocol; and
• The current attempt of the LNT Focus Group to develop a standard protocol definition/demonstration is one of the most important CLEERS focus activities, because it can serve as a template for the other groups.

As for the DPF Focus Group, it appears that the most feasible approach is to begin defining at least some of the most important elements of an LNT protocol, while at the same time trying not to be too comprehensive.

Selective Catalytic Reduction

• Mechanisms for HC-SCR can be very highly variable from catalyst to catalyst, with only a few reaction steps dominating;
• Although it is possible to develop extremely detailed computational models for performance, details should only be added when clearly warranted (Occam’s Razor);
• High throughput trials at GM have demonstrated the value of this methodology for HC-SCR catalyst exploration and is leading to some promising candidates for further study;
• Assessments of the economics for urea-SCR still show that this technology is favorable relative to LNT’s, even considering all costs for the urea infrastructure;
• One of the most challenging issues for urea-SCR simulation is handling the large number of byproduct species that are produced; and
• There are several groups who have constructed global kinetic models for simulating the NOx performance of urea-SCR including the National Renewable Energy Laboratory, Johnson Matthey, and University of Michigan.

Other general feedback coming from the workshop discussions included the following points:

• The basic focus group structure being used to address the key simulation issues for the different technologies appears to be successful in meeting the CLEERS objectives;
• Interest in the public workshops is still very strong and the general format and timing of the workshops still seems to be appropriate;
• Diesel engine companies continue to stress the current lack of accurate rate parameters needed for simulating realistic aftertreatment performance (and the need for CLEERS to assist in providing this information);
• The highest priority for obtaining rate parameters information appears to have shifted over the last two years from LNT’s to DPF and urea-SCR; and
• Perhaps for historical reasons as well as the nature of the technology, the development of standardized procedures for measuring and quantifying the critical rate parameters appears to be furthest along for LNT’s.