2nd and 3rd CLEERS Workshop

Emphasized topic areas:

• Simulation of Lean NOx Traps
• Simulation of Diesel Particulate Filters

Objectives:

• Reduce duplication of effort among separate research groups
• Provide up-to-date information on emissions control simulation tools
• Enhance collaboration among industry, government and universities
• Improve recognition of key research priorities

Purpose

The purpose of previous, these and subsequent CLEERS workshops is to solicit input from prominent researchers in Government, Universities, and Industry on the current state-of-the-art in simulation of lean exhaust emissions control. These are the 2nd and 3rd workshops in a series sponsored by the DOE Office of Heavy Vehicle Technologies (OHVT) 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 2 and 3

The 2nd and 3rd CLEERS workshops were hosted by Ford at the Scientific Research Laboratory in Dearborn, Michigan. The 2nd workshop was held on October 16th and the morning of October 17th (1 ½ days total) and was focused on simulation of “Lean NOx traps (LNTs).” The 3rd workshop focused on simulation of “Diesel Particulate Traps (DPT’s)” was held on the afternoon of October 17th and all day on October 18th (1 ½ days total). Both of these workshops were planned in response to feedback from the first CLEERS workshop held in Knoxville, Tennessee during May 2001.

The workshop agendas and copies of most presentations are available from this site. Workshop discussions have been summarized in a report to DOE, including specific recommendations to the Office of Transportation Technology (OTT) regarding R&D priorities and technical focus in DOE-supported transportation programs.

Planning for 4th and 5th workshops is now underway. These workshops are scheduled to be held April 30th, May 1st, and May 2nd at the University of Michigan in Ann Arbor with the focus themes being “Selective Catalytic Reduction of NOx using Urea/Ammonia and Non-Urea/Ammonia Reductants,” respectively.

Organizing Subcommittee

R. Blint, General Motors
N. Hakim, Detroit Diesel
G. Singh, U. S.-DOE/OHVT/HQ
H. Kung, Northwestern University
C. Rutland, University of Wisconsin, Madison
S. Daw, Oak Ridge National Laboratory

Both the second and third workshops were hosted by Ford at the Scientific Research Laboratory in Dearborn, Michigan. The second workshop was held on October 16th and the morning of October 17th (1 ½ days total) and was focused on simulation of Lean NOx Traps (LNT’s). The third workshop focused on simulation of Diesel Particulate Traps (DPT’s) was held on the afternoon of October 17th and all day on October 18th (1 ½ days total). Both of these workshops were planned in response to feedback from the first CLEERS workshop held in Knoxville, Tennessee during May 2001.

Participants and Overall Agenda

The overall affiliation breakdown was approximately 20% from auto companies, 18% from diesel engine companies, 20% from national labs, 3% from DOE Headquarters, 14% from universities; 11% from consulting and/or software companies, and 11% from fuel/emissions component suppliers. No immediate affiliations were available for the remaining participants. The proximity of many auto and diesel manufacturers made it possible for a large fraction of participants to drive, thereby saving the cost and time of air travel. The travel issue was particularly important at this time because of the continuing effect of the September 11 terrorist attacks.

The detailed meeting agenda for both workshops is posted elsewhere on this website. The NOx Adsorber Workshop lasted from Tuesday morning (Oct. 16th) until noon on Wednesday (Oct. 17th). The Diesel Particulate Workshop lasted from Wednesday afternoon (Oct. 17th) until slightly after noon on Thursday (Oct. 18th).

NOx Adsorber Workshop

Discussion for the NOx adsorber workshop began on Tuesday morning with a welcome by Haren Gandhi of Ford and an overview of CLEERS presented by Dick Blint. Dick reviewed the DOE and Crosscut Team perspectives on CLEERS and the specific workshop objectives. Major points emphasized by Dick included:

• The overall goal of CLEERS is to promote development of simulations of emission control systems under realistic conditions so that engine/aftertreatment systems can be more effectively optimized.
• In order to achieve this goal, we need to develop reliable aftertreatment component submodels, construct suitable integrations of these submodels, and utilize realistic engine-out data as inputs to the component submodels.
• The purpose of the technical workshops is to promote research collaborations that can contribute to the CLEERS objective, to clarify the state of the art for various aftertreatment technologies, and to identify the key unresolved technical issues and ways that these issues can be resolved.
• The first CLEERS workshop revealed a broad consensus for the development of more effective tools for predicting conversion efficiency and catalyst aging in aftertreatment components.
• The specific components identified as high priority in the first workshop were lean NOx adsorbers, diesel particulate filters, sulfur traps, ammonia/urea SCR reactors, engine exhaust heaters/conditioners, and reformers.
• For the high priority components, there are important opportunities for both 0-D and 1-D models for engineering-level analysis and detailed mechanistic models for understanding reaction pathways and rate-limiting steps.
• For the NOx adsorber workshop specifically, the key goals were to define and prioritize the kinetic information, reactor data, and engine data needed to complete the modeling for NOx adsorbers.

Following the introductory talks, an industrial panel consisting of John Li (Ford), Tom Gallant (Cummins), Tim Johnson (Corning), and Pat Szymkowicz (General Motors) described their key concerns and needs in mini-presentations and then fielded questions and comments from the audience. It was evident from these discussions that there is clearly some optimism in industry that NOx adsorbers will provide a viable option for control of NOx emissions in lean exhaust. It was also evident, however, that there are major technical hurdles that have to be addressed for that to happen. Although there were differences of opinion on the level of detail needed for producing successful models, there is no disagreement that modeling and computer simulation are needed.

Subsequent technical presentations included:

• An invited talk by Scott Sluder on the DOE OptiNOx studies at ORNL
• A contributed overview by Tim Johnson from Corning of lean NOx adsorber technology
• A contributed talk by Jim Parks from EmeraChem describing experimental measurements for the SCONOx NOx adsorber catalysts produced by EmeraChem
• A contributed talk by Ford’s Bill Schneider summarizing results from first-principles analysis of NOx and SOx storage on alkaline earth oxides
• A contributed presentation by Bob Weber describing a simulation model developed by A.D. Little for three-way catalysts
• A contributed presentation by Alex Yezerets and Neal Currier on experimental NOx adsorber measurements at Cummins using laboratory micro-reactors, pilot reactors, and Spatially Resolved Mass Spectrometry (SpaciMS)
• A contributed presentation by Tony McDaniel from Sandia National Labs illustrating the possibilities for constructing CHEMKIN-based MATLAB tools for developing standardized models of aftertreatment components
• A review by Chris Rutland of plans for constructing a CLEERS database on reactor data, kinetics, thermophysical properties, and engine out data that could be used as inputs for benchmarking component models
• An invited review by Charles Schenk from EPA at the Tuesday evening no-host dinner on EPA’s recent work with NOx adsorbers
• An invited overview of the Diesel Emissions Control- Sulfur Effects Program (DECSE) program by John Orban of Battelle, Columbus
• A contributed talk by Howard Fang on work at Cummins in applying vibrational, diffuse reflectance IR, and Raman spectroscopy for making detailed transient species measurements on catalyst surfaces
• A contributed presentation by Shawn Midlam-Mohler from Ohio State University on a novel system for managing NOx adsorber inlet temperature

Ron Graves facilitated the wrap-up session for NOx adsorbers before noon on Wednesday. In the ensuing discussion, the following key R&D issues were identified (in order of importance):

• Spatio-temporal aging (from all effects) and S poisoning
• NOx reduction catalysis (during both trap regeneration and storage)
• Desulfation chemistry (including heat and mass transfer effects)
• Solid-phase transport and transformation (including solid-phase diffusion and phase change)
• NOx trap/soot synergisms
• Effects of various types of reductants on regeneration efficiency
• Substrate/washcoat interactions
• Expanding the high performance temperature window
• Reducing the regeneration fuel penalty
• Water gas shift/steam reforming reactions

Of the above issues, the first three were clearly assessed by the participants as being significantly higher in priority than the remainder.

It also appeared that there is a relatively solid consensus on the key technical questions associated with the above issues. These questions are primarily focused in three areas:

• Aging/S poisoning
• NOx reduction catalysis, including the adsorption kinetics of NO on barium, cerium and sodium
• Desulfation chemistry

Diesel Particulate Filter Workshop

Discussion began on Wednesday afternoon with a welcome by Roger Krieger from GM and a discussion of the Diesel Particulate Filter Workshop objectives presented by Dick Blint. Dick briefly reiterated the CLEERS objective statement and the major findings from the first workshop. In addition, Dick pointed out specific issues for diesel particulate filters (DPF’s):

• DPF’s involve unique problems including initiating soot ignition in the presence of relatively cool diesel engine exhaust, management of the strong exotherms produced by soot ignition, modeling pressure drop as a function of monolith properties and flow conditions, exploitation of surface and fuel catalysts and chemical regeneration with NO2, sulfur poisoning effects, and complex soot characteristics.
• DPF regeneration is an especially difficult issue because typical diesel exhaust temperatures are 200 degrees C or more below that needed to initiate soot ignition.
• Once DPF ignition occurs, thermal runaway can seriously damage the monolith surface.
• Systems analysis is crucial because of the strong impact of engine exhaust temperature, composition, and PM properties on DPF performance.
• The specific goals for the DPF workshop were to define and prioritize the types of data needed to understand the detailed surface deposition and oxidation processes, the basic physical properties of the filter media, and the associated engine output characteristics.

The technical presentations began with mini-presentations from the industrial panel, which consisted of Paul Laing (Ford), Mansour Masoudi (Corning), Cornelius Opris (Caterpillar), and Arjun Tuteja (General Motors). Key points made by the panelists included:

• The systems context is particularly important for DPF’s
• DPF models of sufficient accuracy and speed for industrial application are not available
• Timely availability of simple but accurate DPF models (within the next 2-3 years) is critical
• Much basic work has already been done on modeling pressure drop, but the larger uncertainties center on regeneration

Following the panel discussions, technical presentations were given on the following subjects:

• An invited overview by Jason Yang from Michigan Technological University on the status of DPF model development
• A contributed talk by Mansour Masoudi from Corning reviewing previous work on modeling DPF pressure drop in soot-loaded filters
• A contributed talk by Alex Yezerets of Cummins describing the experimental flow reactors being developed at Cummins to measure soot combustion chemistry and kinetics
• A contributed presentation by Cornelius Opris from Caterpillar on the development of systems modeling capabilities for DPF at Caterpillar
• A contributed talk by John Storey of ORNL describing recent characterization results on the physical properties of diesel particulates
• A review by Mansour Masoudi of the major modeling issues involved in regeneration of DPF’s. ce on the current state of the art

Dick Blint facilitated the wrap-up session for DPF’s before noon on Thursday. In a similar manner to Ron’s approach for the NOx Adsorber wrap-up, Dick emphasized the need to identify the major issues for DPF’s and the associated technical questions. The major issues and questions identified were (in no preferential order):

• Effects of soot distribution
• Effects of fuel sulfur
• Effects of fuel additives
• Particle size distribution and composition
• Ash accumulation effects
• Gas emissions during regen
• Support deterioration
• Structural integrity, canning and mounting
• Soot combustion kinetics
• Soot characterization (other than particle size distribution and composition)
• HC volatile fraction characterization
• Species storage (washcoat/filter cake)
• Soot layer properties in the filter

After considerable discussion, it was agreed that the top R&D priorities should focus on:

• Particle morphology and oxidation characteristics
• Soot distribution and impact on maximum temperature
• Ash creation, composition, and transport inside the DPF as a function of operating conditions
• Gas emissions during regeneration