4th and 5th CLEERS Workshop

Emphasized topic areas:

• Selective Catalytic Reduction of NOx with Urea/Ammonia
• Selective Catalytic Reduction of NOx with Hydrocarbons and Non-Ammonia Reductants

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 4th and 5th 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 4 and 5

The 4th and 5th CLEERS workshops were hosted by Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan. The 4th workshop was held on April 30^th and the morning of May 1^st (1 ½ days total) and was focused on simulation of “Selective Catalytic Reduction of NOx with Urea/Ammonia.” The 5th workshop focused on simulation of “Selective Catalytic Reduction of NOx with Hydrocarbons and Non-Ammonia Reductants” was held on the afternoon of May 1^st and the morning of May 2^nd (1 day total). Both of these workshops were planned in response to feedback from the first CLEERS workshop held in Knoxville, Tennessee during May 2001.

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

The fourth and fifth CLEERS workshops on simulation and modeling of lean exhaust emissions control were held on the campus of the University of Michigan in Ann Arbor on April 30th-May 2nd, 2002. The subject of the fourth workshop was selective catalytic reduction (SCR) of nitrogen oxides (NOx) with urea or ammonia injection. The subject of the fifth workshop was NOx SCR with hydrocarbons and non-urea/ammonia reductants.

There were attendees representing a wide range of emissions control stakeholders including auto manufacturers, diesel engine companies, national labs, DOE, universities, consulting and software companies, and emissions control suppliers. Agendas for both workshops were similar to those used in previous workshops and included the following major components:

• A brief review of the CLEERS objectives and reasons for focusing on the technologies discussed in the current workshops
• Invited mini-presentations by industry representatives in which the major industry concerns/perspectives on the focus technology were summarized
• Panel discussions in which the industry representatives answered questions and provided more detailed comments regarding the issues raised in the mini-presentations
• Numerous invited and contributed technical presentations on both types of SCR including experimental results, fundamental chemistry, component modeling/simulation, and systems integration
• Group discussions to identify the highest priority R&D issues that need to be addressed

Based on the group discussions at the end of the fourth workshop, the following modeling/simulation issues were identified as having highest priority for urea/ammonia SCR:

• Ammonia storage
• Urea decomposition
• Catalyst degradation
• The effects of NO/NO2 split in the exhaust

For all of the above, there was general agreement that appropriate kinetics rate expressions are the most important pieces of missing information. It was further agreed that the general term ‘kinetics’ is used broadly by the stakeholder community and can refer to any of the following modeling aspects:

• Gas phase reactions
• Heterogeneous reactions
• Global reaction rates
• Micro-scale (elementary) reaction mechanisms
• Physical or physio-chemical processes in the solid that can become rate limiting or contribute to accumulation of reactants or products (storage)

All of the above simulation/modeling areas were considered important and worthy of further development.

An inter-workshop presentation on plans for developing a CLEERS protocol for generating and reporting laboratory kinetics data led to considerable discussion. While there are minor technical issues remaining to be addressed, it appears that there is a strong consensus supporting the development and implementation of such a protocol.

During the group discussion at the end of the fifth workshop it was clearly evident that the majority of attendees believe that there is little potential for resolving performance shortcomings of non-urea SCR technologies by 2007. Thus it was concluded that this aftertreatment technology should be given lower priority relative to lean NOx adsorbers, diesel particulate filters, and urea/ammonia SCR. It was also agreed, however, that it would be a mistake to abandon all research in non-urea SCR, especially for the longer term. The highest priorities for such longer-term research include:

• The collection of engine out data that accurately reflects realistic transient conditions for benchmark engines
• Utilization of non-standard hydrocarbon reductants (such as alcohols, hydrogen, and carbon monoxide)
• Storage of reductants and NOx
• Speciation of engine-out hydrocarbons under realistic transients
• Kinetics and modeling of on-board reformers

Both workshop groups reiterated the importance of general issues that transcend the specific type of aftertreatment being considered. The most significant of these issues include:

• Effects of non-platinum additives/replacements in SCR catalysts
• The development of adaptive schemes for computing kinetic rates (i.e., numerical methods for reducing the order of kinetic mechanisms during computation so that only the rate-determining steps are computed)
• The development of standard formats (API formats) for interfacing component models with each other and with integrated system models

Beyond SCR, the workshop discussions also included an update on plans for the CLEERS database and plans for structuring and scheduling future workshops. There remains a strong interest among the stakeholder community in populating and maintaining the database, in particular along the lines suggested by the inter-workshop discussion of the kinetic data protocol. Also, there appears to be a strong interest in maintaining the workshops with the current wide diversity of participants, although the frequency of workshop scheduling could be reduced. One suggested difference for future workshops was that more emphasis be placed on reporting detailed results about the previously identified priority areas for lean NOx adsorbers, diesel particulate filters, and urea SCR. Creation of technology-specific working groups (e.g., headed by representatives of Crosscut member companies) was suggested as a way to coordinate R&D efforts and organize future workshops.