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Title: Mechanism Development for the Simulation of LNT Lean/Rich Cycling.


Abstract not provided.

; ; ;
Publication Date:
Research Org.:
Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
Report Number(s):
DOE Contract Number:
Resource Type:
Resource Relation:
Conference: Proposed for presentation at the Tenth CLEERS Workshop held May 1-3, 2007 in Dearborn, MI.
Country of Publication:
United States

Citation Formats

Larson, Richard S., Chakravarthy, Kalyana, Pihl, Josh A., and Daw, C. Stuart. Mechanism Development for the Simulation of LNT Lean/Rich Cycling.. United States: N. p., 2007. Web.
Larson, Richard S., Chakravarthy, Kalyana, Pihl, Josh A., & Daw, C. Stuart. Mechanism Development for the Simulation of LNT Lean/Rich Cycling.. United States.
Larson, Richard S., Chakravarthy, Kalyana, Pihl, Josh A., and Daw, C. Stuart. Sun . "Mechanism Development for the Simulation of LNT Lean/Rich Cycling.". United States. doi:.
title = {Mechanism Development for the Simulation of LNT Lean/Rich Cycling.},
author = {Larson, Richard S. and Chakravarthy, Kalyana and Pihl, Josh A. and Daw, C. Stuart},
abstractNote = {Abstract not provided.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2007},
month = {Sun Apr 01 00:00:00 EDT 2007}

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  • A computer program was developed to study the mixing process in the quick quench region of a rich burn-quick quench mix-lean burn combustor. The computer program developed was based on the density-weighted, ensemble-averaged conservation equations of mass, momentum (full compressible Navier-Stokes), total energy, and species, closed by a k-epsilon turbulence model with wall functions. The combustion process was modeled by a two-step global reaction mechanism, and NO(x) formation was modeled by the Zeldovich mechanism. The formulation employed in the computer program and the essence of the numerical method of solution are described. Some results obtained for nonreacting and reacting flowsmore » with different main-flow to dilution-jet momentum flux ratios are also presented. 17 refs.« less
  • Oxides of nitrogen in the form of nitric oxide (NO) and nitrogen dioxide (NO 2) commonly referred to as NO x, is one of the two chemical precursors that lead to ground-level ozone, a ubiquitous air pollutant in urban areas. A major source of NO x} is generated by equipment and vehicles powered by diesel engines, which have a combustion exhaust that contains NO x in the presence of excess O 2. Catalytic abatement measures that are effective for gasoline-fueled engines such as the precious metal containing three-way catalytic converter (TWC) cannot be used to treat O 2-laden exhaust containingmore » NO x. Two catalytic technologies that have emerged as effective for NO x abatement are NO x storage and reduction (NSR) and selective catalytic reduction (SCR). NSR is similar to TWC but requires much larger quantities of expensive precious metals and sophisticated periodic switching operation, while SCR requires an on-board source of ammonia which serves as the chemical reductant of the NO x. The fact that NSR produces ammonia as a byproduct while SCR requires ammonia to work has led to interest in combining the two together to avoid the need for the cumbersome ammonia generation system. In this project a comprehensive study was carried out of the fundamental aspects and application feasibility of combined NSR/SCR. The project team, which included university, industry, and national lab researchers, investigated the kinetics and mechanistic features of the underlying chemistry in the lean NOx trap (LNT) wherein NSR was carried out, with particular focus on identifying the operating conditions such as temperature and catalytic properties which lead to the production of ammonia in the LNT. The performance features of SCR on both model and commercial catalysts focused on the synergy between the LNT and SCR converters in terms of utilizing the upstream-generated ammonia and alternative reductants such as propylene, representing the hydrocarbon component of diesel exhaust. First-principle models of the LNT and SCR converters, which utilized the mechanistic-based kinetics and realistic treatments of the flow and transport processes, in combination with bench-scale reactor experiments helped to identify the best designs for combining the NSR and SCR catalysts over a range of operating conditions encountered in practice. This included catalysts having multiple zones and layers and additives with the focus on determining the minimal precious metal component needed to meet emission abatement targets over a wide range of operating conditions. The findings from this study provide diesel vehicle and catalyst companies valuable information to develop more cost effective diesel emissions catalysts which helps to expand the use of more fuel efficient diesel power. The fundamental modeling and experimental tools and findings from this project can be applied to catalyst technologies used in the energy and chemical industries. Finally, the project also led to training of several doctoral students who were placed in research jobs in industry and academia.« less
  • In this paper, a new technology named rich/ lean coal combustion is introduced. The technology is used for the low load flame stabilization of pulverized coal without support oil and the prevention of furnace wall stagging. A specially designed two phase flow test facility was set up in Zhejiang University to develop a technology of air--coal mixture separation. The cross section of test pipe is 250 x 250mm. The maximal air flow in the tester can reach 6000 m{sup 3}/h and particles flux is up to 3-4 t/h. The pulverized coal in primary air is separated and two streams ofmore » air- coal- rich pulverized coal stream and lean pulverized coal stream are formed. Rich pulverized coal stream is guided to the high temperature area facing the flame. This contributes to ignition and flame stability of pulverized coal. The lean pulverized coal stream is guided to low temperature area located behind the flame and forms a air film near furnace wall that benefits to reduce the slagging on the wall. The rich/lean combustion also lows NOx emission. The test results of new developed equipment shows that the ratio of the concentration of rich pulverized coal side to concentration of lean side is 7-12:1. Namely, if average CA is equal to 0.6, then C/A in rich side reaches about 1.1 and C/A in lean side is about o.1. The pressure drop of the separate equipment is about 3000-4000Pa. The retrofit of several utility boilers have been made. These include 200MW, 125MW, 100MW, and 50MW utility boilers and the coal types used include brown coal, bituminous coal and anthracite coal. The industrial tests showed that this technology is successful to meet the above three goals. The lowest boiler load of about 40-50% to keep coal flame steady has been obtained without supporting oil. The flow pattern in furnace is good and no slagging is formed on the wall of the retrofitted boilers. The combustion efficiency of the boiler to burn bituminous coal is unproved apparently after the retrofit of the boilers.« less
  • Exposure of Pt/K/Al{sub 2}O{sub 3} to 15 ppm SO{sub 2} reduces the NOx activity at 200, 300, and 400 C at significantly different rates--1.5, 8.5, and 18.0 {micro}mol NOx/(h g{sub cat}), respectively. During the initial sulfation, NOx conversion is directly linked to lean phase storage capacity, and sulfation does not impact the reduction kinetics since the amount of unconverted NOx was constant or decreased with increasing sulfation time. A portion of sulfur stored at 200 C desorbs upon mild heating to 400 C while cycling between lean and rich conditions. This apparently is a result of sulfur being released frommore » Al{sub 2}O{sub 3}; however, performance is not significantly recovered as much of the sulfur is re-adsorbed on the K-phase. This is apparent from analysis of the NOx storage and release profiles. Additional analysis of these profiles suggests that SO{sub 2} initially adsorbs near Pt before interacting with other sites further away from Pt at 300 C. At 400 C, it appears that SO{sub 2} either preferentially adsorbs near Pt and then quickly diffuses along the surface to other less proximal sites, or it directly adsorbs on sites further away from Pt. De-sulfurization up to 800 C using a temperature programmed reduction (TPR) procedure and rich conditions with both CO{sub 2} and H{sub 2}O restored 73=94% of the LNT performance at 300 and 400 C. However, the recovered performance measured at 200 C was only 34-49% of the original NOx reduction activity. H{sub 2}S and SO{sub 2} were the primary de-sulfurization products with H{sub 2}S having a maximum release between 690 and 755 C, while SO{sub 2} had a peak release between 770 and 785 C. The sulfation temperature does not have a significant impact on the recovered performance, the de-sulfurization products or the sulfur release temperature.« less