skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: The effect of flame structure on soot formation and transport in turbulent nonpremixed flames using direct numerical simulation.

Abstract

No abstract prepared.

Authors:
; ;  [1]; ;
  1. (University of Utah, Salt Lake City, UT)
Publication Date:
Research Org.:
Sandia National Laboratories
Sponsoring Org.:
USDOE
OSTI Identifier:
908878
Report Number(s):
SAND2007-0119J
TRN: US200722%%806
DOE Contract Number:
AC04-94AL85000
Resource Type:
Journal Article
Resource Relation:
Journal Name: Proposed for publication in Combustion and Flame.
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; FLAMES; MORPHOLOGY; SOOT; SYNTHESIS; MASS TRANSFER; TURBULENT FLOW; COMPUTERIZED SIMULATION

Citation Formats

Law, Chung K., Lu, Tianfeng, Smith, Philip J., Lignell, David, and Chen, Jacqueline H. The effect of flame structure on soot formation and transport in turbulent nonpremixed flames using direct numerical simulation.. United States: N. p., 2007. Web.
Law, Chung K., Lu, Tianfeng, Smith, Philip J., Lignell, David, & Chen, Jacqueline H. The effect of flame structure on soot formation and transport in turbulent nonpremixed flames using direct numerical simulation.. United States.
Law, Chung K., Lu, Tianfeng, Smith, Philip J., Lignell, David, and Chen, Jacqueline H. Mon . "The effect of flame structure on soot formation and transport in turbulent nonpremixed flames using direct numerical simulation.". United States. doi:.
@article{osti_908878,
title = {The effect of flame structure on soot formation and transport in turbulent nonpremixed flames using direct numerical simulation.},
author = {Law, Chung K. and Lu, Tianfeng and Smith, Philip J. and Lignell, David and Chen, Jacqueline H.},
abstractNote = {No abstract prepared.},
doi = {},
journal = {Proposed for publication in Combustion and Flame.},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Direct numerical simulations of a two-dimensional, nonpremixed, sooting ethylene flame are performed to examine the effects of soot-flame interactions and transport in an unsteady configuration. A 15-step, 19-species (with 10 quasi-steady species) chemical mechanism was used for gas chemistry, with a two-moment, four-step, semiempirical soot model. Flame curvature is shown to result in flames that move, relative to the fluid, either toward or away from rich soot formation regions, resulting in soot being essentially convected into or away from the flame. This relative motion of flame and soot results in a wide spread of soot in the mixture fraction coordinate.more » In regions where the center of curvature of the flame is in the fuel stream, the flame motion is toward the fuel and soot is located near the flame at high temperature and hence has higher reaction rates and radiative heat fluxes. Soot-flame breakthrough is also observed in these regions. Fluid convection and flame displacement velocity relative to fluid convection are of similar magnitudes while thermophoretic diffusion is 5-10 times lower. These results emphasize the importance of both unsteady and multidimensional effects on soot formation and transport in turbulent flames. (author)« less
  • Abstract not provided.
  • Three-dimensional direct numerical simulation of soot formation with complex chemistry is presented. The simulation consists of a temporally evolving, planar, nonpremixed ethylene jet flame with a validated, 19-species reduced mechanism. A four-step, three-moment, semiempirical soot model is employed. Previous two-dimensional decaying turbulence simulations have shown the importance of multidimensional flame dynamical effects on soot concentration [D.O. Lignell, J.H. Chen, P.J. Smith, T. Lu, C.K. Law, Combust. Flame 151 (1-2) (2007) 2-28]. It was shown that flame curvature strongly impacts the diffusive motion of the flame relative to soot (which is essentially convected with the flow), resulting in soot being differentiallymore » transported toward or away from the flame zone. The proximity of the soot to the flame directly influences soot reactivity and radiative properties. Here, the analysis is extended to three dimensions in a temporal jet configuration with mean shear. Results show that similar local flame dynamic effects of strain and curvature are important, but that enhanced turbulent mixing of fuel and oxidizer streams has a first-order effect on transport of soot toward flame zones. Soot modeling in turbulent flames is a challenge due to the complexity of soot formation and transport processes and the lack of detailed experimental soot-flame-flow structural data. The present direct numerical simulation provides the first step toward providing such data. (author)« less
  • Attempts to use complex chemistry and transport in direct numerical simulations (DNS) of premixed combustion (even for kinetically simple systems, such as H{sub 2}/air and CH{sub 4}/air) often result in excessive needs of memory and CPU time. This paper presents a methodology (integrated combustion chemistry [ICC]) capable of integrating complex chemistry effects into DNS while maintaining computational efficiency. The methodology includes the use of a limited number of species and reactions with parameters which are derived to match a number of flame properties. It is illustrated through a four-step reaction mechanism appropriate for a stoichiometric methane/air flame, and which comparesmore » favorably with predictions of the detailed GRI 2.11 mechanism. The proposed scheme includes one reaction for the methane oxidation, one for the thermal, one for the Fenimore, and one for the nonpremixed reburn chemical NO{sub x} routes. The kinetic parameters for the hydrocarbon oxidation were determined by matching the GRI 2.11 predictions for laminar burning velocity and adiabatic flame temperature, main reactants concentrations, and extinction strain rates for both premixed (steady) and nonpremixed (steady and unsteady) strained laminar flames. The chemical parameters for the three steps corresponding to NO{sub x} chemistry were determined by matching the NO{sub x} profiles obtained for strained diffusion flames with GRI 2.11. Finally, this four-step mechanism was used in DNS of two- and three-dimensional turbulent nonpremixed combustion to assess the validity of flamelet approaches. While the flamelet approaches were found to perform well for heat release, their extension to NO{sub x} formation appears to be not as successful because of the existence of compressed zones where products accumulate and increase the No{sub x} production.« less
  • A numerical study of soot formation in the near-field of a strongly radiating, nonpremixed, acetylene-air planar jet flame is conducted using Large Eddy Simulation in two dimensions to examine coupled turbulence, soot chemistry, and radiation effects. The two-dimensional, Favre-filtered, compressible Navier-Stokes, total sensible energy and mixture fraction equations are closed using the Smagorinsky subgrid-scale (SGS) turbulence model. Major species of gas-phase combustion are obtained using a laminar flamelet model by employing experimentally obtained laminar flame state relationships for the major species mass fractions as a function of gas-phase mixture fraction. A combination of a presumed Beta filtered density function andmore » a scale-similarity model are used to account for SGS mixture fraction and scalar dissipation fluctuations on the filtered composition and heat release rate. A soot transport and finite-rate kinetics model accounting for soot nucleation, surface growth, agglomeration, and oxidation is used. Radiation is modeled by integrating the filtered radiative transfer equation using the discrete ordinates method. Both instantaneous and time-averaged results are presented in order to highlight physical and numerical modeling issues and to examine turbulence, soot chemistry, and radiation interactions. Qualitative comparisons are made to precious numerical results and experimental data.« less