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

Title: A numerical study of the stability of one-dimensional laminar premixed flames in inert porous media

Abstract

This work presents a numerical study of the stabilization diagram of methane/air premixed flames in a finite porous media foam with a uniform ambient temperature. A set of steady computations are considered, using a 1D numerical model that takes into account solid and gas energy equations as well as chemistry and radiation models. The present results show that both stable and unstable solutions, for upper and lower flames, exist either at the surface or submerged in the porous matrix. The influence of the 1D computational domain, boundary conditions, and gas/solid interface treatment on the stability of the calculated flames is also discussed. A linearized version of the discrete-ordinates radiation model is included in the linear stability analysis to discuss the influence of radiation on the stability of the flames. The full stabilization diagram and the linear stability analysis provide information on the stability of the flames, pointing to the existence of unstable upstream surface flames as well as unstable submerged flames on the downstream part of the porous media. (author)

Authors:
; ;  [1]
  1. Technical University of Lisbon/Instituto Superior Tecnico, Mechanical Engineering Department, LASEF, Av. Rovisco Pais 1, 1049-001 Lisbon (Portugal)
Publication Date:
OSTI Identifier:
21044861
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 153; Journal Issue: 4; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; POROUS MATERIALS; LAMINAR FLAMES; NUMERICAL SOLUTION; STABILITY; DIAGRAMS; DISCRETE ORDINATE METHOD; METHANE; AIR; COMBUSTION; FOAMS; STABILIZATION; ONE-DIMENSIONAL CALCULATIONS; SOLIDS; GASES; AMBIENT TEMPERATURE; BOUNDARY CONDITIONS; CHEMICAL REACTIONS; RADIANT HEAT TRANSFER; INTERFACES; Premixed combustion; Inert porous media; Linear stability analysis

Citation Formats

Mendes, M.A.A., Pereira, J.M.C., and Pereira, J.C.F. A numerical study of the stability of one-dimensional laminar premixed flames in inert porous media. United States: N. p., 2008. Web. doi:10.1016/J.COMBUSTFLAME.2008.03.010.
Mendes, M.A.A., Pereira, J.M.C., & Pereira, J.C.F. A numerical study of the stability of one-dimensional laminar premixed flames in inert porous media. United States. doi:10.1016/J.COMBUSTFLAME.2008.03.010.
Mendes, M.A.A., Pereira, J.M.C., and Pereira, J.C.F. 2008. "A numerical study of the stability of one-dimensional laminar premixed flames in inert porous media". United States. doi:10.1016/J.COMBUSTFLAME.2008.03.010.
@article{osti_21044861,
title = {A numerical study of the stability of one-dimensional laminar premixed flames in inert porous media},
author = {Mendes, M.A.A. and Pereira, J.M.C. and Pereira, J.C.F.},
abstractNote = {This work presents a numerical study of the stabilization diagram of methane/air premixed flames in a finite porous media foam with a uniform ambient temperature. A set of steady computations are considered, using a 1D numerical model that takes into account solid and gas energy equations as well as chemistry and radiation models. The present results show that both stable and unstable solutions, for upper and lower flames, exist either at the surface or submerged in the porous matrix. The influence of the 1D computational domain, boundary conditions, and gas/solid interface treatment on the stability of the calculated flames is also discussed. A linearized version of the discrete-ordinates radiation model is included in the linear stability analysis to discuss the influence of radiation on the stability of the flames. The full stabilization diagram and the linear stability analysis provide information on the stability of the flames, pointing to the existence of unstable upstream surface flames as well as unstable submerged flames on the downstream part of the porous media. (author)},
doi = {10.1016/J.COMBUSTFLAME.2008.03.010},
journal = {Combustion and Flame},
number = 4,
volume = 153,
place = {United States},
year = 2008,
month = 6
}
  • The structure of adiabatic premixed flames within porous inert media is investigated using the asymptotic expansion method. For this, the flame structure is divided into three characteristic length scales. The two innermost length scales, the gas-phase diffusion length scale and the reaction length scale, are the same scales defined in the classical premixed flame structure analysis. The outermost length scale, the solid-phase diffusion length scale, is related to the heat conduction in the porous matrix. The differences among these three characteristic length-scales result in large temperature differences between the phases and justify the application of asymptotic expansions to determine anmore » approximate (analytical) solution. Since the main focus of this work is the examination of the processes in the outer and the first inner regions, the simplest kinetic mechanism of one global step is adopted to represent the fuel and oxygen consumption. Then, the description of the reaction zone is obtained using the large activation energy asymptotic method. The description of the problem of the order of the gas-phase length scale is obtained using the boundary layer expansion. This work evaluates the influence of the equivalence ratio, the ratio of the solid to the gas thermal conductivities, the porosity of the medium and the fuel Lewis number on such flames. A parameter that universalizes the flame properties is then identified and discussed. (author)« less
  • The structure of adiabatic premixed flames within porous inert media is investigated using the asymptotic expansion method. For this, the flame structure is divided into three characteristic length scales. The two innermost length scales, the gas-phase diffusion length scale and the reaction length scale, are the same scales defined in the classical premixed flame structure analysis. The outermost length scale, the solid-phase diffusion length scale, is related to the heat conduction in the porous matrix. The differences among these three characteristic length-scales result in large temperature differences between the phases and justify the application of asymptotic expansions to determine anmore » approximate (analytical) solution. Since the main focus of this work is the examination of the processes in the outer and the first inner regions, the simplest kinetic mechanism of one global step is adopted to represent the fuel and oxygen consumption. Then, the description of the reaction zone is obtained using the large activation energy asymptotic method. The description of the problem of the order of the gas-phase length scale is obtained using the boundary layer expansion. This work evaluates the influence of the equivalence ratio, the ratio of the solid to the gas thermal conductivities, the porosity of the medium and the fuel Lewis number on such flames. A parameter that universalizes the flame properties is then identified and discussed. (author)« less
  • In this paper, the propagation of a one-dimensional flame front into a reacting combustible mixture is numerically studied. A simplified mathematical method, splitting the problem into a prereaction part and a flame propagation part, was applied to the completely nonstationary problem. Initially stoichimetric mixtures of H{sub 2}/O{sub 2} and C{sub 2}H{sub 6}/O{sub 2} were investigated for isothermal and adiabatic boundary conditions of the prereactions. In the isothermal case, the laminar burning velocity of the mixture decreased gradually with time. In conclusion, the reasons for this decrease are an increasing amount of combustion products combined with the heat loss necessary tomore » maintain isothermal conditions. Compared with these phenomena, the accelerating effect of radical concentrations in the preflame region is of minor importance.« less
  • Direct numerical simulation (DNS) with complex chemistry was used to study statistics of displacement and consumption speeds in turbulent lean premixed methane-air flames. The main focus of the study is an evaluation of the extent to which a turbulent flame in the thin reaction zones regime can be described by an ensemble of strained laminar flames. Conditional averages with respect to strain for displacement and consumption speeds are presented over a wide range of strain typically encountered in a turbulent flame, compared with previous studies that either made local pointwise comparisons or conditioned the data on small strain and curvature.more » The conditional averages for positive strains are compared with calculated data from two different canonical strained laminar configurations to determine which is the optimal representation of a laminar flame structure embedded in a turbulent flame: the reactant-to-product (R-to-P) configuration or the symmetric twin flame configuration. Displacement speed statistics are compared for the progress-variable isosurface of maximum reaction rate and an isosurface toward the fresh gases, which are relevant for both modeling and interpretation of experiment results. Displacement speeds in the inner reaction layer are found to agree very well with the laminar R-to-P calculations over a wide range of strain for higher Damkhler number conditions, well beyond the regime in which agreement was expected. For lower Damkhler numbers, a reduced response to strain is observed, consistent with previous studies and theoretical expectations. Compared with the inner layer, broader and shifted probability density functions (PDFs) of displacement speed were observed in the fresh gases, and the agreement with the R-to-P calculations deteriorated. Consumption speeds show a poorer agreement with strained laminar calculations, which is attributed to multidimensional effects and a more attenuated unsteady response to strain fluctuations; however, they also show less departure from the unstrained laminar value, suggesting that detailed modeling of this quantity may not be critical for the conditions considered. For all quantities investigated, including CO production, the R-to-P laminar configuration provides an improved description relative to the twin flame configuration, which predicts qualitatively incorrect trends and overestimates extinction.« less
  • Direct numerical simulation (DNS) with complex chemistry was used to study statistics of displacement and consumption speeds in turbulent lean premixed methane-air flames. The main focus of the study is an evaluation of the extent to which a turbulent flame in the thin reaction zones regime can be described by an ensemble of strained laminar flames. Conditional averages with respect to strain for displacement and consumption speeds are presented over a wide range of strain typically encountered in a turbulent flame, compared with previous studies that either made local pointwise comparisons or conditioned the data on small strain and curvature.more » The conditional averages for positive strains are compared with calculated data from two different canonical strained laminar configurations to determine which is the optimal representation of a laminar flame structure embedded in a turbulent flame: the reactant-to-product (R-to-P) configuration or the symmetric twin flame configuration. Displacement speed statistics are compared for the progress-variable isosurface of maximum reaction rate and an isosurface toward the fresh gases, which are relevant for both modeling and interpretation of experiment results. Displacement speeds in the inner reaction layer are found to agree very well with the laminar R-to-P calculations over a wide range of strain for higher Damkohler number conditions, well beyond the regime in which agreement was expected. For lower Damkohler numbers, a reduced response to strain is observed, consistent with previous studies and theoretical expectations. Compared with the inner layer, broader and shifted probability density functions (PDFs) of displacement speed were observed in the fresh gases, and the agreement with the R-to-P calculations deteriorated. Consumption speeds show a poorer agreement with strained laminar calculations, which is attributed to multidimensional effects and a more attenuated unsteady response to strain fluctuations; however, they also show less departure from the unstrained laminar value, suggesting that detailed modeling of this quantity may not be critical for the conditions considered. For all quantities investigated, including CO production, the R-to-P laminar configuration provides an improved description relative to the twin flame configuration, which predicts qualitatively incorrect trends and overestimates extinction.« less