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Kaoru Maruta - One of the best experts on this subject based on the ideXlab platform.
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diffusive thermal instability of stretched low Lewis Number flames of slot jet counterflow burners
Proceedings of the Combustion Institute, 2017Co-Authors: Roman Fursenko, S. Minaev, Kaoru Maruta, Sergey MokrinAbstract:Abstract Characteristics and spatial structure of premixed low-Lewis-Number flames in stretched flow of two slot burners are studied numerically and theoretically in the frame of thermo-diffusive model with one-step chemical reaction. Three different combustion regimes are distinguished: twin planar flames, twin wrinkled flames and multiple flame tubes. In the multiple flame tube case the continuous flame front surface does not exist and combustion wave is represented by the set of separate reacting spots of tube-like form. The regions of existence of different combustion regimes in fuel concentration / stretch rate plane were determined. It was found that continuous flames (i.e. wrinkled and planar twin flames) exist inside the C-shape extinction limit curve obtained in the frame of one-dimensional model, while flame tubes appear beyond this limit in the entire range of stretch rates. Investigations of Lewis Number effect allow to conclude that extension of low-Lewis-Number counterflow flame flammability limits is related with the possibility of formation of non-planar flame tube structure caused by the effect of diffusive-thermal instability. Similarities and differences in regime diagrams and spatial flame structure of stretched premixed flames in conventional axisymmetric configuration and in slot-jet arrangement are discussed. Besides that, theoretical and numerical results are compared with experimental data available in a literature.
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near lean limit combustion regimes of low Lewis Number stretched premixed flames
Combustion and Flame, 2015Co-Authors: Roman Fursenko, S. Minaev, Hisashi Nakamura, Takuya Tezuka, Susumu Hasegawa, Koichi Takase, Masato Katsuta, Masao Kikuchi, Tomoya Kobayashi, Kaoru MarutaAbstract:Abstract Dynamic behavior and 3D spatial structure of low-Lewis-Number counterflow premixed flames are numerically studied in the frame of thermo-diffusive model with one-step chemical reaction. The diverse combustion regimes are described and regions of existence of these regimes in equivalence ratio/stretch rate plane are identified. Qualitative comparison between numerical results and results of microgravity experiments are discussed. Experiments and numerical simulations demonstrate that at small stretch rate conditions lean low-Lewis-Number counterflow flames can appear as a set of separate ball-like flames in a state of chaotic motion. The extension of extinction limits associated with existence of sporadic combustion regimes is observed.
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Cellular and sporadic flame regimes of low-Lewis-Number stretched premixed flames
Proceedings of the Combustion Institute, 2013Co-Authors: Roman Fursenko, S. Minaev, Hisashi Nakamura, Takuya Tezuka, Susumu Hasegawa, Koichi Takase, Masato Katsuta, Masao Kikuchi, Xing Li, Kaoru MarutaAbstract:3D structure and dynamical behavior of low-Lewis-Number stretched premixed flames are numerically simulated within the framework of a thermo-diffusive model with one-step chemical reaction. The results are compared with microgravity experiments at qualitative level. The influence of Lewis Number, equivalence ratio, and heat loss intensity on flame structure is investigated. It is experimentally and numerically found that lean counterflow flames can appear as a set of separate ball-like flames in a state of chaotic motion. It is shown that the time averaged flame balls coordinate may be considered as important characteristic similar to coordinate of continuous flame front. Numerical simulations reveal essential incompleteness of combustion at high level of heat losses. This incompleteness occurs in the process of lean mixtures combustion and is caused by fuel leakage through the gaps among ball-like flames. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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cellular and sporadic flame regimes of low Lewis Number stretched premixed flames
Proceedings of the Combustion Institute, 2013Co-Authors: Roman Fursenko, S. Minaev, Hisashi Nakamura, Takuya Tezuka, Susumu Hasegawa, Koichi Takase, Masato Katsuta, Masao Kikuchi, Xing Li, Kaoru MarutaAbstract:Abstract 3D structure and dynamical behavior of low-Lewis-Number stretched premixed flames are numerically simulated within the framework of a thermo-diffusive model with one-step chemical reaction. The results are compared with microgravity experiments at qualitative level. The influence of Lewis Number, equivalence ratio, and heat loss intensity on flame structure is investigated. It is experimentally and numerically found that lean counterflow flames can appear as a set of separate ball-like flames in a state of chaotic motion. It is shown that the time averaged flame balls coordinate may be considered as important characteristic similar to coordinate of continuous flame front. Numerical simulations reveal essential incompleteness of combustion at high level of heat losses. This incompleteness occurs in the process of lean mixtures combustion and is caused by fuel leakage through the gaps among ball-like flames.
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effects of the Lewis Number and radiative heat loss on the bifurcation and extinction of ch4 o2 n2 he flames
Journal of Fluid Mechanics, 1999Co-Authors: Yiguang Ju, Kaoru MarutaAbstract:Eects of the Lewis Number and radiative heat loss on flame bifurcations and extinc- tion of CH 4/O2-N2-He flames are investigated numerically with detailed chemistry. Attention is paid to the interaction between radiation heat loss and the Lewis Number eect. The Planck mean absorption coecients of CO, CO2, and H2O are calculated using the statistical narrow-band model and compared with the data given by Tien. The use of Tien's Planck mean absorption coecients overpredicts radiative heat loss by nearly 30 % in a counterflow conguration. The new Planck mean absorption coecients are then used to calculate the extinction limits of the planar propagating flame and the counterflow flame when the Lewis Number changes from 0.967 to 1.8. The interaction between radiation heat loss and the Lewis Number eect greatly enriches the phenomenon of flame bifurcation. The existence of multiple flames is shown to be a physically intrinsic phenomenon of radiating counterflow flames. Eight kinds of typical patterns of flame bifurcation are identied. The competition between radiation heat loss and the Lewis Number eect results in two distinct phenomena, depending on if the Lewis Number is greater or less than a critical value. Comparisons between the standard limits of the unstrained flames and the flammability limits of the counterflow flames indicate that the flammability limit of the counterflow flame is lower than the standard limit when the Lewis Number is less than the critical value and is equal to the standard limit when the Lewis Number is higher than this critical value. Finally, a G-shaped curve and a K-shaped curve which respectively represent the flammable regions of the multiple flames for Lewis Numbers lower and higher than the critical value are obtained. The G- and K-shaped curves show a clear relationship between the stretched counterflow flame and the unstrained planar flame. The present results provide a good explanation of the physics revealed experimentally in microgravity.
Nilanjan Chakraborty - One of the best experts on this subject based on the ideXlab platform.
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effects of Lewis Number on the evolution of curvature in spherically expanding turbulent premixed flames
Fluids, 2019Co-Authors: Ahmad Alqallaf, M Klein, Nilanjan ChakrabortyAbstract:The effects of Lewis Number on the physical mechanisms pertinent to the curvature evolution have been investigated using three-dimensional Direct Numerical Simulation (DNS) of spherically expanding turbulent premixed flames with characteristic Lewis Number of L e = 0.8 , 1.0 and 1.2. It has been found that the overall burning rate and the extent of flame wrinkling increase with decreasing Lewis Number L e , and this tendency is particularly prevalent for the sub-unity Lewis Number (e.g., L e = 0.8 ) case due to the occurrence of the thermo-diffusive instability. Accordingly, the L e = 0.8 case has been found to exhibit higher probability of finding saddle topologies with large magnitude negative curvatures in comparison to the corresponding L e = 1.0 and 1.2 cases. It has been found that the terms in the curvature transport equation due to normal strain rate gradients and curl of vorticity arising from both fluid flow and flame normal propagation play pivotal roles in the curvature evolution in all cases considered here. The net contribution of the source/sink terms of the curvature transport equation tends to increase the concavity and convexity of the flame surface in the negatively and positively curved locations, respectively for the L e = 0.8 case. This along with the occurrence of high and low temperature (and burning rate) values at the positively and negatively curved zones, respectively acts to augment positive and negative curved wrinkles induced by turbulence in the L e = 0.8 case, which is indicative of thermo-diffusive instability. By contrast, flame propagation effects tend to weakly promote the concavity of the negatively curved cusps, and act to decrease the convexity of the highly positively curved bulges in the L e = 1.0 and 1.2 cases, which are eventually smoothed out due to high and low values of displacement speed S d at negatively and positively curved locations, respectively. Thus, flame propagation tends to smoothen the flame surface in the L e = 1.0 and 1.2 cases.
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effects of Lewis Number on the statistics of the invariants of the velocity gradient tensor and local flow topologies in turbulent premixed flames
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2018Co-Authors: Daniel Wacks, Ilias Konstantinou, Nilanjan ChakrabortyAbstract:The behaviours of the three invariants of the velocity gradient tensor and the resultant local flow topologies in turbulent premixed flames have been analysed using three-dimensional direct numerical simulation data for different values of the characteristic Lewis Number ranging from 0.34 to 1.2. The results have been analysed to reveal the statistical behaviours of the invariants and the flow topologies conditional upon the reaction progress variable. The behaviours of the invariants have been explained in terms of the relative strengths of the thermal and mass diffusions, embodied by the influence of the Lewis Number on turbulent premixed combustion. Similarly, the behaviours of the flow topologies have been explained in terms not only of the Lewis Number but also of the likelihood of the occurrence of individual flow topologies in the different flame regions. Furthermore, the sensitivity of the joint probability density function of the second and third invariants and the joint probability density functions of the mean and Gaussian curvatures to the variation in Lewis Number have similarly been examined. Finally, the dependences of the scalar--turbulence interaction term on augmented heat release and of the vortex-stretching term on flame-induced turbulence have been explained in terms of the Lewis Number, flow topology and reaction progress variable.
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effects of fuel Lewis Number on localised forced ignition of turbulent homogeneous mixtures a numerical investigation
International Journal of Spray and Combustion Dynamics, 2016Co-Authors: Dipal Patel, Nilanjan ChakrabortyAbstract:The influences of fuel Lewis Number LeF (ranging from 0.8 to 1.2) on localised forced ignition and early stages of combustion of stoichiometric and fuel-lean homogeneous mixtures have been analysed using simple chemistry three-dimensional compressible direct numerical simulations for different values of root-mean-square velocity fluctuation and the energy deposition characteristics (i.e. characteristic width and the duration of energy deposition by the ignitor). The localised forced ignition is modelled using a source term in the energy transport equation, which deposits energy in a Gaussian manner from the centre of the ignitor over a stipulated period of time. The fuel Lewis Number LeF has been found to have significant influences on the extent of burning of stoichiometric and fuel-lean homogeneous mixtures. It has been shown that the width of ignition energy deposition and the duration over which the ignition energy is deposited have significant influences on the success of ignition and subsequent flam...
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modeling of the strain rate contribution to the flame surface density transport for non unity Lewis Number flames in large eddy simulations
Combustion Science and Technology, 2014Co-Authors: Mohit Katragadda, Nilanjan ChakrabortyAbstract:The strain rate contribution in the generalized flame surface density (FSD) transport equation remains a leading order unclosed source term, which plays a pivotal role in the modeling of transport for all filter widths in the context of large eddy simulations (LES). To date, most FSD-based closures have been proposed for flames without differential diffusion effects of heat and mass, characterized by a global Lewis Number equal to unity (i.e., ). The effects of differential diffusion arising due to non-unity Lewis Number on the FSD transport have rarely been analyzed in existing literature. In the present analysis, the statistical behaviors of the strain rate term of the FSD transport equation have been analyzed using a DNS database of freely propagating statistically planar turbulent premixed flames with a global Lewis Number ranging from 0.34 to 1.2 (i.e., = 0.34–1.2). The FSD strain rate term has been split into components originating from the gradients of Favre-filtered velocity components (i.e., ), s...
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effects of Lewis Number on conditional fluid velocity statistics in low damkohler Number turbulent premixed combustion a direct numerical simulation analysis
Physics of Fluids, 2013Co-Authors: Nilanjan Chakraborty, Andrei LipatnikovAbstract:The effects of global Lewis Number Le on the statistics of fluid velocity components conditional in unburned reactants and fully burned products in the context of Reynolds Averaged Navier Stokes simulations have been analysed using a Direct Numerical Simulations (DNS) database of statistically planar turbulent premixed flames with a low Damkohler Number and Lewis Number ranging from 0.34 to 1.2. The conditional velocity statistics extracted from DNS data have been analysed with respect to the well-known Bray-Moss-Libby (BML) expressions which were derived based on bi-modal probability density function of reaction progress variable for high Damkohler Number flames. It has been shown that the Lewis Number substantially affects the mean velocity and the velocity fluctuation correlation conditional in products, with the effect being particularly pronounced for low Le. As far as the mean velocity and the velocity fluctuation correlation conditional in reactants are concerned, the BML expressions agree reasonably well with the DNS data reported in the present work. Based on a priori analysis of present and previously reported DNS data, the BML expressions have been empirically modified here in order to account for Lewis Number effects, and the non-bimodal distribution of reaction progress variable. Moreover, it has been demonstrated for the first time that surface averaged velocity components and Reynolds stresses conditional in unburned reactants can be modelled without invoking expressions involving the Lewis Number, as these surface averaged conditional quantities remain approximately equal to their conditionally averaged counterparts in the unburned mixture.
Roman Fursenko - One of the best experts on this subject based on the ideXlab platform.
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diffusive thermal instability of stretched low Lewis Number flames of slot jet counterflow burners
Proceedings of the Combustion Institute, 2017Co-Authors: Roman Fursenko, S. Minaev, Kaoru Maruta, Sergey MokrinAbstract:Abstract Characteristics and spatial structure of premixed low-Lewis-Number flames in stretched flow of two slot burners are studied numerically and theoretically in the frame of thermo-diffusive model with one-step chemical reaction. Three different combustion regimes are distinguished: twin planar flames, twin wrinkled flames and multiple flame tubes. In the multiple flame tube case the continuous flame front surface does not exist and combustion wave is represented by the set of separate reacting spots of tube-like form. The regions of existence of different combustion regimes in fuel concentration / stretch rate plane were determined. It was found that continuous flames (i.e. wrinkled and planar twin flames) exist inside the C-shape extinction limit curve obtained in the frame of one-dimensional model, while flame tubes appear beyond this limit in the entire range of stretch rates. Investigations of Lewis Number effect allow to conclude that extension of low-Lewis-Number counterflow flame flammability limits is related with the possibility of formation of non-planar flame tube structure caused by the effect of diffusive-thermal instability. Similarities and differences in regime diagrams and spatial flame structure of stretched premixed flames in conventional axisymmetric configuration and in slot-jet arrangement are discussed. Besides that, theoretical and numerical results are compared with experimental data available in a literature.
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near lean limit combustion regimes of low Lewis Number stretched premixed flames
Combustion and Flame, 2015Co-Authors: Roman Fursenko, S. Minaev, Hisashi Nakamura, Takuya Tezuka, Susumu Hasegawa, Koichi Takase, Masato Katsuta, Masao Kikuchi, Tomoya Kobayashi, Kaoru MarutaAbstract:Abstract Dynamic behavior and 3D spatial structure of low-Lewis-Number counterflow premixed flames are numerically studied in the frame of thermo-diffusive model with one-step chemical reaction. The diverse combustion regimes are described and regions of existence of these regimes in equivalence ratio/stretch rate plane are identified. Qualitative comparison between numerical results and results of microgravity experiments are discussed. Experiments and numerical simulations demonstrate that at small stretch rate conditions lean low-Lewis-Number counterflow flames can appear as a set of separate ball-like flames in a state of chaotic motion. The extension of extinction limits associated with existence of sporadic combustion regimes is observed.
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Cellular and sporadic flame regimes of low-Lewis-Number stretched premixed flames
Proceedings of the Combustion Institute, 2013Co-Authors: Roman Fursenko, S. Minaev, Hisashi Nakamura, Takuya Tezuka, Susumu Hasegawa, Koichi Takase, Masato Katsuta, Masao Kikuchi, Xing Li, Kaoru MarutaAbstract:3D structure and dynamical behavior of low-Lewis-Number stretched premixed flames are numerically simulated within the framework of a thermo-diffusive model with one-step chemical reaction. The results are compared with microgravity experiments at qualitative level. The influence of Lewis Number, equivalence ratio, and heat loss intensity on flame structure is investigated. It is experimentally and numerically found that lean counterflow flames can appear as a set of separate ball-like flames in a state of chaotic motion. It is shown that the time averaged flame balls coordinate may be considered as important characteristic similar to coordinate of continuous flame front. Numerical simulations reveal essential incompleteness of combustion at high level of heat losses. This incompleteness occurs in the process of lean mixtures combustion and is caused by fuel leakage through the gaps among ball-like flames. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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cellular and sporadic flame regimes of low Lewis Number stretched premixed flames
Proceedings of the Combustion Institute, 2013Co-Authors: Roman Fursenko, S. Minaev, Hisashi Nakamura, Takuya Tezuka, Susumu Hasegawa, Koichi Takase, Masato Katsuta, Masao Kikuchi, Xing Li, Kaoru MarutaAbstract:Abstract 3D structure and dynamical behavior of low-Lewis-Number stretched premixed flames are numerically simulated within the framework of a thermo-diffusive model with one-step chemical reaction. The results are compared with microgravity experiments at qualitative level. The influence of Lewis Number, equivalence ratio, and heat loss intensity on flame structure is investigated. It is experimentally and numerically found that lean counterflow flames can appear as a set of separate ball-like flames in a state of chaotic motion. It is shown that the time averaged flame balls coordinate may be considered as important characteristic similar to coordinate of continuous flame front. Numerical simulations reveal essential incompleteness of combustion at high level of heat losses. This incompleteness occurs in the process of lean mixtures combustion and is caused by fuel leakage through the gaps among ball-like flames.
R S Cant - One of the best experts on this subject based on the ideXlab platform.
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A Priori Assessment of Algebraic Flame Surface Density Models in the Context of Large Eddy Simulation for Nonunity Lewis Number Flames in the Thin Reaction Zones Regime
Journal of Combustion, 2012Co-Authors: Mohit Katragadda, Nilanjan Chakraborty, R S CantAbstract:The performance of algebraic flame surface density (FSD) models has been assessed for flames with nonunity Lewis Number (Le) in the thin reaction zones regime, using a direct numerical simulation (DNS) database of freely propagating turbulent premixed flames with Le ranging from 0.34 to 1.2. The focus is on algebraic FSD models based on a power-law approach, and the effects of Lewis Number on the fractal dimension D and inner cut-off scale ηi have been studied in detail. It has been found that D is strongly affected by Lewis Number and increases significantly with decreasing Le. By contrast, ηi remains close to the laminar flame thermal thickness for all values of Le considered here. A parameterisation of D is proposed such that the effects of Lewis Number are explicitly accounted for. The new parameterisation is used to propose a new algebraic model for FSD. The performance of the new model is assessed with respect to results for the generalised FSD obtained from explicitly LES-filtered DNS data. It has been found that the performance of the most existing models deteriorates with decreasing Lewis Number, while the newly proposed model is found to perform as well or better than the most existing algebraic models for FSD.
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effects of Lewis Number on flame surface density transport in turbulent premixed combustion
Combustion and Flame, 2011Co-Authors: Nilanjan Chakraborty, R S CantAbstract:Abstract The transport of flame surface density (FSD) in turbulent premixed flames has been studied using a database obtained from Direct Numerical Simulation (DNS). Three-dimensional freely propagating developing statistically planar turbulent premixed flames have been examined over a range of global Lewis Numbers from 0.6 to 1.2. Simplified chemistry has been used and the emphasis is on the effects of Lewis Number on FSD transport in the context of Reynolds-averaged closure modelling. Under the same initial conditions of turbulence, flames with low Lewis Numbers are found to exhibit counter-gradient transport of FSD, whereas flames with higher Lewis Numbers tend to exhibit gradient transport of FSD. Stronger heat release effects for lower Lewis Number flames are found to lead to an increase in the positive (negative) value of the dilatation rate (normal strain rate) term in the FSD transport equation with decreasing Lewis Number. The contribution of flame curvature to FSD transport is found to be influenced significantly by the effects of Lewis Number on the curvature dependence of the magnitude of the reaction progress variable gradient, and on the combined reaction and normal diffusion components of displacement speed. The modelling of the various terms of the FSD transport equation has been analysed in detail and the performance of existing models is assessed with respect to the terms assembled from corresponding quantities extracted from DNS data. Based on this assessment, suitable models are identified which are able to address the effects of non-unity Lewis Number on FSD transport, and new or modified models are suggested wherever necessary.
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effects of Lewis Number on turbulent kinetic energy transport in premixed flames
Physics of Fluids, 2011Co-Authors: Nilanjan Chakraborty, Mohit Katragadda, R S CantAbstract:The effects of global Lewis Number on the statistical behaviour of turbulent kinetic energy transport in turbulent premixed flames are analysed using three-dimensional direct numerical simulation (DNS) data for freely propagating statistically planar flames with Lewis Number ranging from 0.34 to 1.2. For flames with Lewis Number significantly smaller than unity, it is observed that the turbulent kinetic energy is significantly augmented within the flame brush due to flame-generated turbulence. In these flames, it is demonstrated that effects of the mean pressure gradient and pressure dilatation are sufficient to overcome the effects of viscous dissipation. By contrast, for flames with Lewis Number close to unity, it is found that the turbulent kinetic energy decays monotonically through the flame brush. In these flames, the effects of the mean pressure gradient and pressure dilatation terms are relatively much weaker than those of viscous dissipation. The modelling of the various unclosed terms of the tur...
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effects of Lewis Number on turbulent scalar transport and its modelling in turbulent premixed flames
Combustion and Flame, 2009Co-Authors: Nilanjan Chakraborty, R S CantAbstract:Abstract The behaviour of the turbulent scalar flux in premixed flames has been studied using Direct Numerical Simulation (DNS) with emphasis on the effects of Lewis Number in the context of Reynolds-averaged closure modelling. A database was obtained from DNS of three-dimensional freely propagating statistically planar turbulent premixed flames with simplified chemistry and a range of global Lewis Numbers from 0.34 to 1.2. Under the same initial conditions of turbulence, flames with low Lewis Numbers are found to exhibit counter-gradient transport, whereas flames with higher Lewis Numbers tend to exhibit gradient transport. The Reynolds-averaged transport equation for the turbulent scalar flux is analysed in detail and the performance of existing models for the unclosed terms is assessed with respect to corresponding quantities extracted from DNS data. Based on this assessment, existing models which are able to address the effects of non-unity Lewis Number on turbulent scalar flux transport are identified, and new or modified models are suggested wherever necessary. In this way, a complete set of closure models for the scalar flux transport equation is prescribed for use in Reynolds-Averaged Navier–Stokes simulations.
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physical insight and modelling for Lewis Number effects on turbulent heat and mass transport in turbulent premixed flames
Numerical Heat Transfer Part A-applications, 2009Co-Authors: Nilanjan Chakraborty, R S CantAbstract:The effects of global Lewis Number on the behavior of Reynolds heat and mass fluxes in turbulent premixed flames are studied based on three-dimensional direct numerical simulation (DNS) of a Number of statistically planar turbulent premixed flames with a global Lewis Number ranging from Le = 0.34 to 1.2. For the same values of initial turbulent flow field parameters and duration of flame-turbulence interaction, it has been found that both Reynolds heat and mass fluxes may exhibit countergradient transport for flames with a Lewis Number significantly smaller than unity; whereas predominantly gradient-type transport is obtained for flames with a Lewis Number closer to unity. It is demonstrated that strong flame normal acceleration due to greater heat release in the low Lewis Number flames acts to promote countergradient transport, and that the magnitude of the flame normal acceleration decreases with increasing Lewis Number. Algebraic models for Reynolds heat and mass fluxes are proposed in which the effect...
S. Minaev - One of the best experts on this subject based on the ideXlab platform.
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diffusive thermal instability of stretched low Lewis Number flames of slot jet counterflow burners
Proceedings of the Combustion Institute, 2017Co-Authors: Roman Fursenko, S. Minaev, Kaoru Maruta, Sergey MokrinAbstract:Abstract Characteristics and spatial structure of premixed low-Lewis-Number flames in stretched flow of two slot burners are studied numerically and theoretically in the frame of thermo-diffusive model with one-step chemical reaction. Three different combustion regimes are distinguished: twin planar flames, twin wrinkled flames and multiple flame tubes. In the multiple flame tube case the continuous flame front surface does not exist and combustion wave is represented by the set of separate reacting spots of tube-like form. The regions of existence of different combustion regimes in fuel concentration / stretch rate plane were determined. It was found that continuous flames (i.e. wrinkled and planar twin flames) exist inside the C-shape extinction limit curve obtained in the frame of one-dimensional model, while flame tubes appear beyond this limit in the entire range of stretch rates. Investigations of Lewis Number effect allow to conclude that extension of low-Lewis-Number counterflow flame flammability limits is related with the possibility of formation of non-planar flame tube structure caused by the effect of diffusive-thermal instability. Similarities and differences in regime diagrams and spatial flame structure of stretched premixed flames in conventional axisymmetric configuration and in slot-jet arrangement are discussed. Besides that, theoretical and numerical results are compared with experimental data available in a literature.
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near lean limit combustion regimes of low Lewis Number stretched premixed flames
Combustion and Flame, 2015Co-Authors: Roman Fursenko, S. Minaev, Hisashi Nakamura, Takuya Tezuka, Susumu Hasegawa, Koichi Takase, Masato Katsuta, Masao Kikuchi, Tomoya Kobayashi, Kaoru MarutaAbstract:Abstract Dynamic behavior and 3D spatial structure of low-Lewis-Number counterflow premixed flames are numerically studied in the frame of thermo-diffusive model with one-step chemical reaction. The diverse combustion regimes are described and regions of existence of these regimes in equivalence ratio/stretch rate plane are identified. Qualitative comparison between numerical results and results of microgravity experiments are discussed. Experiments and numerical simulations demonstrate that at small stretch rate conditions lean low-Lewis-Number counterflow flames can appear as a set of separate ball-like flames in a state of chaotic motion. The extension of extinction limits associated with existence of sporadic combustion regimes is observed.
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Cellular and sporadic flame regimes of low-Lewis-Number stretched premixed flames
Proceedings of the Combustion Institute, 2013Co-Authors: Roman Fursenko, S. Minaev, Hisashi Nakamura, Takuya Tezuka, Susumu Hasegawa, Koichi Takase, Masato Katsuta, Masao Kikuchi, Xing Li, Kaoru MarutaAbstract:3D structure and dynamical behavior of low-Lewis-Number stretched premixed flames are numerically simulated within the framework of a thermo-diffusive model with one-step chemical reaction. The results are compared with microgravity experiments at qualitative level. The influence of Lewis Number, equivalence ratio, and heat loss intensity on flame structure is investigated. It is experimentally and numerically found that lean counterflow flames can appear as a set of separate ball-like flames in a state of chaotic motion. It is shown that the time averaged flame balls coordinate may be considered as important characteristic similar to coordinate of continuous flame front. Numerical simulations reveal essential incompleteness of combustion at high level of heat losses. This incompleteness occurs in the process of lean mixtures combustion and is caused by fuel leakage through the gaps among ball-like flames. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.
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cellular and sporadic flame regimes of low Lewis Number stretched premixed flames
Proceedings of the Combustion Institute, 2013Co-Authors: Roman Fursenko, S. Minaev, Hisashi Nakamura, Takuya Tezuka, Susumu Hasegawa, Koichi Takase, Masato Katsuta, Masao Kikuchi, Xing Li, Kaoru MarutaAbstract:Abstract 3D structure and dynamical behavior of low-Lewis-Number stretched premixed flames are numerically simulated within the framework of a thermo-diffusive model with one-step chemical reaction. The results are compared with microgravity experiments at qualitative level. The influence of Lewis Number, equivalence ratio, and heat loss intensity on flame structure is investigated. It is experimentally and numerically found that lean counterflow flames can appear as a set of separate ball-like flames in a state of chaotic motion. It is shown that the time averaged flame balls coordinate may be considered as important characteristic similar to coordinate of continuous flame front. Numerical simulations reveal essential incompleteness of combustion at high level of heat losses. This incompleteness occurs in the process of lean mixtures combustion and is caused by fuel leakage through the gaps among ball-like flames.
