The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Marcus Alden - One of the best experts on this subject based on the ideXlab platform.
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Thin Reaction Zone and distributed Reaction Zone regimes in turbulent premixed methane/air flames : Scalar distributions and correlations
Combustion and Flame, 2020Co-Authors: Bo Zhou, Christian Brackmann, Zhenkan Wang, Zhongshan Li, Mattias Richter, Marcus AldenAbstract:A series of premixed turbulent methane/air jet flames in the thin Reaction Zone (TRZ) and distributed Reaction Zone (DRZ) regimes were studied using simultaneous three-scalar high-resolution imaging measurements, including HCO/OH/CH2O, CH/OH/CH2O, T/OH/CH2O and T/CH/OH/. These scalar fields offer a possibility of revisiting the structures of turbulent premixed flames in different combustion regimes. In particular, CH2O provides a measure of the preheat Zone, CH/HCO a measure of the inner layer of the Reaction Zone, and OH a measure of the oxidation Zone. Scalar correlations are analyzed on both single-shot and statistical basis, and resolvable correlated structures of ∼100 µm between scalars are captured. With increasing turbulence intensity, it is shown that the preheat Zone and the inner layer of the Reaction Zone become gradually broadened/distributed, and the correlation between HCO and [OH]LIF×[CH2O]LIF decreases. A transition from the TRZ regime to the DRZ regime is found around Karlovitz number of 70–100. The physical and chemical effects on the broadening of the flame are investigated. In the TRZ regime the inner layer marker CH and HCO remains thin in general although occasional local broadening of CH/HCO could be observed. Furthermore, there is a significant probability of finding CH and HCO at rather low temperatures even in the TRZ regime. In the DRZ regime, the broadening of CH and HCO are shown to be mainly a result of local Reactions facilitated by rapid turbulent transport of radicals and intermediate reactants in the upstream of the Reaction paths. Differential diffusion is expected to have an important effect in the DRZ regime, as H radicals seemingly play a more important role than OH radicals.
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Structure and burning velocity of turbulent premixed methane/air jet flames in thin-Reaction Zone and distributed Reaction Zone regimes
Proceedings of the Combustion Institute, 2020Co-Authors: Zhenkan Wang, Bo Zhou, Christian Brackmann, Zhongshan Li, Mattias Richter, Senbin Yu, Marcus AldenAbstract:A series of turbulent premixed methane/air jet flames are studied using simultaneous planar lase diagnostic imaging of OH/CH/temperature and CH/OH/CH2O. The Karlovitz number of the flames ranges from 25 to 1500, and the turbulence intensity ranges from 16 to 200. These flames can be classified as highly turbulent flames in the thin Reactions Zone (TRZ) regime and distributed Reaction Zone (DRZ) regime. The aims of this study are to investigate the structural change of the preheat Zone and the Reaction Zone as the Karlovitz number and turbulent intensity increase, to study the impact of the structural change of the flame on the propagation speed of the flame, and to evaluate the turbulent burning velocity computed in different layers in the preheat Zone and Reaction Zone. It is found that for all investigated flames the preheat Zone characterized with planar laser-induced fluorescence (PLIF) of CH2O is broadened by turbulent eddies. The thickness of the preheat Zone increases with the turbulent intensity and it can be on the order of the turbulent integral length at high Karlovitz numbers. The Reaction Zone characterized using the overlapping layer of OH and CH2O PLIF signals is not significantly broadened by turbulence eddies; however, the CH PLIF layer is found to be broadened significantly by turbulence. The turbulent burning velocity is shown to monotonically increase with turbulent intensity and Karlovitz number. The increase in turbulent burning velocity is mainly due to the enhanced turbulent heat and mass transfer in various layers of the flame, while the contribution of flame front wrinkling to the turbulent burning velocity is rather minor.
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structure and burning velocity of turbulent premixed methane air jet flames in thin Reaction Zone and distributed Reaction Zone regimes
Proceedings of the Combustion Institute, 2019Co-Authors: Zhenkan Wang, Bo Zhou, Christian Brackmann, Zhongshan Li, Mattias Richter, Senbin Yu, Marcus AldenAbstract:A series of turbulent premixed methane/air jet flames are studied using simultaneous planar lase diagnostic imaging of OH/CH/temperature and CH/OH/CH2O. The Karlovitz number of the flames ranges from 25 to 1500, and the turbulence intensity ranges from 16 to 200. These flames can be classified as highly turbulent flames in the thin Reactions Zone (TRZ) regime and distributed Reaction Zone (DRZ) regime. The aims of this study are to investigate the structural change of the preheat Zone and the Reaction Zone as the Karlovitz number and turbulent intensity increase, to study the impact of the structural change of the flame on the propagation speed of the flame, and to evaluate the turbulent burning velocity computed in different layers in the preheat Zone and Reaction Zone. It is found that for all investigated flames the preheat Zone characterized with planar laser-induced fluorescence (PLIF) of CH2O is broadened by turbulent eddies. The thickness of the preheat Zone increases with the turbulent intensity and it can be on the order of the turbulent integral length at high Karlovitz numbers. The Reaction Zone characterized using the overlapping layer of OH and CH2O PLIF signals is not significantly broadened by turbulence eddies; however, the CH PLIF layer is found to be broadened significantly by turbulence. The turbulent burning velocity is shown to monotonically increase with turbulent intensity and Karlovitz number. The increase in turbulent burning velocity is mainly due to the enhanced turbulent heat and mass transfer in various layers of the flame, while the contribution of flame front wrinkling to the turbulent burning velocity is rather minor.
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thin Reaction Zone and distributed Reaction Zone regimes in turbulent premixed methane air flames scalar distributions and correlations
Combustion and Flame, 2017Co-Authors: Bo Zhou, Christian Brackmann, Zhenkan Wang, Zhongshan Li, Mattias Richter, Marcus AldenAbstract:A series of premixed turbulent methane/air jet flames in the thin Reaction Zone (TRZ) and distributed Reaction Zone (DRZ) regimes were studied using simultaneous three-scalar high-resolution imaging measurements, including HCO/OH/CH2O, CH/OH/CH2O, T/OH/CH2O and T/CH/OH/. These scalar fields offer a possibility of revisiting the structures of turbulent premixed flames in different combustion regimes. In particular, CH2O provides a measure of the preheat Zone, CH/HCO a measure of the inner layer of the Reaction Zone, and OH a measure of the oxidation Zone. Scalar correlations are analyzed on both single-shot and statistical basis, and resolvable correlated structures of ∼100 µm between scalars are captured. With increasing turbulence intensity, it is shown that the preheat Zone and the inner layer of the Reaction Zone become gradually broadened/distributed, and the correlation between HCO and [OH]LIF×[CH2O]LIF decreases. A transition from the TRZ regime to the DRZ regime is found around Karlovitz number of 70–100. The physical and chemical effects on the broadening of the flame are investigated. In the TRZ regime the inner layer marker CH and HCO remains thin in general although occasional local broadening of CH/HCO could be observed. Furthermore, there is a significant probability of finding CH and HCO at rather low temperatures even in the TRZ regime. In the DRZ regime, the broadening of CH and HCO are shown to be mainly a result of local Reactions facilitated by rapid turbulent transport of radicals and intermediate reactants in the upstream of the Reaction paths. Differential diffusion is expected to have an important effect in the DRZ regime, as H radicals seemingly play a more important role than OH radicals.
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simultaneous multi species and temperature visualization of premixed flames in distributed Reaction Zone regime
Proceedings of the Combustion Institute; 35(2) pp 1409-1416 (2015), 2015Co-Authors: Bo Zhou, Christian Brackmann, Zhongshan Li, Marcus AldenAbstract:Structures of turbulent premixed flames, operating in the thin and distributed Reaction Zone regimes, were investigated for stoichiometric premixed methane/air jet flames with jet Reynolds number up to 40,000 and corresponding Karlovitz number up to 286. Multi-species planar laser-induced fluorescence with high spatial resolution was applied to simultaneously image combinations of CH/OH/CH2O and HCO/OH/CH2O. In addition, OH/CH2O imaging was performed in combination with simultaneous Rayleigh scattering thermometry. The CH and HCO layers showed progressive broadening along the axial distance for flames with Reynolds number above 21,000 and the corresponding Karlovitz number above 126. At Reynolds number 40,000 and the corresponding Karlovitz number of 286, a mean CH layer thickness more than 10 times larger than that under laminar condition was observed, providing a clear experimental evidence of distributed Reaction Zone owing to turbulence/flame interaction. Additionally, spatial correlations between species show that OH and CH2O locate at mutually exclusive regions. In contrast, both CH and HCO can overlap substantially with CH2O. The regions of strong CH/HCO signals correspond to regions with weak CH2O signals. Moreover, CH and HCO are shown to be able to penetrate deeper into the OH layer than CH2O. Regions where CH and HCO appear distributed show a rather homogeneous temperature distribution with reduced maximum temperature compared with non-distributed conditions.
Robert Weber - One of the best experts on this subject based on the ideXlab platform.
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development of a numerical model for the Reaction Zone design of an aqueous sodium hydroxide seasonal thermal energy storage
Solar Energy, 2015Co-Authors: Xavier Daguenetfrick, Paul Gantenbein, Elimar Frank, Benjamin Fumey, Robert WeberAbstract:Abstract This paper describes a thermochemical seasonal storage with emphasis on the development of a Reaction Zone for an absorption/desorption unit. The heat and mass exchange is modelled and the design of a suitable Reaction Zone is explained. A tube bundle concept is presented for the heat and mass exchangers and the most demanding working conditions they should fulfil are modelled and discussed. To estimate the performance of such a Reaction Zone and to design it, numerical models were developed and are described in this paper. Several parameters influencing these models were tested such as the sensitivity of the models to the correlation used to calculate the heat and mass exchanges, the tube diameter and the tube pitch influence. The final contribution of the tube bundle modelling is to size and design the heat and mass exchanger constituting the Reaction Zone. This work will be used as a basis for the Reaction Zone construction of an aqueous sodium hydroxide seasonal thermal energy storage prototype.
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Reaction Zone development for an aqueous sodium hydroxide seasonal thermal energy storage
Energy Procedia, 2014Co-Authors: Xavier Daguenetfrick, Paul Gantenbein, Elimar Frank, Benjamin Fumey, Robert Weber, Tommy WilliamsonAbstract:Abstract This paper focuses on the development of a Reaction Zone dedicated to an absorption/desorption seasonal thermal energy storage. The modelling of the tube bundle constituting the Reaction Zone is described as well as the boundary conditions in worst working conditions and some modelling results are presented for the desorber/absorber. In parallel to this sizing work, investigations were lead on the tube bundle optimisation by studying the wetting and fluid distribution. A specific developed experimental set up based on imaging enabled to quantify the influence of tube texturing and to improve the manifold design. This work will lead to the Reaction Zone construction for an aqueous sodium hydroxide seasonal thermal energy storage prototype.
Bo Zhou - One of the best experts on this subject based on the ideXlab platform.
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Thin Reaction Zone and distributed Reaction Zone regimes in turbulent premixed methane/air flames : Scalar distributions and correlations
Combustion and Flame, 2020Co-Authors: Bo Zhou, Christian Brackmann, Zhenkan Wang, Zhongshan Li, Mattias Richter, Marcus AldenAbstract:A series of premixed turbulent methane/air jet flames in the thin Reaction Zone (TRZ) and distributed Reaction Zone (DRZ) regimes were studied using simultaneous three-scalar high-resolution imaging measurements, including HCO/OH/CH2O, CH/OH/CH2O, T/OH/CH2O and T/CH/OH/. These scalar fields offer a possibility of revisiting the structures of turbulent premixed flames in different combustion regimes. In particular, CH2O provides a measure of the preheat Zone, CH/HCO a measure of the inner layer of the Reaction Zone, and OH a measure of the oxidation Zone. Scalar correlations are analyzed on both single-shot and statistical basis, and resolvable correlated structures of ∼100 µm between scalars are captured. With increasing turbulence intensity, it is shown that the preheat Zone and the inner layer of the Reaction Zone become gradually broadened/distributed, and the correlation between HCO and [OH]LIF×[CH2O]LIF decreases. A transition from the TRZ regime to the DRZ regime is found around Karlovitz number of 70–100. The physical and chemical effects on the broadening of the flame are investigated. In the TRZ regime the inner layer marker CH and HCO remains thin in general although occasional local broadening of CH/HCO could be observed. Furthermore, there is a significant probability of finding CH and HCO at rather low temperatures even in the TRZ regime. In the DRZ regime, the broadening of CH and HCO are shown to be mainly a result of local Reactions facilitated by rapid turbulent transport of radicals and intermediate reactants in the upstream of the Reaction paths. Differential diffusion is expected to have an important effect in the DRZ regime, as H radicals seemingly play a more important role than OH radicals.
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Structure and burning velocity of turbulent premixed methane/air jet flames in thin-Reaction Zone and distributed Reaction Zone regimes
Proceedings of the Combustion Institute, 2020Co-Authors: Zhenkan Wang, Bo Zhou, Christian Brackmann, Zhongshan Li, Mattias Richter, Senbin Yu, Marcus AldenAbstract:A series of turbulent premixed methane/air jet flames are studied using simultaneous planar lase diagnostic imaging of OH/CH/temperature and CH/OH/CH2O. The Karlovitz number of the flames ranges from 25 to 1500, and the turbulence intensity ranges from 16 to 200. These flames can be classified as highly turbulent flames in the thin Reactions Zone (TRZ) regime and distributed Reaction Zone (DRZ) regime. The aims of this study are to investigate the structural change of the preheat Zone and the Reaction Zone as the Karlovitz number and turbulent intensity increase, to study the impact of the structural change of the flame on the propagation speed of the flame, and to evaluate the turbulent burning velocity computed in different layers in the preheat Zone and Reaction Zone. It is found that for all investigated flames the preheat Zone characterized with planar laser-induced fluorescence (PLIF) of CH2O is broadened by turbulent eddies. The thickness of the preheat Zone increases with the turbulent intensity and it can be on the order of the turbulent integral length at high Karlovitz numbers. The Reaction Zone characterized using the overlapping layer of OH and CH2O PLIF signals is not significantly broadened by turbulence eddies; however, the CH PLIF layer is found to be broadened significantly by turbulence. The turbulent burning velocity is shown to monotonically increase with turbulent intensity and Karlovitz number. The increase in turbulent burning velocity is mainly due to the enhanced turbulent heat and mass transfer in various layers of the flame, while the contribution of flame front wrinkling to the turbulent burning velocity is rather minor.
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structure and burning velocity of turbulent premixed methane air jet flames in thin Reaction Zone and distributed Reaction Zone regimes
Proceedings of the Combustion Institute, 2019Co-Authors: Zhenkan Wang, Bo Zhou, Christian Brackmann, Zhongshan Li, Mattias Richter, Senbin Yu, Marcus AldenAbstract:A series of turbulent premixed methane/air jet flames are studied using simultaneous planar lase diagnostic imaging of OH/CH/temperature and CH/OH/CH2O. The Karlovitz number of the flames ranges from 25 to 1500, and the turbulence intensity ranges from 16 to 200. These flames can be classified as highly turbulent flames in the thin Reactions Zone (TRZ) regime and distributed Reaction Zone (DRZ) regime. The aims of this study are to investigate the structural change of the preheat Zone and the Reaction Zone as the Karlovitz number and turbulent intensity increase, to study the impact of the structural change of the flame on the propagation speed of the flame, and to evaluate the turbulent burning velocity computed in different layers in the preheat Zone and Reaction Zone. It is found that for all investigated flames the preheat Zone characterized with planar laser-induced fluorescence (PLIF) of CH2O is broadened by turbulent eddies. The thickness of the preheat Zone increases with the turbulent intensity and it can be on the order of the turbulent integral length at high Karlovitz numbers. The Reaction Zone characterized using the overlapping layer of OH and CH2O PLIF signals is not significantly broadened by turbulence eddies; however, the CH PLIF layer is found to be broadened significantly by turbulence. The turbulent burning velocity is shown to monotonically increase with turbulent intensity and Karlovitz number. The increase in turbulent burning velocity is mainly due to the enhanced turbulent heat and mass transfer in various layers of the flame, while the contribution of flame front wrinkling to the turbulent burning velocity is rather minor.
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thin Reaction Zone and distributed Reaction Zone regimes in turbulent premixed methane air flames scalar distributions and correlations
Combustion and Flame, 2017Co-Authors: Bo Zhou, Christian Brackmann, Zhenkan Wang, Zhongshan Li, Mattias Richter, Marcus AldenAbstract:A series of premixed turbulent methane/air jet flames in the thin Reaction Zone (TRZ) and distributed Reaction Zone (DRZ) regimes were studied using simultaneous three-scalar high-resolution imaging measurements, including HCO/OH/CH2O, CH/OH/CH2O, T/OH/CH2O and T/CH/OH/. These scalar fields offer a possibility of revisiting the structures of turbulent premixed flames in different combustion regimes. In particular, CH2O provides a measure of the preheat Zone, CH/HCO a measure of the inner layer of the Reaction Zone, and OH a measure of the oxidation Zone. Scalar correlations are analyzed on both single-shot and statistical basis, and resolvable correlated structures of ∼100 µm between scalars are captured. With increasing turbulence intensity, it is shown that the preheat Zone and the inner layer of the Reaction Zone become gradually broadened/distributed, and the correlation between HCO and [OH]LIF×[CH2O]LIF decreases. A transition from the TRZ regime to the DRZ regime is found around Karlovitz number of 70–100. The physical and chemical effects on the broadening of the flame are investigated. In the TRZ regime the inner layer marker CH and HCO remains thin in general although occasional local broadening of CH/HCO could be observed. Furthermore, there is a significant probability of finding CH and HCO at rather low temperatures even in the TRZ regime. In the DRZ regime, the broadening of CH and HCO are shown to be mainly a result of local Reactions facilitated by rapid turbulent transport of radicals and intermediate reactants in the upstream of the Reaction paths. Differential diffusion is expected to have an important effect in the DRZ regime, as H radicals seemingly play a more important role than OH radicals.
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simultaneous multi species and temperature visualization of premixed flames in distributed Reaction Zone regime
Proceedings of the Combustion Institute; 35(2) pp 1409-1416 (2015), 2015Co-Authors: Bo Zhou, Christian Brackmann, Zhongshan Li, Marcus AldenAbstract:Structures of turbulent premixed flames, operating in the thin and distributed Reaction Zone regimes, were investigated for stoichiometric premixed methane/air jet flames with jet Reynolds number up to 40,000 and corresponding Karlovitz number up to 286. Multi-species planar laser-induced fluorescence with high spatial resolution was applied to simultaneously image combinations of CH/OH/CH2O and HCO/OH/CH2O. In addition, OH/CH2O imaging was performed in combination with simultaneous Rayleigh scattering thermometry. The CH and HCO layers showed progressive broadening along the axial distance for flames with Reynolds number above 21,000 and the corresponding Karlovitz number above 126. At Reynolds number 40,000 and the corresponding Karlovitz number of 286, a mean CH layer thickness more than 10 times larger than that under laminar condition was observed, providing a clear experimental evidence of distributed Reaction Zone owing to turbulence/flame interaction. Additionally, spatial correlations between species show that OH and CH2O locate at mutually exclusive regions. In contrast, both CH and HCO can overlap substantially with CH2O. The regions of strong CH/HCO signals correspond to regions with weak CH2O signals. Moreover, CH and HCO are shown to be able to penetrate deeper into the OH layer than CH2O. Regions where CH and HCO appear distributed show a rather homogeneous temperature distribution with reduced maximum temperature compared with non-distributed conditions.
Xavier Daguenetfrick - One of the best experts on this subject based on the ideXlab platform.
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development of a numerical model for the Reaction Zone design of an aqueous sodium hydroxide seasonal thermal energy storage
Solar Energy, 2015Co-Authors: Xavier Daguenetfrick, Paul Gantenbein, Elimar Frank, Benjamin Fumey, Robert WeberAbstract:Abstract This paper describes a thermochemical seasonal storage with emphasis on the development of a Reaction Zone for an absorption/desorption unit. The heat and mass exchange is modelled and the design of a suitable Reaction Zone is explained. A tube bundle concept is presented for the heat and mass exchangers and the most demanding working conditions they should fulfil are modelled and discussed. To estimate the performance of such a Reaction Zone and to design it, numerical models were developed and are described in this paper. Several parameters influencing these models were tested such as the sensitivity of the models to the correlation used to calculate the heat and mass exchanges, the tube diameter and the tube pitch influence. The final contribution of the tube bundle modelling is to size and design the heat and mass exchanger constituting the Reaction Zone. This work will be used as a basis for the Reaction Zone construction of an aqueous sodium hydroxide seasonal thermal energy storage prototype.
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Reaction Zone development for an aqueous sodium hydroxide seasonal thermal energy storage
Energy Procedia, 2014Co-Authors: Xavier Daguenetfrick, Paul Gantenbein, Elimar Frank, Benjamin Fumey, Robert Weber, Tommy WilliamsonAbstract:Abstract This paper focuses on the development of a Reaction Zone dedicated to an absorption/desorption seasonal thermal energy storage. The modelling of the tube bundle constituting the Reaction Zone is described as well as the boundary conditions in worst working conditions and some modelling results are presented for the desorber/absorber. In parallel to this sizing work, investigations were lead on the tube bundle optimisation by studying the wetting and fluid distribution. A specific developed experimental set up based on imaging enabled to quantify the influence of tube texturing and to improve the manifold design. This work will lead to the Reaction Zone construction for an aqueous sodium hydroxide seasonal thermal energy storage prototype.
Zhongshan Li - One of the best experts on this subject based on the ideXlab platform.
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Thin Reaction Zone and distributed Reaction Zone regimes in turbulent premixed methane/air flames : Scalar distributions and correlations
Combustion and Flame, 2020Co-Authors: Bo Zhou, Christian Brackmann, Zhenkan Wang, Zhongshan Li, Mattias Richter, Marcus AldenAbstract:A series of premixed turbulent methane/air jet flames in the thin Reaction Zone (TRZ) and distributed Reaction Zone (DRZ) regimes were studied using simultaneous three-scalar high-resolution imaging measurements, including HCO/OH/CH2O, CH/OH/CH2O, T/OH/CH2O and T/CH/OH/. These scalar fields offer a possibility of revisiting the structures of turbulent premixed flames in different combustion regimes. In particular, CH2O provides a measure of the preheat Zone, CH/HCO a measure of the inner layer of the Reaction Zone, and OH a measure of the oxidation Zone. Scalar correlations are analyzed on both single-shot and statistical basis, and resolvable correlated structures of ∼100 µm between scalars are captured. With increasing turbulence intensity, it is shown that the preheat Zone and the inner layer of the Reaction Zone become gradually broadened/distributed, and the correlation between HCO and [OH]LIF×[CH2O]LIF decreases. A transition from the TRZ regime to the DRZ regime is found around Karlovitz number of 70–100. The physical and chemical effects on the broadening of the flame are investigated. In the TRZ regime the inner layer marker CH and HCO remains thin in general although occasional local broadening of CH/HCO could be observed. Furthermore, there is a significant probability of finding CH and HCO at rather low temperatures even in the TRZ regime. In the DRZ regime, the broadening of CH and HCO are shown to be mainly a result of local Reactions facilitated by rapid turbulent transport of radicals and intermediate reactants in the upstream of the Reaction paths. Differential diffusion is expected to have an important effect in the DRZ regime, as H radicals seemingly play a more important role than OH radicals.
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Structure and burning velocity of turbulent premixed methane/air jet flames in thin-Reaction Zone and distributed Reaction Zone regimes
Proceedings of the Combustion Institute, 2020Co-Authors: Zhenkan Wang, Bo Zhou, Christian Brackmann, Zhongshan Li, Mattias Richter, Senbin Yu, Marcus AldenAbstract:A series of turbulent premixed methane/air jet flames are studied using simultaneous planar lase diagnostic imaging of OH/CH/temperature and CH/OH/CH2O. The Karlovitz number of the flames ranges from 25 to 1500, and the turbulence intensity ranges from 16 to 200. These flames can be classified as highly turbulent flames in the thin Reactions Zone (TRZ) regime and distributed Reaction Zone (DRZ) regime. The aims of this study are to investigate the structural change of the preheat Zone and the Reaction Zone as the Karlovitz number and turbulent intensity increase, to study the impact of the structural change of the flame on the propagation speed of the flame, and to evaluate the turbulent burning velocity computed in different layers in the preheat Zone and Reaction Zone. It is found that for all investigated flames the preheat Zone characterized with planar laser-induced fluorescence (PLIF) of CH2O is broadened by turbulent eddies. The thickness of the preheat Zone increases with the turbulent intensity and it can be on the order of the turbulent integral length at high Karlovitz numbers. The Reaction Zone characterized using the overlapping layer of OH and CH2O PLIF signals is not significantly broadened by turbulence eddies; however, the CH PLIF layer is found to be broadened significantly by turbulence. The turbulent burning velocity is shown to monotonically increase with turbulent intensity and Karlovitz number. The increase in turbulent burning velocity is mainly due to the enhanced turbulent heat and mass transfer in various layers of the flame, while the contribution of flame front wrinkling to the turbulent burning velocity is rather minor.
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structure and burning velocity of turbulent premixed methane air jet flames in thin Reaction Zone and distributed Reaction Zone regimes
Proceedings of the Combustion Institute, 2019Co-Authors: Zhenkan Wang, Bo Zhou, Christian Brackmann, Zhongshan Li, Mattias Richter, Senbin Yu, Marcus AldenAbstract:A series of turbulent premixed methane/air jet flames are studied using simultaneous planar lase diagnostic imaging of OH/CH/temperature and CH/OH/CH2O. The Karlovitz number of the flames ranges from 25 to 1500, and the turbulence intensity ranges from 16 to 200. These flames can be classified as highly turbulent flames in the thin Reactions Zone (TRZ) regime and distributed Reaction Zone (DRZ) regime. The aims of this study are to investigate the structural change of the preheat Zone and the Reaction Zone as the Karlovitz number and turbulent intensity increase, to study the impact of the structural change of the flame on the propagation speed of the flame, and to evaluate the turbulent burning velocity computed in different layers in the preheat Zone and Reaction Zone. It is found that for all investigated flames the preheat Zone characterized with planar laser-induced fluorescence (PLIF) of CH2O is broadened by turbulent eddies. The thickness of the preheat Zone increases with the turbulent intensity and it can be on the order of the turbulent integral length at high Karlovitz numbers. The Reaction Zone characterized using the overlapping layer of OH and CH2O PLIF signals is not significantly broadened by turbulence eddies; however, the CH PLIF layer is found to be broadened significantly by turbulence. The turbulent burning velocity is shown to monotonically increase with turbulent intensity and Karlovitz number. The increase in turbulent burning velocity is mainly due to the enhanced turbulent heat and mass transfer in various layers of the flame, while the contribution of flame front wrinkling to the turbulent burning velocity is rather minor.
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thin Reaction Zone and distributed Reaction Zone regimes in turbulent premixed methane air flames scalar distributions and correlations
Combustion and Flame, 2017Co-Authors: Bo Zhou, Christian Brackmann, Zhenkan Wang, Zhongshan Li, Mattias Richter, Marcus AldenAbstract:A series of premixed turbulent methane/air jet flames in the thin Reaction Zone (TRZ) and distributed Reaction Zone (DRZ) regimes were studied using simultaneous three-scalar high-resolution imaging measurements, including HCO/OH/CH2O, CH/OH/CH2O, T/OH/CH2O and T/CH/OH/. These scalar fields offer a possibility of revisiting the structures of turbulent premixed flames in different combustion regimes. In particular, CH2O provides a measure of the preheat Zone, CH/HCO a measure of the inner layer of the Reaction Zone, and OH a measure of the oxidation Zone. Scalar correlations are analyzed on both single-shot and statistical basis, and resolvable correlated structures of ∼100 µm between scalars are captured. With increasing turbulence intensity, it is shown that the preheat Zone and the inner layer of the Reaction Zone become gradually broadened/distributed, and the correlation between HCO and [OH]LIF×[CH2O]LIF decreases. A transition from the TRZ regime to the DRZ regime is found around Karlovitz number of 70–100. The physical and chemical effects on the broadening of the flame are investigated. In the TRZ regime the inner layer marker CH and HCO remains thin in general although occasional local broadening of CH/HCO could be observed. Furthermore, there is a significant probability of finding CH and HCO at rather low temperatures even in the TRZ regime. In the DRZ regime, the broadening of CH and HCO are shown to be mainly a result of local Reactions facilitated by rapid turbulent transport of radicals and intermediate reactants in the upstream of the Reaction paths. Differential diffusion is expected to have an important effect in the DRZ regime, as H radicals seemingly play a more important role than OH radicals.
-
simultaneous multi species and temperature visualization of premixed flames in distributed Reaction Zone regime
Proceedings of the Combustion Institute; 35(2) pp 1409-1416 (2015), 2015Co-Authors: Bo Zhou, Christian Brackmann, Zhongshan Li, Marcus AldenAbstract:Structures of turbulent premixed flames, operating in the thin and distributed Reaction Zone regimes, were investigated for stoichiometric premixed methane/air jet flames with jet Reynolds number up to 40,000 and corresponding Karlovitz number up to 286. Multi-species planar laser-induced fluorescence with high spatial resolution was applied to simultaneously image combinations of CH/OH/CH2O and HCO/OH/CH2O. In addition, OH/CH2O imaging was performed in combination with simultaneous Rayleigh scattering thermometry. The CH and HCO layers showed progressive broadening along the axial distance for flames with Reynolds number above 21,000 and the corresponding Karlovitz number above 126. At Reynolds number 40,000 and the corresponding Karlovitz number of 286, a mean CH layer thickness more than 10 times larger than that under laminar condition was observed, providing a clear experimental evidence of distributed Reaction Zone owing to turbulence/flame interaction. Additionally, spatial correlations between species show that OH and CH2O locate at mutually exclusive regions. In contrast, both CH and HCO can overlap substantially with CH2O. The regions of strong CH/HCO signals correspond to regions with weak CH2O signals. Moreover, CH and HCO are shown to be able to penetrate deeper into the OH layer than CH2O. Regions where CH and HCO appear distributed show a rather homogeneous temperature distribution with reduced maximum temperature compared with non-distributed conditions.
