The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform

Kaoru Maruta - One of the best experts on this subject based on the ideXlab platform.

  • broken c shaped extinction curve and near limit flame behaviors of low lewis number counterflow flames under microgravity
    Combustion and Flame, 2018
    Co-Authors: Tomoya Okuno, S. Minaev, Roman Fursenko, Takuya Tezuka, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Kaoru Maruta, Takaki Akiba
    Abstract:

    Abstract To examine the effect of Lewis number on the extinction boundary, flame regimes, and the formation of sporadic flames, microgravity experiments on counterflow flames for CH4/O2/Kr (Le ≈ 0.7–0.8) and CH4/O2/Xe (Le ≈ 0.5) mixtures, and three types of computations, which are one-dimensional computations with a PREMIX-based code using detailed chemistry, and three- and one-dimensional computations with the thermal-diffusion model using an overall one-step reaction were conducted. In the microgravity experiments, planar flames, planar flames with propagating edges, planar flames with receding edges, star-shaped flames, cellular flames, and sporadic flames were identified, and their regions of existence in the equivalence ratio-stretch rate plane were obtained. Sporadic flames were formed for Xe mixtures but not for Kr mixtures in the experiments. Similarly, sporadic flames were formed at Le = 0.50 but not at Le = 0.75 in the three-dimensional computations with the thermal-diffusion model. Also, the flame regime of sporadic flames extended far beyond the extinction boundaries obtained in the one-dimensional computations in both experiments and the three-dimensional computations. Furthermore, a comparison of the sporadic flames and flame balls in the three-dimensional computations showed that sporadic flames are intermediate combustion modes that segue flame balls to propagating flames.

  • diffusive thermal instability of stretched low lewis number flames of slot jet counterflow burners
    Proceedings of the Combustion Institute, 2017
    Co-Authors: Roman Fursenko, S. Minaev, Sergey Mokrin, Kaoru Maruta
    Abstract:

    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.

  • study on the combustion limit near limit extinction boundary and flame regimes of low lewis number ch4 o2 co2 counterflow flames under microgravity
    Combustion and Flame, 2016
    Co-Authors: Tomoya Okuno, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Kaoru Maruta
    Abstract:

    Abstract To obtain an accurate and comprehensive understanding on the fuel-lean combustion limit, near-limit extinction boundary and flame regimes, experimental and numerical investigations using premixed counterflow flames were conducted for low-Lewis-number mixtures. Counterflow flame experiments were conducted under microgravity (2.2 ≦ a ≦ 12.9 s−1) and under normal gravity (35 ≦ a ≦ 150 s−1) using fuel-lean CH4/O2/CO2 mixtures (Le = 0.75) where a is the stretch rate. The mole fraction ratio of O2 to CO2 in the mixtures was 0.40. Microgravity experiments at a = 2.7–3.2 s−1 showed that transitions from planar flames to ball-like flames occurred near extinction for the investigated mixture. In addition to planar flames and ball-like flames, multi-dimensional flames such as cellular flames and twin-curved flames were also observed at a = 2.2–5.5 s−1 in microgravity experiments. In conjunction with experimental results under normal gravity, experimental flame regimes for overall stretch rates were obtained for the first time and the region where ball-like flames were observed showed a qualitative agreement with our previous study based on the 3-D transient computations with the diffusive-thermal model. Extinction points obtained by microgravity experiments were found to scatter at very low stretch rates where multi-dimensional flames such as ball-like flames and cellular flames were observed, indicating the existence of a flame regime at lower stretch rates leaner than the planar counterflow flame extinction boundary. In addition, flame bifurcation at low stretch rates and at ϕ = 0.58 and 0.60 were experimentally observed for the present low-Lewis-number mixture, indicating the validity of the previous computational and theoretical studies on the G-shaped extinction curve of planar counterflow flames.

  • Cellular and sporadic flame regimes of low-Lewis-number stretched premixed flames
    Proceedings of the Combustion Institute, 2013
    Co-Authors: Roman Fursenko, S. Minaev, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Xing Li, Kaoru Maruta
    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. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

  • cellular and sporadic flame regimes of low lewis number stretched premixed flames
    Proceedings of the Combustion Institute, 2013
    Co-Authors: Roman Fursenko, S. Minaev, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Xing Li, Kaoru Maruta
    Abstract:

    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.

Roman Fursenko - One of the best experts on this subject based on the ideXlab platform.

  • broken c shaped extinction curve and near limit flame behaviors of low lewis number counterflow flames under microgravity
    Combustion and Flame, 2018
    Co-Authors: Tomoya Okuno, S. Minaev, Roman Fursenko, Takuya Tezuka, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Kaoru Maruta, Takaki Akiba
    Abstract:

    Abstract To examine the effect of Lewis number on the extinction boundary, flame regimes, and the formation of sporadic flames, microgravity experiments on counterflow flames for CH4/O2/Kr (Le ≈ 0.7–0.8) and CH4/O2/Xe (Le ≈ 0.5) mixtures, and three types of computations, which are one-dimensional computations with a PREMIX-based code using detailed chemistry, and three- and one-dimensional computations with the thermal-diffusion model using an overall one-step reaction were conducted. In the microgravity experiments, planar flames, planar flames with propagating edges, planar flames with receding edges, star-shaped flames, cellular flames, and sporadic flames were identified, and their regions of existence in the equivalence ratio-stretch rate plane were obtained. Sporadic flames were formed for Xe mixtures but not for Kr mixtures in the experiments. Similarly, sporadic flames were formed at Le = 0.50 but not at Le = 0.75 in the three-dimensional computations with the thermal-diffusion model. Also, the flame regime of sporadic flames extended far beyond the extinction boundaries obtained in the one-dimensional computations in both experiments and the three-dimensional computations. Furthermore, a comparison of the sporadic flames and flame balls in the three-dimensional computations showed that sporadic flames are intermediate combustion modes that segue flame balls to propagating flames.

  • diffusive thermal instability of stretched low lewis number flames of slot jet counterflow burners
    Proceedings of the Combustion Institute, 2017
    Co-Authors: Roman Fursenko, S. Minaev, Sergey Mokrin, Kaoru Maruta
    Abstract:

    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.

  • Cellular and sporadic flame regimes of low-Lewis-number stretched premixed flames
    Proceedings of the Combustion Institute, 2013
    Co-Authors: Roman Fursenko, S. Minaev, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Xing Li, Kaoru Maruta
    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. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

  • cellular and sporadic flame regimes of low lewis number stretched premixed flames
    Proceedings of the Combustion Institute, 2013
    Co-Authors: Roman Fursenko, S. Minaev, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Xing Li, Kaoru Maruta
    Abstract:

    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.

Hisashi Nakamura - One of the best experts on this subject based on the ideXlab platform.

  • broken c shaped extinction curve and near limit flame behaviors of low lewis number counterflow flames under microgravity
    Combustion and Flame, 2018
    Co-Authors: Tomoya Okuno, S. Minaev, Roman Fursenko, Takuya Tezuka, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Kaoru Maruta, Takaki Akiba
    Abstract:

    Abstract To examine the effect of Lewis number on the extinction boundary, flame regimes, and the formation of sporadic flames, microgravity experiments on counterflow flames for CH4/O2/Kr (Le ≈ 0.7–0.8) and CH4/O2/Xe (Le ≈ 0.5) mixtures, and three types of computations, which are one-dimensional computations with a PREMIX-based code using detailed chemistry, and three- and one-dimensional computations with the thermal-diffusion model using an overall one-step reaction were conducted. In the microgravity experiments, planar flames, planar flames with propagating edges, planar flames with receding edges, star-shaped flames, cellular flames, and sporadic flames were identified, and their regions of existence in the equivalence ratio-stretch rate plane were obtained. Sporadic flames were formed for Xe mixtures but not for Kr mixtures in the experiments. Similarly, sporadic flames were formed at Le = 0.50 but not at Le = 0.75 in the three-dimensional computations with the thermal-diffusion model. Also, the flame regime of sporadic flames extended far beyond the extinction boundaries obtained in the one-dimensional computations in both experiments and the three-dimensional computations. Furthermore, a comparison of the sporadic flames and flame balls in the three-dimensional computations showed that sporadic flames are intermediate combustion modes that segue flame balls to propagating flames.

  • study on the combustion limit near limit extinction boundary and flame regimes of low lewis number ch4 o2 co2 counterflow flames under microgravity
    Combustion and Flame, 2016
    Co-Authors: Tomoya Okuno, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Kaoru Maruta
    Abstract:

    Abstract To obtain an accurate and comprehensive understanding on the fuel-lean combustion limit, near-limit extinction boundary and flame regimes, experimental and numerical investigations using premixed counterflow flames were conducted for low-Lewis-number mixtures. Counterflow flame experiments were conducted under microgravity (2.2 ≦ a ≦ 12.9 s−1) and under normal gravity (35 ≦ a ≦ 150 s−1) using fuel-lean CH4/O2/CO2 mixtures (Le = 0.75) where a is the stretch rate. The mole fraction ratio of O2 to CO2 in the mixtures was 0.40. Microgravity experiments at a = 2.7–3.2 s−1 showed that transitions from planar flames to ball-like flames occurred near extinction for the investigated mixture. In addition to planar flames and ball-like flames, multi-dimensional flames such as cellular flames and twin-curved flames were also observed at a = 2.2–5.5 s−1 in microgravity experiments. In conjunction with experimental results under normal gravity, experimental flame regimes for overall stretch rates were obtained for the first time and the region where ball-like flames were observed showed a qualitative agreement with our previous study based on the 3-D transient computations with the diffusive-thermal model. Extinction points obtained by microgravity experiments were found to scatter at very low stretch rates where multi-dimensional flames such as ball-like flames and cellular flames were observed, indicating the existence of a flame regime at lower stretch rates leaner than the planar counterflow flame extinction boundary. In addition, flame bifurcation at low stretch rates and at ϕ = 0.58 and 0.60 were experimentally observed for the present low-Lewis-number mixture, indicating the validity of the previous computational and theoretical studies on the G-shaped extinction curve of planar counterflow flames.

  • Cellular and sporadic flame regimes of low-Lewis-number stretched premixed flames
    Proceedings of the Combustion Institute, 2013
    Co-Authors: Roman Fursenko, S. Minaev, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Xing Li, Kaoru Maruta
    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. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

  • cellular and sporadic flame regimes of low lewis number stretched premixed flames
    Proceedings of the Combustion Institute, 2013
    Co-Authors: Roman Fursenko, S. Minaev, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Xing Li, Kaoru Maruta
    Abstract:

    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.

  • stabilized three stage oxidation of gaseous n heptane air mixture in a micro flow reactor with a controlled temperature profile
    Proceedings of the Combustion Institute, 2011
    Co-Authors: Akira Yamamoto, Takuya Tezuka, Susumu Hasegawa, Hisashi Nakamura, Hiroshi Oshibe, Kaoru Maruta
    Abstract:

    Abstract Ignition and combustion characteristics of a stoichiometric gaseous n -heptane/air mixture were investigated using a micro flow reactor with a controlled temperature profile which smoothly ramped from room temperature to ignition temperature. At atmospheric pressure condition, normal stable flames in high mixture flow velocity region, unstable flames with repetitive extinction and ignition (FREI) in intermediate velocity region, and stable weak flames in low velocity region were experimentally observed. Especially at low velocity condition, distinct two luminous weak flames and one broaden luminous zone were observed. Gas sampling and analysis were conducted to interpret this phenomenon and it was supposed that those luminous flames consist of three-stage oxidation process. Computational results also showed that there are co-existing three heat-release-rate peaks in the flow direction at low velocity condition, which qualitatively supported the experimental observations. From the concentration profiles of the species, these three reactions are confirmed so-called cool, blue and hot flames, respectively. In addition, the effect of pressure on the three-stage oxidation process was examined by conducting experiments and computations at high pressure conditions. With an increase of pressure, the first and second weak flames were intensified and the third flame was weakened. Moreover, the position of the first and second weak flames shifted to low temperature side with the increase of pressure. Consequently, the first and second flames in the three-stage oxidation process become more significant at higher pressure conditions.

Susumu Hasegawa - One of the best experts on this subject based on the ideXlab platform.

  • broken c shaped extinction curve and near limit flame behaviors of low lewis number counterflow flames under microgravity
    Combustion and Flame, 2018
    Co-Authors: Tomoya Okuno, S. Minaev, Roman Fursenko, Takuya Tezuka, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Kaoru Maruta, Takaki Akiba
    Abstract:

    Abstract To examine the effect of Lewis number on the extinction boundary, flame regimes, and the formation of sporadic flames, microgravity experiments on counterflow flames for CH4/O2/Kr (Le ≈ 0.7–0.8) and CH4/O2/Xe (Le ≈ 0.5) mixtures, and three types of computations, which are one-dimensional computations with a PREMIX-based code using detailed chemistry, and three- and one-dimensional computations with the thermal-diffusion model using an overall one-step reaction were conducted. In the microgravity experiments, planar flames, planar flames with propagating edges, planar flames with receding edges, star-shaped flames, cellular flames, and sporadic flames were identified, and their regions of existence in the equivalence ratio-stretch rate plane were obtained. Sporadic flames were formed for Xe mixtures but not for Kr mixtures in the experiments. Similarly, sporadic flames were formed at Le = 0.50 but not at Le = 0.75 in the three-dimensional computations with the thermal-diffusion model. Also, the flame regime of sporadic flames extended far beyond the extinction boundaries obtained in the one-dimensional computations in both experiments and the three-dimensional computations. Furthermore, a comparison of the sporadic flames and flame balls in the three-dimensional computations showed that sporadic flames are intermediate combustion modes that segue flame balls to propagating flames.

  • study on the combustion limit near limit extinction boundary and flame regimes of low lewis number ch4 o2 co2 counterflow flames under microgravity
    Combustion and Flame, 2016
    Co-Authors: Tomoya Okuno, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Kaoru Maruta
    Abstract:

    Abstract To obtain an accurate and comprehensive understanding on the fuel-lean combustion limit, near-limit extinction boundary and flame regimes, experimental and numerical investigations using premixed counterflow flames were conducted for low-Lewis-number mixtures. Counterflow flame experiments were conducted under microgravity (2.2 ≦ a ≦ 12.9 s−1) and under normal gravity (35 ≦ a ≦ 150 s−1) using fuel-lean CH4/O2/CO2 mixtures (Le = 0.75) where a is the stretch rate. The mole fraction ratio of O2 to CO2 in the mixtures was 0.40. Microgravity experiments at a = 2.7–3.2 s−1 showed that transitions from planar flames to ball-like flames occurred near extinction for the investigated mixture. In addition to planar flames and ball-like flames, multi-dimensional flames such as cellular flames and twin-curved flames were also observed at a = 2.2–5.5 s−1 in microgravity experiments. In conjunction with experimental results under normal gravity, experimental flame regimes for overall stretch rates were obtained for the first time and the region where ball-like flames were observed showed a qualitative agreement with our previous study based on the 3-D transient computations with the diffusive-thermal model. Extinction points obtained by microgravity experiments were found to scatter at very low stretch rates where multi-dimensional flames such as ball-like flames and cellular flames were observed, indicating the existence of a flame regime at lower stretch rates leaner than the planar counterflow flame extinction boundary. In addition, flame bifurcation at low stretch rates and at ϕ = 0.58 and 0.60 were experimentally observed for the present low-Lewis-number mixture, indicating the validity of the previous computational and theoretical studies on the G-shaped extinction curve of planar counterflow flames.

  • Cellular and sporadic flame regimes of low-Lewis-number stretched premixed flames
    Proceedings of the Combustion Institute, 2013
    Co-Authors: Roman Fursenko, S. Minaev, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Xing Li, Kaoru Maruta
    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. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

  • cellular and sporadic flame regimes of low lewis number stretched premixed flames
    Proceedings of the Combustion Institute, 2013
    Co-Authors: Roman Fursenko, S. Minaev, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Xing Li, Kaoru Maruta
    Abstract:

    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.

  • stabilized three stage oxidation of gaseous n heptane air mixture in a micro flow reactor with a controlled temperature profile
    Proceedings of the Combustion Institute, 2011
    Co-Authors: Akira Yamamoto, Takuya Tezuka, Susumu Hasegawa, Hisashi Nakamura, Hiroshi Oshibe, Kaoru Maruta
    Abstract:

    Abstract Ignition and combustion characteristics of a stoichiometric gaseous n -heptane/air mixture were investigated using a micro flow reactor with a controlled temperature profile which smoothly ramped from room temperature to ignition temperature. At atmospheric pressure condition, normal stable flames in high mixture flow velocity region, unstable flames with repetitive extinction and ignition (FREI) in intermediate velocity region, and stable weak flames in low velocity region were experimentally observed. Especially at low velocity condition, distinct two luminous weak flames and one broaden luminous zone were observed. Gas sampling and analysis were conducted to interpret this phenomenon and it was supposed that those luminous flames consist of three-stage oxidation process. Computational results also showed that there are co-existing three heat-release-rate peaks in the flow direction at low velocity condition, which qualitatively supported the experimental observations. From the concentration profiles of the species, these three reactions are confirmed so-called cool, blue and hot flames, respectively. In addition, the effect of pressure on the three-stage oxidation process was examined by conducting experiments and computations at high pressure conditions. With an increase of pressure, the first and second weak flames were intensified and the third flame was weakened. Moreover, the position of the first and second weak flames shifted to low temperature side with the increase of pressure. Consequently, the first and second flames in the three-stage oxidation process become more significant at higher pressure conditions.

Takuya Tezuka - One of the best experts on this subject based on the ideXlab platform.

  • broken c shaped extinction curve and near limit flame behaviors of low lewis number counterflow flames under microgravity
    Combustion and Flame, 2018
    Co-Authors: Tomoya Okuno, S. Minaev, Roman Fursenko, Takuya Tezuka, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Kaoru Maruta, Takaki Akiba
    Abstract:

    Abstract To examine the effect of Lewis number on the extinction boundary, flame regimes, and the formation of sporadic flames, microgravity experiments on counterflow flames for CH4/O2/Kr (Le ≈ 0.7–0.8) and CH4/O2/Xe (Le ≈ 0.5) mixtures, and three types of computations, which are one-dimensional computations with a PREMIX-based code using detailed chemistry, and three- and one-dimensional computations with the thermal-diffusion model using an overall one-step reaction were conducted. In the microgravity experiments, planar flames, planar flames with propagating edges, planar flames with receding edges, star-shaped flames, cellular flames, and sporadic flames were identified, and their regions of existence in the equivalence ratio-stretch rate plane were obtained. Sporadic flames were formed for Xe mixtures but not for Kr mixtures in the experiments. Similarly, sporadic flames were formed at Le = 0.50 but not at Le = 0.75 in the three-dimensional computations with the thermal-diffusion model. Also, the flame regime of sporadic flames extended far beyond the extinction boundaries obtained in the one-dimensional computations in both experiments and the three-dimensional computations. Furthermore, a comparison of the sporadic flames and flame balls in the three-dimensional computations showed that sporadic flames are intermediate combustion modes that segue flame balls to propagating flames.

  • study on the combustion limit near limit extinction boundary and flame regimes of low lewis number ch4 o2 co2 counterflow flames under microgravity
    Combustion and Flame, 2016
    Co-Authors: Tomoya Okuno, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Kaoru Maruta
    Abstract:

    Abstract To obtain an accurate and comprehensive understanding on the fuel-lean combustion limit, near-limit extinction boundary and flame regimes, experimental and numerical investigations using premixed counterflow flames were conducted for low-Lewis-number mixtures. Counterflow flame experiments were conducted under microgravity (2.2 ≦ a ≦ 12.9 s−1) and under normal gravity (35 ≦ a ≦ 150 s−1) using fuel-lean CH4/O2/CO2 mixtures (Le = 0.75) where a is the stretch rate. The mole fraction ratio of O2 to CO2 in the mixtures was 0.40. Microgravity experiments at a = 2.7–3.2 s−1 showed that transitions from planar flames to ball-like flames occurred near extinction for the investigated mixture. In addition to planar flames and ball-like flames, multi-dimensional flames such as cellular flames and twin-curved flames were also observed at a = 2.2–5.5 s−1 in microgravity experiments. In conjunction with experimental results under normal gravity, experimental flame regimes for overall stretch rates were obtained for the first time and the region where ball-like flames were observed showed a qualitative agreement with our previous study based on the 3-D transient computations with the diffusive-thermal model. Extinction points obtained by microgravity experiments were found to scatter at very low stretch rates where multi-dimensional flames such as ball-like flames and cellular flames were observed, indicating the existence of a flame regime at lower stretch rates leaner than the planar counterflow flame extinction boundary. In addition, flame bifurcation at low stretch rates and at ϕ = 0.58 and 0.60 were experimentally observed for the present low-Lewis-number mixture, indicating the validity of the previous computational and theoretical studies on the G-shaped extinction curve of planar counterflow flames.

  • Cellular and sporadic flame regimes of low-Lewis-number stretched premixed flames
    Proceedings of the Combustion Institute, 2013
    Co-Authors: Roman Fursenko, S. Minaev, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Xing Li, Kaoru Maruta
    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. © 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

  • cellular and sporadic flame regimes of low lewis number stretched premixed flames
    Proceedings of the Combustion Institute, 2013
    Co-Authors: Roman Fursenko, S. Minaev, Takuya Tezuka, Koichi Takase, Masato Katsuta, Susumu Hasegawa, Masao Kikuchi, Hisashi Nakamura, Xing Li, Kaoru Maruta
    Abstract:

    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.

  • stabilized three stage oxidation of gaseous n heptane air mixture in a micro flow reactor with a controlled temperature profile
    Proceedings of the Combustion Institute, 2011
    Co-Authors: Akira Yamamoto, Takuya Tezuka, Susumu Hasegawa, Hisashi Nakamura, Hiroshi Oshibe, Kaoru Maruta
    Abstract:

    Abstract Ignition and combustion characteristics of a stoichiometric gaseous n -heptane/air mixture were investigated using a micro flow reactor with a controlled temperature profile which smoothly ramped from room temperature to ignition temperature. At atmospheric pressure condition, normal stable flames in high mixture flow velocity region, unstable flames with repetitive extinction and ignition (FREI) in intermediate velocity region, and stable weak flames in low velocity region were experimentally observed. Especially at low velocity condition, distinct two luminous weak flames and one broaden luminous zone were observed. Gas sampling and analysis were conducted to interpret this phenomenon and it was supposed that those luminous flames consist of three-stage oxidation process. Computational results also showed that there are co-existing three heat-release-rate peaks in the flow direction at low velocity condition, which qualitatively supported the experimental observations. From the concentration profiles of the species, these three reactions are confirmed so-called cool, blue and hot flames, respectively. In addition, the effect of pressure on the three-stage oxidation process was examined by conducting experiments and computations at high pressure conditions. With an increase of pressure, the first and second weak flames were intensified and the third flame was weakened. Moreover, the position of the first and second weak flames shifted to low temperature side with the increase of pressure. Consequently, the first and second flames in the three-stage oxidation process become more significant at higher pressure conditions.