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Ömer L. Gülder - One of the best experts on this subject based on the ideXlab platform.

  • a comment on papers by zhou et al cnf 2018 and zhou et al cst 2019 Flame displacement speed Flame Front velocity and edge reactants velocity
    Combustion and Flame, 2019
    Co-Authors: Sina Kheirkhah, Ömer L. Gülder
    Abstract:

    Abstract In two recent articles published in Combustion and Flame (Zhou et al., 2018) and Combustion Science and Technology (Zhou et al., 2019), Zhou et al. misinterpreted the Flame Front velocity and Flame displacement speed definitions. The mistake in these papers are discussed in this short communication.

  • effects of mixture composition and turbulence intensity on Flame Front structure and burning velocities of premixed turbulent hydrocarbon air bunsen Flames
    Combustion and Flame, 2015
    Co-Authors: Parsa Tamadonfar, Ömer L. Gülder
    Abstract:

    Abstract The influences of the equivalence ratio, turbulence intensity, and different thermo-diffusive characteristics on the Flame brush characteristics, instantaneous Flame Front structures, and burning velocities of premixed turbulent methane/–, ethane/–, and propane/air Bunsen Flames were investigated systematically. Particle image velocimetry and Mie scattering techniques were utilized to measure the turbulence statistics and to visualize Flame Front corrugations, respectively. All experiments were performed under a constant bulk flow velocity of 21.0 m/s. The equivalence ratio range was from 0.7 to 1.35 for methane/air Flames, 0.7–1.45 for ethane/air Flames, and 0.8–1.35 for propane/air Flames. Two perforated plates were used to produce different turbulence levels. A series of comprehensive parameters including the characteristic Flame height, mean Flame brush thickness, mean volume of the turbulent Flame region, mean fuel consumption rate, two-dimensional Flame Front curvature, local Flame Front angle, two-dimensional Flame surface density, wrinkled Flame surface area, turbulent burning velocity, mean Flamelet consumption velocity, and mean turbulent Flame stretch factor were obtained. The mean turbulent Flame stretch factor displayed a dependence on the equivalence ratio and turbulence intensity. Results show that the mean turbulent Flame stretch factors for lean/stoichiometric and rich mixtures were not equal when the unstrained premixed laminar burning velocity, non-dimensional bulk flow velocity, non-dimensional turbulence intensity, and non-dimensional longitudinal integral length scale were kept constant.

  • influence of edge velocity on Flame Front position and displacement speed in turbulent premixed combustion
    Combustion and Flame, 2014
    Co-Authors: Sina Kheirkhah, Ömer L. Gülder
    Abstract:

    Abstract Using a novel concept, the present study experimentally investigates underlying physics pertaining to statistics of the Flame Front position and the Flame Front velocity in turbulent premixed V-shaped Flames. The concept is associated with characteristics of the reactants velocity at the vicinity of the Flame Front, referred to as the edge velocity. The experiments are performed using simultaneous Mie scattering and Particle Image Velocimetry techniques. Three mean streamwise exit velocities of: 4.0, 6.2, and 8.6 m/s along with three fuel–air equivalence ratios of: 0.7, 0.8, and 0.9 are examined. The results show that fluctuations of the Flame Front position and the Flame Front velocity are induced by the fluctuations of the component of the edge velocity transverse to the mean flow direction. Analysis of the results show that the mean of the Flame Front velocity in the normal direction to the Flame Front is significantly dependent on the vertical distance from the Flame-holder. Relatively close to the Flame-holder, the mean of the Flame Front velocity in the direction normal to the Flame Front is about zero; however, it increases to values several times larger than the laminar Flame speed by increasing the vertical distance from the Flame-holder.

  • turbulent premixed combustion in v shaped Flames characteristics of Flame Front
    Physics of Fluids, 2013
    Co-Authors: Sina Kheirkhah, Ömer L. Gülder
    Abstract:

    Flame Front characteristics of turbulent premixed V-shaped Flames were investigated experimentally using the Mie scattering and the particle image velocimetry techniques. The experiments were performed at mean streamwise exit velocities of 4.0, 6.2, and 8.6 m/s, along with fuel-air equivalence ratios of 0.7, 0.8, and 0.9. Effects of vertical distance from the Flame-holder, mean streamwise exit velocity, and fuel-air equivalence ratio on statistics of the distance between the Flame Front and the vertical axis, Flame brush thickness, Flame Front curvature, and angle between tangent to the Flame Front and the horizontal axis were studied. The results show that increasing the vertical distance from the Flame-holder and the fuel-air equivalence ratio increase the mean and root-mean-square (RMS) of the distance between the Flame Front and the vertical axis; however, increasing the mean streamwise exit velocity decreases these statistics. Spectral analysis of the fluctuations of the Flame Front position depicts that the normalized and averaged power-spectrum-densities collapse and show a power-law relation with the normalized wave number. The Flame brush thickness is linearly correlated with RMS of the distance between the Flame Front and the vertical axis. Analysis of the curvature of the Flame Front data shows that the mean curvature is independent of the experimental conditions tested and equals to zero. Values of the inverse of the RMS of Flame Front curvature are similar to those of the integral length scale, suggesting that the large eddies in the flow make a significant contribution in wrinkling of the Flame Front. Spectral analyses of the Flame Front curvature as well as the angle between tangent to the Flame Front and the horizontal axis show that the power-spectrum-densities feature a peak. Value of the inverse of the wave number pertaining to the peak is larger than that of the integral length scale.

  • turbulent premixed Flame Front dynamics and implications for limits of Flamelet hypothesis
    Proceedings of the Combustion Institute, 2013
    Co-Authors: Frank T C Yuen, Ömer L. Gülder
    Abstract:

    Abstract Turbulent premixed Flames of methane–air and propane–air stabilized on a Bunsen-type burner were studied to investigate the dynamics and structure of the Flame Front at a wide range of turbulence intensities. The non-dimensional turbulence rms velocity, rms velocity divided by the laminar Flame velocity, covered the range from about 3 to 24. The equivalence ratio was varied from 0.6 (0.7 for propane) to stoichiometric. The Flame Front data were obtained using planar Rayleigh imaging, and particle image velocimetry was used to measure instantaneous velocity field for the experimental conditions studied. The gradients of temperature profiles decreased noticeably with increasing non-dimensional turbulence rms velocity. Flame Front curvature statistics indicated that the curvature probability density functions are highly symmetric. Frequency of crossing from negative to positive (and vice versa) curvatures did not show any clear sensitivity to non-dimensional turbulence rms velocity, but decreased by increasing fuel–air equivalence ratio. The product of curvature and diffusivity, a crucial term in the level-set equation proposed for the thin reaction zones regime, was found to be very small as compared to laminar burning velocity, but the product of rms curvature and diffusivity was higher than the laminar burning velocity. Flame surface densities integrated over the Flame brush volume did not show any sensitivity to the non-dimensional turbulence rms velocity. Some of the single shot Rayleigh temperature profiles at higher turbulence intensities were radically different than those at lower intensities which are similar to laminar Flame profiles. These findings question the validity of the Flamelet hypothesis in the thin reaction zones regime where Karlovitz number exceeds unity.

Hideaki Kobayashi - One of the best experts on this subject based on the ideXlab platform.

  • burning velocity and statistical Flame Front structure of turbulent premixed Flames at high pressure up to 1 0 mpa
    Experimental Thermal and Fluid Science, 2015
    Co-Authors: Jinhua Wang, Zuohua Huang, Meng Zhang, Shuang Chen, Senbin Yu, Hideaki Kobayashi
    Abstract:

    Abstract Statistical Flame Front structure of turbulent premixed Flames at high pressure up to 1.0 MPa was measured on a nozzle-type Bunsen burner with OH-PLIF technique. Turbulent burning velocity, Flame surface density and Flame brush thickness, as well as the local curvature and radius of curvature were derived from the experimental OH-PLIF images. Turbulence–Flame interaction was analyzed based on the geometric parameters combined with laminar Flame properties and turbulence length scales. Results show that the Flame wrinkles at high pressure are dominated by small scale cusps superimposed with large scale Flame branches which is a general characteristic of the turbulent premixed Flames at high pressure. S T / S L increases remarkably with u ′/ S L and the influence of elevated pressure on S T / S L is significant. This is mainly due to the increase of Flame Front area caused by the turbulence wrinkling. Flame surface density significantly increases with the increase of pressure indicating that there is a large amount of fine cusps and small wrinkles in the Flame Front at high pressure. This would be due to the enhancement of the Flame instability represented by effective Lewis number Le eff and Flame intrinsic instability scale l i . With the increase of turbulence intensity, the Σ at high pressure increases while slightly decreases at normal pressure. The most frequent length scale of the Flame Front moves to smaller value and the possibility increases with the increase of u ′/ S L for all pressures. The effect of Flame intrinsic instability on finer Flame Front at high pressure is mainly on the formation of a large number of convex structures which enlarge the effective contact surface between Flame Front and unburned reactants, resulting in the increase of S T / S L .

  • Flame Front structure of turbulent premixed Flames of syngas oxyfuel mixtures
    International Journal of Hydrogen Energy, 2014
    Co-Authors: Meng Zhang, Jinhua Wang, Zuohua Huang, Z L Wei, Hideaki Kobayashi
    Abstract:

    Abstract In order to investigate oxyfuel combustion characteristics of typical composition of coal gasification syngas connected to CCS systems. Instantaneous Flame Front structure of turbulent premixed Flames of CO/H2/O2/CO2 mixtures which represent syngas oxyfuel combustion was quantitatively studied comparing with CH4/air and syngas/air Flames by using a nozzle-type Bunsen burner. Hot-wire anemometer and OH-PLIF were used to measure the turbulent flow and detect the instantaneous Flame Front structure, respectively. Image processing and statistical analyzing were performed using the Matlab Software. Flame surface density, mean progress variable, local curvature radius, mean Flame volume, and Flame thickness, were obtained. Results show that turbulent premixed Flames of syngas possess wrinkled Flame Front structure which is a general feature of turbulent premixed Flames. Flame surface density for the CO/H2/O2/CO2 Flame is much larger than that of CO/H2/O2/air and CH4/air Flames. This is mainly caused by the smaller Flame intrinsic instability scale, which would lead to smaller scales and less Flame passivity response to turbulence presented by Markstain length, which reduce the local Flame stretch against turbulence vortex. Peak value of Possibility Density Function (PDF) distribution of local curvature radius, R, for CO/H2/O2/CO2 Flames is larger than those of CO/H2/O2/air and CH4/air Flames at both positive and negative side and the corresponding R of absolute peak PDF is the smallest. This demonstrates that the most frequent scale is the smallest for CO/H2/O2/CO2 Flames. Mean Flame volume of CO/H2/O2/CO2 Flame is smaller than that of CH4/air Flame even smaller than that of CO/H2/O2/air Flame. This would be due to the lower Flame height and smaller Flame wrinkles.

  • measurement on instantaneous Flame Front structure of turbulent premixed ch4 h2 air Flames
    Experimental Thermal and Fluid Science, 2014
    Co-Authors: Meng Zhang, Jinhua Wang, Zuohua Huang, Yongliang Xie, Wu Jin, Z L Wei, Hideaki Kobayashi
    Abstract:

    Abstract Instantaneous Flame Front structure of turbulent premixed CH 4 /H 2 /air Flames (hydrogen fraction of 0%, 5%, 10% and 20% by mole fraction) was investigated quantitatively using a nozzle-type Bunsen burner. Hot wire anemometer and OH-PLIF were used to measure the turbulent flow and detect the instantaneous Flame Front structure, respectively. Turbulent burning velocity, S T , Flame surface density, Σ , and mean Flame volume, V f , were calculated by processing the OH-PLIF images. Results show that the Flame Front structures of the turbulent premixed Flames are the wrinkled Flame Front and it becomes much finer with the increase of turbulence intensity as well as hydrogen fraction. The value of S T /S L significantly increases with the increase of u ′/ S L and it slightly increases with the increase of hydrogen fraction. Flame surface density profile are symmetric and gives its maximum value at about 〈 c 〉 = 0.5. Hydrogen addition slightly enhances the Σ and the tendency is more obvious under higher turbulence intensity. The decrease of Σ with the increase of turbulence intensity is mainly due to the effect of Flame volume. The mean Flame volume of Flame region obviously increases with the increase of turbulence intensity within the experimental range due to the increase in depth of the large scale Flame wrinkles and Flame height. Hydrogen addition is not a predominant factor within the hydrogen fraction range in this study.

  • Measurement of the instantaneous Flame Front structure of syngas turbulent premixed Flames at high pressure
    Combustion and Flame, 2013
    Co-Authors: Jinhua Wang, Zuohua Huang, Taku Kudo, Meng Zhang, Hideaki Kobayashi
    Abstract:

    Abstract Instantaneous Flame Front structure of syngas turbulent premixed Flames including the local radius of curvature, the characteristic radius of curvature, the fractal inner cutoff scale and the local Flame angle were derived from the experimental OH-PLIF images. The CO/H 2 /CO 2 /air Flames as a model of syngas/air combustion were investigated at pressure of 0.5 MPa and compared to that of CH 4 /air Flames. The convex and concave structures of the Flame Front were detected and statistical analysis including the PDF and ADF of the local radius of curvature and local Flame angle were conducted. Results show that the Flame Front of turbulent premixed Flames at high pressure is a wrinkled Flame Front with small scale convex and concave structures superimposed with large scale Flame branches. The convex structures are much more frequent than the concave ones on Flame Front which reflects a general characteristic of the turbulent premixed Flames at high pressure. The syngas Flames possess much wrinkled Flame Front with much smaller fine cusps structure compared to that of CH 4 /air Flames and the main difference is on the convex structure. The effect of turbulence on the general wrinkled scale of Flame Front is much weaker than that of the smallest wrinkled scale. The general wrinkled scale is mainly dominated by the turbulence vortex scale, while, the smallest wrinkled scale is strongly affected by the Flame intrinsic instability. The effect of Flame intrinsic instability on Flame Front of turbulent premixed Flame is mainly on the formation of a large number of convex structure propagating to the unburned reactants and enlarge the effective contact surface between Flame Front and unburned reactants.

  • Flame Front structure and burning velocity of turbulent premixed ch4 h2 air Flames
    International Journal of Hydrogen Energy, 2013
    Co-Authors: Meng Zhang, Jinhua Wang, Zuohua Huang, Yongliang Xie, Wu Jin, Z L Wei, Hideaki Kobayashi
    Abstract:

    Flame Front structure of turbulent premixed CH4/H2/air Flames at various hydrogen frac- tions was investigated with OH-PLIF technique. A nozzle-type burner was used to achieve the stabilized turbulent premixed Flames. Hot-wire anemometer measurement and OH- PLIF observation were performed to measure the turbulent flow and detect the instanta- neous Flame Front structure, respectively. The hydrogen fractions of 0%, 5%, 10% and 20% were studied. Results show that the Flame Front structures of the turbulent premixed Flames are wrinkled Flame Front with small scale convex and concave structures compared to that of the laminar-Flame Front. The wrinkle intensity of Flame Front is promoted with the increase of turbulence intensity as well as hydrogen fraction. Hydrogen addition pro- motes the Flame intrinsic instability which leads to the active response of laminar Flame to turbulence and results in the much more wrinkled Flame Front structure. The value of ST/SL increases monotonically with the increase of u 0 /SL and hydrogen fraction. The increase of ST/SL with the increase of hydrogen fraction is mainly attributed to the diffusive-thermal instability effects represented by the effective Lewis number, Leeff. A general correlation between ST/SL and u0/SL is provided from the experimental data fitting in the form of ST/

Zuohua Huang - One of the best experts on this subject based on the ideXlab platform.

  • Flame Front identification and its effect on turbulent premixed Flames topology at high pressure
    Experimental Thermal and Fluid Science, 2019
    Co-Authors: Jinhua Wang, Meng Zhang, Min Chang, Shuang Chen, Zuohua Huang
    Abstract:

    Abstract Image processing is of primary importance in the laser diagnostic on turbulent combustion, which can provide quantitative information, such as velocity field, intermediate species profile. Turbulent premixed Flame Front indicates the Flame-turbulence interaction, can be decided from the OH-PLIF (Planar Laser Induced Fluorescence) technique due to the sharp increase of the OH distribution from unburned to burned region. In this paper, an adaptive threshold binarization method was proposed based on the local gray histogram of the OH-PLIF images when the signal-noise ratio is relatively low, i.e. turbulent Flames at intensive turbulence and high pressure. The noise was eliminated by seed-mediated growth to obtain the legible Flame Front. Effect of different Flame Front identification methods, namely global binarization method, the canny operator of Matlab and the proposed adaptive threshold binarization method, on the Flame structure parameters at various conditions was investigated. Results show that the Flame Fronts are seriously vague using the global binarization and the canny operator when the signal-noise ratio is low at intensive turbulence and high pressure, while continuous Flame Front can still be attracted by the proposed adaptive threshold binarization method. The turbulent Flame Front parameters from different methods are almost identical at weak turbulence and atmospheric pressure. While due to the noise introduced, the value of Flame brush thickness, Flame height and Flame surface density from the proposed method is smaller than that of other two methods at high pressure. The adaptive threshold binarization method can obtain a better Flame Front identification at low signal-noise ratio conditions, results in reasonable premixed turbulent Flame Front parameters at intensive turbulence and high pressure.

  • effect of h2o addition on the Flame Front evolution of syngas spherical propagation Flames
    Combustion Science and Technology, 2016
    Co-Authors: Jinhua Wang, Yongliang Xie, Xiao Cai, Yaohui Nie, Cheng Peng, Zuohua Huang
    Abstract:

    ABSTRACTAn experimental study on the cellular instability of spherical propagation syngas Flames with H2O addition was performed in a constant volume combustion bomb over a wide range of CO/H2 ratios at elevated pressures. Schlieren images were recorded to observe and analyze the Flame Front evolution of spherical propagation Flames. Results show that the cellular instability of syngas Flames is promoted at atmospheric pressure and suppressed at elevated pressure with H2O addition for syngas mixtures with CO/H2 ratio of 80/20. At elevated pressure, critical radius, beyond which Flame Front starts to accelerate, increases with H2O addition for syngas mixtures with higher CO/H2 ratios of 65/35 and 50/50, while decreases for syngas mixtures with lower CO/H2 ratios of 20/80 and 0/100. Critical Peclet number decreases with H2O addition for all of the mixtures. The acceleration exponent increases with the Flame radius and reaches a constant value at some points. This implies that both self-acceleration and self...

  • burning velocity and statistical Flame Front structure of turbulent premixed Flames at high pressure up to 1 0 mpa
    Experimental Thermal and Fluid Science, 2015
    Co-Authors: Jinhua Wang, Zuohua Huang, Meng Zhang, Shuang Chen, Senbin Yu, Hideaki Kobayashi
    Abstract:

    Abstract Statistical Flame Front structure of turbulent premixed Flames at high pressure up to 1.0 MPa was measured on a nozzle-type Bunsen burner with OH-PLIF technique. Turbulent burning velocity, Flame surface density and Flame brush thickness, as well as the local curvature and radius of curvature were derived from the experimental OH-PLIF images. Turbulence–Flame interaction was analyzed based on the geometric parameters combined with laminar Flame properties and turbulence length scales. Results show that the Flame wrinkles at high pressure are dominated by small scale cusps superimposed with large scale Flame branches which is a general characteristic of the turbulent premixed Flames at high pressure. S T / S L increases remarkably with u ′/ S L and the influence of elevated pressure on S T / S L is significant. This is mainly due to the increase of Flame Front area caused by the turbulence wrinkling. Flame surface density significantly increases with the increase of pressure indicating that there is a large amount of fine cusps and small wrinkles in the Flame Front at high pressure. This would be due to the enhancement of the Flame instability represented by effective Lewis number Le eff and Flame intrinsic instability scale l i . With the increase of turbulence intensity, the Σ at high pressure increases while slightly decreases at normal pressure. The most frequent length scale of the Flame Front moves to smaller value and the possibility increases with the increase of u ′/ S L for all pressures. The effect of Flame intrinsic instability on finer Flame Front at high pressure is mainly on the formation of a large number of convex structures which enlarge the effective contact surface between Flame Front and unburned reactants, resulting in the increase of S T / S L .

  • Flame Front structure of turbulent premixed Flames of syngas oxyfuel mixtures
    International Journal of Hydrogen Energy, 2014
    Co-Authors: Meng Zhang, Jinhua Wang, Zuohua Huang, Z L Wei, Hideaki Kobayashi
    Abstract:

    Abstract In order to investigate oxyfuel combustion characteristics of typical composition of coal gasification syngas connected to CCS systems. Instantaneous Flame Front structure of turbulent premixed Flames of CO/H2/O2/CO2 mixtures which represent syngas oxyfuel combustion was quantitatively studied comparing with CH4/air and syngas/air Flames by using a nozzle-type Bunsen burner. Hot-wire anemometer and OH-PLIF were used to measure the turbulent flow and detect the instantaneous Flame Front structure, respectively. Image processing and statistical analyzing were performed using the Matlab Software. Flame surface density, mean progress variable, local curvature radius, mean Flame volume, and Flame thickness, were obtained. Results show that turbulent premixed Flames of syngas possess wrinkled Flame Front structure which is a general feature of turbulent premixed Flames. Flame surface density for the CO/H2/O2/CO2 Flame is much larger than that of CO/H2/O2/air and CH4/air Flames. This is mainly caused by the smaller Flame intrinsic instability scale, which would lead to smaller scales and less Flame passivity response to turbulence presented by Markstain length, which reduce the local Flame stretch against turbulence vortex. Peak value of Possibility Density Function (PDF) distribution of local curvature radius, R, for CO/H2/O2/CO2 Flames is larger than those of CO/H2/O2/air and CH4/air Flames at both positive and negative side and the corresponding R of absolute peak PDF is the smallest. This demonstrates that the most frequent scale is the smallest for CO/H2/O2/CO2 Flames. Mean Flame volume of CO/H2/O2/CO2 Flame is smaller than that of CH4/air Flame even smaller than that of CO/H2/O2/air Flame. This would be due to the lower Flame height and smaller Flame wrinkles.

  • measurement on instantaneous Flame Front structure of turbulent premixed ch4 h2 air Flames
    Experimental Thermal and Fluid Science, 2014
    Co-Authors: Meng Zhang, Jinhua Wang, Zuohua Huang, Yongliang Xie, Wu Jin, Z L Wei, Hideaki Kobayashi
    Abstract:

    Abstract Instantaneous Flame Front structure of turbulent premixed CH 4 /H 2 /air Flames (hydrogen fraction of 0%, 5%, 10% and 20% by mole fraction) was investigated quantitatively using a nozzle-type Bunsen burner. Hot wire anemometer and OH-PLIF were used to measure the turbulent flow and detect the instantaneous Flame Front structure, respectively. Turbulent burning velocity, S T , Flame surface density, Σ , and mean Flame volume, V f , were calculated by processing the OH-PLIF images. Results show that the Flame Front structures of the turbulent premixed Flames are the wrinkled Flame Front and it becomes much finer with the increase of turbulence intensity as well as hydrogen fraction. The value of S T /S L significantly increases with the increase of u ′/ S L and it slightly increases with the increase of hydrogen fraction. Flame surface density profile are symmetric and gives its maximum value at about 〈 c 〉 = 0.5. Hydrogen addition slightly enhances the Σ and the tendency is more obvious under higher turbulence intensity. The decrease of Σ with the increase of turbulence intensity is mainly due to the effect of Flame volume. The mean Flame volume of Flame region obviously increases with the increase of turbulence intensity within the experimental range due to the increase in depth of the large scale Flame wrinkles and Flame height. Hydrogen addition is not a predominant factor within the hydrogen fraction range in this study.

Jinhua Wang - One of the best experts on this subject based on the ideXlab platform.

  • Flame Front identification and its effect on turbulent premixed Flames topology at high pressure
    Experimental Thermal and Fluid Science, 2019
    Co-Authors: Jinhua Wang, Meng Zhang, Min Chang, Shuang Chen, Zuohua Huang
    Abstract:

    Abstract Image processing is of primary importance in the laser diagnostic on turbulent combustion, which can provide quantitative information, such as velocity field, intermediate species profile. Turbulent premixed Flame Front indicates the Flame-turbulence interaction, can be decided from the OH-PLIF (Planar Laser Induced Fluorescence) technique due to the sharp increase of the OH distribution from unburned to burned region. In this paper, an adaptive threshold binarization method was proposed based on the local gray histogram of the OH-PLIF images when the signal-noise ratio is relatively low, i.e. turbulent Flames at intensive turbulence and high pressure. The noise was eliminated by seed-mediated growth to obtain the legible Flame Front. Effect of different Flame Front identification methods, namely global binarization method, the canny operator of Matlab and the proposed adaptive threshold binarization method, on the Flame structure parameters at various conditions was investigated. Results show that the Flame Fronts are seriously vague using the global binarization and the canny operator when the signal-noise ratio is low at intensive turbulence and high pressure, while continuous Flame Front can still be attracted by the proposed adaptive threshold binarization method. The turbulent Flame Front parameters from different methods are almost identical at weak turbulence and atmospheric pressure. While due to the noise introduced, the value of Flame brush thickness, Flame height and Flame surface density from the proposed method is smaller than that of other two methods at high pressure. The adaptive threshold binarization method can obtain a better Flame Front identification at low signal-noise ratio conditions, results in reasonable premixed turbulent Flame Front parameters at intensive turbulence and high pressure.

  • effect of h2o addition on the Flame Front evolution of syngas spherical propagation Flames
    Combustion Science and Technology, 2016
    Co-Authors: Jinhua Wang, Yongliang Xie, Xiao Cai, Yaohui Nie, Cheng Peng, Zuohua Huang
    Abstract:

    ABSTRACTAn experimental study on the cellular instability of spherical propagation syngas Flames with H2O addition was performed in a constant volume combustion bomb over a wide range of CO/H2 ratios at elevated pressures. Schlieren images were recorded to observe and analyze the Flame Front evolution of spherical propagation Flames. Results show that the cellular instability of syngas Flames is promoted at atmospheric pressure and suppressed at elevated pressure with H2O addition for syngas mixtures with CO/H2 ratio of 80/20. At elevated pressure, critical radius, beyond which Flame Front starts to accelerate, increases with H2O addition for syngas mixtures with higher CO/H2 ratios of 65/35 and 50/50, while decreases for syngas mixtures with lower CO/H2 ratios of 20/80 and 0/100. Critical Peclet number decreases with H2O addition for all of the mixtures. The acceleration exponent increases with the Flame radius and reaches a constant value at some points. This implies that both self-acceleration and self...

  • burning velocity and statistical Flame Front structure of turbulent premixed Flames at high pressure up to 1 0 mpa
    Experimental Thermal and Fluid Science, 2015
    Co-Authors: Jinhua Wang, Zuohua Huang, Meng Zhang, Shuang Chen, Senbin Yu, Hideaki Kobayashi
    Abstract:

    Abstract Statistical Flame Front structure of turbulent premixed Flames at high pressure up to 1.0 MPa was measured on a nozzle-type Bunsen burner with OH-PLIF technique. Turbulent burning velocity, Flame surface density and Flame brush thickness, as well as the local curvature and radius of curvature were derived from the experimental OH-PLIF images. Turbulence–Flame interaction was analyzed based on the geometric parameters combined with laminar Flame properties and turbulence length scales. Results show that the Flame wrinkles at high pressure are dominated by small scale cusps superimposed with large scale Flame branches which is a general characteristic of the turbulent premixed Flames at high pressure. S T / S L increases remarkably with u ′/ S L and the influence of elevated pressure on S T / S L is significant. This is mainly due to the increase of Flame Front area caused by the turbulence wrinkling. Flame surface density significantly increases with the increase of pressure indicating that there is a large amount of fine cusps and small wrinkles in the Flame Front at high pressure. This would be due to the enhancement of the Flame instability represented by effective Lewis number Le eff and Flame intrinsic instability scale l i . With the increase of turbulence intensity, the Σ at high pressure increases while slightly decreases at normal pressure. The most frequent length scale of the Flame Front moves to smaller value and the possibility increases with the increase of u ′/ S L for all pressures. The effect of Flame intrinsic instability on finer Flame Front at high pressure is mainly on the formation of a large number of convex structures which enlarge the effective contact surface between Flame Front and unburned reactants, resulting in the increase of S T / S L .

  • Flame Front structure of turbulent premixed Flames of syngas oxyfuel mixtures
    International Journal of Hydrogen Energy, 2014
    Co-Authors: Meng Zhang, Jinhua Wang, Zuohua Huang, Z L Wei, Hideaki Kobayashi
    Abstract:

    Abstract In order to investigate oxyfuel combustion characteristics of typical composition of coal gasification syngas connected to CCS systems. Instantaneous Flame Front structure of turbulent premixed Flames of CO/H2/O2/CO2 mixtures which represent syngas oxyfuel combustion was quantitatively studied comparing with CH4/air and syngas/air Flames by using a nozzle-type Bunsen burner. Hot-wire anemometer and OH-PLIF were used to measure the turbulent flow and detect the instantaneous Flame Front structure, respectively. Image processing and statistical analyzing were performed using the Matlab Software. Flame surface density, mean progress variable, local curvature radius, mean Flame volume, and Flame thickness, were obtained. Results show that turbulent premixed Flames of syngas possess wrinkled Flame Front structure which is a general feature of turbulent premixed Flames. Flame surface density for the CO/H2/O2/CO2 Flame is much larger than that of CO/H2/O2/air and CH4/air Flames. This is mainly caused by the smaller Flame intrinsic instability scale, which would lead to smaller scales and less Flame passivity response to turbulence presented by Markstain length, which reduce the local Flame stretch against turbulence vortex. Peak value of Possibility Density Function (PDF) distribution of local curvature radius, R, for CO/H2/O2/CO2 Flames is larger than those of CO/H2/O2/air and CH4/air Flames at both positive and negative side and the corresponding R of absolute peak PDF is the smallest. This demonstrates that the most frequent scale is the smallest for CO/H2/O2/CO2 Flames. Mean Flame volume of CO/H2/O2/CO2 Flame is smaller than that of CH4/air Flame even smaller than that of CO/H2/O2/air Flame. This would be due to the lower Flame height and smaller Flame wrinkles.

  • measurement on instantaneous Flame Front structure of turbulent premixed ch4 h2 air Flames
    Experimental Thermal and Fluid Science, 2014
    Co-Authors: Meng Zhang, Jinhua Wang, Zuohua Huang, Yongliang Xie, Wu Jin, Z L Wei, Hideaki Kobayashi
    Abstract:

    Abstract Instantaneous Flame Front structure of turbulent premixed CH 4 /H 2 /air Flames (hydrogen fraction of 0%, 5%, 10% and 20% by mole fraction) was investigated quantitatively using a nozzle-type Bunsen burner. Hot wire anemometer and OH-PLIF were used to measure the turbulent flow and detect the instantaneous Flame Front structure, respectively. Turbulent burning velocity, S T , Flame surface density, Σ , and mean Flame volume, V f , were calculated by processing the OH-PLIF images. Results show that the Flame Front structures of the turbulent premixed Flames are the wrinkled Flame Front and it becomes much finer with the increase of turbulence intensity as well as hydrogen fraction. The value of S T /S L significantly increases with the increase of u ′/ S L and it slightly increases with the increase of hydrogen fraction. Flame surface density profile are symmetric and gives its maximum value at about 〈 c 〉 = 0.5. Hydrogen addition slightly enhances the Σ and the tendency is more obvious under higher turbulence intensity. The decrease of Σ with the increase of turbulence intensity is mainly due to the effect of Flame volume. The mean Flame volume of Flame region obviously increases with the increase of turbulence intensity within the experimental range due to the increase in depth of the large scale Flame wrinkles and Flame height. Hydrogen addition is not a predominant factor within the hydrogen fraction range in this study.

Meng Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Flame Front identification and its effect on turbulent premixed Flames topology at high pressure
    Experimental Thermal and Fluid Science, 2019
    Co-Authors: Jinhua Wang, Meng Zhang, Min Chang, Shuang Chen, Zuohua Huang
    Abstract:

    Abstract Image processing is of primary importance in the laser diagnostic on turbulent combustion, which can provide quantitative information, such as velocity field, intermediate species profile. Turbulent premixed Flame Front indicates the Flame-turbulence interaction, can be decided from the OH-PLIF (Planar Laser Induced Fluorescence) technique due to the sharp increase of the OH distribution from unburned to burned region. In this paper, an adaptive threshold binarization method was proposed based on the local gray histogram of the OH-PLIF images when the signal-noise ratio is relatively low, i.e. turbulent Flames at intensive turbulence and high pressure. The noise was eliminated by seed-mediated growth to obtain the legible Flame Front. Effect of different Flame Front identification methods, namely global binarization method, the canny operator of Matlab and the proposed adaptive threshold binarization method, on the Flame structure parameters at various conditions was investigated. Results show that the Flame Fronts are seriously vague using the global binarization and the canny operator when the signal-noise ratio is low at intensive turbulence and high pressure, while continuous Flame Front can still be attracted by the proposed adaptive threshold binarization method. The turbulent Flame Front parameters from different methods are almost identical at weak turbulence and atmospheric pressure. While due to the noise introduced, the value of Flame brush thickness, Flame height and Flame surface density from the proposed method is smaller than that of other two methods at high pressure. The adaptive threshold binarization method can obtain a better Flame Front identification at low signal-noise ratio conditions, results in reasonable premixed turbulent Flame Front parameters at intensive turbulence and high pressure.

  • burning velocity and statistical Flame Front structure of turbulent premixed Flames at high pressure up to 1 0 mpa
    Experimental Thermal and Fluid Science, 2015
    Co-Authors: Jinhua Wang, Zuohua Huang, Meng Zhang, Shuang Chen, Senbin Yu, Hideaki Kobayashi
    Abstract:

    Abstract Statistical Flame Front structure of turbulent premixed Flames at high pressure up to 1.0 MPa was measured on a nozzle-type Bunsen burner with OH-PLIF technique. Turbulent burning velocity, Flame surface density and Flame brush thickness, as well as the local curvature and radius of curvature were derived from the experimental OH-PLIF images. Turbulence–Flame interaction was analyzed based on the geometric parameters combined with laminar Flame properties and turbulence length scales. Results show that the Flame wrinkles at high pressure are dominated by small scale cusps superimposed with large scale Flame branches which is a general characteristic of the turbulent premixed Flames at high pressure. S T / S L increases remarkably with u ′/ S L and the influence of elevated pressure on S T / S L is significant. This is mainly due to the increase of Flame Front area caused by the turbulence wrinkling. Flame surface density significantly increases with the increase of pressure indicating that there is a large amount of fine cusps and small wrinkles in the Flame Front at high pressure. This would be due to the enhancement of the Flame instability represented by effective Lewis number Le eff and Flame intrinsic instability scale l i . With the increase of turbulence intensity, the Σ at high pressure increases while slightly decreases at normal pressure. The most frequent length scale of the Flame Front moves to smaller value and the possibility increases with the increase of u ′/ S L for all pressures. The effect of Flame intrinsic instability on finer Flame Front at high pressure is mainly on the formation of a large number of convex structures which enlarge the effective contact surface between Flame Front and unburned reactants, resulting in the increase of S T / S L .

  • Flame Front structure of turbulent premixed Flames of syngas oxyfuel mixtures
    International Journal of Hydrogen Energy, 2014
    Co-Authors: Meng Zhang, Jinhua Wang, Zuohua Huang, Z L Wei, Hideaki Kobayashi
    Abstract:

    Abstract In order to investigate oxyfuel combustion characteristics of typical composition of coal gasification syngas connected to CCS systems. Instantaneous Flame Front structure of turbulent premixed Flames of CO/H2/O2/CO2 mixtures which represent syngas oxyfuel combustion was quantitatively studied comparing with CH4/air and syngas/air Flames by using a nozzle-type Bunsen burner. Hot-wire anemometer and OH-PLIF were used to measure the turbulent flow and detect the instantaneous Flame Front structure, respectively. Image processing and statistical analyzing were performed using the Matlab Software. Flame surface density, mean progress variable, local curvature radius, mean Flame volume, and Flame thickness, were obtained. Results show that turbulent premixed Flames of syngas possess wrinkled Flame Front structure which is a general feature of turbulent premixed Flames. Flame surface density for the CO/H2/O2/CO2 Flame is much larger than that of CO/H2/O2/air and CH4/air Flames. This is mainly caused by the smaller Flame intrinsic instability scale, which would lead to smaller scales and less Flame passivity response to turbulence presented by Markstain length, which reduce the local Flame stretch against turbulence vortex. Peak value of Possibility Density Function (PDF) distribution of local curvature radius, R, for CO/H2/O2/CO2 Flames is larger than those of CO/H2/O2/air and CH4/air Flames at both positive and negative side and the corresponding R of absolute peak PDF is the smallest. This demonstrates that the most frequent scale is the smallest for CO/H2/O2/CO2 Flames. Mean Flame volume of CO/H2/O2/CO2 Flame is smaller than that of CH4/air Flame even smaller than that of CO/H2/O2/air Flame. This would be due to the lower Flame height and smaller Flame wrinkles.

  • measurement on instantaneous Flame Front structure of turbulent premixed ch4 h2 air Flames
    Experimental Thermal and Fluid Science, 2014
    Co-Authors: Meng Zhang, Jinhua Wang, Zuohua Huang, Yongliang Xie, Wu Jin, Z L Wei, Hideaki Kobayashi
    Abstract:

    Abstract Instantaneous Flame Front structure of turbulent premixed CH 4 /H 2 /air Flames (hydrogen fraction of 0%, 5%, 10% and 20% by mole fraction) was investigated quantitatively using a nozzle-type Bunsen burner. Hot wire anemometer and OH-PLIF were used to measure the turbulent flow and detect the instantaneous Flame Front structure, respectively. Turbulent burning velocity, S T , Flame surface density, Σ , and mean Flame volume, V f , were calculated by processing the OH-PLIF images. Results show that the Flame Front structures of the turbulent premixed Flames are the wrinkled Flame Front and it becomes much finer with the increase of turbulence intensity as well as hydrogen fraction. The value of S T /S L significantly increases with the increase of u ′/ S L and it slightly increases with the increase of hydrogen fraction. Flame surface density profile are symmetric and gives its maximum value at about 〈 c 〉 = 0.5. Hydrogen addition slightly enhances the Σ and the tendency is more obvious under higher turbulence intensity. The decrease of Σ with the increase of turbulence intensity is mainly due to the effect of Flame volume. The mean Flame volume of Flame region obviously increases with the increase of turbulence intensity within the experimental range due to the increase in depth of the large scale Flame wrinkles and Flame height. Hydrogen addition is not a predominant factor within the hydrogen fraction range in this study.

  • Measurement of the instantaneous Flame Front structure of syngas turbulent premixed Flames at high pressure
    Combustion and Flame, 2013
    Co-Authors: Jinhua Wang, Zuohua Huang, Taku Kudo, Meng Zhang, Hideaki Kobayashi
    Abstract:

    Abstract Instantaneous Flame Front structure of syngas turbulent premixed Flames including the local radius of curvature, the characteristic radius of curvature, the fractal inner cutoff scale and the local Flame angle were derived from the experimental OH-PLIF images. The CO/H 2 /CO 2 /air Flames as a model of syngas/air combustion were investigated at pressure of 0.5 MPa and compared to that of CH 4 /air Flames. The convex and concave structures of the Flame Front were detected and statistical analysis including the PDF and ADF of the local radius of curvature and local Flame angle were conducted. Results show that the Flame Front of turbulent premixed Flames at high pressure is a wrinkled Flame Front with small scale convex and concave structures superimposed with large scale Flame branches. The convex structures are much more frequent than the concave ones on Flame Front which reflects a general characteristic of the turbulent premixed Flames at high pressure. The syngas Flames possess much wrinkled Flame Front with much smaller fine cusps structure compared to that of CH 4 /air Flames and the main difference is on the convex structure. The effect of turbulence on the general wrinkled scale of Flame Front is much weaker than that of the smallest wrinkled scale. The general wrinkled scale is mainly dominated by the turbulence vortex scale, while, the smallest wrinkled scale is strongly affected by the Flame intrinsic instability. The effect of Flame intrinsic instability on Flame Front of turbulent premixed Flame is mainly on the formation of a large number of convex structure propagating to the unburned reactants and enlarge the effective contact surface between Flame Front and unburned reactants.