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An Experimental and Computational Study of Burner

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An Experimental and Computational Study of Burner AN EXPERIMENTAL AND COMPUTATIONAL STUDY OF BURNER- GENERATED LOW STRETCH GASEOUS DIFFUSION FLAMES by BAI HAN Submitted in partial fulfillment of the requirements For the degree of Doctor of Philosophy Dissertation Adviser: Dr. Chih-Jen Sung Department of Mechanical and Aerospace Engineering CASE WESTERN RESERVE UNIVERSITY May, 2005 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the dissertation of ______________________________________________________ candidate for the Ph.D. degree *. (signed)_______________________________________________ (chair of the committee) ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ (date) _______________________ *We also certify that written approval has been obtained for any proprietary material contained therein. Table of Contents 1 LIST OF TABLES . 6 LIST OF FIGURES . 7 ACKNOWLEDGEMENTS . 14 LIST OF ABBREVIATIONS . 15 ABSTRACT . 23 CHAPTER 1 INTRODUCTION . 25 1.1 Diffusion Flame Structure and Response 26 1.2 Effects of Stretch on Diffusion Flames 31 1.2.1 Flame Stretch 31 1.2.2 Counterflow Diffusion Flames 31 1.2.2.1 Counterflow Facilities 33 1.2.2.1.1 Opposed Jet Burner 34 1.2.2.1.2 “Tsuji” Burner 35 1.2.2.2 Studies of Counterflow Diffusion Flames 36 1.2.2.2.1 Steady Counterflow Diffusion Flames 36 1.2.2.2.2 Instabilities in Counterflow Diffusion Flames 38 1.3 Studies of Low Stretch Diffusion Flame 41 1.3.1 Low Stretch Diffusion Flame Behavior 41 1.3.2 Diffusion Flame under Micro-gravity 45 1.3.3 Alternative Low-Stretch Diffusion Flame Configuration 46 1 1.3.4 Flame Instabilities of Low Stretch Diffusion Flames 48 1.4 Motivations and Objectives of Study 50 1.4.1 Motivations 50 1.4.2 Objectives 51 CHAPTER 2 EXPERIMENTAL SETUP . 54 2.1 Definitions 54 2.1.1 Buoyancy-Induced Stretch Rate 54 2.1.2 Nominal Fuel Mixture Injection Speed 56 2.2 Burner Facility 57 2.2.1 Overview 57 2.2.2 Porous Burner 60 2.2.3 Burner Body 62 2.2.4 Experimental Operation 62 2.2.5 Demonstration of Quasi-1D Low-stretch Diffusion Flames 64 2.2.6 Uncertainty Analysis 66 2.2.6.1 Repeatability 66 2.2.6.2 Flow Rate Control 67 CHAPTER 3 OPTICAL DIAGNOSTICS SYSTEMS . 68 3.1 Spontaneous Raman Spectroscopy 70 3.1.1 Experimental Setup and Capability 70 3.1.2 Quantitative Temperature Measurement 78 2 3.1.3 Qualitative Species Measurement 81 3.1.4 Uncertainty Analysis for Raman Temperature Measurements 82 3.1.4.1 Uncertainty of Spatial Location Determination 82 3.1.4.1.1 Mechanical Translation System 83 3.1.4.1.2 Steering Effect 83 3.1.4.2 Uncertainty of Temperature Measurement 84 3.2 OH-PLIF (Planar Laser-Induced Fluorescence) 86 3.2.1 Overview 86 3.2.2 Experimental Setup 88 3.2.3 Data Analysis 92 3.3 IR Imaging 93 3.3.1 Important Factors of IR Camera 94 3.3.2 Surface Temperature Measurement 97 3.4 Chemiluminescence Imaging 101 3.4.1 Experimental Facilities 101 3.4.2 Data Analysis 102 CHAPTER 4 NUMERICAL METHODOLOGY . 106 4.1 Justification of Stagnation-Point Boundary Layer Model 107 4.2 Flame Radiation Model 109 4.2.1 Overview 109 4.2.2 Radiation Modeling 110 4.3 Numerical Modeling 114 3 4.3.1 Formulation 114 4.3.1.1 Assumptions 114 4.3.1.2 Governing Equations 114 4.3.2 Transformed Governing Equations 116 4.3.2.1 Similarity Transformation 116 4.3.2.2 Boundary Conditions 117 4.3.2.3 Heat Balance at Burner Surface 118 4.3.3 Numerical Method 120 CHAPTER 5 RESULTS AND DISCUSSION . 122 5.1 Uniformity of Quasi-1D Diffusion Flames 122 5.2 Flammability and Instability Map of Low Stretch Diffusion Flames 126 5.2.1 Sooting Flame Boundary 127 5.2.2 Extinction Limits Boundary 128 5.2.2.1 Burner Heat Loss Extinction 129 5.2.2.2 Radiative Extinction 130 5.3 Detailed Structure of Quasi-1D Diffusion Flames 131 5.3.1 Temperature Profiles 131 5.3.1.1 Thermocouple Measurement 131 5.3.1.1.1 Radiation Correction 132 5.3.1.1.2 Temperature Distributions of Steady Flames 134 5.3.1.2 Raman Scattering Measurement 136 5.3.1.3 Comparison of Measured Temperature Profiles 142 4 5.3.2 Qualitative Species Distributions 155 5.4 Multi-Dimensional Flame Instabilities 163 5.4.1 Instability Patterns 163 5.4.2 Mechanisms of Instability of Low-stretch Diffusion Flames 171 5.4.2.1 Rayleigh-Taylor Instability 171 5.4.2.2 Thermal-Diffusive Instability 172 5.4.2.3 Instability Related to Heat Los 173 5.5 Computational Results 174 5.5.1 Effects of Three Controlling Parameter 174 5.5.2 Comparison of Experimental and Computational Temperature Profiles 178 5.5.3 Extinction Limits 182 CHAPTER 6 SUMMARY AND RECOMMENDATION FOR FUTURE WORKS 192 6.1 Summary 192 6.2 Future Works 195 APPENDIX A Fundamentals of Raman Scattering . 197 APPENDIX B Fundamentals of LIF/PLIF . 201 APPENDIX C Modeling for Spectral and Directional Radiative Heat Transfer . 206 BIBLIOGRAPHY . 211 5 List of Tables Table 5.1 Five representative cases for Raman measurement Table 5.2 Comparison of experimental data and simulated results for all five cases Table 5.3 Heat flux analysis at two extinction limits 6 List of Figures Figure 1.1 Flame response for an adiabatic diffusion flame system-“S-curve” (Nanduri, 2002). It shows the extinction and ignition conditions. Figure 1.2 Radiative diffusion flame response-“flame isola” (Nanduri, 2002). It shows the radiative extinction limit and the blow-off extinction limit. Figure 1.3 Schematic of opposed-jet burner configuration. Figure 1.4 Schematic of Tsuji type burner configuration. Figure 2.1 Schematic of present experimental setup. R is the radius of curvature of burner surface. Figure 2.2 Diagonal view from underneath of the present burner, including a quasi- one dimensional low-stretch diffusion flame. Figure 2.3 Side-views of steady quasi-1D flames under various nitrogen dilution levels (in terms of mole fraction). It shows the uniformity of the quasi-1D flames at different conditions. Figure 3.1 Experimental setup of Raman scattering system. Figure 3.2 Schematic of Raman scattering setup. Figure 3.3 Picture showing the laser beam (green line in the middle) and a flame (bottom) along with a burner head (top) and scale. For this demonstration flame, the nitrogen dilution is 75% and the fuel mixture injection speed is 1.00 cm/s. Figure 3.4 Picture of optical collection system. 7 Figure 3.5 Comparison of experimental and theoretical spectra at the “best-fit” temperature of 1530±25K. The experimental data are taken at 11.2 mm away from burner surface in a diffusion flame (75% nitrogen/ 25% methane burning in air), with fuel mixture injection speed of 1.10 cm/s. Figure 3.6 Raman spectra for the diluted methane/air diffusion flame. The dilution level is 75% nitrogen and the fuel mixture injection speed is 1.10cm/s. (a) Spectra at different locations marked in (b). (c) Nitrogen spectra for this case at different locations. Figure 3.7 Comparison of experimental spectrum and theoretical Spectra at different temperatures for a diffusion flame with 40%N2 /60%CH4 burning in air. The fuel injection speed is 0.30 cm/s and the position of measurement is 6.0 mm away from the burner surface. Figure 3.8 Schematic of OH-PLIF system. Figure 3.9 Schematic of laser sheet generation optics. Figure 3.10 Flow chart of controlling system for OH-PLIF measurements. Figure 3.11 Emissivity of the bronze porous plate calibrated by an imbedded thermocouple. Figure 3.12 Direct IR images taken from the bottom of the burner. (a) IR image after the flame is extinguished. (b) IR image for the combination of flame and burner surface. Figure 3.13 Time variation of the burner surface temperature after the flame is extinguished at time=0. Symbols are the mean temperature in the core 8 region (cf., Fig. 3.12) obtained by the IR camera. Line denotes the result using linear regression. Figure 3.14 Side chemiluminescence image across the flame. Nitrogen dilution is 75% and fuel mixture injection speed is 1.10 cm/s. Figure 3.15 Normalized chemiluminescence distribution across the flame. Nitrogen dilution is 75% and fuel mixture injection speed is 1.10 cm/s. Figure 4.1 Configuration of the present quasi-one-dimensional diffusion flame. Figure 4.2 Schematic of energy balance at the burner surface. Figure 5.1 (a) OH-PLIF image of a steady quasi-1D flame. (b) Comparison of OH- PLIF intensity profiles at varying radial locations. Figure 5.2 Steady diffusion flame standoff distance, OH-FWHM thickness, and burner surface temperature as a function of fuel mixture injection speed: (a) 25% CH4/75% N2 and (b) 60% CH4/40% N2. Figure 5.3 Flammability and instability diagram for the present low-stretch methane diffusion flames. Nitrogen dilution represents the nitrogen mole fraction in fuel mixture. Shaded regions represent the flame instability conditions. Figure 5.4 Schematic of the thermocouple configuration used in this study. Figure 5.5 Comparison of thermocouple-measured temperature distributions at different fuel mixture injection speeds for the 60%CH4/40%N2 mixture. Figure 5.6 Five selected cases for detailed Raman scattering measurement. Figure 5.7 Averaged (5000 shots) Raman spectra at varying distance from the burner surface for Case A (40% nitrogen dilution and 0.55 cm/s fuel mixture injection speed). 9 Figure 5.8 Averaged (5000 shots) Raman spectra of nitrogen at varying distance from the burner surface for Case A (40% nitrogen dilution and 0.55 cm/s fuel mixture injection speed).
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