臺灣博碩士論文加值系統

本文中透過實驗觀察、理論預測以及數值模擬等方法對內徑從186到778微米的不鏽鋼管上所穩駐的微噴流甲烷擴散火燄做探討。由於微噴流火焰可以被應用到許多微裝置上做為動力源，其尺寸大小與能否提供微裝置運轉所需的最小能量，是微火焰能否應用在微裝置上的最主要限制，所以本研究首先著重在對火燄外型、火焰長度以及熄滅極限的探討。實驗量測到的火燄外型、火焰長度以及近熄滅時的燃料流速將與多種理論模式所預測及數值模擬所得結果相互比較，結果顯示僅有Roper提出的噴流火焰模式可以成功的被應用來預測微噴流甲烷擴散火焰的火焰高度及近熄滅時燃料流速。搭配Smooke提出的化學反應機構所得到的數值模擬與實驗量測所得的結果非常吻合，藉由數值模擬結果顯示，微噴流甲烷擴散火焰在接近熄滅極限時的火焰結構仍與擴散火焰相同，而噴嘴的材質對於火焰與噴嘴管壁之間的間距大小有明顯影響。

由於微噴流甲烷擴散火焰的火焰結構與常尺寸下的噴流火焰有許多不同，最明顯可見的就是其近乎圓形的火焰外型及漂浮在噴嘴管口上方的火焰；本研究採用完整的甲烷化學反應機構GRI-Mech3.0來針對微噴流甲烷擴散火焰與噴嘴之間的火焰結構作詳細探討，結果顯示漂浮的微噴流甲烷擴散火焰並非由雙重火焰或三歧火焰的結構所穩駐，而是由於噴嘴管壁的熱損失而在火燄底部與管壁間生成許多的HO2等中間產物，由於該特殊的火焰結構，在火燄底部形成一個高熱釋放率的區域，快速的熱釋放供給噴嘴管壁的熱損失以及維持火焰反應的持續進行，進而形成漂浮在噴嘴管口上的微噴流甲烷擴散火焰。

本研究對微噴流甲烷擴散火焰做詳細探討，所得結論可做為後續應用微火燄於各種微裝置之參考。

Characteristics of microjet methane diffusion flames stabilized on top of the vertically oriented, stainless-steel tubes with an inner diameter ranging from 186 to 778 �慆 are investigated experimentally, theoretically, and numerically. Of particular interest are the flame shape, flame length, and quenching limit, as they may be related to the minimum size and power of the devices in which such flames would be used for future micro power generation. Experimental measurements of the flame shape, flame length, and quenching velocity are compared with theoretical predictions as well as detailed numerical simulations. Comparisons of the theoretical predictions with measured results show that only Roper’s model can satisfactorily predict the flame height and quenching velocity of microjet methane flames. Detailed numerical simulations, using skeletal chemical kinetic mechanism, of the flames stabilized at the tip of d = 186, 324, and 529 �慆 tubes are performed to investigate the flame structures and the effects of burner materials on the standoff distance near extinction limit. The computed flame shape and flame length for the d = 186 �慆 flame are in excellent agreement with experimental results. Numerical predictions of the flame structures strongly suggest that the flame burns in a diffusion mode near the extinction limit. The calculated OH mass fraction isopleths indicate that different tube materials have a minor effect on the standoff distance, but influence the quenching gap between the flame and the tube.

The flame structure and stabilization mechanism of a microjet methane diffusion flame near extinction are numerically investigated using multi-component transport model coupled with GRI-Mech 3.0 chemical kinetic mechanisms. Of particular interest is the flame structure in the standoff region, as it would directly relate to the mixing, diffusion, and chemical kinetic processes as well as flame stabilization. Neither a double flame nor a triple flame is observed in the computed structures, suggesting that the standoff flame is stabilized by the hot zone that connects to the reaction kernel, through the formation of HO2 layer and subsequent key radical reactions.

誌謝 i
摘要 ii
ABSTRACT xi
CONTENTS xiii
LIST OF TABLES xv
LIST OF FIGURES xvi
NOMENCLATURE xx
CHAPTER I INTRODUCTION 1
1-1 Background 1
1-2 Diffusion Flame 2
1-3 Microjet Diffusion Flame 2
1-4 Motivation and Objective 4
1-5 Thesis Outline 5
CHAPTER II METHODOLOGY 6
2-1 Experimental Setup 6
2-1.1 Burner and Fuel System 6
2-1.2 Image Capture System 6
2-1.3 2D LIPF System 7
2-1.4 Raman System 8
2-2 Mathematical Formulation 9
2-2.1 Numerical Simulation 10
2-2.2 Theoretical Models 12
CHAPTER III HYDROGEN JET DIFFUSION FLAMES 16
3-1 Introduction 16
3-2. Experimental Setup for Hydrogen Jet Diffusion Flames 18
3-2.1 UV Raman/LIPF System 19
3-3 Numerical Simulation for Hydrogen Jet Diffusion Flames 21
3-4 Results and Discussion 23
3-4.1 Flame Visualization, OH Imaging, and OH Simulation 23
3-4.2 Structures of the Re = 330 Flame 24
3-4.3. Structures of the Re = 30 Flame 27
3-4.4. Effects of Burner Wall Boundary Conditions on Computed Results 29
3-5. Summary 31
CHAPTER IV GENERAL CHARACTERISTICS OF MICROJET METHANE DIFFUSION FLAMES 33
4-1 Introduction 33
4-2 Flame Visualization 34
4-3 Verification of Theoretical Models 35
4-3.1 Flame Shape 35
4-3.2 Flame Length 36
4-3.3 Quenching Velocity 39
4-4 Numerical Simulations of the d = 186 �慆 Flames 40
4-4.1 Flame Shape and Flame Length 40
4-4.2 Flame Structure near Extinction 41
4-5 Effect of Burner Wall Boundary Condition on the Standoff Distance 46
4-6 Summary 47
CHAPTER V FLAME STRUCTURE AND STABILIZATION MECHANISM 48
5-1 Introduction 48
5-1.1 Flame Image 48
5-1.2 Numerical Simulation 49
5-2 Results and Discussion 50
5-2.1 Flame Height Prediction 50
5-2.2 Validation of Simulation 51
5-2.3 Flame Structure 52
5-3 Stabilization Mechanism 55
CHAPTER VI CLOSURE 60
6-1 Conclusions 60
6-2 Future Work 61
REFERENCE 63
TABLES 69
FIGURES 80
PUBLICATION LIST 127
VITA 129
著作權聲明 130

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