為了因應高效率低汙染燃燒器操作上的先天限制問題，例如貧油燃燒所產生的火焰不穩定現象，低成本的高電壓電子性放電技術已被廣泛地探討與實際地應用在輔助火焰燃燒與增強火焰穩駐特性。本論文主要是藉由施加重覆式DC高電壓脈衝於一尖端狀黃銅電極以產生電暈放電來探討不同的重覆放電頻率與放電極性對丙烷紊流噴流跳脫火焰的穩駐特性之影響。實驗結果顯示，當施加正極性的電壓脈衝與較高的重覆頻率時，跳脫火焰底端能穩駐於更高速的上游流場甚至能往上游傳遞進而回駐於噴嘴管口，此意謂著脈衝電暈放電能延伸火焰的穩駐極限並抑制火焰不穩定現象的發生。
因此在此論文中，跳脫火焰底端與脈衝電暈放電的交互作用過程為主要的研究目標，利用高速攝影機與二維粒子影像測速系統(Particle image velocimetry)同步對火焰底端的三歧火焰回駐傳遞過程做移動速度之量測與瞬時流場速度分佈之分析，經由比較不同放電頻率的火焰回駐影像，發現在回駐過程中都會經歷兩種不同的電子脈衝放電作用模式影響: 電場放電與電暈放電。此外分析火焰底端移動速度與瞬時流場速度分佈發現在高頻放電火焰能回駐的情況下，主導跳脫火焰底端回駐特性的三歧火焰傳遞速度會大於丙烷的當量層流火焰燃燒速度，此機制與火焰回駐過程所誘發的電暈放電作用模式有很大的相關性。

Among the recently prevailing flame stabilization enhancement by electric field and plasma, repetitive D.C. electric pulse discharge is applied to a turbulent lifted diffusion jet flame to improve the reattachment limit in this study. The present study demonstrates the feasibility of enhancement in lifted jet flame reattachment by applying a repetitive high-voltage pulsed DC discharge to a proposed electrode configuration. To characterize experimentally the stability and the reattachment behaviors and process of lifted flames under the electric pulse effect with a proposed electrode configuration is the main objective. The effects of pulse repetition frequency (PRF) and diverse voltage polarity on flame are investigated. The result shows the reattachment velocity is enhanced more than double for positive polarity case with PRF of 1500 Hz as compared to the without discharge case. According to the sequence high speed images, the time history of flame base trace and displacement speed are presented and compared for 200 Hz and 1500 Hz cases under applying positive DC pulses. Both processes could be divided into two different types of electrical discharge. The electrical corona plasma is observed during upstream propagation process for both cases, and it plays a key role in enhancing flame displacement speed. Furthermore, in order to reveal the gas velocity distribution for the complicated flame-flow interaction during rapid reattachment process, a conditional particle image velocimetry (cond-PIV) measurement is used to analyze the detailed flame-flow interaction of complete reattachment process. By simultaneously using shuttered PIV and high speed camera imaging to record the instantaneous planar gas velocity field measurement conditioned on high speed sequence images. The results show that the instantaneous axial velocity is low and suitable for flame upstream propagation and reattachment. Finally the conditionally instantaneous leading-edge propagation speed is enhanced and exceeds 3 times that of stoichiometric laminar flame speed for 1500 Hz case, which leads to flame reattachment.

摘要 I
ABSTRACT III
CONTENTS V
LIST OF FIGURES VII
NOMENCLATURE XI
CHAPTER I INTRODUCTION 1
1.1 Background 1
1.2 Atmospheric pressure plasmas 4
1.3 Lifted diffusion jet flame 7
1.4 Thesis Outline 11
CHAPTER II ELECTRICALLY DISCHARGE-ASSISTED COMBUSTION 13
2.1 Stabilization enhancement by DC/AC electric fields 13
2.2 Plasma-assisted flame stabilization 16
2.3 Motivation and Objectives 19
CHAPTER III EXPERIMENTAL APPARATUS AND METHODS 23
3.1 Burner and pulsed electrical discharge system 23
3.2 High-speed video camera imaging measurement 27
3.3 Conditional 2D velocity measurement system 29
CHAPTER IV STABILIZATION ENHANCEMENT BY PULSE DC DISCHARGE 34
4.1 Modification of flame stabilization behavior 34
4.2 Pulsed-discharge effect on liftoff height and reattachment stability 37
CHAPTER V REATTACHMENT ENHANCEMENT BY POSITIVE DC PULSE DISCHARGE 40
5.1 Reattachment process with applying various repetition frequency 40
5.2 Conditional instantaneous velocity field during reattachment process 45
5.3 Enhancement of leading-edge flame propagation velocity 50
5.4 Summary 54
CHAPTER VI CONCLUSIONS 56
REFERENCES 59
FIGURES 65

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