보염기로 안정화된 음향가진 예혼합 화염의 날림 메커니즘에 대한 실험적 연구

학위논문 (석사)-- 서울대학교 대학원 : 기계항공공학부, 2014. 2. 윤영빈.Flame blowoff phenomenon in combustor with bluff-body has been a topic of extensive research such as gas turbine, rocket, ramjet, and so on. The blowoff generally occurs when the chemical reaction time scale for ignition exceeds the characteristic flow time of unburned reactant. In the process of the blowoff, external acoustic excitation has a significant impact on the blowoff conditions and structural features of the flame. However, there has been almost no research on blowoff in premixed combustor when external excitation is present. In this study, blowoff was investigated in a ducted combustor with the bluff-body when acoustic excitation was forced. Natural gas mainly composed of methane was used as fuel. Lowering the equivalence ratio, lean blowoff was to occur. Blowoff equivalence ratio was measured with varying m ̇air, excitation frequency and sound pressure to analyze the blowoff. As a result, we confirmed that the blowoff equivalence ratio was increased at specific frequency. This frequency is determined as a frequency related to the frequency of shear layer, therefore flame images were taken for measurement of the frequency on the flame. To observe the flame structure, OH* chemiluminescence was used. Chemiluminescence images were analyzed by applying POD (Proper Orthogonal Decomposition) algorithm to obtain the dominant mode and the frequency of shear layer. Depending on the experimental conditions, blowoff equivalence ratio was valued very differently. Vortex frequency behind the bluff-body and resonance effect in combustor are the main factors that affect the blowoff equivalence ratios with the excitation. As a final result, we defined the blowoff mechanism with and without external excitation based on the measured equivalence ratio values and image analysis.Contents Abstract i Contents iii List of Figures v List of Tables vii Nomenclature viii Chapter 1 INTRODUCTION 1 1.1 Bluff-Body-Stabilized Flame 1 1.2 Blowoff 3 1.3 Excitation Effect 4 Chapter 2 APPARATUS & EXPERIMENTAL METHOD 6 2.1 Apparatus 6 2.1.1 Overall Configuration 6 2.1.2 Acoustically-Forcing System 9 2.1.3 Data Acquisition System 10 2.2 Experimental Method 11 2.2.1 Blowoff Method 11 2.2.2 OH* Chemiluminescence 12 2.2.3 POD Algorithm 13 2.3 Experimental Condition 14 Chapter 3 RESULT & DISCUSSION 15 3.1 Flammable Range 15 3.2 Blowoff Equivalence Ratio 17 3.2.1 Sound Pressure Effect 17 3.2.2 Air Mass Flowrate Effect 19 3.3 Image Analysis 22 3.3.1 Blowoff without External Excitation 22 3.3.2 Blowoff with External Excitation 25 3.4 POD Analysis 28 3.4.1 Vortex Shedding Frequency 28 3.4.2 Comparative Analysis 32 3.5 Blowoff Mechanism 34 Chapter 4 CONCLUSION 36 Appendix A Voltage Adjustment 38 Appendix B Sound Pressure Level 40 Appendix C Acoustic Resonance 42 Bibliography 44 Abstract in Korean 47Maste

Characteristics and process optimization of anti-hypertensive peptides derived from soybean foods

학위논문(박사)--서울대학교 대학원 :식품공학과,1997.Docto