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λ μ΄μ λμ κ³μΈ‘μ μ΄μ©ν Puffed νμΌμ ꡬ쑰μ νΉμ±μ κ΄ν μ€νμ μ°κ΅¬
νμλ
Όλ¬Έ (μμ¬)-- μμΈλνκ΅ λνμ : 곡과λν κΈ°κ³ν곡곡νλΆ, 2019. 2. μ€μλΉ.μ΄ λ°©μΆλκ³Ό νμΌλ©΄ μ¬μ΄μλ μΌλ ¨μ κ΄κ³κ° μ‘΄μ¬νκΈ° λλ¬Έμ μ°μλΆμμ μ λν μμΈ‘μ μν΄μλ νμΌ κ΅¬μ‘°μ κ΄ν μ°κ΅¬κ° νμνλ€. μ°μλΆμμ μ μ΄λ₯Ό ꡬμ±νλ μΈ κ°μ§ μλμ΄ μμ± νΌλλ°± 루νλ₯Ό νμ±νμμ λ λ°μ λ° μ¦ννκΈ° λλ¬Έμ κ°κ°μ μΈ κ°μ§ μλμ λν΄ μμΈν κ³ λ €ν νμκ° μλ€. λ³Έ μ°κ΅¬μμλ μ°μλΆμμ μ κ΄ν μ°κ΅¬μ μΌνμΌλ‘ puffed νμΌμ΄λΌ λΆλ¦¬λ νΉμ΄ νμΌ κ΅¬μ‘°μ κ΄ν μ°κ΅¬λ₯Ό μννμλ€. μ΄μ μ°κ΅¬μμ, κΉ λ±[1]μ νΉμ μ£Όνμ λ° μ
λ ₯ μλ μλ μμμμ puffed νμΌμ΄ λ°μνλ κ²μ νμΈνμλ€. λ°λΌμ λ³Έ μ°κ΅¬μμλ μ΄λ¬ν puffed νμΌμ κ΄ν λ°μ μμΈκ³Ό μλ΅ νΉμ±μ κ΄ν΄ μ°κ΅¬νμλ€. κ·Έμ λ°λΌ, OH-PLIF μ PIV λμ κ³μΈ‘μ μννμλ€.
μ€νμ νμ° νμΌμ ν μ’
λ₯μΈ, μ°λ£ λΆμΆ μλμ μ°νμ λΆμΆ μλκ° μλ‘ λμΌν λ²ν¬ μλ§ νμΌμ κ΄ν΄ μ§ννμλ€. λ©νκ³Ό μμμ νΌν©κΈ°κ° μ°λ£λ‘ μ¬μ©λμκ³ μ°νμ λ‘λ μμ¨ κ³΅κΈ°κ° μ¬μ©λμλ€. μ°μλΆμμ νμμ λͺ¨μ¬νκΈ° μν μΈλΆ μν₯ κ°μ§μ 100 Hz λΆν° 180 Hz κΉμ§ 20 Hz κ°κ²©μΌλ‘ μΈκ°λμλ€. λν μ
λ ₯ μλ μλ μ§νμ 0.1μμ 0.5 κΉμ§ 0.1μ κ°κ²©μΌλ‘ μ μ©λμλ€.
λ μ΄μ λμ κ³μΈ‘μ μν΄ μλμ₯, strain rateμ₯, OH λΆν¬λ λμμ κ³μΈ‘λμλ€. λμ κ³μΈ‘μ κ²°κ³Όλ‘ νμΌμ μλ΅ νΉμ±κ³Ό μ λμ κ±°λμ κ°μ μκ°λμ λν΄ λΆμλμλ€. OH-PLIF κ³μΈ‘μ μ΄μ©νμ¬ νμΌ κ΅¬μ‘°λ₯Ό νμΈνμμΌλ©° μ΄ μΈμ λ€λ₯Έ μ λμ κ³μΈ‘μ PIV κ³μΈ‘μ μ΄μ©νμ¬ μννμλ€.
λμΌν μΈλΆ μν₯ κ°μ§ μ£Όνμ μμμμλ νΉμ μ
λ ₯ μλ μ΄μμμ flame puffed νμμ΄ λ°μλμλ€. μΈλΆ μν₯ κ°μ§ μ£Όνμκ° μ¦κ°νλ κ²½μ°μλ νμΌμ λΆλ¦¬νκΈ° μν΄ λ ν° μ
λ ₯ μλ μλμ΄ νμνμλ€. μ΄λ νμΌμ΄ μ μ νν° λΌλ κ²μ λ€μ ν λ² μ μ μκ² νμλ€. λν flame puffed νμμ μΈλΆ μν₯ κ°μ§ μ£Όνμμ λ°λΌ μ£ΌκΈ°μ μΌλ‘ λ°νλ¨μ νμΈν μ μμλ€.
PIVμ OH-PLIFμ λμ κ³μΈ‘μ ν΅ν΄ λμ strain rate μ μ°νμ μ μ μ
μ΄ νμΌμ μ λ¨ κ³Όμ μ μμ΄ μ£Όμν μμΈμ΄ λ¨μ νμ
νμλ€. μ€ν κ²°κ³Όμ λ°λΌ, λμ strain rateκ° μμ©νλ©΄ νμΌλ©΄μ΄ μλνκ³ νμΌλͺ©μ΄ λμ± μ’μμ§κ² λλ€. λν flame puffed κ³Όμ μ΄ μ§νλ¨μ λ°λΌ, μ μ λ λμ strain rate κ° νμΌλ©΄μ μμ©νλ κ²μ νμΈνμλ€. Flame puffed κ³Όμ μ λ§μ§λ§ λ¨κ³μμ μΌλ°μ μ΄μ§ μμ κΈκ²©ν λ³νλ₯Ό 보μ΄λ μ λμ΄ κ³μΈ‘λμκ³ μ΄λ‘ μΈν΄ λμ± λμ strain rate κ° νμΌλ©΄μ μμ©νμλ€.
μ΄μ λμμ, νμΌμΌλ‘μ μ°νμ μ μ μ
μ νμΌ μ λ¨ νμμ λ λ€λ₯Έ μμΈμ΄λΌ ν μ μμλ€. Flame puffed κ³Όμ μ΄ μ§νλλ©΄μ μ£Όμ κ³΅κΈ°κ° μ μ°¨ νμΌ μ€κ° μμμΌλ‘ μΉ¨μ
νμμΌλ©° μ΄λ‘ μΈν΄ κ²°κ΅μ νμΌμ΄ μμ ν λΆλ¦¬λκ³ μ°νμ κ° ν΄λΉ μμ μ€κ°μΌλ‘ μλ²½νκ² μΉ¨ν¬λλ€.
Flame puffed νμμ΄ λ°μνλ©΄ νμΌμ μλ΅ νΉμ±μ μν₯ κ°μ§μ μΈκ°νμ§ μμ κ²½μ°μ μμ ν λ¬λΌμ§λ€. νμΌμ κΈΈμ΄μ λ©΄μ μ λ³΄λ€ μ§§μμ§κ² λλ νμΌμ κΈΈμ΄ λ° λ©΄μ μλμ ν° νμΌλ‘ μ¦κ°νλ€. μ¦, flame puffed νμμ΄ λ°μνλ κ²½μ°μ νμΌμ λ³΄λ€ λΆμμ ν μνκ° λλ€κ³ ν μ μλ€.To predict combustion instability, the study of the flame surface is necessary because there is a relationship between the heat release rate and the flame surface. Combustion instability is occurred and amplified when the three components of the perturbation constitute a positive feedback. Thus each of three components should be considered carefully. In order to predict the combustion instability, in this paper, the unique flame structure, called as the puffed flame, was investigated. In the previous work, Kim et al. [1] discovered the puffed flame structure at the specific forcing frequency and the velocity perturbation region. In this paper, therefore, we revealed the causes and the dynamic characteristics of the puffed flame. Thus, simultaneous OH-PLIF and PIV measurements were conducted.
In case of the flame, the burke-schumann flame, a special case of the non-premixed flame, was considered. The mixture of the methane and hydrogen was used as the fuel, and the air was used as the oxidizer. The acoustic forcing was applied for the several frequency regionfrom 100 Hz to 180 Hz with 20 Hz steps. Also incoming velocity perturbation amplitude was varied from 0.1 to 0.5 with 0.1 steps.
The velocity, strain rate, and the distribution of the OH radical were measured at the same time due to the simultaneous laser diagnostics. From these results, the response characteristics and the flow behavior were found at the exact same time. Flame structure was captured from the OH-PLIF measurement and the other quantitative results such as velocity vector and strain rate field were measured from the PIV.
In the same forcing frequency region, the flame puffed phenomenon was occurred over the specific velocity perturbation amplitude. If the forcing frequency became higher, the more velocity perturbation amplitude was necessary for the flame puffed. With this results, we could realize that the flame acts as a low pass filter. Also, it was revealed that the flame puffed phenomenon was periodic process which was following the external acoustic excitation wave.
With the simultaneous PIV and OH-PLIF results, we could find out the relative high strain rate and the oxidizer entrainment played important roles for the puffed process. High strain rate make flame wrinkle and flame throat more thinner. As the process proceeded, more higher strain rate was applied to the flame surface as well. At the final stage of the flame puffed phenomenon, highly irregular flow was generated, so that the strain rate became much higher.
Meanwhile, oxidizer entrainment could be another reason for the puffed flame. During the process, surrounding air was continuously invaded into the middle of the flame. At last, flame was separated into two regions due to the entrainment of the surrounding air.
When the flame puffed phenomenon was occurred, the dynamic characteristics became different from the non-excitation flame case. The flame length became more smaller and the flame surface area also decreased. However, flame length and the surface area perturbation were increased. In other words, when the flame puffed, we could say that the flame became more unstable.Contents
Chapter 1 INTRODUCTION 1
1.1 Combustion instability 1
1.2 Strain rate 4
1.3 Previous research 8
Chapter 2 EXPERIMENTAL APPARATUS AND METHODS 12
2.1 Burke-schumann flame combustor 12
2.2 Test condition 15
2.3 Particle image velocimetry 20
2.4 OH Planar laser induced fluorescence 23
2.5 Simultaneous laser diagnostics 26
Chapter 3 Results and Discussion 28
3.1 OH-PLIF images for the puffed flame 28
3.1.1 OH-PLIF images for the various forcing frequencies 28
3.1.2 OH-PLIF images for the various velocity
perturbation amplitudes 32
3.1.3 Averaged OH-PLIF images 35
3.2 Results of the simultaneous laser diagnostics 37
3.2.1 Radial velocity generation 37
3.2.2 The beginning of the flame surface wrinkling 41
3.2.3 Strain rate distribution near the critical region 43
3.2.4 Comparison of the strain rate distribution 49
3.2.5 The effect of the strain rate to the puffed flame throat 52
3.2.6 The maximum and the minimum strain rate 55
3.2.7 Surrounding air entrainment 61
3.3 Dynamic characteristics of the puffed flame 64
3.3.1 Flame length and surface area 65
3.3.2 Flame length and surface area perturbation 69
Chapter 4 CONCLUSION 71
Appendix A Theoretical understanding of resonance frequency 74
Bibliography 77
Abstract in Korean 83Maste