本研究以數值模擬方法分析燃燒室內甲烷噴流火焰的流場特徵和火焰燃燒特性，探討不同設定下流場結構和溫度分布的變化特徵，並分析各項參數對燃燒室流場、溫度場、濃度場的影響。模擬分析分為二部分；第一部分為燃燒室內冷流場分析，確認其燃燒室邊界設定與甲烷噴流位置的影響性。燃燒室邊界設定分為二個開放邊界及一個固體邊界，其中開放邊界分為壓力進口 (燃燒室內與外界壓力梯度為0)以及速度進口 (固定空氣速度)，並分別探討低速進口噴流 (Vi = 1 m/s)與高速進口噴流(Vi = 5 m/s)的情況，由Vi = 1 m/s與Vi = 5 m/s在r1= 60的結果比較後發現，使用固體邊界作為邊界數值設定的結果與開放邊界幾乎相同，因此可以判斷在此模型中的噴流特性 (Jet flow) 不會被壁面所影響，其現象可以參考自由噴流 (Free jet)。接著將改變燃燒室外徑及增加出口處的縮口角度，以確認邊界對流場造成的影響，最後發現在冷流場中，Vi 的值不影響軸向速度剪切層角度 (α)；出口縮口角度 (θ)不影響整體流場的結構。
第二部分為燃燒室內反應流分析，探討甲烷噴流燃燒過程的火焰形成、穩定性。首先探討引火源設定，將燃料及空氣入口處設置了一個3 mm x 3 mm高溫區域，為燃料及氧化劑交界處提供適當溫度，讓甲烷與空氣產生引燃的化學反應。此引火源區域設定固定高溫，藉此達到穩焰的效果。燃燒室內反應流分析，首先討論低速及高速進口噴流參數；接著探討燃燒室外徑 (r1)變化的影響性。結果發現，縮小燃燒室外徑 (r1)會導致空氣進口流場邊界下降，壓迫到噴流流場，使得軸向速度剪切層角度 (α)會有減少的現象。當燃燒室外徑 (r1)縮小至36的時候，燃燒室內的迴流氣體變多，導致部分的氣體無法從出口排出。而在同r1的情況下，Vi較大，迴流強度會略為增加，但不影響整體結構。
若燃燒室出口外徑 (r2)太小，其縮口的璧面會阻礙氣體排出，導致部分熱量及氣體往燃燒室內迴流。燃燒室長度 (l2)變化的參數結果顯示，流場結構會因為燃燒室長度 (l2)太長，造成二種不同的速度剪切層斜率，以及出口縮口角度 (θ)越大越不易增加迴流強度。在本研究的模型中，θ = 60°, l2 = 160為最佳設計。

This study analyzes the flow field characteristics and combustion properties of methane jet flame in a combustion chamber using numerical simulation methods. It investigates the variations in flow field structures and temperature distribution under different settings and examines the influence of various parameters on the flow field, temperature field, and concentration field within the combustion chamber. The simulation analysis is divided into two parts, cold flow field and reactive flow analysis.
In the cold flow analysis, it was found that the value of inlet velocity (Vi) does not affect the axial velocity shear layer angle (α), and the outlet contraction angle (θ) does not influence the overall flow field structure.
In the reactive flow analysis, it was found that reducing the outer diameter (r1) of the combustion chamber lowers the boundary of the air inlet flow field, compressing the jet flow field and reducing α. Under the same r1 conditions, a higher Vi slightly increases the recirculation intensity but does not affect the overall structure.
The analysis of parameter variations in combustion chamber length (l2) shows that an excessively long l2 results in two different velocity shear layer slopes. Additionally, the larger θ, the more difficult it becomes to increase the recirculation intensity.

[1] Our World in Data. “Global fossil fuel consumption,” https://ourworldindata.org/fossil-fuels.
[2] G. L. Borman and K. W. Ragland, Combustion Engineering. Boston: WCB/McGraw-Hill, 1998.
[3] T. Trüpel, Über die Einwirkung eines Luftstrahles auf die umgebende Luft. Oldenbourg, 1914.
[4] N. W. M. Ko and A. S. H. Kwan, “The initial region of subsonic coaxial jets,” J. Fluid Mech., vol. 73, no. 2, pp. 305-332, 1976.
[5] A. S. H. Kwan and N. W. M. Ko, “The initial region of subsonic coaxial jets. Part 2,” J. Fluid Mech., vol. 82, no. 2, pp. 273-287, 1977.
[6] N. W. M. Ko and H. Au, "Coaxial jets of different mean velocity ratios," Journal of Sound and Vibration, vol. 100, no. 2, pp. 211-232, 1985.
[7] H. Au and N. W. M. Ko, “Coaxial jets of different mean velocity ratios, part 2,” Journal of Sound and Vibration, vol. 116, no. 3, pp. 427-443, 1987.
[8] R. v. Hout, S. Murugan, A. Mitra, and B. Cukurel, “Coaxial Circular Jets—A Review,” Fluids, vol. 6, no. 4, pp. 147, 2021.
[9] P. M. Sforza, M. H. Steiger, and N. Trentacoste, “Studies on three-dimensional viscous jets,” AIAA J., vol. 4, no. 5, pp. 800-806, 1966.
[10] N. Trentacoste and P. M. Sforza, “Further Experimental Results for Three-Dimensional Viscous Jets,” AIAA J., vol. 5, no. 5, pp. 885-891, 1967.
[11] P. M. Sforza, “A Quasi-Axisymmetric Approximation for Turbulent, Three-Dimensional Jets and Wakes,” AIAA J., vol. 7, pp. 1380-1383, 1969.
[12] I. Glassman. R. A. Yetter. N. G. Glumac, Combustion, 5 ed. Academic Press, 2014.
[13] C. E. B. Jr., Heat Transfer in Industrial Combustion. CRC Press, 2000.
[14] Ansys. “什麼是計算流體動力學 (CFD)？,” https://www.ansys.com/zh-tw/simulation-topics/what-is-computational-fluid-dynamics.
[15] P. R. Spalart and S. R. Allmaras, “A one-equation turbulence model for aerodynamic flows,” American Institute of Aeronautics and Astronautics, 1992, vol. Technical Report AIAA-92-0439.
[16] B. E. Launder and D. B. Spalding, Lectures in Mathematical Models of Turbulence. London, England: Academic Press, 1972.
[17] S. A. Orszag et al., “Renormalization Group Modeling and Turbulence Simulations,” presented at the In International Conference on Near-Wall Turbulent Flows, 1993.
[18] T. H. Shih, W. W. Liou, A. Shabbir, Z. Yang, and J. Zhu, “A new k-ϵ eddy viscosity model for high reynolds number turbulent flows,” Computers & Fluids, vol. 24, no. 3, pp. 227-238, 1995.
[19] B. E. Launder, “Second-Moment Closure: Present... and Future,” International Journal of Heat and Fluid Flow, vol. 10, no. 4, pp. 282-300, 1989.
[20] B. E. Launder, G. J. Reece, and W. Rodi, “Progress in the Development of a Reynolds-Stress Turbulence Closure,” Journal of Fluid Mechanics, vol. 68, no. 3, pp. 537-566, 1975.
[21] M. M. Gibson and B. E. Launder, “Ground Effects on Pressure Fluctuations in the Atmospheric Boundary Layer,” Journal of Fluid Mechanics, vol. 86, pp. 491-511, 1978.
[22] B. F. Magnussen, “On the Structure of Turbulence and a Generalized Eddy Dissipation Concept for Chemical Reaction in Turbulent Flow,” presented at the Nineteenth AIAA Meeting, St. Louis, 1981.
[23] I. R. Gran and B. F. Magnussen, “A numerical study of a bluff-body stabilized diffusion flame. part 2. influence of combustion modeling and finite-rate chemistry,” Combustion Science and Technology, vol. 119, no. 1-6, pp. 191–217, 1996.
[24] C. M. Rhie and W. L. Chow, “Numerical Study of the Turbulent Flow Past an Airfoil with Trailing Edge Separation,” AIAA J., vol. 21, no. 11, pp. 1525-1532, 1983.
[25] S. Majumdar, “Role of Underrelaxation in Momentum Interpolation for Calculation of Flow With Nonstaggered Grids,” Numerical Heat Transfer, vol. 13, no. 1, pp. 125-132, 1988.
[26] 林大惠， “燃燒火焰知多少”科學發展， vol. 355， pp. 4-11， 2002。
[27] A. M. Kanury, Introduction to Combustion Phenomena. Gordon & Breach, 1975.
[28] H. R. N. Jones, The Application of Combustion Principles to Domestic Gas Burner Design. British Gas, 1989.
[29] E. M. Combustión. “Combustion chambers – Hot gas generators,” https://emcombustion.es/en/combustion-chambers-hot-gas-generators/.