本研究透過數值模擬方法分析同軸雙環燃燒器之噴流擴散火焰特性，在進行燃燒模擬前，先針對燃燒器內管做格點獨立性分析以檢視較適合之網格型態；再建立同軸雙環燃燒器之模型並做管內及管外噴流之冷流場分析，確立了結果之合理性後，根據其結果建構用於燃燒模擬之計算模型。本研究主要藉由簡化之甲烷化學動力反應模型來模擬噴流擴散火焰，首先探討在外環管中以空氣作為氧化劑之甲烷噴流擴散火焰特性，在不同內管和外環管噴流出口速度下，先以不含浮力作用之穩態方法探討火焰溫度和燃燒產物分布情形後，再以含浮力作用之暫態方法檢視火焰型態、火焰高度、火焰穩定性以及火焰振盪頻率之變化情形，並以文獻實驗結果驗證其準確性。下一個部分則藉由改變外環管內氧化劑組成以探討富氧甲烷噴流擴散火焰特性，首先通過不含浮力作用之穩態方法討論外環管中氧氣以及二氧化碳濃度對於火焰型態、火焰溫度和燃燒產物分布情形，之後進一步透過含浮力作用之暫態方法討論氧氣及二氧化碳濃度對於火焰型態、火焰溫度、火焰穩定性、火焰高度、火焰振盪頻率之影響，從中主要發現隨著氧氣濃度增加，火焰溫度會大幅上升、主要燃燒產物濃度增加、火焰高度變小、火焰振盪頻率降低、火焰穩定性增加；而在適量的氧氣濃度下，以二氧化碳取代氮氣作為稀釋氣體能進一步降低火焰振盪頻率，穩定火焰振盪性，且能控制在富氧燃燒狀態下之火焰溫度。

The characteristics of jet diffusion flame are studied using numerical simulation method with methane reduced reaction mechanism. Before doing combustion simulation, the grid independence test is done to choose the suitable grid density, and the physical reliability check is finished by cold flow simulation. At first, the simulation of methane jet diffusion flame with air coflow is discussed. Under the effect of different jet exit velocity of inner and annular tube, the distribution of flame temperature and combustion products are studied by steady analysis method without buoyancy force effect. Next, the buoyancy force is added to the transient simulation to analyze the flame shape, height, stability and flickering frequency. The results are checked with the experimental data done by other scholars. Second, by changing the composition of the oxidizer in the annular tube to discuss the characteristics of methane jet diffusion flames under oxygen enrichment is showed. By using the same numerical analysis method applied in the previous jet diffusion flame with air coflow, the flame shape, temperature, products, stability, height, flickering frequency are analyzed under the effect of the concentration of oxygen and carbon dioxide in the annular tube. The results mainly showed that the oxygen concentration has the great effect on increasing flame temperature, products’ concentration and flame stability and decreasing flame height, flickering frequency. Under the moderate content of oxygen in the oxidizer, replacing nitrogen with carbon dioxide has the further improvement in flame characteristics.

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