為了解富氧燃燒結合煙道氣回流系統的燃燒特性，本研究內容分為兩部份：(1)理論分析富氧燃燒的質能平衡特性；(2)實驗分析天然氣噴流擴散火焰特性。
第一部份以天然氣及柴油做為燃料，在完全燃燒，固定總熱釋放率為1MW條件下，進行富氧燃燒(氧濃度=21%~100%)結合煙道氣回流(FGR=0%~75%)的質能平衡特性之理論分析。減少氮氣以提高助燃氣體中的氧濃度，會因為總進氣流率的減少而造成絕熱火焰溫度的快速增加。在純氧狀態下，絕熱火焰溫度會高於4000℃。因此配合煙道氣回流，利用煙道氣中的二氧化碳去取代氮氣作為稀釋載體，可有效降低富氧燃燒所產生絕熱火焰溫度過高的問題；並且回流煙道氣中所含熱量可減少燃料供應率。此外，煙道氣中二氧化碳濃度也會隨著助燃氣體氧濃度的提高而增加，對於二氧化碳的捕捉有顯著的幫助。
第二部份以雙環同軸燃燒器，建立富氧環境下之噴流擴散火焰。透過改變燃料、助燃氣體出口速度、助燃氣體氧濃度以及助燃氣體中氮氣及二氧化碳的比例，探討其對火焰高度及火焰型態的影響。研究結果顯示，擴散火焰在無外管助燃氣體流速的情況下，火焰高度與火焰擺盪幅度隨內管燃料出口流速的提升而變高變大。當固定助燃氣體氧濃度及燃料出口流速，火焰高度不隨助燃氣體的速度變化。固定燃料及助燃氣體噴流出口速度，噴流擴散火焰的高度隨助燃氣體氧濃度的提升而降低、火焰會隨之變亮。當助燃氣體氧濃度為21%時，隨著二氧化碳濃度的增加，火焰亮度會變暗，最後火焰會開始上飄形成浮火；且當助燃氣體流速愈大，浮火上飄的高度會愈高，擺盪幅度也愈大。

For developing the technology of oxy-fuel combustion, the mass and energy balance characteristics and experimental tests of oxy-fuel jet diffusion flames were investigated.
In the first part, the theoretical prediction of oxy-fuel combustion with nature gas and diesel were calculated. The mass and energy balance characteristics were considered with flue gas recirculation. Although it is benefit to capture CO2 in flue gas with increasing oxygen concentration, the furnace temperature would be rapidly increased. Particularly, it would be higher than 4000oC with pure oxygen. However, flue gas recirculation system would bring back CO2, and that would decrease the furnace temperature considerably. Besides, the waste heat carried back in the flue gas would also reduce the fuel quantity needed.
In the second part, the coaxial methane jet diffusion flames were setup to simulate the oxy-fuel combustion. Without annular flow, the flame height and flickering range would be proportioned to the velocity of inner tube. When the concentration of oxygen and the velocity of fuel were fixed, the height of flame stayed the same with increasing velocity of oxidizer. As we fixed velocities of fuel and oxidizer, the flame would be shortened and brighter with oxygen concentration increasing. When the concentration of CO2 increased, the flame brightness would be less luminous, and finally yielded a lifted flame.

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