臺灣大學: 機械工程學研究所潘國隆何蔡興Ho, Tsai-HsingTsai-HsingHo2013-04-012018-06-282013-04-012018-06-282012http://ntur.lib.ntu.edu.tw//handle/246246/255713本文接續了改善傳統鈍體穩焰裝置之目的所提出的帽頂機構之研究，參考過去所嘗試之實驗與模擬得到的經驗，得知中心燃氣與環流空氣在帽頂機構內部確實有預混效果之作用。為了試圖了解結合帽頂機構之燃燒器熱流場型態，並且輔助直接火焰影像之觀察，建立了光暗影成像技術、粒子影像流場可視化法、初步的PIV運算分析以及溫度分佈量測等方式，用以了解帽頂機構內部之預混功效對於熱流場型態變化之關鍵和駐焰機制之影響。 從基本火焰形態之變化可以大致上將火焰隨著環空氣噴流速率由低到高的增加分類成四個階段。火焰在第一階段時環流空氣的影響較弱，因此以具有褶皺狀火焰結構的中心燃氣噴流火焰為主要特徵；第二階段為即將發展出迴流火焰的過渡火焰形態；第三階段之似預混迴流火焰模式則由於迴流火焰結構發展成熟以及中心來自帽頂機構內部預混後產生的藍焰噴流之間的回饋關係，大幅地拓展穩焰能力；當環空氣噴流速率提升到火焰形態轉變為蕈狀似預混噴流火焰時為第四階段。與傳統鈍體助焰裝置在高環空氣速率下所產生之完全迴流火焰不同，顯示帽頂機構內部提供之混合空間得以使燃料獲得足夠的助燃氣體並直接在離開帽頂機構後進行反應，該火焰模式將維持至火焰因環空氣噴流輸入之速率太快而熄滅。 由粒子影像流場可視化配合PIV運算分析，得知由環空氣噴流所主導的外側渦流結構為影響火焰形態變化之重要因子。其渦流結構中心(前停滯點)位置的改變將促成似預混迴流火焰中迴流火焰結構之發展趨向成熟，成為帽頂機構內部之外另一處能提供燃氣滯留並混合之空間，體現出帽頂機構結合傳統鈍體助焰效果的設計概念之結果，使燃料能更完全地燃燒並釋放能量。The present study focused on the stabilizing mechanism of a cap combustor. According to our previous studies, premixing could be created between the central fuel jet and annual air flow in the cap. To understand the thermal flow pattern of the cap combustor, we studied the flow field by using photographic methods of Shadowgraph and Schlieren, Particle Image Velocimetry (PIV), and temperature measurement. The results showed that the flame pattern of the cap combustor with changing of the relative velocities of fuel and air could be classified into four modes: jet-like flame, transition, premixed-like recirculated flame, and premixed-like jet flame. Flame in jet-like condition is characterized by rotated folding structure; recirculated flame around the cap surface began to develop in transition flame; premixed-like recirculated flame was formed by the fully developed recirculated flame and obvious central blue flame. The central blue flame was yielded due to the mixing of gas and air in the cap, and the interaction of central blue flame and recirculated flame could extend the range of flame stabilization; premixed-like jet flame was characterized by a central jet flame of mushroom shape without the recirculated flame, which revealed that the mixed gas in such flow condition could be ignited immediately after passing through the central exit of the cap. Flame then extinguished because of high speed of the input air. From the results of flow visualization integrated with PIV analysis, we found the air-driven outer vortex structure was the important factor of changing flow patterns. The change of location of the center of outer vortex (forward stagnation point) would promote the development of recirculated flame in premixed-like recirculated flame, and provide another space for mixing.3313946 bytesapplication/pdfen-US帽頂機構雙噴流燃燒器粒子影像流場可視化法粒子影像測速法capconcentric-flows burnerParticle Image Velocimetry (PIV)flow visualizationthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/255713/1/ntu-101-R99522317-1.pdf