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    题名: 負拉伸火焰在正拉伸流場的研究
    A Negatively-Stretched Flame in a Positively-Stretched Flow
    作者: 侯順雄
    关键词: 火焰拉伸
    停滯面流場
    火焰曲率
    優先擴散
    Le數
    flame stretch
    Stagnation-point flow
    Flame curvature
    Preferential diffusion
    Lewis Number
    日期: 2005-07-31
    上传时间: 2009-12-30 15:52:20 (UTC+8)
    摘要: 火焰拉伸(flame stretch)會強烈影響火焰的結構、燃燒強度、熄滅、穩定性及傳播速度等燃燒特性。因此,火焰拉伸為影響燃燒現象之眾多參數中非常重要的一項效應。當混合氣之Le數不等於1(即存在優先擴散(preferential diffusion)時),火焰拉伸效應將益形凸顯,變得格外重要。過去有關火焰拉伸效應對火焰燃燒特性影響的研究,大都侷限於以停滯面流或對沖流來探討流場的正拉伸(positive stretch)效應,或是以本生燈火焰來分析火焰面曲率引起的負拉伸(negative stretch)效應。截至目前為止有關探討預混火焰同時承受負拉伸和正拉伸交互作用的文獻則尚付之闕如。由於曲面火焰在停滯面流場中顯然地會同時受到負拉伸和正拉伸耦合效應的強烈影響,為了進一步了解並釐清火焰曲率負拉伸、流場正拉伸和優先擴散三者強烈耦合效應下對火焰燃燒特性的重大影響,本計畫將以實驗研究、數值方法和理論分析三大部分深入探討負拉伸火焰(曲面火焰)在正拉伸流場(停滯面流場)中的燃燒特性。故本計畫具有高度原創性和重要性。本研究計畫內容主要分成三大部分,第一部分為利用單管噴流燃燒器與停滯面板組合而成的停滯面流場進行實驗研究,實驗中將變化噴流出口速度、停滯面高度、噴流出口燃料濃度、停滯面板型式(石英玻璃或不鏽鋼水冷式停滯面板),藉以分析火焰型態、火焰面位置、火焰面溫度(燃燒強度)和火焰拉伸的大小。其中選定貧油甲烷火焰之Le數小於1,而富油甲烷火焰之Le數大於1。第二部分則是利用停滯面流場的數值解分析和火焰面預測模式,預測火焰型態及火焰面位置和火焰拉伸大小。最後並將火焰面預測結果及沿火面的火焰拉伸大小與實驗結果相互做比對驗證。第三部分係採用高活化能近似微擾分析法,分析一建立於停滯面流場中的曲面火焰,以探討負拉伸火焰在受到正拉伸流場的作用下之火焰燃燒特性,主要探討參數包含流場正拉伸、火焰面曲率、優先擴散和下游熱損失的耦合效應。
    Traditionally, combustion researches on flame stretch deal with positive stretch in the stagnation flow and negative stretch along the Bunsen flame. Only a very limited amount of research has been devoted to studying the behavior of a conical Bunsen flame established in a stagnation flow, which is significantly affected by the combined effects of the curvature stretch and the aerodynamic straining. This investigation is aimed at studying the characteristics of laminar conical premixed flames in an impinging jet flow experimentally, numerically and theoretically. Firstly, the flame appearance, flame structure, and flame stability are experimentally observed using image processing techniques. Then, the temperature distribution measurements along the flame front are obtained by using a thin silica-coated R-type thermocouple. Secondly, we analyze the transport processes of a nonreactive impinging jet flow numerically. The predicted flame shapes using a simple model incorporated with the numerical results will be compared with the experimental observations. The calculation of stretch and measurement of flame temperature for the conical flame established in a stagnation flow will help us to understand how the combined effects of positive aerodynamic straining, negative curvature stretch and preferential diffusion dominate the combustion characteristics. Thirdly, we analyze the structure of Bunsen flame tip under the influence of aerodynamic stretch, flame curvature stretch, preferential diffusion and downstream heat loss by using large activation energy asymptotics.
    显示于类别:[機械工程系所] 研究計畫

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