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研究生： 蘇瑞期
Rei-Qi Su
論文名稱： 自由傳播預混焰與紊流尾流交互作用﹔火焰拉伸率和燃燒速率之量測
指導教授： 施聖洋
Shenqyang Shy
口試委員:
學位類別： 碩士
Master
系所名稱： 工學院 - 機械工程學系
Department of Mechanical Engineering
畢業學年度： 89
語文別： 中文
論文頁數： 107
中文關鍵詞： 紊流尾流 、預混焰 、拉伸率 、紊流燃燒速度
外文關鍵詞： turbulent wake, premixed flame, stretch rate
相關次數： 點閱：12  下載：0 
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    • 沿著雷射斷層火焰面來計算火焰局部拉伸率(含曲率項和應變項)，發現越靠近擴張應變渦漩之渦心時，其拉伸率值越大，此結果與Driscoll et al. (1994)在單一軸對稱渦漩(軸心線與預混焰平面呈90°)之結果相同。當越靠近渦心時， 沿著火焰面切線方向的速度梯度(應變項)越大，故有較大的拉伸率。吾人發現曲率項對火焰拉伸之影響遠比應變項大，因此可用曲率項來近似火焰拉伸率。由拉伸率之機率密度函數分佈，可發現拉伸率會隨著時間的增加而減小，顯示非定常效應，若紊流能量不能由外界繼續提供，紊流尾流結構會迅速消散，加上燃燒生成物具高溫會大大提高生成物之運動黏滯係數(最高約是原反應物之25倍)，故皺摺火焰會有層流化的現象產生。
    為了量測不同紊流強度對紊流燃燒速度的影響，吾人於平板上加裝不同厚度之擾流板來增加紊流強度，所得結果並與先前實驗和理論結果作比較。本實驗所得之紊流燃燒速度結果明顯大於先前我們在十字型燃燒爐(近似等向性紊流場)所獲之結果，主要原因為後者乃一三維紊流場，可觀測到有部分火焰會相互撞擊，造成整體火焰面積並非隨著紊流強度作線性增加，而使得紊流燃燒速度增加幅度不如本實驗。然而紊流尾流會隨時間而消散，從紊流燃燒速度的量測可明顯看出兩不同區域的存在，因此對本實驗所得之紊流燃燒速度，雖然其具有學術參考價值，但必須小心的看待，因其燃燒速度會隨時間作小改變。


    We calculate the local flame stretching rate (including the curvature rate and the aerodynamic strain rate) along the wrinkled flame front at different times using laser tomography and PIV techniques. For the extensive strain vortex pair, values of the stretching rate increase along the wrinkled flame front from the vortex tip to the position which is close to the vortex core. This result is similar to that of Driscoll et al. (1994) using a single axisymmetric vortex pair interacting with a premixed flame. It is found that the curvature term is much more important than the strain rate term. Thus, the stretching rate may be approximated by the curvature term alone. From the probability density function of the stretching rate, we found that the stretching rate changes with time , indicating that the unsteady effect cannot be neglected.
    In order to measure the effect of turbulent intensity to ST, we put the thin disturbance slices with different heights on the edge of the sliding plate. The results are then compared with previous experimental and theoretical results. It is found that the present ST measurements are much higher than our previous data using a cruciform burner which can produce a near-isotropic turbulent flow field. This may be because in the 3-D near-isotropic turbulent flow field many flame-flame collisions and annihilations are frequently observed. Therefore, the increase of the total flame area is not linearly proportional to the turbulent intensity, values of ST obtained in 3-D near-isotropic turbulence field using the cruciform burner are found to be much less than that of the present measurements for 2-D flame-wake interactions. However, the latter is not stationary and must be viewed with caution.

    摘要...............................................................................................................I 英文摘要.................................................................................................... II 誌謝.............................................................................................................III 目錄.............................................................................................................IV 圖表目錄....................................................................................................VI 符號說明.....................................................................................................X 第一章 前言.................................................................................................1 1.1 動機.....................................................................................................1 1.2 問題所在............................................................................................2 1.3 解決提案和論文架構.......................................................................4 第二章 文獻回顧........................................................................................7 2.1 薄碎焰(Flamelet)理論........................................................................7 2.2 預混紊流燃燒區域圖.......................................................................8 2.3 拉伸效應對預混焰的影響.............................................................12 2.3.1 拉伸的基本定義................................................................12 2.3.2 正拉伸與負拉伸................................................................13 2.4 預混焰流力和擴散不穩定性........................................................15 2.5 非定常火焰拉伸效應.....................................................................17 第三章 實驗設備和量測方法.................................................................24 3.1 紊流尾流燃燒設備介紹.................................................................24 3.2 紊流尾流...........................................................................................27 3.3 雷射斷層攝影術..................................................................................29 3.4 影像處理...............................................................................................32 3.5 質點影像測速儀..................................................................................33 3.6 拉伸率之計算..................................................................................... 34 3.6.1 曲率項之計算...............................................................................34 3.6.2 空氣動力應變項及膨脹率之計算............................................35 3.7紊流強度和紊流燃燒速度之量測估算...........................................35 3.8實驗誤差評估......................................................................................37 3.8.1 雷射斷層攝影術..........................................................................37 3.8.2 PIV之量測精確度........................................................................38 第四章 預混焰與尾流之非定常拉伸分析...........................................48 4.1火焰動態傳播分析，應用雷射斷層攝影術...............................48 4.2拉伸率與膨脹率之關係..................................................................51 4.3拉伸率、應變率及曲率之間的關係............................................55 4.4拉伸率、應變率、曲率及膨脹率之機率密度函數分佈.........57 第五章 紊流燃燒速度估算.....................................................................83 5.1 紊流強度對燃燒速度的影響........................................................83 5.2 相關實驗理論與結果之比較........................................................85 第六章 結論與未來工作..........................................................................98 6.1 結論....................................................................................................98 6.2 未來工作.........................................................................................100 參考文獻...................................................................................................102 附錄A-曲率之計算..................................................................................107

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