本論文實驗量測預混貧油甲烷/空氣紊焰與一近似等向性紊流場交相干涉之非定常拉伸效應，並探討預混焰受不同紊流強度拉伸作用時，雷諾數效應(Reynolds number effect, Re)對局部火焰特性的影響。關於非定常拉伸效應的定量量測，實驗設備採用已發展多年之十字型燃燒器，它可產生一近似等向性紊流場於其大水平圓管，而其長垂直圓管可用來引燃一預混層焰，由上而下傳播並與等向性紊流交相干涉。我們使用高速粒子質點影像測速技術(high-speed particle image velocimetry, PIV)以擷取傳播火焰動態影像，並計算分析沿著火焰面之應變率(strain rate)、曲率(curvature)、拉伸率(stretch rate)和膨脹率(dilatation rate)等重要參數之相互關係。結果發現在當量比? = 0.7，Lewis數Le < 1和紊流強度為u?= 32.34 cm/s(Ref = 1020)時，拉伸率與膨脹率並沒有明顯之相關性，這與Driscoll和其團隊(C. J. Mueller, D. L. Reuss & M. C. Drake)在單一軸對稱渦對與貧油預混層焰交互作用之結果不同。在中央紊流區，紊焰拉伸率由應變率和曲率所共同主導，隨著紊焰傳播，曲率逐漸重要，成為主導拉伸率之主要項。有關雷諾數效應，當紊流強度由u?= 32.34 cm/s(Ref = 1020)增為u?= 46.2 cm/s(Ref = 1750)時，拉伸率與膨脹率更加沒有相關性，且隨著火焰與紊流場交相干涉時，拉伸率始終由應變率主導，顯示雷諾數效應會導致應變率增強進而主導拉伸率。 This thesis investigates experimentally the effect of unsteady stretch for lean premixed turbulent methane/air flames interacting with near-isotropic turbulence. We study the effect of Reynolds number (Ref) on local properties of lean premixed flames at two different turbulent intensities. The near-isotropic turbulence is generated in a large cruciform burner that includes a long vertical vessel and a large horizontal vessel equipped with a pair of counter-rotating fans and perforated plates. The long vertical vessel can be used to produce a downward propagating premixed flame to interact with near-isotropic turbulence. We apply high-speed particle imaging velocimetry (PIV) to measure flame-turbulence interactions, and thus the corresponding strain rate, curvature, stretch rate, and dilatation rate fields along the wrinkled flame front can be obtained. Results show that, at the equivalence ratio ? = 0.7, and the turbulent intensity u? = 32.34 cm/s (Ref = 1020), no apparent correlations between the stretch rate and the dilatation can be observed. This differs with that found by Driscoll and his co-workers who used a single vortex interacting with a lean premixed flame. It is found that at Ref = 1020, the stretch rate is dominated by both the strain rate and the curvature term. This situation gradually changes as flame propagating, in which the curvature becomes more and more important that eventually dominates the stretch rate. For large values of Ref up to 1750 (u? = 46.2 cm/s), the possible correlation between the stretch rate and the dilatation rate is even worse, and the strain rate term plays a more important role than the curvature term, indicating the effect of Reynolds number on the stretch rate.
