預混甲烷紊焰拉伸量測，應用高速PIV; Stretch Measurements of Turbulent Premixed Methane/Air Flames Using High-speed PIV

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題名:	預混甲烷紊焰拉伸量測，應用高速PIV;Stretch Measurements of Turbulent Premixed Methane/Air Flames Using High-speed PIV
作者:	張中千;Chung-Chien Chang
貢獻者:	機械工程研究所
關鍵詞:	高速質點影像測速技術;雷射斷層攝影術;應變率;曲率;膨脹率;拉伸率;curvature;strain rate;high-speed particle image velocimetry;laser tomography;stretch rate;dilatation rate
日期:	2004-07-06
上傳時間:	2009-09-21 11:46:08 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文實驗量測探討預混甲烷/空氣層焰與紊流場交互作用之非定常拉伸效應，紊流場有二：一為紊流尾流燃燒器所產生之紊流尾流渦對；另一為十字型燃燒器所產生之近似等向性紊流場，配合高速質點影像測速技術(high-speed particle image velocimetry, PIV)與雷射斷層攝影術(laser tomography)，定量量測火焰前緣空氣動力應變率(strain rate)、曲率(curvature)與膨脹率(dilatation rate)，以及由應變率和曲率所合成的拉伸率(stretch rate)。有關預混層焰與紊流尾流拉伸率之量測，針對貧油(化學當量比?=0.7)甲烷/空氣火焰，在固定層流燃燒速度10 cm/s條件，添加不等百分比之稀釋氣體二氧化碳（具高輻射熱損失）與氮氣（具低輻射熱損失）以研究輻射熱損失效應。結果顯示火焰前緣最大火焰強度位於正曲率區域，整體拉伸率顯示Le<1火焰受正拉伸(positive stretch)作用會提高局部燃燒率與火焰強度。此外，對Le<1甲烷預混火焰之拉伸率而言，以曲率項為主導，應變率項為次要，在尾流渦對平均渦漩速度與層焰速度達 ? 2仍如此。結果證實輻射熱損失效應對火焰傳遞速度與最大正膨脹率值有抑制減少的影響。利用我們實驗室建立之大型十字型燃燒器，執行富油(?=1.45)甲烷/空氣火焰與等向性紊流之非定常拉伸率量測。實驗結果顯示富油甲烷火焰(Le>1)受負應變拉伸作用時，其火焰強度會增強，同時火焰前緣以凸向反應物區正曲率區域燃燒較為激烈。由整體拉伸率顯示Le>1火焰受負拉伸(negative stretch)作用時，會提高局部燃燒率與火焰強度。高速PIV量測非定常拉伸效應，結果顯示拉伸效應起先由空氣應變率項所主導，隨著火焰傳播，曲率項越來越重要，逐漸成為拉伸率主導項。 This thesis investigates experimentally the effect of unsteady stretch on laminar premixed flames interacting with turbulent flows. Using a turbulent wake burner and a large cruciform burner, a von Kármán turbulent wake and near-isotropic turbulent flows can be generated, respectively. We applied high-speed particle image velocimetry (PIV) and the laser tomography to quantitatively measure the corresponding strain rate, curvature, stretch rate, and dilatation rate along the interacting flame front with turbulent wake and near-isotropic turbulence. Experiments in the turbulent wake burner were conducted to study the effect of radiative heat losses on stretching of premixed CH4 flames by using two diluting gases, CO2 (large radiative heat loss) and N2 (small radiative heat loss),respectively. Note that the laminar burning velocities for both CO2- and N2-diluted flames are kept constant with SL = 10 cm/s at a fixed equivalence ratio Φ = 0.7. Experimental results reveal that the maximum burning rate that may be indicated by the maximum dilatation rate occurs in regions of high positive curvature rates. This confirms that the reaction rate of Le<1 flames is increased by the positive stretch, as already suggested by Law and many other researchers. The curvature team is more important than the strain rate term in the overall stretch consideration for the present lean CH4/air premixed flames with Le<1, at least for the ratio of the mean tangential velocity of the staggered vortex pair of the wake to the laminar burning velocity, uθ/SL , up to 2. By comparing CO2- and N2-diluted flames, the wrinkled flame propagation speeds and the peak values of the dilatation rate are largely decreased by the increase of radiative heat loss. Experiments in the cruciform burner were conducted to investigate the effect of unsteady stretch for rich (Φ = 1.45) methane/air flames interacting with near-isotropic turbulence, where the root-mean-square turbulent intensity u'=32.3 cm/s and u'/SL = 2.2. The experimental data suggest that the reaction of rich CH4 flames (Le>1) is strengthened by the negative strain rate, but the flame is burned more intensely near regions of the flame front whose curvature is positive. For the unsteady stretch of rich CH4 flames, the strain rate term plays a dominate role on the stretch rate in the beginning of the flame-turbulence interaction, but during the interaction the curvature term gradually becomes a dominate term.
顯示於類別:	[機械工程研究所] 博碩士論文

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