| 摘要: | 本論文主要量測氦氣稀釋氫氣(H2/O2/He)混合物的層流火焰速度(SL)，以及使用調整稀釋劑氮氣濃度(XN2)的目標導向氫氣與甲烷混合燃氣(H2/O2/N2和CH4/O2/N2)，來研究Lewis數(Le)、層流火焰厚度(dL)、壓力(p)與未燃氣溫度(Tu)，對紊流火焰速度(ST)之影響。實驗研究採用已建置之高溫高壓高紊流雙腔體十字型爆炸設備，此設備由一大型安全等壓外腔體與十字型風扇擾動內腔體組成。球狀火焰傳遞過程是使用高速攝影機(Phantom V711)與紋影光學影像技術來記錄，拍攝張數為每秒10,000幀、畫面解析度為800 x 800像素，拍攝尺寸固定為125 x 125 mm2。將這些球狀火焰影像經過處理和分析後，可獲得火焰半徑隨時間變化的關係，並以此量測出SL與ST。本論文之實驗研究結果可分為兩部份。
第一部份針對貧油氦氣稀釋氫氣火焰的層流火焰速度進行量測，並評估七種最先進的化學反應機制對其的預測能力。在phi = 0.3、0.45、0.6，p = 1、3、5 atm，Tu = 300K與400K的條件下，共進行11組H2/O2/He混合燃氣實驗，並採用四種先進的火焰速度修正方法來獲得SL。結果顯示，以He取代N2能有效抑制熱擴散不穩定性，並拓展可量測SL的phi與p範圍。此外，將N2替換為He顯著減少了與火焰拉伸率相關的非線性效應，從而提高量測SL的準確度。然而，當比較實驗量測與化學動力學模型預測之結果，發現所有受測的化學反應機制均無法準確預測全部實驗量測結果，尤其是在Tu = 400K、phi = 0.45、p = 3和5 atm的條件下，差異最為顯著。此結果強調了未來針對高溫條件對於模型評估與發展的重要性。此外，這些差異可能部分來自於所採用之傳輸模型的限制，因此需對傳輸模型進行後續改進與驗證。第二部分則探討紊流火焰速度ST。使用前述之二種混合燃氣H2/O2/N2 (phi = 0.45, Le = 0.35)和CH4/O2/N2 (phi = 1.0, Le ~= 1.0)在p = 1、2、5 atm，Tu = 300K與400K的條件下，來研究Le、p、Tu與dL的對ST的影響。實驗結果顯示ST隨p或Tu增加而上升，但ST/SL隨Tu增加而下降。此外，ST亦隨dL減少而增加，且低Le數火焰之 ST會因壓力上升而顯著提升，但又會因Tu增加而抑制。最後，H2/O2/N2火焰的ST可透過planar, twin, critically strained laminar flames的SL與dL特性進行量化描述，這與leading point概念的一致。;This dissertation measures the laminar flame speed (SL) using helium-diluted hydrogen (H2/O2/He) mixtures and investigates various effects on turbulent flame speeds (ST) using hydrogen (H2/O2/N2) and methane (CH4/O2/N2) as fuels with different nitrogen (N2) diluents concentrations (XN2) to understand the dependence of ST on Lewis number (Le), laminar flame thickness (dL), pressure (p), and unburned gas temperature (Tu). Experiments are conducted in an already-established high-pressure, high-temperature and high-turbulence dual-chamber cruciform explosion facility. Such explosion facility was constructed by a huge capsule-like outer chamber and a large inner cruciform fan-stirred combustion chamber. The self-propagation spherical flames are recorded by a Phantom V711 high-speed camera using the schlieren imaging technique operated at a frame rate of 10,000 frames/s with 800 x 800 pixels having a fixed view field of 125 x 125 mm2. By processing these spherical flame images, the dependency of the flame radius <R> on time is extracted, from which the values of SL and ST are obtained. The results of this dissertation are divided into two main parts.
The first part is to measure the laminar flame speed of lean helium-diluted hydrogen spherical flames and evaluate the performance of seven state-of-the-art chemical kinetic mechanisms. 11 cases of lean H2/O2/He mixtures are conducted under the conditions of phi = 0.3, 0.45, and 0.6, p = 1, 3, and 5 atm, and Tu = 300K and 400K and laminar flame speeds are evaluated adopting four state-of-the-art flame-speed-correction methods. The obtained results show that substitution of N2 with He offers the opportunity to suppress thermal-diffusional instability under the studied conditions, enabling the measurement of lean hydrogen laminar flame speeds over a broader range of equivalence ratios and pressures. Furthermore, substituting N2 with He significantly reduces the influence of nonlinear effects related to flame stretch rate, thereby improving the accuracy of SL evaluations. When the measured data and the chemical kinetics predicted data are compared, it is found that none of the tested chemical models can match the experimental data, with differences particularly pronounced in preheated (Tu = 400K) moderately lean (phi = 0.45) flames under elevated pressures (p = 3 and 5 atm). Since chemical kinetic mechanisms of lean hydrogen burning have not yet been tested against experimental data on SL, obtained at Tu = 400K, the present results call for further assessment and development of such models for elevated temperature conditions. These differences between the measured and computed flame speeds could in part be attributed to limitations of the adopted transport models, thus also calling for further assessment and development of them. The second part is regarding the ST; the H2/O2/N2 (phi = 0.45, Le = 0.35) and CH4/O2/N2 (phi = 1.0, Le ~= 1.0) mixtures are used to study the effect of Le, p, Tu, dL on ST under the conditions of p = 1, 2, and 5 atm, and Tu = 300K and 400K. Results show that the measured ST increase with increasing p and/or Tu, whereas ST/SL is decreased with increasing Tu. Furthermore, ST increases with decreasing the thickness dL. An increase in ST of low-Lewis-number flames is promoted by an increase in pressure, but is mitigated by an increase in Tu. The results of H2/O2/N2 flame can quantitatively be described by substituting SL and dL with the counterpart characteristics of planar, twin, critically strained laminar flames, in line with leading point concept. |
