為了模擬超音速衝壓引擎之燃燒室，本研究採用全溫1700 K連管風洞進行實驗。相較於其他的駐焰機構，凹槽駐焰器則具有全壓損失較低且能在燃燒室內創造一低速迴流區，使燃料能有更長的滯留時間進行碎裂霧化；因此本研究將探討深度16.5 mm、長深比3且具後斜壁面傾斜22.5°之凹槽；並使用不同噴注孔徑(0.5 mm和0.9 mm)的噴注器、搭配三股斜向45°進行燃油噴注。本研究使用液旋式點火器進行槽內的建溫與建壓，透過調整槽內燃油噴注質量流率(3 g/s~6 g/s)，分別進行冷流與熱燃點火實驗，並利用光學測量技術觀察燃料與火焰分布（OH*螢光與視流紋影法）以及駐焰行為。
透過冷流實驗得到的結果指出大孔徑（0.9 mm）噴注具較低的動量通量，使燃油更容易滯留於主迴流區，提升燃燒穩定性；小孔徑噴注會因撞擊在剪切層上的強度較高，使燃料較容易被帶出槽外，且造成凹槽流場較不穩定。
後續的點火實驗結果發現，在本研究中孔徑為 0.9 mm搭配噴注流量3 g/s為較佳的配置；點火器作為母火能將槽內建溫至約1500 K、駐焰穩定維持在平均溫度 1310 K，並持續達到預期的 8 秒駐焰時間，與冷流實驗對於火焰穩定性的預測結果相符。在接續綜合比較各組條件後，實驗顯示使用孔徑0.9 mm並搭配質量流率3 g/s至3.5 g/s 滿足迴流區內產生適當之空燃比(O/F)而得以穩定駐焰。另外，透過觀察火焰的OH*螢光強度分布則顯示，駐焰位置都位於凹槽的主迴流區內，與槽內燃油水平噴注時的駐焰位置相似。

To simulate the combustion chamber of a supersonic scramjet engine, this study conducted experiments using a direct wind tunnel at a total temperature of 1700 K. Compared to other flameholding devices, a cavity flame holder has the advantages of lower total pressure loss and the ability to create a low-speed recirculation zone within the combustion chamber, allowing for a longer residence time for fuel to undergo fragmentation and atomization. Therefore, this study will investigate a cavity flame holder with a depth of 16.5 mm, a length-to-depth ratio of 3, and a rear wall rear- at 22.5°. Different injector orifice diameters (0.5 mm and 0.9 mm) will be used, along with three jets injected at a 45° angle for fuel injection. A liquid-rotating igniter will be employed to establish temperature and pressure within the chamber. By adjusting the mass flow rate of fuel injection (3 g/s to 6 g/s), both cold flow and ignition experiments will be conducted, and optical measurement techniques will be utilized to observe the distribution of fuel and flame (using OH* fluorescence and schlieren photography) as well as the flame-holding behavior.
The results obtained from the cold flow experiments indicate that the large orifice diameter (0.9 mm) injectors have a lower momentum flux, which allows the fuel to remain more easily in the primary recirculation zone, enhancing combustion stability. In contrast, small diameter injectors have a higher inject strength on the shear layer, making it easier for the fuel to be carried out of the cavity, resulting in a less stable flow field in the cavity.
Subsequent ignition experiment results revealed that in this study, a large orifice diameter of 0.9 mm combined with an injection flow rate of 3 g/s was the optimal configuration. The igniter, serving as the pilot flame, was able to raise the temperature inside the chamber to approximately 1500 K, maintaining a stable flame at an average temperature of 1310 K, and consistently achieving the expected 8 seconds of stable flame duration, which aligns with the predictions from cold flow experiments regarding flame stability. After a comprehensive comparison of various conditions, the experiments showed that using a large orifice diameter of 0.9 mm along with a mass flow rate of 3 g/s to 3.5 g/s satisfied the appropriate air-fuel ratio (O/F) in the recirculation zone, allowing for stable flame retention. Additionally, observations of the OH* fluorescence intensity distribution indicated that the flameholding position was located within the primary recirculation zone of the cavity, similar to the flameholding position when the fuel jet was injected horizontally into the cavity.

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