在超音速燃燒衝壓引擎中，由於燃油停留在燃燒室的時間極為短暫，因此燃油的霧化混合特性是成功駐焰的因素之一。本研究利用反射式震波風洞產生 2 馬赫的自由流進行冷流實驗，探討凹槽駐焰器上游燃油噴注霧化的分布特性，以及燃油與凹槽的交互作用現象。實驗方法透過紋影法搭配高速攝影機觀察流場，定量分析燃油噴霧的消散長度、穿透高度以及抬升高度。本研究主要設計參數為燃油噴注孔徑(d=0.5mm、0.7mm)以及燃油側向噴注前傾角度0°及45°，改變燃油噴注與空氣自由流之動量通量比(J=3.93~7.43)進行觀察。實驗結果顯示，垂直噴注且孔徑 d=0.5mm 條件下，與平板流側向噴注相較，加入本實驗所採用的凹槽構型後，燃油噴霧具有較大的甩盪幅度，並且提升與空氣的混合效果，對於液態燃油的霧化混合具有正面的幫助。在相同動量通量比條件下，加大燃油噴注孔直徑至 d=0.7mm，因燃油液柱較粗，使燃油中心無法迅速與外部氣流接觸，會產生較長的消散長度以及較大的穿透高度。在相同動量通量比條件下，將燃油噴注角度向上游傾斜45°後，因燃油噴霧更劇烈的甩盪，使噴霧具有較短的消散長度、較大的穿透高度；同時在傾斜噴注條件下，燃油噴霧擁有較小的垂直動量分量，因此有較小的抬升高度，亦增加燃油噴霧與凹槽交互作用的程度。綜合以上消散長度、穿透高度以及抬升高度比較，顯示前傾45°的噴注模式較適合做為凹槽上游燃油噴注孔的設計。

In supersonic combustion ramjet engines, due to the extremely short residence time of fuel within the combustion chamber, the atomization and mixing characteristics of the fuel play a vital role in achieving successful flame stabilization. This study employed a reflected shock wave wind tunnel to generate a Mach 2 free stream for conducting cold flow experiments. The research aimed to investigate the distribution characteristics of atomized fuel injected upstream of a cavity flame holder and the interactive phenomena between the fuel and the cavity structure. The experimental approach involved schlieren visualization coupled with high-speed cameras to observe the flow field and quantitatively analyze parameters such as dissipation length, penetration height, and lift-off height of the fuel spray.
The primary design parameters of this study included the fuel injection hole diameter (d = 0.5mm, 0.7mm) and the fuel injection angle (0° and 45° inclination) with respect to the air stream. The variations in fuel injection momentum flux ratio (J = 3.93~7.43) were also examined. The experimental results showed that under vertical injection with a hole diameter of d = 0.5mm and the introduction of the cavity geometry (as used in the experiment), the fuel spray exhibited larger oscillation amplitudes and enhanced mixing with the air, leading to favorable atomization and mixing of the liquid fuel. Under the same conditions of momentum flux ratio, increasing the fuel injection hole diameter to d = 0.7mm resulted in a coarser fuel column, which hindered quick contact between the central fuel and the external airflow, thus leading to longer dissipation lengths and greater penetration heights.Under the conditions of the same momentum flux ratio, when the fuel injection angle was inclined 45° upstream, the more intense spray oscillation led to shorter dissipation lengths and larger penetration heights. Additionally, the inclined injection configuration resulted in a smaller vertical momentum component of the fuel spray, leading to a smaller lift-off height and a higher level of interaction between the fuel spray and the cavity structure.
Considering the comparisons of dissipation length, penetration height, and lift-off height, the inclined 45° injection mode was found to be more suitable for designing fuel injection orifices upstream of the cavity flame holder.

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