由於氣流進入超燃衝壓引擎燃燒室時速度極高、滯留時間極短，增進其與燃料間的混合是目前的噴注器設計重點。而為了增加引擎推力，一般採用多噴孔陣列噴注器以增加燃料流量，了解燃料液柱間的交互作用，為設計高混合效益噴注器之必要條件。本研究應用並排雙噴注孔，噴注方向與自由流方向垂直，將JP-4燃料注入2馬赫空氣流場，並改變噴注孔間的距離，以觀察燃料液柱間交互作用的模式，以及霧化混合的機制。實驗結果顯示，液柱引發之弓形震波的交互作用會造成氣流減速，對燃料與氣流的霧化混合效果有負面影響，且兩弓形震波之交互作用愈強，流場穩定性愈高；故雙噴注間距愈小，霧化混合效果愈差、液滴消散距離愈長。雙噴注間距愈大，其發展則與單噴注相似度愈高。因穿透高度與噴注本身之動量通量較具關聯性，故震波交互作用對穿透高度無顯著影響。

The scramjet engine performance is highly related to the mixing efficiency between liquid fuel and airflow because of the short residence time of the supersonic airflow. Since multi-point fuel injection is required in scramjet engine, better understand the effect of interactions between jets on fuel-air mixing is important to the scramjet fuel injection design. This thesis research utilizes a reflected shock tunnel to produce Mach 2 airflow. The experiments are conducted with singlet and doublet injection orifices of 0.5mm in diameter laterally aligned to the airflow. The spacing between the doublet orifices are 5mm, 7.5mm, and 10mm. JP-4 fuel is used as the working fluid and injected into the supersonic airflow. Schlieren photography and Mie scattering are adopted to observe the spray structure during the experiments. The experimental observations show that the dissipation distance of spray increase with decreasing spacing between adjacent jets, that is, worse mixing between the fuel spray and air. Further analyses indicate that the shock/shock interactions between the bow shocks induced by adjacent liquid jets enhance the stability of the air flow field and less surface disturbance and more stable spray is observed. As the spacing between the adjacent jets increases to 10mm, the mixing behavior of the doublet jets is similar to the singlet one. It is understood that the penetration heights of jets are crucially sensitive to the momentum flux ratio of jet to airflow, and the experiment results do not show significant variation of penetration heights in cases of different spacing between jets. Concluded from the present observations, the spacing between span-wise align jets is recommended to be more than 20 times of the orifice diameter in engineering applications to achieve adequate mixing of fuel and Mach 2 cross flow of air.

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