在超音速燃燒衝壓引擎中，由於其燃料停留在流場中的時間極為短暫，因此必須在流場中設立駐焰機制。為了減少全壓損失，選擇在流道加入凹槽達到駐焰效果。本研究採雙噴注系統，同時於凹槽外及凹槽內進行噴注，並將凹槽內噴注視為母火，藉由母火期望使凹槽外主噴注得以於超音速流場中穩定燃燒。本實驗藉由不同的凹槽外噴注與凹槽前壁面距離，觀察凹槽在不同條件下的燃料夾帶現象。結果顯示當凹槽外噴注孔與凹槽壁面距離較短時，凹槽的燃料夾帶會大於較遠的噴注孔距離。在凹槽內噴注方面，藉由改變凹槽內噴注角度、動量通量比，觀察不同噴注條件下燃料霧化的現象，實驗結果顯示，當凹槽內噴注角度、動量通量比不同時，進入凹槽內迴流區的燃料比例也不同，因此得以藉由控制凹槽內噴注角度調整燃料進入迴流區的比例。當雙噴注於流場時，凹槽內迴流區受氣流壓制較多，致使迴流區的範圍較小。除此之外，當凹槽內噴注的角度、動量通量比改變時，除了改變迴流區的流場現象，內外雙噴注間的交互作用亦不相同。

In scramjet engines, the flame holding mechanism must be established in the flow field. The cavity is selected to be added into the flow field to achieve the flame-holding effect. In this study, a double injection system is adopted. The fuel will be injected within and outside the cavity at the same time. The injection inside the cavity is considered as the pilot flame, and the injection outside the cavity is considered as the main injection.
In this experiment, the different distance between the injector outside the cavity and the front wall of the cavity cause different fuel entrainment phenomenon. The results show that when the distance is short, the fuel entrainment will be greater than the distance is far from the injector, but the fuel gasification effect is poorer than the distance is farther.
In the case of injection inside the cavity, the injection angle(δ^*) and the momentum flux ratio(Q) are changed. The results show that when the injection angle and momentum flux ratio are different, the proportion of fuel entering the recirculation zone inside the cavity is also different.
When the fuel sprays injected within and outside the cavity, the recirculation zone inside the cavity is pressed by the freestream. In addition, when the angle of injection and the momentum flux ratio inside the cavity are changed, not only changing the flow field phenomenon in the recirculation zone, but also the interaction between internal injection and the external injection is different.

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