摘要
本研究探討液態燃料在超音速自由流中的霧化及混合特性，以反射式震波風洞模擬超音速燃燒衝壓引擎燃燒室入口自由流速度及溫度，並以平板噴注的模式將燃料注入超音速流場中，觀察燃料的碎裂霧化特性。實驗利用紋影法視流技術及米氏散色光雷射技術，配合高速攝影機觀察燃料在超音速流場中的碎裂霧化過程。實驗結果顯示，燃料液柱與超音速氣流相遇隨即碎裂霧化成許多液滴，但受到周圍震波加壓及紊流作用影響，在噴注口附近之液滴較為集中無法散開，而燃料噴霧也因邊界層分離引起的震波交互作用而產生劇烈的甩動現象，造成液滴開始消散並與空氣混合形成燃氣。為探討燃料噴霧消散的特性，本研究根據實驗觀察之結果定義燃料噴注的消散距離L作為燃料與空氣混合程度的指標。消散距離受到燃料噴注引起之弓形震波與邊界層分離斜震波交互作用影響；當燃料噴注前傾角度增加時，會因震波交互作用加強而使得消散距離顯著的縮短。為進一步探討震波的交互作用，本研究設計一雙垂直噴注器，藉由改變前方及後方噴注口噴注動量來控制震波交互作用點，探討交互作用的位置對燃料消散距離的影響，實驗結果顯示固定燃料總流量的狀況下燃料的消散距離會隨著前方噴注減少而縮短。此結果也驗證了控制震波/震波交互作用，即可調整燃料噴霧的消散距離，亦即調整了燃料與空氣的混合特性。

Abstract
An experimental investigation of JP-4 injection in a supersonic cross flow of air is presented in this paper. Shock tunnel operation was used to create a high-enthalpy supersonic cross flow (Mach 2, Tt = 1750 K, Pt = 12 bars). A flat plate mounted with a single orifice model was used and JP-4 fuel was injected into the supersonic flow through the 0.5-mm orifice. The exit velocity of the JP-4 was controlled at 78–100 m/s, corresponding to a moment flux ratio of 4.1–6.8. A high-speed Schlieren imaging (100,000 fps) technique was used to observe and analyze the interactions between the liquid jet and supersonic air flow. Laser Mie scattering was also used to observe top-view spray behavior. Observation of the Schlieren images indicated significant vaporization of liquid on the windward side of the spray, and both high-speed Schlieren and top-view Mie scattering video revealed that the liquid spray’s whipping motion crucially affects the mixing behavior between the liquid and air. Spray dissipation distance is used in this research to justify the mixing effectiveness between spray and supersonic air flow. The observations show that the spray dissipation distance decreases with increasing momentum flux ratio and angle of forward inclination of the liquid jet. Detailed analysis indicates that the source of the whipping motion, crucial effect on dissipation distance, is from the unstable bow shock/boundary separation shock interaction as well as the occurrence of the vortex surrounding the spray. To verify this effect on mixing, a simple double injection module was used to create different shock/shock interactions, and the results indicate that by managing the flow rates between the double-orifice injector, the dissipation distance or the mixing behavior between the liquid jet and the supersonic airflow can be controlled.

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