近年來太空推進發展上興起一波追求低汙染及低成本的風潮，因此傳統的高毒性、可自燃性推進劑將漸漸的被較安全且環保的推進劑取代。在性能、安全性及成本的多重考量下，液態氧/煤油成了最適合發展重型運載火箭的推進劑組合。在眾多發動機循環中，富氧燃燒分級循環是使用液態氧/煤油此一推進劑組合中循環效率最高的，但西方世界對於此循環卻非常陌生。富氧燃燒分級循環在俄羅斯已經有數十年發展的歷史，而俄羅斯也已成功開發數款採用此循環的發動機，如RD-170、RD-180等。由於太空推進有國防與國家利益上的考量，因此世界各國都將研發資料與數據列為機密，因此我們有必要自行開展富氧燃燒分級循環的研究，建立我國在液態火箭推進上的深厚基礎。
噴注器掌握著液態火箭發動機的工作穩定性與性能，噴注器的設計與推進劑種類、燃燒室幾何型態、操作需求(質流量、壓力差、操作壽命)有關。另外因為氣體中心旋流同軸噴注器的氣液流體配置與傳統的剪力同軸噴注器相反，且相關設計方法及噴霧特性參考資料極少，因此本研究目的為研究並建立氣體中心旋流同軸噴注器(gas-centered swirl co-axial injector, GCSC injector)的基礎噴霧特性，在冷流實驗中透過改變噴注器氣體管道內縮比(recess ratio)及氣液動量通量比(momentum flux ratio)來探討操作動量通量比及幾何設計上的混合腔長度改變對噴霧形態的影響，進而改變環境壓力以探討在不同環境壓力下噴霧型態的變化，並搭配視流法與雷射光學量測法，初步定性地探討氣體中心旋流同軸噴注器的噴霧特性，建立噴霧角(spray angle)、噴霧形態(spray pattern)、二維質量機率分布(two dimensional mass probability distribution)、索特平均粒徑(Sauter mean diameter)隨實驗參數變動的趨勢變化，並將資料統整作為後續發展富氧燃燒分級循環發動機的參考基礎。冷流實驗結果顯示內縮比與動量通量比均對噴霧特性有影響，且氣體中心旋流同軸噴注器的噴霧特性與剪力同軸噴注器有些差異存在。GCSC噴注器的噴霧角隨著氣液動量通量比與內縮比增加而下降，此特性與剪力同軸噴注器相反。由於噴霧角代表液滴在空間中的分布情形，因此較小的噴霧角表示液滴密度較高，此現象可能會顯著地影響點火及燃燒效能。另外GCSC噴注器在大氣環境下會出現內外兩噴霧區，隨著內縮比及動量通量比的增加，噴霧轉為由內區主導，此時液膜被霧化的較完全，因此噴注器出口看不到未霧化的液塊及大液滴存在。另外發現內縮比與動量通量比的搭配可以有效的改變霧化形態，較大的內縮比可以搭配較低的動量通量比即可得到較小內縮比搭配較高動量通量比的噴霧效果，此一特性可以作為未來設計噴注器的基礎。高壓環境下噴霧形態較常壓環境緻密且噴霧角度較常壓環境下小，且內外兩區的差別不顯著，在高壓下主要是由內區主導，而高壓下的質量機率分布形態也比常壓環境均勻且對稱。

The objective of this thesis is to investigate further into the spray characteristics of the gas-centered swirl injector, which is the injector type recently attracts intensive research interests and is to be used for Lox/Kerosene propellant combination for future economical green propulsion for various space applications. The experiment method used in this thesis include spray visualization, such as spray angle measurement and spray pattern identification, and planar laser induced fluorescence for spray mass distribution. The experimental parameters are the momentum flux ratio between central gas and co-axial swirl liquid, the recess ratio of the central tube relative to the coaxial outer tube and the environmental pressure. The experimental results show that when in atmospheric and high pressure conditions, the spray angle decreases as the momentum flux ratio and the recess ratio are increased. But the variation of spray angle in high pressure condition is smaller as compared to atmospheric condition. The spray pattern shows two distinct spray zones, the inner and outer zones, for cases of atmospheric condition, but the outer zone disappears as the increase of the recess ratio and momentum flux ratio. The planar fluorescence measurement results show that at atmospheric condition the mass distribution of the spray is asymmetric and the high density region become large as the momentum flux ratio and recess ratio are increased. When at high pressure condition, the spray is dominated by the inner zone, and the mass distribution is rather symmetric and the distribution becomes flat when the momentum flux ratio and recess ratio are increase. We conclude that this type of injector is recommended to operate at higher gas velocities to acquire good and uniform atomization. A key breakup mechanism for the gas-centered swirl coaxial injector is proposed based on the Kelvin-Helmholtz instability of the momentum flux ratio and the recess ratio between the central gas and the coaxial liquid. The length of the gas-centered coaxial injector’s mixing cup affects the key breakup mechanism and can significantly affect combustion efficiency.

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