近年來，混合火箭受到世界各地研究單位所看重，因其改善了固態火箭在燃料操作上的危險，也減低液態火箭系統上的複雜度；而其低成本及低污染的可能性使其成為探索高空科學研究的一大利器，舉凡學校之研究單位到國家等級之太空中心皆可投入此相對安全與低成本之研究。然而，混合火箭雖有以上優點，其液態氧化劑與固態燃料在混合機制上的搭配，將會直接影響發動機之性能，因此，將液態氧化劑注入燃燒室之噴注器的設計即成為混合火箭設計上的主要關鍵。過去有許多文獻皆在探討不同流道設計之噴注器對於發動機性能的影響，其結果顯示在以液態N2O作為氧化劑的情況下，加入旋流效果之旋流式噴注器較傳統軸向式噴注器及蓮蓬頭式噴注器其發動機性能明顯提升。由於液態N2O在常溫下，蒸氣壓相對其他流體高，自加壓效果對於混合火箭在氧化劑上的選擇實為相當有利。然而，N2O為一強氧化劑，且因其高蒸氣壓的特性，使之在冷流噴霧的實驗觀測研究上具有相當的難度。過去已有許多在使用N2O進行實驗時，發生爆炸造成嚴重傷亡的案例；因此，史丹佛大學團隊嘗試將物理性質相似的CO2與N2O進行分析與比較，發現CO2與N2O在許多熱力性質的差異度皆小於5%，故提出以CO2取代N2O做為冷流實驗之工作流體，降低安全風險。本研究透過CO2模擬N2O做為觀測流體，於高壓噴霧觀測艙中觀察高壓環境時的噴霧情況，並導入PLIF光學量測法，更進一步觀察在不同出口距離的二維噴霧機率分佈。經實驗證實，透過此分析方法可以取得噴注器在不同出口距離的質量機率分佈；且發現隨著出口距離越大，其噴霧範圍越廣，且質量分佈越均勻。

Self-pressurizing rocket propellants are currently gaining popularity in the propulsion community, especially in hybrid rocket applications. Self-pressurizing oxidizers with its high vapor pressure, can be driven out from the storage tank and injected into combustion chamber without additional complicated pressurization systems. Among the various self-pressurizing oxidizers, nitrous oxide (N2O) is a highly regarded candidate, especially for hybrid rocket applications. In order to effectively atomize the liquid oxidizer, pressure-swirl injector has been widely used. With its inherent high vapor pressure, nitrous oxide spray characteristics in high pressure environments has been an important topics of intensive research interest. However, nitrous oxide is a strong oxidizer and may cause dramatic damage in improper handling. For safety consideration, carbon dioxide (CO2), with identical molecular weight and similar vapor pressure as well as physical and thermodynamic properties is identified as a possible analogous simulant for nitrous oxide (N2O) in order to greatly reduce hazards, environmental impact, and costs. A novel quantitative Planar Laser-Induced Fluorescence (PLIF) method is adapted and developed to characterize the mass distribution of the CO2 spray. A new facility is also developed in this study for the characterization of pressure-swirl injector atomization and vaporization using high speed video photography. A description of the new CO2 Planar Laser-Induced Fluorescence (PLIF) technique and test apparatus is presented in this thesis, along with details of the spray experiments using carbon dioxide as a simulant for nitrous oxide. Preliminary test results suggest that introducing the PLIF method into the cold flow test can successfully reveal the oxidizer mass flow distribution. In other words, this method not only can effectively observe the vaporization process of high vapor pressure fluid, but also can be used to assist the design of nitrous oxide injectors.

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