依據混合式火箭實驗模型以數值模擬分析其 燃燒引擎的燃燒推進過程的研究

Abstract

混合式火箭由液態或氣態的氧化劑以及固態燃料組成，與固態以及液態火箭比較下，混合式火箭有以下幾個優點： 1.安全性 2.對於裂縫以及缺陷處的敏感度較低，不會過度燃燒 3.可依賴性 4.能量的控制性 5.多用途燃料 6.設計可改變的空間較大 7.環保 8.花費較低。 混合式火箭還是有一些缺點：1.低燃料燃燒效率 2.低體積填充速率 3.燃料在燃燒過後需殘留以防止燒到管壁 4.氧化劑以及燃料的混合比例在燃燒過程中不斷變化 5.混合以及燃燒效率較低。 但由於混合式火箭所具有的安全性，低花費以及設計可改變的空間較大，很適合用來做學術研究。 在交大吳宗信老師的APPL實驗室中，混合式火箭分為實驗組和模擬組，而我負責模擬實驗組設計火箭的燃燒式推進並分析結果。 數值模擬中，使用由太空中心的陳彥升博士及其同僚發展出來的UNIC軟體來模擬，至於模擬的目標，由於混合式火箭的燃燒效率和推力較低，需改善這兩個項目，模擬的部分分為一開始分別以以C4H6和N2O為燃料和氧化劑先完成一個基本模型，之後改變入口噴嘴的面積比、火箭燃燒室預熱區尺寸改變、內部燃料管道直徑改變、氧化劑質量流率改變以及入口噴入區域形狀改變，最後分析及比較其結果。 從實驗以及模擬結果來看，由太空中心陳博士所設計的新型燃燒室氧化劑噴嘴 相當的實用，其可使噴嘴週遭區域在低溫狀態，實際測試幾次後無損壞並可重複使用，並且可平順地將氧化劑導入預熱區和燃料管道中。

Hybrid-Rocket is composed by gaseous or liquid oxidizer and solid fuel. Unlike with Solid and Liquid fuel, Hybrid-Rocket has these advantages: 1.Safety 2. Insensitivity to cracks and imperfections 3.Reliability 4.Energy management 5.Fuel versatility 6.Design flexibility 7.Environmental friendliness 8.Low cost. Of course it has disadvantages like: 1.Slow regression rate 2.Low volumetric loading 3.Fuel residuals 4.Mixture ratio shift 5.Mixing/combustion inefficiencies. And because of its safety, low cost and Design flexibility, hybrid rocket is suitable for academic research. In Dr. Wu’s APPL Lab, Hybrid-Rocket research is separated into two groups, the experimental group and simulation group. And I’m in charge of the Hybrid-Rocket combustion CFD simulation, based on the model of experimental group. In the simulation, we used the simulation code “UNIC” made by Dr. Chen and his colleagues in NSPO. As for our goal, mixing ratio and thrust of Hybrid-Rocket is smaller, so they are the main factors to improve. We used C4H6 and N2O as fuel and oxidizer to finish the basic model. Then, based on this model, we changed the simulation conditions area ratio of pintle injector, port size, pre-combustion chamber size, inlet mass flow rate of oxidizer and inlet region geometry. Then we compared the results with the basic model. From the experimental results, we can see the pintle injector designed by Dr. Chen is quite useful. It maintains a low Temperature region near the pintle injector and thus the pintle injector can be reused for many times without any damage. It can also direct the oxidizer flow well into pre-combustion and fuel port region.