混合式火箭推進劑燃料HTPB藥柱之製程優化及機械性質研究

Abstract

混合式火箭近年來因其系統簡單、操作安全性高及可控制其推力而備受矚目。其中在混合式火箭中最常見的燃料藥柱為端羥基聚丁二烯( Hydroxyl-terminated Polybutadiene, HTPB)。對於一個穩定與良好性能的混合燃燒來說，HTPB藥柱是否可以承受如此大的壓力是很重要的。本論文已完成一套標準燃料藥柱製作流程，其中包含HTPB與異佛爾酮二異氰酸酯( Isophorone diisocyanate, IPDI)做混合固化，再加上些許碳粉吸收輻射熱避免藥柱在燃燒過程中軟化。在本論文中，探討了不同IPDI比例下之機械性質探討。其中，IPDI比例增加會增強其機械性質，但不宜超過12.5%，會發生固化時間太快而氣泡無法成功抽出之問題。而在加入各種不同比例的蓖麻油與催化劑後得知，蓖麻油比例5%是不錯的選擇，可有效降低燃料黏度，而再加入0.02%的催化劑經過測試可以縮短固化時間而又可以將氣泡順利被抽出。加入5%的蓖麻油已經過小型推力地面測試成功，且增加火箭引擎的比衝值(Specific Impulse, Isp)，與使用軟體Propep模擬結果相符。

Hybrid rocket propulsion has been an important research subject for the past few years because of some outstanding characteristics such as system simplicity, high operation safety, and thrust controllability. In hybrid propulsion system, one of the commonest fuel grains is Hydroxyl-terminated Polybutadiene (HTPB). To design a stable hybrid propulsion system, complete characterization of the material properties of HTPB grain is necessary. In this thesis, baseline and advanced processes of preparing fuel grain are developed and tested. For the baseline process, we have used HTPB and IPDI (Isophorone diisocyanate) with different mixing ratios with addition of a small amount of carbon powder for preventing radiation transfer from the flame through the grain. For the advanced process, we have added castor oil for reducing mixture viscosity and catalyst for greatly speeding up necessary curing process. Several important mechanical properties are measured, respectively, for the baseline and advanced processed fuel grains. The results show that the maximal fraction of IPDI is 12.5%, above which bubbles are trapped in the grain even after a long period of curing time with vacuum pumping. In addition, it is found that 5% of castor oil can effectively reduce the mixture viscosity without affecting the material properties much as compared the baseline procedure. Moreover, addition of 0.02% of catalyst can dramatically shorten the required curing time and can still make bubbles pumped out efficiently. Finally, we have performed several static burn tests and have found that Isp (specific impulse) of the fuel grain with 5% addition of castor oil is higher than that of the baseline procedure, which is in consistent with the prediction made by a public available software, Propep.