固態糖火箭推進劑燃燒速率之量測

由於固態火箭存在不可控制推力的缺點，因此設計一個能提供適當推力的引擎是必要的，為了要準確的預估引擎推力，推進劑的燃燒速率是個非常重要的參數。燃燒速率是艙壓的函數，其函數名稱為燃燒速率方程式(r = a*Pn)，其中a值跟n值必須由實驗來取得。量測燃燒速率的方式主要分為兩種，分別為克勞佛燃燒艙(Crawford strand burner)及真實引擎推估法(BEM)。兩者各有其優點，克勞佛燃燒艙可以在實驗室中快速地取得資料，而真實引擎推估法可以創造真實的燃燒艙環境。本研究選用真實引擎推估法來做固態糖推進劑之燃燒速率量測。本研究所使用的固態糖推進劑是由山梨糖醇(Sorbitol)及硝酸鉀(KNO3)所組成，山梨糖醇是主要的燃料，同時也具備了黏著劑的功用，而硝酸鉀則是氧化劑，除此之外還加入了少量的氧化鐵(Fe2O3)作為催化劑。此類的固態糖火箭推進劑已經被使用在ARRC 團隊的小型固態糖火箭上，並成功的進行了數次的飛行測試。本研究製作了兩種不同的推進引擎(單管與端點式)來量測推進劑在不同壓力下的燃燒速率，利用改變噴嘴的喉部大小來創造不同的艙壓環境。取得推力及壓力曲線後，假設燃燒速率的方向垂直於推進劑表面並計算出在不同壓力下推進劑的燃燒速率，並將燃燒速率與艙壓依照燃燒速率方程式 (r = a*Pn) 來做分析。實驗的結果顯示燃燒速率會在小於12 atm的區域有起伏的現象，隨後便與壓力呈現正相關。由於本實驗使用的是真實的推進引擎，所以也特別針對燃燒面積與壓力的關係做了分析，並得到了燃燒面積與壓力的關係圖，圖中呈現了燃燒面積與壓力呈現正相關。總結來說，使用目前的量測方法所得到的結果與其他文獻所提供的資料有相同的趨勢。此外本研究同時也在實驗中量測引擎的推力曲線，因此利用量測所取得的壓力及推力曲線便可以對兩種引擎的性能做分析，分別計算出引擎的比衝值(Isp)、特徵排氣速度(C*)及推力參數(CF)。

關鍵字

固態推進劑；燃燒速率；糖火箭推進劑；山梨糖醇-硝酸鉀；真實引擎推估法

並列摘要

Solid rocket is nearly impossible for throttling capability, therefore designing a motor which can produce a desired thrust curve is necessary. In order to precisely predict a thrust curve, a realistic burning rate correlation is very important. The burning rate is a function of combustor pressure and is described by the burning rate equation (r = a*Pn). The parameters “a” and “n” is generally obtained from experimental data. Usually, there are two methods of measurements, which include Crawford strand burner and Ballistic Evaluation Motor (BEM). Crawford strand burner can quickly acquire the data in the laboratory and BEM can create realistic environment of combustion chamber. BEM is selected as the method for measuring the burning rate of solid sugar propellant in this study. The propellant used in this study is composed of Sorbitol and Potassium nitrate (KNO3). Sorbitol is the major fuel which also acts as a binder of propellant and KNO3 is the oxidizer. Iron oxide was also added for its catalytic effect. This type of propulsion system has already been used in several flight missions in our group.. Two different types of experimental combustors (single-port, end burning) were used in this study to investigate the burning rate of the stated propellant at different chamber pressures. These combustors are designed to operate at different chamber pressures with minimal adjustments. Nozzles with various throat diameters were used to produce the desired chamber pressures. After acquiring the real-time thrust and chamber pressure, with the assumption that all propellant regression is normal to the grain surface, the propellant consumption rate and the regression rate are both estimated by the pressure curve. Therefore, burning rate equation can be used to correlate the regression rate with combustor pressure. The results show that burning rate of propellant undulates under 12 atm. and then increase along with pressure increase after 12 atm. Since real motor is used in this study, it is easy to obtain the relationship between burning area and chamber pressure. With the results, we can conclude that the relationship between burning area and chamber pressure is positively correlated. In general, the present measurements agree reasonably well with previous published data. Since the thrust curve of motor is acquired during test, these data can be also used to predict the performance parameters like specific impulse (Isp)、characteristic exhaust velocity (C*) and thrust coefficient (CF) and use these coefficients to analyze the performance of motor.

並列關鍵字

Solid propellant ； Burning rate ； Sugar rocket propellant ； BEM ； Sorbitol-KN

參考文獻

[2] Atwood, A.I., Boggs, T.L., Curran, P.O., Parr, T.P. and Hanson Parr, D.M., “Burning Rate of Solid Propellant Ingredients, Part 2: Determination of Burning Rate Temperature Sensitivity”, Journal Of Propulsion And Power, Vol.15, No.6, November–December, 1999.

[3] Aziz, A., Mamat, R. and Wan Ali, W.K., ‘‘Low Pressure Strand Burner for Solid Propellant Burning Rate Studies’’, International Conference on Mechnical Engineering Research, 2013.

[4] Carro, R., Stephens, M., Aryanetest, J., Powell, A., and Petersen, E., “High-Pressure Testing of Composite Solid Propellant Mixtures: Burner Facility Characterization”, AIAA Paper 2005-3617, 2005.

[5] Crawford, B. L., Jr., Huggett, C., Farrington, D. and Wilfong, R. E., “Direct Determination of Burning Rates of Propellant Powders”, Analytical Chemistry, Vol. 19, No. 9, 1947.

[6] Eisenreich, N., Kugler, H. P. and Sinn, F., “An Optical System for Measuring the Burning Rate of Solid Propellant”, Propellant, Explosives, Pyrotechnics, 1987.

國際替代計量

固態糖火箭推進劑燃燒速率之量測

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