傳統推進劑可分為兩種：固態推進劑與液態推進劑，固態推進劑優點為保存方便可快速使用，但缺點為比衝較低且一但點燃不能停止；液態推進劑優點為比衝較高，且可以利用控制開關閥啟閉來控制推進器的啟閉，但缺點為通常液態推進劑擁有極高的毒性，且不好保存。凝膠推進劑作為一種新型推進劑同時擁有液態及固態推進劑之優點，將水溶液加入結膠劑後會使水溶液凝膠化，在平常保存時類似於固態推進劑。凝膠為一非牛頓流體，當剪切應力增大時黏度會降低，最後黏度與液體相似，可以利用噴嘴使其霧化，與液態推進劑相同。凝膠推進劑對於未來推進器發展具有巨大潛力，所以研究凝膠推進劑是具有價值的。
HAN (硝酸羥胺：NH3OHNO3)是一種新型綠色推進劑，相對於傳統太空推進所使用的聯胺(hydrazine, N2H4)，HAN擁有相對較大的比衝量、較低的毒性且易於儲存。本研究為將HAN水溶液凝膠化，先擬定HAN水溶液凝膠之製備參數，再研究其線燃速反應，並探討其反應機制。之後透過水凝膠作為HAN水溶液凝膠之模擬物探討凝膠噴霧之型態。
根據線燃速實驗結果表明，HAN水溶液凝膠線燃速與壓力呈現高度線性化關係，並在壓力大於3.1 MPa時線燃速有緩降的趨勢，有趣的是加入fumed silica後會使HAN水溶液凝膠自持性反應降低至0.1 MPa。結果表明加入fumed silica有效抑制在1.1-1.6 MPa下HAN水溶液線燃速突增之過渡區其原因為fumed silica會使水吸附於二氧化矽的表面上，使高濃度HAN充滿二氧化矽網絡當中，反應時水不會直接參與反應，而是由高濃度HAN水溶液傳遞反應。
對於凝膠噴霧而言，為了降低安全與實驗成本，本實驗以水凝膠作為HAN水溶液凝膠之模擬物，利用壓力旋流式噴嘴成功將其霧化，並利用影像辨識系統化計算噴霧參數。本實驗探討了上游壓力、噴嘴孔徑及結膠劑比例對於噴霧特性之影響，研究指出增加上游壓力、噴嘴孔徑變大會使噴霧角變大，破碎距離變短，增加結膠劑比例會使噴霧角變小，破碎距離縮小。這些結果對於未來凝膠推進器的研製極為重要。

This study investigates the analysis of burn rate and spraying characteristics of HAN gel propellant. The results indicate a highly linear relationship between the burn rate of HAN gel and pressure, with a gradual decrease in burn rate at pressures above 5.1 MPa. Interestingly, the addition of fumed silica reduces the self-sustained reaction of HAN gel to 0.1 MPa. The results demonstrate that the inclusion of fumed silica effectively suppresses the excessive increase in burn rate of HAN water solution in the pressure range of 1.1-1.6 MPa. This can be attributed to water adsorption on the surface of silica, leading to the high concentration of HAN being distributed within the silica network. During the reaction, water does not directly participate but is transferred by the high-concentration HAN solution. Regarding gel spraying, for the purpose of safety and cost reduction, water gel is used as a surrogate for HAN gel in this experiment. The pressure-swirl nozzle successfully atomizes the gel, and spray parameters are calculated using an image recognition system. The study investigates the influence of upstream pressure, nozzle orifice size, and gelling agent ratio on spray characteristics. The research indicates that increasing upstream pressure and enlarging the nozzle orifice result in larger spray angles and shorter breakup distances, while increasing the gelling agent ratio leads to smaller spray angles and reduced breakup distances. These findings are crucial for future development of gel propellant systems.

[1] B.P. Mason and C.M. Roland (2019), Solid propellants, Rubber Chemistry and Technology 92(1), 1-24.
[2] M.B. Padwal, B. Natan and D.P. Mishra (2021), Gel propellants, Progress in Energy and Combustion Science 83, 1-150.
[3] E.J. Hopfinger and V. Baumbach (2009), Liquid sloshing in cylindrical fuel tanks, Progress in Propulsion Physics 1, 279-292.
[4] H.G. Bundenberg (1949), A survey of the study objects in this volume, Colloid Science 2, 2-17.
[5] P.H. Hermans (1949), Gels, Colloid Science 2, 483-494.
[6] C.J. Brinker and G.W. Scherer, Sol-gel Science, Boston, USA, Academic Press, 1990.
[7] F. Tepper, M.I. Lerner and D.S. Ginley, Metallic nanopowders: an overview, Dekker Encyclopedia of Nanoscience and Nanotechnology, Boca Raton, USA, CRC Press, 2011.
[8] K. Hodge, T Crofoot and S. Nelson, Gelled propellants for tactical missile applications, AIAA Paper 1999-2976, 1999.
[9] W.B. Tarpley, Thixotropic Oxidizer Propellant Mixtures, US Patent 3449178A, 1960.
[10] J.A. Cabeal, System analysis of gelled space-storable propellants, AIAA Paper 1970-609, 1970.
[11] H.K. Ciezki and K.W. Naumann (2016), Some aspects on safety and environmental impact of the german green gel propulsion technology, Propellants, Explosives, Pyrotechnics 41(3), 539-547.
[12] K.F. Hodge, T.A. Crofoot and S. Nelson, Gelled propellants for tactical missile applications, AIAA Paper 1999-2976, 1999.
[13] S.Y. Jejurkar, G. Yadav and D.P. Mishra (2018), Characterization of impinging jet sprays of gelled propellants loaded with nanoparticles in the impact wave regime, Fuel 228, 10-22.
[14] S.Y. Jejurkar, G. Yadav and D.P. Mishra (2018), Visualizations of sheet breakup of non-newtonian gels loaded with nanoparticles, International Journal of Multiphase Flow 100, 57-76.
[15] T.L. Connell, G.A. Risha and R.A. Yetter (2018), Ignition of hydrogen peroxide with gel hydrocarbon fuels, Journal of Propulsion and Power 34(1), 170-181.
[16] P.H.S. Santos, O.H. Campanella and M.A. Carignano (2010), Brownian dynamics study of gel-forming colloidal particles, The Journal of Physical Chemistry B 114(41), 13052-13058.
[17] R. Aggarwal, I.K. Patel and P.B. Sharma (2015), A comprehensive study on gelled propellants, International Journal of Research in Engineering and Technologye 4(9), 286-290.
[18] J.D. Dennis, C. Yoon, P.H. Santos, J.A. Mallory, C.N. Fineman, T.L. Pourpoint, S.F. Son, S.D. Heister, P.E. Sojka and O.H. Campanella, Characterization of gelling systems for development of hypergolic Gels, 4th European Conference for Aerospace Science, St. Petersburg, Russia, July 4-8, 2011.
[19] S.L. Coguill, Synthesis of highly loaded gelled propellants, AIChE Annual Meeting, San Fransico, CA, USA, November 16-21, 2003.
[20] R. Arnold, P.H.S. Santos, T. Kubal, O. Campanella and W.E. Anderson, Investigation of gelled JP-8 and RP-1 fuels, Proceedings of the World Congress on Engineering and Computer Science, San Francisco, CA, USA, October 20-22, 2009.
[21] P.H. Santos, M.A. Carignano and O.H. Campanella (2011), Qualitative study of thixotropy in gelled hydrocarbon fuels, Engineering Letters 19(1), 1-7.
[22] B. Natan and S. Rahimi (2002), The status of gelled propellants in year 2000, International Journal of Energetic Materials and Chemical Propulsion 5, 172-194.
[23] G. Baek and C. Kim (2011), Rheological properties of carbopol containing nanoparticles, Journal of Rheology 55(2), 313-330.
[24] J.M. Green, D.C. Rapp and J. Roncac, Flow visualization of a rocket injector spray using gelled propellant simulants, AIAA Paper 1991-2198, 1991.
[25] W.B. Tarpley, Thixotropic gel fuels, US Patent 4156594A, 1979.
[26] M. Varma and R. Pein (2009), Optimisation of processing conditions for gel propellant production, International Journal of Energetic Materials and Chemical Propulsion 8(6), 501-513.
[27] D.P. Mishra and A. Patyal (2012), Effects of initial droplet diameter and pressure on burning of ATF gel propellant droplets, Fuel 95, 226-33.
[28] M.B. Padwal and D.P. Mishra (2016), Characteristics of gelled jet A1 sprays formed by internal impingement of micro air jets, Fuel 185, 599-611.
[29] M. Calabro (2011), Overview on hybrid propulsion, Progress in Propulsion Physics 2, 353-274.
[30] S. Kang and S. Kwon (2021), Preparation and performance evaluation of platinum barium hexaaluminate catalyst for green propellant hydroxylamine nitrate thrusters, Materials 14, 2828.
[31] T. Katsumi, K. Hori, R. Matsuda and T. Inoue, Combustion wave structure of hydroxylammonium nitrate aqueous solutions, AIAA Paper 2010-900, 2010.
[32] R. Amrousse, T. Katsumi, N. Azuma and K. Hori (2017), Hydroxylammonium nitrate (HAN)-based green propellant as alternative energy resource for potential hydrazine substitution: from lab scale to pilot plant scale-up, Combustion and Flame 176, 334-348.
[33] R.E. Ferguson, A.A. Esparza and E. Shafirovich (2021), Combustion of aqueous HAN/methanol propellants at high pressures, Proceedings of the Combustion Institute 38(2), 3295-3302.
[34] N. Rasmont, E. Broemmelesiek and J. Rovey (2020), Linear burn rate of green ionic liquid multimode monopropellant, Combustion and Flame 219, 212-224.
[35] J.V. Kampen, F. Alberio and H.K. Ciezki (2007), Spray and combustion characteristics of aluminized gelled fuels with an impinging jet injector, Aerospace Science and Technology 11(1), 77-83.
[36] A.H. Lefebvre and V.G, McDonell, Atomization and Sprays 2, Boca Raton, USA, CRC Press, 2017.
[37] S. Rahimi and B. Natan, Atomization characteristics of gel fuels, AIAA Paper 1998-3830, 1998.
[38] B. Pizziol, M. Costa, M.O. Panão and A. Silva (2018), Multiple impinging jet air-assisted atomization, Experimental Thermal and Fluid Science 96, 303-310.
[39] T.L. Connell, G.A. Risha, R.A. Yetter and B. Natan (2018), Hypergolic ignition of hydrogen peroxide/gel fuel impinging jets, Journal of Propulsion and Power 34(1), 182-188.
[40] G.D. Martin, S.D. Hoath and I.M. Hutchings (2008), Inkjet printing- the physics of manipulating liquid jets and drops, Journal of Physics: Conference Series 105(1), 012001.
[41] C. Ramasubramanian, V. Notaro and J.G. Lee (2015), Characterization of near-field spray of non-gelled and gelled-impinging doublets at high pressure, Journal of Propulsion and Power 31, 1642-1652.
[42] A.L. Yarin (2006), Drop impact dynamics: splashing, Annual Review of Fluid Mechanics 38, 159-192.
[43] A. Mansour and N. Chigier (1995), Air-blast atomization of non-newtonian liquids, Journal of Non-Newtonian Fluid Mechanics 58, 161-194.
[44] L.J. Yang, Q.F. Fu, Y.Y. Qu, W. Zhang, M.L. Du and B.R. Xu (2012), Spray characteristics of gelled propellants in swirl injectors, Fuel 97, 253-261.
[45] H.S. Guan, G.X. Li and N.Y. Zhang (2018), Experimental investigation of atomization characteristics of swirling spray by ADN gelled propellant, Acta Astronautica 144, 199-155.
[46] B.C. Urbon, Atomization and combustion of a gelled, metallized slurry fuel, Master Thesis, Naval Postgraduate School, Monterey, USA, 1992.
[47] S.D. Sovania, P.E. Sojkaa and A.H. Lefebvre (2001), Effervescent atomization, Progress in Energy and Combustion Science 27, 483-521.
[48] J.J. Sutherland, P.E. Sojka and M.W. Plesniak (1997), Ligament-controlled effervescent atomization, Atomization Sprays 7, 383-406.
[49] V. Chernov and B. Natan (2008), Effect of periodic disturbances on non-newtonian fluid sprays, Atomization Sprays 18, 723-738.
[50] L.J. Yang, Q.F. Fu, W. Zhang, M.L. Du and M.X. Tong (2013), Spray characteristics of gelled propellants in novel impinging jet injector, Journal of Propulsion and Power 29(1), 104-113.
[51] M.B. Padwal and D.P. Mishra (2016), Experimental characterization of gelled jet A1 spray flames, Flow, Turbulence and Combustion 97(1), 295-337.
[52] F.A. Hammad, K. Sun, Z. Che, J. Jedelsky and T. Wang (2021), Internal two-phase flow and spray characteristics of outside-in-liquid twin-fluid atomizers, Applied Thermal Engineering 187(25), 116555.
[53] S. Hoyani, P. Patel, C. Oommen and R. Rajeev (2017), Thermal stability of hydroxylammonium nitrate (HAN), Journal of Thermal Analysis and Calorimetry 129(2), 1083-1093.
[54] I.Y. Tsai, Reaction characteristics of hydroxylammonium nitrate based propellants and the development of prototype microthrusters, Master Thesis, National Cheng Kung University, Taiwan, 2023.
[55] A. Mundahl, S.P. Berg and J. Rovey, Linear burn rates of monopropellants for multi-mode micropropulsion, AIAA Paper 2016-4579, 2016.
[56] B.N. Kondrikov, V.É. Annikov, V.Y. Egorshev and L.T.D. Luca(2000), Burning of hydroxylammonium nitrate, Combustion, Explosion, and Shock Waves 36, 135-145.