本論文使用奈秒重覆脈衝放電(Nanosecond Repetitively Pulsed Discharges, NRPD)，針對氨氣/空氣混合燃氣在當量比 = 1、固定電極間距dgap = 2 mm及重覆脈衝頻率PRF = 40 kHz之條件下，量測最小引燃能量(Minimum Ignition Energy, MIE)隨均方根擾動速度(u′)之變化關係，MIE為具50%引燃機率的能量。引燃實驗在一大型高壓雙腔體之十字型預混紊流燃燒器中進行，其腔體正中心處設有一對不銹鋼之尖端電極以進行放電，且在大水平圓管腔體兩側各裝有一風扇，可透過反向旋轉特製扇葉在中心處產生一近似等向性紊流場。首先，在層流條件下，使用不同當量比( = 0.9、1.0和1.1)來進行層流MIE (MIEL)之量測，結果顯示，MIEL = 80.4, 72.6 和71.8 mJ 在  = 0.9, 1.0和1.1，即MIEL值會隨著值的增加而下降。再者，我們選擇  = 1.0的條件，進行紊流MIE (MIET)之量測，我們找到一MIE轉變，即在u′小於一臨界u′c ≈ 1 m/s時，MIET值會隨著u′的增加而緩慢上升，但當u′ > u′c時，MIET值則會隨u′值增加而急遽攀升。同樣地，本研究也有找出氨氣之正規化MIET/MIEL與火核反應區Péclet數(Pe = u′k/RZ)之關係，其中k為Kolmogorov長度尺度，RZ (≈ SLδRZ)為反應區熱擴散係數，SL為層流火焰速度，δRZ為層流火焰厚度，並發現其臨界Pec ≈ 4.4，與本實驗室之前量測到的甲烷/空氣(Pec ≈ 4.5)及汽油替代燃料(Pec ≈ 4.2)之結果接近。最後，在電極間距dgap = 1 mm時，即使使用數千個NRPD脈衝（總能量約為2 J），也無法成功引燃在化學計量之氨氣/空氣混合燃氣。前述結果，對以氨為燃料正發展中發電用之燃氣輪機的引燃，應有所助益。

This thesis measures the minimum ignition energy (MIE) of the stoichiometric ammonia/air mixture as a function of root-mean-square (r.m.s) turbulent fluctuation velocities (u′). Using nanosecond repetitively pulsed discharges (NRPD) via a pair of stainless-steel electrodes with sharp ends at a fixed inter-electrode gap (dgap = 2 mm) and at a fixed pulsed repetitive frequency (PRF = 40 kHz). Ignition experiments are conducted in a dual-chamber, fan-stirred cruciform burner capable of generating near-isotropic turbulence. First, values of laminar MIE (MIEL) are measured at three different equivalence ratios ( = 0.9, 1.0 and 1.1 )；MIEL decreases with increasing , MIEL = 80.4, 72.6 and 71.8 mJ at  = 0.9, 1.0 and 1.1, respectively。Second, at the selected  = 1.0, a MIE transition is found. When u′ is less than a critical value of u′c ≈ 1 m/s, turbulent MIE (MIET) only increases gradually with increasing u′. But when u′ > u′c, a drastic increase of MIET is observed. We also find a function of normalized MIET/MIEL and Péclet number (Pe = u′k/RZ) for ammonia/air mixture, where k is the Kolmogorov length scale and the reaction zone thermal diffusivity RZ (≈ SLδRZ)；SL is the laminar burning velocity and δRZ is the laminar flame thickness. It is found the critical Pec occurs at a value of about 4.4 which is very close to the methane/air mixture (Pec ≈ 4.5) and the primary reference automobile fuel/air mixture (Pec ≈ 4.2) our laboratory done before. Finally, when dgap = 1 mm, even using several thousands of NRPD pulses (total energy ~ 2J) cannot ignite the ammonia/air mixture at  = 1.0 and at PRF = 40 kHz. These results may be useful to our understanding of ignition for the developing ammonia gas turbines for electricity generation.

[1] P. Dimitriou, R. Javaid, A review of ammonia as a compression ignition engine fuel, Int. J. Hydrog. Energy 45 (2020) 7098-7118.
[2] J.S. Cardoso, V. Silva, R.C. Rocha, M.J. Hall, M. Costa, D. Eusébio, Ammonia as an energy vector: Current and future prospects for low-carbon fuel applications in internal combustion engines, J. Clean. Prod. 296 (2021) 126562.
[3] M. Comotti, S. Frigo, Hydrogen generation system for ammonia–hydrogen fuelled internal combustion engines, Int. J. Hydrog. Energy, 40 (2015) 10673-10686.
[4] A.V. Medina, S. Morris, J. Runyon, D.G. Pugh, R. Marsh, P. Beasley, T. Hughes, Ammonia, Methane and Hydrogen for Gas Turbines, Energy Procedia 75 (2015) 118-123.
[5] D. Pashchenko, R. Mustafin, I. Karpilov, Ammonia-fired chemically recuperated gas turbine: Thermodynamic analysis of cycle and recuperation system, Energy 252 (2022) 124081.
[6] M. Keller, M. Koshi, J. Otomo, H. Iwasaki, T. Mitsumori, K. Yamada, Thermodynamic evaluation of an ammonia-fueled combined-cycle gas turbine process operated under fuel-rich conditions, Energy 194 (2020) 116894.
[7] B. Wang, T. Li, F. Gong, M.H.D. Othman, R. Xiao, Ammonia as a green energy carrier: Electrochemical synthesis and direct ammonia fuel cell - a comprehensive review, Fuel Process. Technol. 235 (2022) 107380.
[8] T.Q. Quach, V.T. Giap, D.K. Lee, T.P. Israel, K.Y. Ahn, High-efficiency ammonia-fed solid oxide fuel cell systems for distributed power generation, Appl. Energy 324 (2022) 119718.
[9] M. Ilbas, B. Kumuk, M.A. Alemu, B. Arslan, Numerical investigation of a direct ammonia tubular solid oxide fuel cell in comparison with hydrogen, Int. J. Hydrog. Energy 45 (2020) 35108-35117.
[10] D. Frattini, G. Cinti, G. Bidini, U. Desideri, R. Cioffi, E. Jannelli, A system approach in energy evaluation of different renewable energies sources integration in ammonia production plants, Renew. Energ. 99 (2016) 472-482.
[11] J. Armijo, C. Philibert, Flexible production of green hydrogen and ammonia from variable solar and wind energy: Case study of Chile and Argentina, Int. J. Hydrog. Energy 45 (2020) 1541-1558.
[12] Hybrid LNG & Ammonia Infrastructure: Key to a Green Economy, Black & Veatch, 2020. https://www.bv.com/resources/hybrid-lng-ammonia-infrastructure-key-green-economy-ebook.
[13] H. Lesmana, M. Zhu, Z. Zhang, J. Gao, J. Wu, D. Zhang, An experimental investigation into the effect of spark gap and duration on minimum ignition energy of partially dissociated NH3 in air, Combust. Flame 241 (2022) 112053.
[14] S.S. Shy, W.T. Shih, C.C. Liu, More on minimum ignition energy transition for lean premixed turbulent methane combustion in flamelet and distributed regimes, Combust. Sci. Technol. 180 (2008) 1735-1747.
[15] S.S. Shy, C.C. Liu, W.T. Shih, Ignition transition in turbulent premixed combustion, Combust. fiame 157 (2010) 341-350.
[16] M.W. Peng, S.S. Shy, Y.W. Shiu, C.C. Liu, High pressure ignition kernel development and minimum ignition energy measurements in different regimes of premixed turbulent combustion, Combust. Flame 160 (2013) 1755-1766.
[17] L.J. Jiang, S.S. Shy, M.T. Nguyen, S.Y. Huang, D.W. Yu, Spark ignition probability and minimum ignition energy transition of the lean iso-octane/air mixture in premixed turbulent combustion, Combust. Flame 187 (2018) 87-95.
[18] S.S. Shy, M.T. Nguyen, S.Y. Huang, Effects of electrode spark gap, differential diffusion, and turbulent dissipation on two distinct phenomena: Turbulent facilitated ignition versus minimum ignition energy transition, Combust. Flame 205 (2019) 371-377.
[19] L. Haar, J.S. Gallagher, Thermodynamic properties of ammonia, J. Phys. Chem. Ref. Data 635 (1978)
[20] Y. Feng, J. Zhu, Y. Mao, M. Raza, Y. Qian, L. Yu, X. Lu, Low-temperature auto-ignition characteristics of NH3/diesel binary fuel: Ignition delay time measurement and kinetic analysis, Fuel 281 (2020) 118761.
[21] J. Yang, W. Weng, W. Xiao, Electrochemical synthesis of ammonia in molten salts, J. Energy Chem. 43 (2020) 195-207.
[22] U.J. Pfahl, M.C. Ross, J.E. Shepherd, K.O. Pasamehmetoglu, C. Unal, Flammability limits, ignition energy, and flame speeds in H2–CH4–NH3–N2O–O2–N2 mixtures, Combust. Flame 123 (2000) 140-158.
[23] B. Shu, S.K. Vallabhuni, X. He, G. Issayev, K. Moshammer, A. Farooq, R.X. Fernandes, A shock tube and modeling study on the autoignition properties of ammonia at intermediate temperatures, Proc. Combust. Inst. 37 (2019) 205-211.
[24] H. Lesmana, M. Zhu, Z. Zhang, J. Gao, J. Wu, D. Zhang, Experimental and kinetic modelling studies of flammability limits of partially dissociated NH3 and air mixtures, Proc. Combust. Inst. 38 (2021) 2023-2030.
[25] Y. Tang, D. Xie, B. Shi, N. Wang, S. Li, Flammability enhancement of swirling ammonia/air combustion using AC powered gliding arc discharges, Fuel 313 (2022) 122674.
[26] D.R. Jenkins, Hypersonics Before the Shuttle: A Concise History of the X-15 Research Airplane, NASA Publication (2000).
[27] O. Kurata, N. Iki, T. Matsunuma, T. Inoue, T. Tsujimura, H. Furutani, H. Kobayashi, A. Hayakawa, Performances and emission characteristics of NH3–air and NH3single bondCH4–air combustion gas-turbine power generations, Proc. Combust. Inst. 36 (2017) 3351-3359.
[28] H. Lesmana, M. Zhu, Z. Zhang, J. Gao, J. Wu, D. Zhang, An experimental investigation into the effect of spark gap and duration on minimum ignition energy of partially dissociated NH3 in air, Combust. Flame 241 (2022) 112053.
[29] Y. Ju, W. Sun, Plasma assisted combustion: Dynamics and chemistry, Prog. Energy Combust. Sci. 48 (2015) 21-83.
[30] A. Fridman, S. Nester, L.A. Kennedy, A. Saveliev, M.Y. Ozlem, Gliding arc gas discharge, Prog. Energy Combust. Sci. 25 (1999) 211-231.
[31] T. Hammer, T. Kappes, M. Baldauf, Plasma catalytic hybrid processes: gas discharge initiation and plasma activation of catalytic processes, Catal. Today 89 (2004) 5-14.
[32] X. Tao, M. Bai, X. Li, H. Long, S. Shang, Y. Yin, X. Dai, CH4–CO2 reforming by plasma – challenges and opportunities, Prog. Energy Combust. Sci. 37 (2011) 113-124.
[33] H. Do, S.K. Im, M.A. Cappelli, M.G. Mungal, Plasma assisted flame ignition of supersonic flows over a flat wall, Combust. Flame 157 (2010) 2298-2305.
[34] Y.P. Raizer, Gas Discharge Physics, Barcelona: Springer, 1991.
[35] V.T. Walter, L. Merotto, M. Balmelli, P. Soltic, Experimental study of the ignition of lean methane/air mixtures using inductive and NRPD ignition systems in the pre-chamber and turbulent jet ignition in the main chamber, Energy Conv. Manag. 252 (2022) 115012.
[36] J.A.T. Gray, D.A. Lacoste, Effect of the plasma location on the deflagration-to-detonation transition of a hydrogen–air flame enhanced by nanosecond repetitively pulsed discharges, Proc. Combust. Inst. 38 (2021) 3463-3472.
[37] M.T. Nguyen, S.S. Shy, Y.R. Chen, B.L. Lin, S.Y. Huang, C.C. Liu, Conventional spark versus nanosecond repetitively pulsed discharge for a turbulence facilitated ignition phenomenon, Proc. Combust. Inst. 38 (2021) 2801-2808.
[38] B. Lewis, G. von Elbe, Combustion, Flames and Explosions of Gases, 3rd ed., Academic Press, Orlando, 1987.
[39] A.P. Kelley, C.K. Law, Nonlinear effects in the extraction of laminar flame speeds from expanding spherical flames, Combust. Flame 156 (2009) 1844-1851.
[40] S.P.M. Bane, Spark ignition: Experimental and numerical investigation with application to aviation safety, California Institute of Technology, Ph.D. thesis, 2010.
[41] 石泰光，壓力效應對奈秒重覆脈衝放電引燃機率之影響，國立中央大學機械工程研究所，碩士論文，2022。
[42] X. Chen, Q. Liu, Z. Mou, Y. Shen, J. Huang, H. Ma, Flame front evolution and laminar flame parameter evaluation of buoyancy-affected ammonia/air flames, Int. J. Hydrog. Energy 46 (2021) 38504-38518.
[43] S.S. Shy, Y.C. Liao, Y.R. Chen, S.Y. Huang, Two ignition transition modes at small and large distances between electrodes of a lean primary reference automobile fuel/air mixture at 373 K with Lewis number >> 1, Combust. Flame 225 (2021) 340-348.