本研究透過實驗研究了滑動電弧放電對不同含水之甲醇擴散火焰穩定之影響，在原甲醇(Crude methanol)中，水是最為常見之雜質且佔有相當大的比例，當甲醇作為燃料時，必需對甲醇進行脫水的程序，而脫水過程為甲醇製成中，最為耗能的步驟。因此，本研究利用低功率的滑動電弧電漿輔助甲醇中加入不同比例的水作為噴霧燃燒的燃料之可行性與評估甲醇混合物中含水量上限。結果發現在含水量之甲醇噴霧燃燒下之滑動電弧放電過程中的週期隨空氣流量增加而減少，並且出現兩種放電類型。在低流量下，放電為輝光型放電，出現較少電流峰值；在高流量下，放電轉為火花型放電的機率增加，因為出現較多次數的電流峰值。在30 SLM空氣流量下，隨著含水量上升之甲醇燃料，平均功率沒有太大的變化。不論有無滑動電弧電漿輔助，隨著甲醇中之含水量上升火焰長度隨之變短。反之，無電漿輔助之跳脫高度則隨著含水量增加而增加；有電漿輔助之跳脫高度離噴嘴不超過50mm，表明電漿有助於增加含水甲醇之燃燒穩定性。根據CH*活性自由基分布發現滑動電弧電漿增加了火焰熱釋放率，可能是滑動電弧電漿延長可燃性極限的原因之一。最後，對有和沒有電漿輔助含水甲醇噴霧燃燒及其可燃性極限、排放與燃燒效率作探討，將進一步有效地應用含水甲醇噴霧燃燒。

In this study, the effect of gliding arc discharge on the flame stability of methanol diffusion combustion with different water content was investigated through experiments. In crude methanol, water is the most common impurity and occupies a considerable proportion. When methanol is used as fuel, it is necessary to dehydrate the crude methanol into high-grade methanol. The dehydration process is the most energy-intensive step in methanol production. Therefore, this thesis investigated the feasibility of adding different proportions of water to methanol as a fuel for spray combustion using low-power gliding arc plasma-assisted. The phenomenon of flame behaviors such as the flame length and lift-off height show that plasma positively affects combustion enhancement. It was found that the period during the gliding arc discharge under methanol/water spray combustion decreased as the airflow increased, and two types of discharge occurred. At the low flow rate, the discharge is a glow-type discharge with fewer current peaks; at the high flow rate, the probability of spark-type discharge increases because of more current peaks. Furthermore, the flame length decreased as the water content in the methanol increased with or without gliding arc plasma assisted. On the contrary, the lift-off height without plasma-assisted increases with the increase of water content; the lift-off height with plasma-assisted isn’t over 50mm from the nozzle, indicating that plasma helps to enhance combustion stability. According to the distribution of CH* radicals, it was discovered that the gliding arc plasma increases the flame heat release rate, which may be one of the reasons why the flammability limits of water content in methanol was extended. Finally, with and without plasma-assisted methanol/water mixtures spray combustion, its flammability limits, emissions, and combustion efficiency are discussed. We hope that the methanol/water mixtures spray combustion will be further effectively applied in the future.

[1] Okonko, I.O., et al., Current trends in biofuel production and its use as an alternative energy security. Electronic Journal of Environmental, Agricultural & Food Chemistry, 2009. 8(12).
[2] Shamsul, N.S., et al., An overview on the production of bio-methanol as potential renewable energy. Renewable & Sustainable Energy Reviews, 2014. 33: p. 578-588.
[3] <english_paris_agreement.pdf>.
[4] Tans, P. and R. Keeling, NOAA. ESRL (www. esrl. noaa. gov/gmd/ccgg/trends/), 2010.
[5] Ju, Y. and W. Sun, Plasma assisted combustion: Dynamics and chemistry. Progress in Energy and Combustion Science, 2015. 48: p. 21-83.
[6] Agreement, P., UNFCCC, Adoption of the Paris agreement. COP. 25th session Paris, 2015. 30.
[7] Yousaf, M., et al., Techno-economic analysis of integrated hydrogen and methanol production process by CO2 hydrogenation. International Journal of Greenhouse Gas Control, 2022. 115: p. 103615.
[8] Pérez-Fortes, M., et al., Methanol synthesis using captured CO2 as raw material: Techno-economic and environmental assessment. Applied Energy, 2016. 161: p. 718-732.
[9] Lin, B., et al., Experimental investigation of gliding arc plasma fuel injector for ignition and extinction performance improvement. Applied Energy, 2019. 235: p. 1017-1026.
[10] Leonov, S.B., et al., Modes of plasma-stabilized combustion in cavity-based M= 2 configuration. Experimental Thermal and Fluid Science, 2021. 124: p. 110355.
[11] Choe, J., et al., Plasma assisted ammonia combustion: Simultaneous NOx reduction and flame enhancement. Combustion and Flame, 2021. 228: p. 430-432.
[12] Feng, R., et al., Ignition and combustion enhancement in a cavity-based supersonic combustor by a multi-channel gliding arc plasma. Experimental Thermal and Fluid Science, 2021. 120: p. 110248.
[13] Zare, S., et al., On the low-temperature plasma discharge in methane/air diffusion flames. Energy, 2020. 197: p. 117185.
[14] Zhang, H.-L., et al., Experimental study on ignition characteristics of kerosene–air mixtures in V-shaped burner with DC plasma jet igniter. Aerospace Science and Technology, 2018. 74: p. 56-62.
[15] Vincent-Randonnier, A., et al. Expermiental study of a methane diffusion flame under dielectric barrier discharge assistance. in The 33rd IEEE International Conference on Plasma Science, 2006. ICOPS 2006. IEEE Conference Record-Abstracts. 2006. IEEE.
[16] Tang, Y., et al., Non-premixed flame dynamics excited by flow fluctuations generated from Dielectric-Barrier-Discharge plasma. Combustion and Flame, 2019. 204: p. 58-67.
[17] Liao, Y.-H. and X.-H. Zhao, Plasma-assisted stabilization of lifted non-premixed jet flames. Energy & Fuels, 2018. 32(3): p. 3967-3974.
[18] Walsh, J.L., et al., Three distinct modes in a cold atmospheric pressure plasma jet. Journal of Physics D: Applied Physics, 2010. 43(7): p. 075201.
[19] Zhu, J., et al., Spatiotemporally resolved characteristics of a gliding arc discharge in a turbulent air flow at atmospheric pressure. Physics of Plasmas, 2017. 24(1): p. 013514.
[20] Ghasemi, A., P. Heidarnejad, and A. Noorpoor, A novel solar-biomass based multi-generation energy system including water desalination and liquefaction of natural gas system: Thermodynamic and thermoeconomic optimization. Journal of Cleaner Production, 2018. 196: p. 424-437.
[21] Cao, Y., et al., A novel multi-objective spiral optimization algorithm for an innovative solar/biomass-based multi-generation energy system: 3E analyses, and optimization algorithms comparison. Energy Conversion and Management, 2020. 219: p. 112961.
[22] Shayesteh, A.A., et al., Determination of the ORC-RO system optimum parameters based on 4E analysis; Water–Energy-Environment nexus. Energy Conversion and Management, 2019. 183: p. 772-790.
[23] Maurya, P., P. Muthukumar, and R. Anandalakshmi, Methanol cookstove a potential alternative to LPG cookstove: Usability, safety and sustainability studies. Sustainable Energy Technologies and Assessments, 2022. 53: p. 102508.
[24] Cifre, P.G. and O. Badr, Renewable hydrogen utilisation for the production of methanol. Energy conversion and management, 2007. 48(2): p. 519-527.
[25] Ganesh, I., Conversion of carbon dioxide into methanol–a potential liquid fuel: Fundamental challenges and opportunities (a review). Renewable and Sustainable Energy Reviews, 2014. 31: p. 221-257.
[26] Liu, C., et al., Methanol as a Fuel for Internal Combustion Engines, in Engines and Fuels for Future Transport. 2022, Springer. p. 281-324.
[27] Zhen, X. and Y. Wang, An overview of methanol as an internal combustion engine fuel. Renewable and Sustainable Energy Reviews, 2015. 52: p. 477-493.
[28] Brynolf, S., E. Fridell, and K. Andersson, Environmental assessment of marine fuels: liquefied natural gas, liquefied biogas, methanol and bio-methanol. Journal of cleaner production, 2014. 74: p. 86-95.
[29] Ellis, J. and K. Tanneberger, Study on the use of ethyl and methyl alcohol as alternative fuels in shipping. Eur. Marit. Saf. Agency, 2015.
[30] Zhen, X. and Y. Wang, Numerical analysis on original emissions for a spark ignition methanol engine based on detailed chemical kinetics. Renewable Energy, 2015. 81: p. 43-51.
[31] Chen, Z., L. Wang, and K. Zeng, A comparative study on the combustion and emissions of dual-fuel engine fueled with natural gas/methanol, natural gas/ethanol, and natural gas/n-butanol. Energy Conversion and Management, 2019. 192: p. 11-19.
[32] Zhang, Z., et al., Effects of low-level water addition on spray, combustion and emission characteristics of a medium speed diesel engine fueled with biodiesel fuel. Fuel, 2019. 239: p. 245-262.
[33] Wu, C.-Y. and B.-Y. Hu, Characterisation of the effect of water content on the methanol spray combustion. International Journal of Exergy, 2022. 38(2): p. 139-157.
[34] Starikovskii, A.Y., Plasma supported combustion. Proceedings of the Combustion Institute, 2005. 30(2): p. 2405-2417.
[35] Kim, W., M.G. Mungal, and M.A. Cappelli, The role of in situ reforming in plasma enhanced ultra lean premixed methane/air flames. Combustion and Flame, 2010. 157(2): p. 374-383.
[36] Huang, Y. and V. Yang, Dynamics and stability of lean-premixed swirl-stabilized combustion. Progress in energy and combustion science, 2009. 35(4): p. 293-364.
[37] Sun, W., et al., Effects of non-equilibrium plasma discharge on counterflow diffusion flame extinction. Proceedings of the Combustion Institute, 2011. 33(2): p. 3211-3218.
[38] Hicks, A., et al., Singlet oxygen generation in a high pressure non-self-sustained electric discharge. Journal of Physics D: Applied Physics, 2005. 38(20): p. 3812.
[39] Raizer, Y.P. and J.E. Allen, Gas discharge physics. Vol. 1. 1991: Springer.
[40] Tang, J., W. Zhao, and Y. Duan, In-depth study on propane–air combustion enhancement with dielectric barrier discharge. IEEE Transactions on Plasma Science, 2010. 38(12): p. 3272-3281.
[41] Fridman, A., et al., Characteristics of Gliding Arc and Its Application in Combustion Enhancement. Journal of Propulsion and Power, 2008. 24(6): p. 1216-1228.
[42] Chen, W., et al., Characteristics of Gliding Arc Plasma and Its Application in Swirl Flame Static Instability Control. Processes, 2020. 8(6): p. 684.
[43] Ju, R.-Y., et al., Effect of Rotating Gliding Arc Plasma on Lean Blow-Off Limit and Flame Structure of Bluff Body and Swirl-Stabilized Premixed Flames. IEEE Transactions on Plasma Science, 2021. 49(11): p. 3554-3565.
[44] Khacef, A., J.M. Cormier, and J.M. Pouvesle, NOx remediation in oxygen-rich exhaust gas using atmospheric pressure non-thermal plasma generated by a pulsed nanosecond dielectric barrier discharge. Journal of Physics D: Applied Physics, 2002. 35(13): p. 1491.
[45] Tang, Y., et al., Flammability enhancement of swirling ammonia/air combustion using AC powered gliding arc discharges. Fuel, 2022. 313: p. 122674.
[46] Anastas, P.T. and J.C. Warner, Green chemistry. Frontiers, 1998. 640: p. 1998.
[47] Chen, F., et al., Hydrogen production from alcohols and ethers via cold plasma: A review. International journal of hydrogen energy, 2014. 39(17): p. 9036-9046.
[48] Du, C., et al., Hydrogen production by steam-oxidative reforming of bio-ethanol assisted by Laval nozzle arc discharge. International Journal of Hydrogen Energy, 2012. 37(10): p. 8318-8329.
[49] Romanovsky, G. and I. Matveev. Development of a plasma fuel nozzle and results of the experimental investigations. in Proc. Nikolaev Shipbuilding Inst. Thermal Energy Air Conditioning. 1983.
[50] Matveev, I.B., et al., Plasma fuel nozzle as a prospective way to plasma-assisted combustion. IEEE Transactions on Plasma Science, 2010. 38(12): p. 3313-3318.
[51] Barbosa, S., et al., Influence of nanosecond repetitively pulsed discharges on the stability of a swirled propane/air burner representative of an aeronautical combustor. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2015. 373(2048): p. 20140335.
[52] Gomez del Campo, F., D.E. Weibel, and C. Wen. Preliminary results from a plasma-assisted 7-point Lean Direct Injection (LDI) combustor and resulting impacts on combustor stability and combustion dynamics. in 53rd AIAA/SAE/ASEE joint propulsion conference. 2017.
[53] Wang, Q., et al., Lift-off of jet diffusion flame in sub-atmospheric pressures: An experimental investigation and interpretation based on laminar flame speed. Combustion and flame, 2014. 161(4): p. 1125-1130.
[54] Zhou, W., et al., Experimental and numerical investigations on the spray characteristics of liquid-gas pintle injector. Aerospace Science and Technology, 2022. 121: p. 107354.
[55] Zhang, X., et al., Flame extension area of unconfined thermal ceiling jets induced by rectangular-source jet fire impingement. Applied Thermal Engineering, 2018. 132: p. 801-807.
[56] Qi, D., et al., Comprehensive optical diagnostics for flame behavior and soot emission response to a non-equilibrium plasma. Energy, 2022. 255: p. 124555.
[57] Xie, K., et al., Study on threshold selection method of continuous flame images of spray combustion in the low-pressure chamber. Case Studies in Thermal Engineering, 2021. 26: p. 101195.
[58] Otsu, N., A threshold selection method from gray-level histograms. IEEE transactions on systems, man, and cybernetics, 1979. 9(1): p. 62-66.
[59] Kittler, J. and J. Illingworth, Minimum error thresholding. Pattern recognition, 1986. 19(1): p. 41-47.
[60] Prewitt, J.M. and M.L. Mendelsohn, The analysis of cell images. Annals of the New York Academy of Sciences, 1966. 128(3): p. 1035-1053.
[61] Tao, C., et al., The experimental study of flame height and lift-off height of propane diffusion flames diluted by carbon dioxide. Fuel, 2021. 290: p. 119958.
[62] Zhou, Z., et al., Experimental study on determination of flame height and lift-off distance of rectangular source fuel jet fires. Applied Thermal Engineering, 2019. 152: p. 430-436.
[63] Turns, S.R., Introduction to combustion. Vol. 287. 1996: McGraw-Hill Companies New York, NY, USA.
[64] Joseph, D., et al., Evaluation of the Efficiency of Industrial Flares: Background- Experimental Design- Facility. 1983.
[65] Johnson, M. and L. Kostiuk, Efficiencies of low-momentum jet diffusion flames in crosswinds. Combustion and Flame, 2000. 123(1-2): p. 189-200.
[66] Corbin, D.J. and M.R. Johnson, Detailed expressions and methodologies for measuring flare combustion efficiency, species emission rates, and associated uncertainties. Industrial & Engineering Chemistry Research, 2014. 53(49): p. 19359-19369.
[67] Singh, A.P., et al., Spatio-temporal effect of the breakdown zone in the laser-initiated ignition of atomized ethyl alcohol-air mixture. Applied Energy, 2019. 247: p. 140-154.
[68] Shervani-Tabar, M.T., M. Sheykhvazayefi, and M. Ghorbani, Numerical study on the effect of the injection pressure on spray penetration length. Applied Mathematical Modelling, 2013. 37(14-15): p. 7778-7788.
[69] Rho, B.-J., et al., Swirl effect on the spray characteristics of a twin-fluid jet. KSME International Journal, 1998. 12(5): p. 899-906.
[70] Niu, Z., et al., Effect of flow rate on the characteristics of repetitive microsecond-pulse gliding discharges. Wuli Xuebao, 2015. 64(19): p. 195204-195204.
[71] Feng, R., et al., Experimental research on discharge characteristics of multiple-channel gliding arc discharge. High Volt. Eng, 2018. 44: p. 4052-4060.
[72] You, B., et al., Experimental study of gliding arc plasma-assisted combustion in a blast furnace gas fuel model combustor: Flame structures, extinction limits and combustion stability. Fuel, 2022. 322: p. 124280.
[73] Kong, C., et al., Characteristics of a gliding arc discharge under the influence of a laminar premixed flame. IEEE Transactions on Plasma Science, 2018. 47(1): p. 403-409.
[74] Gangoli, S.P., Experimental and modeling study of warm plasmas and their applications. 2007, Drexel University.
[75] Kong, C., et al., Characterization of an AC glow-type gliding arc discharge in atmospheric air with a current-voltage lumped model. Physics of Plasmas, 2017. 24(9): p. 093515.
[76] Bartnikas, R. and J. Novak, On the spark to pseudoglow and glow transition mechanism and discharge detectability. IEEE transactions on electrical insulation, 1992. 27(1): p. 3-14.
[77] Korolev, Y.D., et al., Glow-to-spark transitions in a plasma system for ignition and combustion control. IEEE transactions on plasma science, 2007. 35(6): p. 1651-1657.
[78] Ashpis, D.E., M.C. Laun, and E.L. Griebeler, Progress toward accurate measurement of dielectric barrier discharge plasma actuator power. AIAA Journal, 2017. 55(7): p. 2254-2268.
[79] Yoshida, A., et al., Experimental and numerical investigation of flame speed retardation by water mist. Combustion and Flame, 2015. 162(5): p. 1772-1777.
[80] Elbaz, A.M. and W.L. Roberts, Flame structure of methane inverse diffusion flame. Experimental thermal and fluid science, 2014. 56: p. 23-32.
[81] Liang, K. and R. Stone, Laminar burning velocity measurement of hydrous methanol at elevated temperatures and pressures. Fuel, 2017. 204: p. 206-213.
[82] Higgins, B. and D. Siebers, Measurement of the flame lift-off location on DI diesel sprays using OH chemiluminescence. SAE Transactions, 2001: p. 739-753.
[83] Hu, L., et al., Flame radiation fraction behaviors of sooty buoyant turbulent jet diffusion flames in reduced-and normal atmospheric pressures and a global correlation with Reynolds number. Fuel, 2014. 116: p. 781-786.
[84] Reddy, V.M., D. Trivedi, and S. Kumar, Experimental investigations on lifted spray flames for a range of coflow conditions. Combustion science and technology, 2012. 184(1): p. 44-63.
[85] Gao, J., et al., Visualization of instantaneous structure and dynamics of large-scale turbulent flames stabilized by a gliding arc discharge. Proceedings of the Combustion Institute, 2019. 37(4): p. 5629-5636.
[86] Li, T., I.V. Adamovich, and J.A. Sutton, Effects of non-equilibrium plasmas on low-pressure, premixed flames. Part 1: CH* chemiluminescence, temperature, and OH. Combustion and Flame, 2016. 165: p. 50-67.
[87] Huang, S., et al., Experimental investigation of multichannel plasma igniter in a supersonic model combustor. Experimental Thermal and Fluid Science, 2018. 99: p. 315-323.
[88] Bandaru, R.V., et al. Sensors for measuring primary zone equivalence ratio in gas turbine combustors. in Advanced Sensors and Monitors for Process Industries and the Environment. 1999. SPIE.
[89] Venkataraman, K., et al., Mechanism of combustion instability in a lean premixed dump combustor. Journal of Propulsion and Power, 1999. 15(6): p. 909-918.
[90] Zhu, Z., et al., Laminar Flame Characteristics of Premixed Methanol–Water–Air Mixture. Energies, 2020. 13(24): p. 6504.
[91] Sobhy, A., I. Butler, and J. Kozinski, Selected profiles of high-pressure methanol–air flames in supercritical water. Proceedings of the Combustion Institute, 2007. 31(2): p. 3369-3376.
[92] Liu, D.-H., et al., High intensity combustion of coal with water injection. Combustion and flame, 1986. 63(1-2): p. 49-57.
[93] Chintala, N., et al., Measurements of combustion efficiency in nonequilibrium RF plasma-ignited flows. Combustion and flame, 2006. 144(4): p. 744-756.
[94] Belhi, M., et al., Three-dimensional simulation of ionic wind in a laminar premixed Bunsen flame subjected to a transverse DC electric field. Combustion and Flame, 2019. 202: p. 90-106.
[95] Gardiner, W.C. and A. Burcat, Combustion chemistry. 1984: Springer.
[96] Sayed-Kassem, A., et al., Numerical modelling to study the effect of DC electric field on a laminar ethylene diffusion flame. International Communications in Heat and Mass Transfer, 2021. 122: p. 105167.
[97] Nikiforov, A.Y., A. Sarani, and C. Leys, The influence of water vapor content on electrical and spectral properties of an atmospheric pressure plasma jet. Plasma Sources Science and Technology, 2011. 20(1): p. 015014.
[98] Bruggeman, P. and D.C. Schram, On OH production in water containing atmospheric pressure plasmas. Plasma Sources Science and Technology, 2010. 19(4).
[99] Benstaali, B., et al., Density and rotational temperature measurements of the OH and NO radicals produced by a gliding arc in humid air. Plasma chemistry and plasma processing, 2002. 22(4): p. 553-571.
[100] Itikawa, Y. and N. Mason, Cross sections for electron collisions with water molecules. Journal of Physical and Chemical reference data, 2005. 34(1): p. 1-22.
[101] Jensen, M., et al., Dissociative recombination and excitation of H 2 O+ and HDO+. Physical Review A, 1999. 60(4): p. 2970.
[102] Millar, T., P. Farquhar, and K. Willacy, The UMIST database for astrochemistry 1995. Astronomy and Astrophysics Supplement Series, 1997. 121(1): p. 139-185.
[103] Brisset, A., et al., Chemical kinetics and density measurements of OH in an atmospheric pressure He+ O2+ H2O radiofrequency plasma. Journal of Physics D: Applied Physics, 2021. 54(28): p. 285201.
[104] Ombrello, T. and Y. Ju, Kinetic Ignition Enhancement of $hbox {H} _ {2} $ Versus Fuel-Blended Air Diffusion Flames Using Nonequilibrium Plasma. IEEE Transactions on Plasma Science, 2008. 36(6): p. 2924-2932.
[105] Kim, W., et al., Investigation of NO production and flame structure in plasma enhanced premixed combustion. Proceedings of the Combustion Institute, 2007. 31(2): p. 3319-3326.
[106] Rao, X., I.B. Matveev, and T. Lee, Nitric oxide formation in a premixed flame with high-level plasma energy coupling. IEEE Transactions on plasma science, 2009. 37(12): p. 2303-2313.
[107] Burlica, R., B. Hnatiuc, and E. Hnatiuc. Hydrogen and hydrogen peroxide formation in the AC water-spray gliding arc reactor. in 2010 12th International Conference on Optimization of Electrical and Electronic Equipment. 2010. IEEE.
[108] Du, C. and J. Yan, Electrical and spectral characteristics of a hybrid gliding arc discharge in air–water. IEEE transactions on plasma science, 2007. 35(6): p. 1648-1650.
[109] Ni, C. and X. Cheng, Ab initio study of the second positive system of N2 at high temperature. Computational and Theoretical Chemistry, 2021. 1197: p. 113158.