外加微波可藉由影響火焰中帶電離子和電子的運動而達成增加火焰燃燒速度並有效穩駐火焰於近貧油燃燒極限之目的，根據此原理與想法本研究建立一微波產生系統以觀測研究在不同微波功率下對於火焰外型與穩駐極限的影響。微波藉由共振腔的設計而放大功率，由測量結果可知功率最大值位於距離節點微波1/4波長的奇數倍位置處。此外本論文設計一嶄新的集中微波燃燒器以期能進一步集中微波能量並提高火焰吸收微波的效率，配合數值模擬所得之電場強度分布結果做為後續設計的參考依據。本論文中，根據微波輸入功率的不同，微波增強火燄的機制可區分三個階段。低功率(<40瓦特)單純由微波電場對火焰中的化學反應產生增強的作用。中高功率(40-60瓦特)則為過渡階段，這時火焰增強的效應主要來自於電漿後方離子和周圍中性分子碰撞所造成的局部升溫作用，當功率超過60瓦特時，則由電漿內生成的高能活性基直接和火焰偶合而大幅增強火焰強度，微波能量的耦合效率亦在本研究中加以計算和討論。由結果顯示微波和火焰面中的帶電粒子耦合反應後，可產生一電漿穩駐之次極限貧油預混火焰，藉由光譜分析得知電漿火焰中產生大量的CH和OH活性基而貧油燃燒極限當量比亦可從原本的0.82降低至0.38，遠低於一般預混甲烷火焰的貧油燃燒極限。最後將此生成電漿概念應用於離子推進器，在常溫大氣環境下建立一微波電漿推進器並加以測試和分析。結果顯示電漿生成後可提升部分推力，使得比衝值高於一般冷流體條件，由於此實驗皆於大氣環境下進行，是故僅可利用離子與中性氣體間碰撞反應加熱氣體進行熱電加速方式。電能式推進器就原理上而言越高等級的真空條件可以達到更高的電離度，便於採用靜電亦或電磁感應方式來加速離子，這些方式可將推進器比衝值提升至2000~3000 s以上，日後推進器的改良與規劃上亦將朝向此一發展方向進行。

By affecting the ion motions and electron temperature in the flame, microwave is shown to effectively enhance and stabilize the flame in the sub-limit lean premixed region. In this study, we first develop and set up the concentrated-microwave jet combustor system for fundamental studies of the stabilization mechanism of the sub-lean limit flames. The control parameters and operation characteristics of the integrated system is further investigated. The microwave energy is enhanced and applied to the combustion system by means of a rectangular resonant cavity. In the resonator, standing waves occur due to resonance. In order to concentrate the microwave energy and enhance the absorption of microwave energy by the flame, a novel design of microwave centralized burner is used to incorporate microwave (2.45 GHz) electromagnetic energy directly into the reaction zone of a premixed laminar methane–air flame for flame enhancement. Depending upon the input microwave power, three enhanced stages (1) Electric Field Enhanced (2) Transition and (3) Full Plasma Assisted can be categorized. The stabilization process, mechanism of the lean and sub-limit lean methane flame and coupling efficiency is also discussed and calculated. The results show that with the onset of a plasma flame by microwave, a significant rise in both excited state species, CH and OH radical numbers was observed and has been shown to broaden the lean flammability limit with microwave induced plasma. Finally, a prototype of a novel microwave induced plasma thruster system suitable even for atmospheric ground tests is proposed and developed.

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