因為能源議題與環保意識崛起，研發有效率兼具降低汙染物生成的燃燒科技為最可行策略之一。為了避免火焰在不同的操作方式與環境下出現燃燒不穩定現象，吾人嘗試以新型燃燒方式，透過添加強氧化劑來輔助燃燒與控制火焰型態。強氧化劑分別為三種：不同氧氣濃度下之氮氣與氧氣混合氣(定義Ω)、氧化亞氮(N2O, Nitrous oxide)與過氧化氫(H2O2, Hydrogen peroxide)。其中N2O與H2O2是推進系統常用之高能氧化劑，受熱分解會提供氧氣與大量熱釋放，部分文獻也指出兩者在火焰系統中會提供額外自由基，因此值得深究。
考量實用性與安全性，工業應用上為多噴口燃燒器居多，因此本實驗以同軸三環燃燒器進行。藉由中心管通入氧化劑，第二環為燃料甲烷，最外環為空氣，檢視不同氧化劑/燃料的出口流速比(R=V1/V2)下的火焰現象觀測，並且搭配理論預測模型探討影響火焰外型變化之參數。
理論模型顯示，噴流出口流速、濃度與溫度的選定是影響火焰結構變化之重要參數。初步實驗結果顯示氧化劑為富氧濃度40%以上(Ω≥40%)、N2O或H2O2的加入皆會形成雙火焰結構，即內部的反置擴散火焰(IDF, Inverse Diffusion Flame)與外部的標準擴散火焰(NDF, Normal Diffusion Flame)，其中IDF為隨著氧氣量的增加，火焰下游處局部熱釋放率上升至臨界點時，部分預混火焰(PPF, Partially Premixed Flame)往上游傳遞所形成，此時NDF高度會突然上升。若持續增加流速，會發現IDF與NDF頂端皆出現缺口，此為過多的氧化劑消耗局部燃料的緣故。同時，實驗也探討了IDF的形成機制，並發現不同的氧氣濃度與出口流速搭配下會有兩種類型。此外，由形成IDF的R值操作區間圖可發現當N2O作為氧化劑時，對於燃燒系統強度之增加相當於富氧濃度70%，推論為N2O參與化學反應提供了自由基亦或是分解產生之大量熱釋放的影響。

Increasing concerns of issues on global warming and climate change have urged stringent expectation on new energy conversion devices for much higher thermal efficiency and carbon dioxide capture and sequestration. In order to avoid the combustion instability during lean operation for lower fuel consumption, the strong oxidizer concept, such as employing oxy-enriched conditions, nitrous oxide (N2O) or hydrogen peroxide (H2O2) to enhance combustion and control the flame configurations, is proposed in this study. N2O or H2O2 are often used as the oxidizer propellant for propulsion systems, because the chemical dissociation produces oxygen in addition to exothermic heat release. It has been illustrated in the literature that both of them can also enhance the combustion by inducing enhanced free radicals in the flame.
Multi-port burners are widely used in industry to achieve the purpose of safety and emission control. The objective of this work is to theoretically and experimentally investigate the flame behaviors of strong oxidizer addition to methane diffusion flames by varying the ratio of oxidizer jet velocity to that of the fuel jet (R=V1/V2), carried out on a three port co-annular burner.
The theoretical results show that the stream velocities, fuel and oxidizer concentrations and stream temperatures are important parameters for flame structures. The experiment results reveal that formation of the particular double flame structure: an inner inverse diffusion flame (IDF) and an outer normal diffusion flame (NDF) can be observed only by using N2O or H2O2 as an oxidizer and oxy-enriched conditions of Ω≥40%. It is conjectured that by increasing the oxygen content the local heat release rate rises to a critical condition so that the induced partially premixed flame propagates rapidly upstream to form the inner IDF and, the outer NDF flame height will suddenly increase in the meanwhile. If the R value increases continuously, the open flame tip phenomenon of IDF and NDF can be observed, this is because the fuel is consumed locally by the considerable amount of oxidizers. Furthermore, the IDF formation mechanism is also discussed based upon the experimental results. It shows that two types of IDF ignition are observed by varying the oxygen concentration and stream velocity. In addition, it is found that when N2O is used as the oxidizer operating condition of the R value of IDF are quite similar to that for Ω=70%. Results also suggest that free radicals and large heat release from N2O dissociation enhance the intensity and stabilization of the combustion system.

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