側口對於漸擴型燃燒器在有無外圍流場之影響

Abstract

由羽球空氣動力學的啟發，提出一新概念設計的開側口型漸擴燃燒器，本研究藉由實驗量測與流場模擬，利用開側口型漸擴燃燒器與無側口型漸擴燃燒器進行對照實驗，分析側口對於漸擴型燃燒器的影響。實驗量測分為兩部分，第一部分為無外圍流場的甲烷預混火焰，第二部分為有外圍流場的甲烷擴散火焰，由火焰型態觀察火焰定性表現並紀錄操作區間；量測溫度場分佈、自由基化學螢光以及廢氣排放，評估側口對於甲烷火焰燃燒效能的助益。並透過粒子影像測速法、FLUENT等溫流場模擬觀察流場行為，藉此分析其穩焰機制與流場結構。 第一部分，經由調整甲烷預混火焰的當量比觀察由側口引入環境空氣對漸擴型燃燒器的影響。溫度量測的結果顯示，開側口型漸擴燃燒器的燃燒效能相較無側口型略為提升。當甲烷預混火焰在較低的當量比時，火焰型態的改變會造成環境的自然空氣引入效果下降。 第二部分，改變甲烷流率與外圍流場流速，觀察側口與外圍流場對甲烷擴散火焰的影響。結果顯示，開側口型漸擴燃燒器之甲烷擴散火焰有較好的穩定性與燃燒效能，其自由基螢光強度與火焰中心線溫度相較於無側口型大幅提升。當外圍流場流速提升時，有、無側口燃燒器兩者之火焰長度皆縮短，高溫區溫度皆提升。其中，具側口之燃燒器的火焰自由基螢光分佈會往燃燒器杯口集中，燃料與氧化劑可在火焰上游進行充分的混合與反應。廢氣量測結果顯示，開側口型相較無側口型漸擴燃燒器有較低的CO排放濃度。 開側口型漸擴燃燒器於有外圍流場的環境下，能藉由側口將外圍流場的空氣導入燃燒器漸擴段，在擴散段供給更多的氧化劑並充分混合，漸擴段壁面提供鈍體效果造成迴流區增加滯留時間，因此可顯著提升火焰穩定性、燃燒效能及降低CO排放。此側口設計概念可提供未來燃燒器設計上的不同思維。

Inspired from the aerodynamics of a shuttlecock, we proposed a new concept for the designing a diffuser burner with side-opening. The diffuser burner with and without side-opening structure were experimentally and.numerically analyzed under with and without a co-flow condition. We observed quantitative flame behavior and recorded the operating maps through direct flame images. The measurement of the flame temperature, chemiluminescence of free radicals and exhaust gas were also performed to assess the benefits of combustion efficiency of a diffuser burner with a side-opening structure. Through the particle image velocimetry (PIV) and the simulation of isothermal flow field in FLUENT, we analyzed the mechanism of stabilization and flow field structure. In the first part, we adjusted the equivalence ratio of a premixed methane flame. The results show that the flame temperature slightly improved when a diffuser burner with a side-opening structure. When premixed methane flame has a lower equivalence ratio, transformed flame pattern would cause a decrease in air entrainment. In the second part, we adjusted the flow rate of methane and co-flow velocity. The results show the flame stability and combustion efficiency of the diffuser burner with a side-opening structure is better than that of without a side-opening structure. The chemiluminescence intensity of free radicals and temperature along flame center line have greatly improved when a diffuser burner with a side-opening structure. As the co-flow velocity increasing, the flame length of both burner types was shortened, and the temperature within the high temperature area increased. Moreover, the distribution of free radicals not only concentrated toward burner tip but also increased its intensity, which makes a sufficient reaction of fuels and oxidant in the flame upstream when a diffuser burner with a side-opening structure. The results of measurement of exhaust gas show that a lower CO emission was achieved when a diffuser burner with a side-opening structure. More fresh air injects into the diffusing section of a diffuser burner through side-opening structure under co-flow condition. Therefore, more supplied oxidant in this section causes an improvement of flame stability and combustion efficiency. The concept of side-opening structure of a diffuser burner offers an innovative reference for the future burner design.