特徵流場結構與擴散火焰交互作用研究

The interaction between characteristic flow structures and diffusion flame

陳傳昇(Chuan-Sheng Chen)

指導教授 ： 楊鏡堂

國立臺灣大學/工學院/機械工程學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.02463

摘要

本研究使用鈍體燃燒器為載具，探討特徵流場結構對擴散燃燒反應影響的機制。實驗固定中央燃料噴流出口流速，藉由改變環空氣共伴流出口流速，製造不同特徵之鈍體尾流結構，分析其對燃燒反應在空間分布上及隨時間變化的交互作用效果。首先以雷射斷層攝影術(laser tomography)拍攝火焰型態與燃燒流場可視化，觀察其個別特徵，並從中選取局部特徵流場明顯或具特殊燃燒場型態之條件，進一步同步量測燃燒反應場與流場資訊。同步量測的兩種實驗技術分別為化學螢光法(chemiluminescence)與高速粒子影像測速法(particle image velocimetry, PIV)。利用這兩種量測技術的同步使用，記錄每一暫態時刻，流場的訊息與其相對應之火焰化學螢光強度，達到解析流場結構與燃燒反應強度之間瞬時交互作用的目的，同時也將不同區域的量測數據以訊號處理方法，分別以時間域和頻率域角度呈現，觀察其在不同空間的反應特性，歸納出最具特色之區分特點，最後再使用同調性(coherence)分析，以統計方式得到燃燒反應與流場間的相依關係。
研究結果顯示，燃燒反應在不同位置受流場渦漩結構影響，擁有不同的反應強度與週期。首先鈍體尾流形成的迴流結構不僅有助於迴流火焰穩定駐焰外，其內部高頻渦漩結構會增加迴流區的熱釋放效率，間接影響中下游流場結構的發展週期，對於整體燃燒場的燃燒效率都有相當分量的影響力。其次，剪流層區因流場速度梯度引發流場不穩定效應，將在特定位置形成渦漩對，除了增強剪流層區域燃氣的對流混合效果外，並會對火焰面形成程度不等的拉伸與壓縮效應，同時將高溫產物集中在部分區域，大幅增加局部的溫度，進而加速局部的反應進行。但當共伴流流速增快時，渦漩對向中央匯集的趨勢減緩，加上迴流火焰提前消耗氧氣，反倒會使剪流層區出現反應斷層。最後大尺度渦漩內不同頻率的複雜渦漩結構，可提供反應物反應速率不等的反應環境，綜合提升此區的熱釋放效率。

關鍵字

擴散火焰 ； 化學螢光法 ； 高速粒子影像測速法 ； 同步量測 ； 頻譜分析

並列摘要

The interaction between characteristic flow structures formed by a bluff-body burner and diffusion flame reactions had been experimentally investigated. This interaction could be attributed to the coupled effects of both flow vorticity and heat release in the combustion field. The objectives aim to unveil how the interaction produces different combustion efficiency distribution and to characterize spatial patterns in fluctuating heat release for future control purposes.
In this study, the different kinds of characteristic flow structures were created by adjusting the air co-flow outlet velocity, while the outlet velocity of central jet, consisting of pure propane, was fixed. The reacting flow field was characterized using 1kHz high-speed particle imaging velocimetry (PIV), while the corresponding combustion pattern was investigated exploiting employing implementing C2* and CH* chemiluminescence which detecting the spontaneous light emitted by the flame.
The results showed that the flame intensity and reaction frequency differed from each location, including the recirculation zone, vortex pair shear layer and buoyancy toroidal vortex active zone, because of the various flow characters. At the recirculation zone, there were complicated vorticity structures with wide spectrum distribution acted. The vorticity structure enhanced the air-fuel mixing and heat transfer efficiency at different frequency, providing a set of suitable environments for chemical reactions. As a result, a series of complex reactions would happen in various intensity and frequency at the recirculation zone. Furthermore, the heat release from the recirculation zone would induce the flow buoyancy instability, dominating the creation of toroidal vortexes which contain much more complicated vorticity structures; consequently, these structures caused the reaction to proceed at a wide range of reaction rates, even at a high frequency response. This flow-flame interaction mechanism significantly influences the combustion efficiency of non-premixed bluff-body burner.

並列關鍵字

flow-flame interaction ； diffusion flame ； chemiluminescence ； PIV ； spectrum analysis

參考文獻

陳靖瑋，2011，三環丙烷火焰暫態反應強度與流場之交互作用研究，國立台灣大學機械工程學系碩士論文。

Azzoni, R., Ratti, S., Aggarwal, S. K., and Puri, I. K., 1999, “The structure of triple flames stabilized on a slot burner,” Combustion and Flame, Vol. 119, pp. 23-40.

Ballester, J., and Garcia-Armingol, T., 2010, “Diagnostic Techniques for the Monitoring and Control of Practical Flames,” Progress in Energy and Combustion Science, Vol. 36, pp. 375-411.

Barlow, R. S., 2007, “Laser Diagnostics and their Interplay with Computations to Understand Turbulent Combustion,” Proceedings of the Combustion Institute, Vol. 31, pp. 49-75.

Bendat, J.S., and Piersol, A.G., 1986, Random Data: Analysis & Measurement Procedures, Wiley-Interscience, New York.