應用粒子影像測速儀分析帽頂燃燒器之流場

PIV Measurement and Flow Field Analysis for a Cap Burner

郭柏賢(Po-Hsien Kuo)

指導教授 ： 潘國隆

國立臺灣大學/工學院/機械工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.01759

摘要

本文所研究之燃燒器為結合部分預混以及鈍體燃燒器之設計概念所設計出之新燃燒器：帽頂燃燒器。為了能定性及定量地分析帽頂燃燒器後方流場與火焰的動態特性，本研究建立一完善的粒子影像測速系統，將中心燃氣噴流流速固定為3 m/s，並調整環流空氣流速為0.38、1.50、2.65以及3.75 m/s，以探討四種火焰型態的流場結構如何影響火焰結構，混合以及燃燒效率。
本研究使用高速攝影機，調整其拍攝速度為每秒1000、4000以及5000張，以精準地擷取不同速度下粒子的動態影像，再使用粒子影像測速儀，計算在不同火焰型態時之瞬時速度場分佈，進而得到平均以及瞬時之燃燒流場，以分析流場之速度強度、渦度、水平以及垂直擾動量，以及紊流強度分佈。發現隨著環流空氣流速的增快，迴流結構、渦度以及紊流強度會隨之增強。迴流結構以及渦度之增強，使迴流結構擷取中心噴流的能力增加，更多的燃氣被捲入迴流區內燃燒，但也使火焰高度大幅下降。擾動量以及紊流強度的分佈讓我們得知燃氣與空氣混合最為強烈的位置大多為環流空氣與中心噴流所產生之停滯點，以及迴流區內，但帽頂燃燒器內部之預混效果最終主導了整個火焰的燃燒情形。
本研究為了探討帽頂燃燒器內部對於下游燃燒效能之影響，使用一透明的帽頂燃燒器。發現帽頂燃燒器內部之火焰之抖動行為與環流空氣流速有關，並深深地影響了下游火焰的穩定極限以及內部之預混效果。而預混效果的增強，讓火焰型態從擴散火焰轉變為預混火焰，燃燒效率大為提升，且避免了回火的危險。

關鍵字

部分預混 ； 鈍體燃燒器 ； 帽頂燃燒器 ； 粒子影像測速儀 ； 迴流結構 ； 紊流強度

並列摘要

The cap burner for this research is an innovation based on theories of the partially premixed burner and the bluff-body burner. This research is aimed at building a Particle Image Velocimetry (PIV) system and analyzing the dynamic characteristics of flow field and flame downstream from the cap burner qualitatively and quantitatively. In this research, the velocity of central fuel ejection is set at 3 m/s while the co-air flow velocity is set at 0.38, 1.50, 2.65, and 3.75 m/s to investigate the influence of flow field pattern on the structure of flame for all four flame types.
We use high speed camera to take images at flame rate of 1000, 4000 and 5000 flames per second to obtain particle image under different velocities, and use PIV to calculate the distribution of instantaneous velocity field for all flame types to analyze velocity magnitude, vorticity, horizontal and vertical fluctuation and turbulent intensity. The result indicates that as co-air velocity increases, the intensity of recirculation zone, vorticity and turbulent intensity also increase. The intensity increase of recirculation zone and vorticity result in an increase of recirculation zone in ability of dragging central ejection indicating more combustion in re-circulation zone and lower flame height. According to fluctuation distribution and turbulent intensity, the most intense mixing of air and fuel locates around the stagnation point formed by both co-air and central ejection and inside the recirculation zone. But premixing happened inside the cap dominates the combustion.
To study the effect of the cap inside on downstream combustion efficiency, a transparent glass cap is used. It reveals that flickering of the flame is related to co-air flow velocity, and influences downstream flame stability limit and inner premix. The enhanced premixing contributed to converting flame type from diffusion flame to premixed flame, promoting combustion efficiency and avoiding the danger of flash back.

並列關鍵字

partially premixed ； bluff-body burner ； cap burner ； Particle Image Velocimetry(PIV) ； re-circulation zone ； turbulent intensity

參考文獻

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