應用粒子影像測速法分析多孔性圓柱燃燒器擴散火焰之流場

PIV Measurement for Flow Field Analysis of Diffusion Flame over a Porous Cylindrical Burner

郭承剛(Chang-Gang Guo)

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(2014年)

https://doi.org/10.6342/NTU.2014.01945

摘要

本研究主要利用粒子影像測速儀，在強制對流環境下多孔圓柱燃燒器擴散火焰模式下之尾流區的熱流場分析，使用不鏽鋼材質的多孔性圓柱管為燃燒器，將燃料出口流率固定並調整強制對流的風速，分別為0.4 m/s (Re=24.85)、0.9 m/s (Re=74.55)、1.9 m/s (Re=157.3)、2.4 m/s (Re=199)，其所對應之火焰型態分別為包絡焰、側焰、尾焰以及尾焰(無黃焰)；另外使用化學螢光法，拍攝火焰之化學反應所激發之化學影像以及利用熱電偶量測圓柱周圍的溫度場，與粒子影像測速儀的結果作結合，探討流場結構與火焰之交互作用。
當火焰型態為包絡焰時，圓柱下游形成一低速之尾流區，但受浮力效應之影響，此時並無迴流區存在，大部分未反應的燃料往更下游處移動並且反應。將強制對流增強，圓柱上游停滯火焰面被破壞，火焰型態為側焰，上游空氣直接進入圓柱內部造成預混的作用，而在圓柱兩側部分，則形成小規模之迴流區使此區具有部分預混的效果，形成薄層藍焰穩定於側，〖C_2〗^*螢光反應在此處較為黯淡，顯示此處當量比較低。再將風速增強，形成尾焰，圓柱後方形成一對停滯的渦流，火焰尖端受迴流區影響，形成一凹入圓柱後方的圓弧曲線，此時在渦流中心與圓柱兩側附近有著較高之渦度，空氣與燃料在此處較能充分混合，使此型態火焰具有預混與擴散兩種模式。最後將風速再增強，此時圓柱後方迴流區擴大，中間之黃焰因迴流區流速過快而熄滅，空氣與燃料在迴流區內部加速混合並在圓柱兩側與圓柱下游面反應，因此形成一存在於圓柱兩側與圓柱下游面之薄層火焰型態。

關鍵字

粒子影像測速儀 擴散火焰 ； 化學螢光法 ； 多孔圓柱燃燒器 ； 強制對流 ； 迴流區

並列摘要

The present study is aimed to understand the dynamic characteristics of flow field and flame downstream from the porous cylindrical burner. A Particle Image Velocimetry (PIV) system was built to analyze the flow field qualitatively and quantitatively. In this research, the fuel flow rate is fixed while the upstream wind speed is set to 0.4 m/s (Re=24.85), 0.9 m/s (Re=77.55), 1.9 m/s (Re=157.3), 2.4 m/s (Re=199). The chemiluminescence images and the flame temperature distribution was compared with PIV. Influences on flow field pattern and structure of flame for four flame types could be investigated.
When the flame type is envelope flame, a low speed region is formed downstream from the porous cylinder. There is no recirculation zone exist because the effect of buoyancy. The flame in the forward stagnation region was unable to sustain where air went into the interior of cylindrical directly when wind speed enhanced. A small region of recirculation zone where fuel can be mixed with air was observed in both side of cylinder where 〖C_2〗^* fluorescent reaction here is bleaker. We observed that there is a pair of large scale vortex could bring intermediate products and wasted heat to reaction zone behind the cylinder when the flame type is wake flame. We also observed that the shape of yellow flame front which looks like a concave curve downward is contributed to effect of recirculation zone. The range of recirculation zone was extended when the wind speed got higher. Thus the yellow flame was unable to be sustained due to the high velocity of recirculation zone. However, air and fuel were mixed more efficiently in recirculation zone and reacted on both sides of cylinder, then brings blue flame layer formed on both sides of the porous cylinder burner.

並列關鍵字

Particle Image Velocimetry (PIV) ； chemiluminescence ； cylindrical burner ； diffusion flame ； recirculation zone ； forced convection

參考文獻

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