丙烷與合成氣混燒特性研究

Abstract

本研究將生質合成氣最主要的兩種成分：氫氣和一氧化碳，添加入預混丙烷火焰中進行混燒特性研究，實驗載具使用具有層狀化結構的環形鈍體燃燒器，利用化學螢光法擷取CH*與C2*自由基訊號強度，並量測燃燒場中的溫度分布和流場資訊，歸納出不同流速、不同當量比以及不同組成比例的氫氣與一氧化碳燃料組合對於丙烷混燒火焰的影響。 環形火焰基本型態可以分成錐焰、半錐焰與飄焰三種，對於貧油預混丙烷火焰，若於其中添加不同比例的一氧化碳或氫氣，皆能有效地增強火焰傳播速度，強化駐焰效能，雖然兩者在單位體積的熱值相近，其中氫氣穩焰的效果又較一氧化碳為佳。針對丙烷、氫氣和一氧化碳三種燃料一起混燒的火焰，在同一出口流速與當量比下，固定丙烷體積流率佔整體燃料的20 %，並改變氫氣與一氧化碳相互間的體積比率，發現當氫氣所佔比率越大時，火焰之局部溫度得以提升，透過高速粒子影像測速法(particle image velocimetry, PIV)可發現越多比例的氫氣使火焰由飄焰轉變為半錐焰，甚至是錐焰，通入的燃料有效地經過火焰面，便可將更多的熱值釋放出來。除此之外，本研究更劃分成兩種情況探討，第一：「固定出口流速1.50 m/s，改變當量比」，隨著當量比由0.55、0.50到0.45逐步地降低，火焰漸趨不穩定，化學螢光強度與溫度皆會隨之減少；第二：「固定當量比0.55，改變出口流速」：出口流速由1.50 m/s 增加到2.00 m/s時，局部的高溫會逐漸減少，CH*螢光強度極值降低，此可歸因於流速的增大不僅會迅速帶走反應區的熱量，減少鈍體區的預熱效果，而且火焰的跳脫高度增加，未能完整地包覆住燃氣出口，讓更多的燃料未通過火焰面進行燃燒反應，便逸散到空氣中，因而降低整體火焰的熱釋放率。

In this research, two main kinds of compositions of syngas, carbon monoxide and hydrogen, have been added to premixed propane flame. A stratified burner with three concentric rings has been used to burn fuels. The objectives aim to find characteristics of co-incineration of propane and syngas flame in different exit speed, equivalence ratio and fuel compositions. The basic flame patterns can be separated into cone flame, half-cone flame and liftoff flame when premixed fuels are only in the middle ring. The empirical results revealed that flame burning velocity can accelerate with addition of hydrogen or carbon monoxide in propane flames. However, due to its highly flammable nature, hydrogen is more powerful in stabilizing flame than carbon monoxide. Furthermore, in cases of co-incineration of propane and syngas, fixed volumetric proportion of propane and changeable mutual proportion of hydrogen and carbon monoxide are executed. As proportion of hydrogen increases, flames are stabilized and more fuels can pass through flame fronts effectively. It causes temperature distribution and CH* chemiluminescence intensity to increase. Besides, how flames react in different exit speed and equivalence ratio are also explored. On the one hand, fixed exit speed is 1.50 m/s and equivalence ratios are 0.55, 0.50 and 0.45. When equivalence ratios decrease, flames turn to unstable modes and temperature and CH* intensity diminish because of less fuel supply. On the other hand, fixed equivalence ratio is 0.55 and exit speeds are 1.50 m/s, 1.75 m/s and 2.00 m/s. As exit speeds increase, more heat can be removed easily and liftoff heights extend. The phenomena make flames unable to cover the whole middle ring and let fuels leak out which can be seen in PIV flow fields. Without burning effectively, heat release rates, temperature and CH* intensity decline accordingly.