- 學位論文
應用化學螢光法於液滴碰撞與預混之燃燒特性研究
Application of Chemiluminescence on Burning Characteristics of Collided and Premixed Binary Droplets
摘要
本研究設計製造液滴碰撞機構，使得不同組份的油料液滴，能夠以需要的尺寸、碰撞角度以及速度碰撞，並且以結合的形式落入燃燒室點燃；將可互溶的雙組份液滴作為對照組，固定液滴尺寸為500±10 微米，利用化學螢光法對燃燒中的液滴進行分段量測，觀察液滴燃燒的火焰型態，比較可互溶與不可互溶油料的差異性。碰撞結合液滴使用乙醇與十六烷而預混液滴使用異丙醇與十六烷；高速攝影機以每秒10000張拍攝在液滴通過燃燒室時火焰結構的暫態變化過程與火焰縮口現象。藉由量測燃燒反應中具代表性之碳氫基空間強度分布，定義液滴燃燒時熱釋放率指標、火焰面位置以及化學螢光強度分布。 對於碰撞結合與預混液滴來說其熱釋放率指標，火焰面面積，絕對化學螢光強度並不會因為其混合的比例而產生比例上的變化，雙組份液滴的燃燒過程依序出現單一種燃料的燃燒特性，甚至從頭到尾只出現單一種燃料的燃燒特性隨即熄滅。而在燃燒過程中是否會依序出現兩種燃料的燃燒特性與其混合比例還有燃料的熱力學特性有關。藉由pdf (Probability density function)分析火焰面化學螢光的分布，醇類與烷類呈現兩種分布型態；相對於醇類，烷類燃燒反應的化學螢光分布範圍較廣，而pdf分布的峰值高但出現機率較低。烷類燃燒反應在接近熄滅時會以大幅減少火焰面面積的手段來減少熱的散失，使得絕對化學螢光強度下降程度減低，可以維持燃燒反應的進行，然而大幅降低的火焰面面積也使得熱釋放不足以長久的維持液滴燃燒，因此隨即會熄滅；相對的醇類燃燒反應沒有此種機制，因此其熄滅位置通常會較烷類提前很多。 將熱釋放率進行加總，在含25%乙醇的液滴燃燒中，其在觀測區域的總熱釋放率會大於含25%異丙醇的液滴，甚至大於純十六烷的總熱釋放率，因此液滴碰撞的液滴結合形式相對於預混與單一燃料來說對熱釋放率的提高是有幫助的。
並列摘要
A droplet collision mechanism has been designed for droplets to collide on the assigned size, collision angle, and velocity. Eventually, fall into combustion chamber on coalescence state. The premixed miscible fuel used for control groups. Fixed the droplets’ size at 500±10 micrometer for all cases. Investigated the droplet burning flame structure in different vertical distance from the entrance of combustion chamber by chemiluminescence and then the differences between miscible and immiscible fuels can be compared. Ethanol and hexadecane were used for droplets of collision coalescence and iso-propanol and hexadecane were used for premixed droplets. The droplets were ignited when passed through the flat flame and the high speed camera was used for record the difference of flame structure and the process of flame shrinkage at 10000 frames per second. Heat release, flame area, and chemiluminescence intensity distribution were defined by employing CH* instantaneous distribution. The heat release, flame area, and absolute chemiluminescence intensity at different vertical distance was related to what fuel leading the droplet burning at that instantaneous only. There is no influence on the ratio of the composition of the binary droplets. With the pdf (Probability density function) we find that compared to alcohols, hexadecane has wider distribution of chemiluminescence intensity , higher peak location of pdf, and higher probability of peak. When near extinction, if hexadecane lead the droplet burning, the flame area will decrease violently. It prolonged the life time of flame for little vertical distance by reducing the heat loss from wide flame area. Summed the heat release at all vertical distance, the droplet including 25% ethanol has the highest heat release , even more than pure hexadecane. This means droplet from collision coalescence has a good effect on heat release, It can burn droplets more sufficient.