研究成果

碩士生: 陳俊翰

畢業年分: 2018年7月

論文名稱: 添加稀釋物對甲烷/一氧化二氮反置擴散火焰之燃燒特性影響 (中文) / Effects of Diluent Addition on Combustion Characertistics of Methane/Nitriys Oxide Inverse Diffusion Flame

中文摘要: 

本研究利用實驗及數值模擬來探討添加稀釋氣體於N2O/CH4反置擴散火焰之燃燒特性影響，本研究的目的是為了了解添加不同稀釋氣體對CH4/N2O IDF燃燒特性的影響，因此將選擇三種不同的稀釋氣體，即He，CO2和Ar。實驗方面，藉由中心管通入一氧化二氮與不同的稀釋氣體(Ar、He、CO2)之混合氣，第二環為燃料甲烷，最外環為33% O2與67% N2之混合氣，來探討添加不同濃度的稀釋氣體及流速改變對火焰型態上的影響，並利用理論解模型預測火焰型態變化，進而得到反置擴散火焰的形成過程，最後利用廢氣量測，針對重要的污染物(O2、CO2、NOX、CO)進行討論。在瞭解初步的添加稀釋氣體對燃燒特性的效應後，吾人將利用CHEMKIN PRO針對添加稀釋氣體對火焰結構、溫度、污染物排放及污染物生成機制進行較深入的探討，而本研究將把添加稀釋氣體對燃燒特性影響分為為三種效應來進行探討，分別為:稀釋效應(inert effect)、熱/擴散效應(thermal/diffusion effect)和化學效應(chemical effect)。

初步實驗結果顯示，在火焰現象中，隨著不同濃度的稀釋氣體添加後，發現火焰存在著數種不同的形態:標準擴散火焰、閉口反置擴散火焰、開口反置擴散火焰、跳脫火焰等，在理論解預測結果中，反置擴散火焰的形成可以分成幾個階段: (1)先形成一標準擴散火焰，(2)內部火焰的富油、當量條件、貧油分支會依序出現，形成反置擴散火焰，(3)內部及外部火焰的富油、當量條件、貧油分支會依序形成包絡狀火焰，(4)最後形成開口狀反置擴散火焰。

在數值模擬的部分，thermal/diffusion effect主導著添加Ar條件之火焰溫度上升，而inert effect及chemical effect則是主導著添加Ar及CO2為稀釋氣體條件之火焰溫度下降，並且針對NO形成的五種機制: Thermal route、N2O-intermediate route、NNH-intermediate route、HNO-intermediate route、Prompt route進行探討，得到在添加不同濃度稀釋氣體情況下，主導NO形成的機制變化。

英文摘要: 

In this study, the effect of adding dilution gas on the combustion characteristics of N2O/CH4 inverse diffusion flame (IDF) was conducted experimentally and numerically. The purpose of this study was to examine the combustion characteristics of CH4/N2O IDF with different dilution gases. Therefore, three different dilution gases, that is He, CO2 and Ar, were selected.

In the experiment, a mixture of nitrous oxide and different dilution gases (Ar, He, CO2) was introduced through the central tube, the second port was introduced with methane fuel, and the outer port was introduced with a mixture of 33% O2 and 67% N2. It attempted to investigate the effect of adding different concentrations of dilution gas and flow rate change on the flame pattern, and meantime the theoretical solution model was employed to predict the alternation of flame type in order to inception of the inverse diffusion flame. Eventually, some important contaminants (O2, CO2, NOX, CO) were discussed through exhaust gas measuring method.

After understanding the effect of the initial addition of dilution gas on the combustion characteristics, CHEMKIN PRO was used to conduct a more in-depth discussion on the flame structure, temperature, pollutant emission and pollutant generation mechanism for the addition of dilution gas. The study divided the effect of dilution gas addition on combustion characteristics into three effects, namely, inert effect, thermal/diffusion effect and chemical effect. Preliminary experimental results showed that in the flame phenomenon, with the addition of different concentrations of dilution gas, it found that there are several different forms of flame: normal diffusion flame, closed-tip inverse diffusion flame, opened-tip inverse diffusion flame, liftoff flame. In the theoretical solution of prediction results, the formation of the inverse diffusion flame can be divided into several stages: (1) the formation of a normal diffusion flame, and (2) the appearance of the rich-branch, the equivalent condition, and the lean branch of the inner flame sequentially, forming an inverse diffusion flame, (3) the rich, equivalent conditions and lean branches of inner and outer flame form an closed-tip flame in sequence, and finally an opened-tip inverse diffusion flame is formed.

In the numerical simulation part, the thermal/diffusion effect dominates the rise of flame temperature with the addition of Ar conditions, while the inert effect and chemical effect dominate the flame temperature drop with the addition of Ar and CO2 as the diluent gas conditions. Five NO formation mechanisms: Thermal route, N2O-intermediate route, NNH-intermediate route, HNO-intermediate route, Prompt route were discussed in order to obtain the mechanism of dominant NO formation under the condition of adding different concentrations of dilution gas.