本研究採用三環燃燒器，並通過數值模擬研究CH4-N2O擴散火焰的熵生成率隨 R 值的變化。為了研究N2O分解所產生的熱效應對熵生成率的影響，在CH4-N2-O2擴散火焰中使用了與N2O相同的氮氧比(N/O = 2)的富氧氣體以利比較。此外，由於N2O分解後會生成富氧氣體，因此本研究亦利用 CH4-air擴散火焰研究了富氧效應對於熵生成率的影響。結果表明，在R值為1的條件下，富氧效應並不會影響火焰的性質和熵產生率。但是，當R值足夠大（R=5）時，CH4-N2-O2擴散火焰會呈現雙火焰結構以及更高的熵產生率。由於雙火焰結構，儘管在CH4-air和CH4-N2-O2擴散火焰中擁有類似的主要反應途徑，但是大部分的主要反應皆會得到增強。因此，由於反應區更強且分佈更廣，化學反應項將主導CH4-N2-O2擴散火焰中熵產生率的增強。在CH4-N2O擴散火焰中，當N2O在靠近中心管口附近發生分解時，會產生放熱反應。此外，由於與N2O相關的數個反應會參與反應過程，因此在CH4-N2O擴散火焰中會呈現出不同於前兩者的主要反應途徑。因此，CH4-N2O 擴散火焰中的反應會更加劇烈，且由於反應強度的增強，化學反應項將會導致更高的熵產生率發生於CH4-N2O擴散火焰中。當 R 值增加（R = 3）時，雙火焰結構亦會呈現在CH4-N2O擴散火焰中，且是在 R 值低於CH4-N2-O2擴散火焰(R = 5)的條件下，這代表N2O分解的熱效應有助於提升反應的的速率。由於CH4-N2O擴散火焰中的反應更劇烈且火焰溫度更高，熵產生率會因此而更進一步增加，並且也由化學反應項主導此差距。CH4-air擴散火焰於此研究中皆呈現單一火焰結構，其不可逆性主要由熱傳導和化學反應主導。在R值小於5的條件下，CH4-N2-O2擴散火焰亦是如此。但當R值=5條件下，CH4-N2-O2擴散火焰將會形成雙火焰結構，由於反應增強而使化學反應項主導不可逆性的生成。在CH4−N2O擴散火焰中，由於N2O分解的熱效應引起的反應更加強烈，因此在所有R值條件下，化學反應始終主導著不可逆性的產生。此外，在R值 = 3 的條件下，化學反應的不可逆性幾乎是CH4-N2-O2擴散火焰(R = 5)的兩倍，儘管在 CH4-N2-O2 擴散火焰中亦呈現出雙重火焰結構。有了這些結果，化學反應項將是提高 CH4-N2O 擴散火焰效率的關鍵點之一。

A triple-port burner was used in this study, and a numerical simulation was employed to investigate the entropy generation rate of CH4−N2O diffusion flames with the change of the R ratio. To scrutinize the decomposition effect of N2O on entropy generation, an oxygen-enriched gas with the same nitrogen to oxygen ratio as N2O (N/O = 2) was used in CH4−N2−O2 diffusion flames. Besides, the N2O could decompose into the oxygen-enriched gas; the oxygen-enriched effect was also studied by the CH4−air diffusion flames that were conducted in this research. The results showed that the oxygen-enriched effect would not affect the properties and entropy generation rate in a condition of the R ratio = 1. However, when the R ratio increased enough (R = 5), the CH4−N2−O2 diffusion flames would present the dual flame structure and the higher entropy generation. Because of the dual flame structure, most of the reactions would be enhanced, although a similar major reaction pathway was presented in the CH4−air and CH4−N2−O2 diffusion flames. Then the entropy generation rate in the chemical reaction term would dominate the enhancement of the entropy generation in CH4−N2−O2 diffusion flames due to the more intense and broader reaction area. In the CH4−N2O diffusion flames, the among of heat release would be produced when the N2O decomposed near the vicinity of the center nozzle rim. Besides, the different major reaction pathways would be performed in CH4−N2O diffusion flames due to the several reactions relative to the N2O that would take part in the combustion process. Then, the reactions would be more intense in CH4−N2O diffusion flames, and the higher entropy generation would be produced by increasing the chemical reaction term because of the high reaction intensity. When the R ratio was increased (R = 3), the dual flame structure was also presented in CH4−N2O diffusion flames at a lower R ratio than CH4−N2−O2 diffusion flames that contributed to the thermal effect from the N2O decomposition. The entropy generation would be further higher due to the more intense reactions and higher temperature in CH4−N2O diffusion flames, and the chemical reaction term also dominated it. The irreversibility of CH4−air diffusion flames, which presented the single flame structure, would be dominated by heat conduction and chemical reaction. It was the same with CH4−N2−O2 diffusion flames in the condition of the R ratio < 5. When the dual flame structure formed in CH4−N2−O2 diffusion flames in the condition of the R ratio = 5, the chemical reaction would dominate the irreversibility due to the enhancement of the reactions. In CH4−N2O diffusion flames, the chemical reaction always dominated the irreversibility in all R ratio conditions because of the more intense reaction caused by the thermal effect of N2O decomposition. Furthermore, the irreversibility in chemical reaction would be almost two times greater than CH4−N2−O2 diffusion flames in the condition of the R ratio = 5, although the dual flame structure was presented in CH4−N2−O2 diffusion flames. With these results, the chemical reaction would be one of the critical points that could improve the efficiency of CH4−N2O diffusion flames.

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