This study investigates the diluent-dependent diffusion flames of an axisymmetric methane jet in annular hot coflow (JHC) of oxidizer diluted by “inert” N₂, CO₂, and H₂O, respectively. The fuel jet issues at an exit Reynolds number of ≈10 000, while the hot (1300 K) coflow oxygen level (molar fraction) varies between 6 and 23%. To identify the chemical and physical factors, simulations of the diffusion flames diluted by fictitious gases XH₂O and XCO₂ are also conducted. Inspections and analyses to combustion radicals and heat release rates are made on the stoichiometric sheet. Results show that the stoichiometric length, temperature, and volumetric heat release rate vary drastically with coflow oxygen level or dilution extent. The flame volume increases greatly when replacing the diluent N₂ with CO₂ but reduces substantially under the H₂O dilution. Such discrepancies are found to stem mainly from specific physical properties of N₂, CO₂, and H₂O. The CO₂ and H₂O dilutions show more chemical impact on the formations of key intermediate species. Besides, the dilution by CO₂ weakens all the main reactions, thus producing the mildest flame, whereas that by H₂O promotes the formations of radicals OH and H₂, enhancing the heat release rate. Last, the global heat contributions of C-included and C-excluded (H₂–O₂) reactions are examined so as to understand the roles of the H₂–O₂ kinetics in oxy-combustion.

中文翻译：

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热氧化剂流中CH ₄喷射火焰的热特性：CO ₂和H ₂ O的稀释作用

这项研究研究了分别由“惰性” N ₂，CO ₂和H ₂ O稀释的氧化剂的环形热同流（JHC）中轴对称甲烷射流的稀释剂依赖性扩散火焰。喷油嘴的雷诺数约为10000，而热的（1300 K）同流氧气含量（摩尔分数）则在6％和23％之间变化。为了确定化学和物理因素，模拟气体XH ₂ O和XCO ₂稀释了扩散火焰也进行。在化学计量表上进行了燃烧自由基和放热率的检查和分析。结果表明，化学计量长度，温度和体积放热率随同流氧气水平或稀释程度而显着变化。当用CO ₂代替稀释剂N ₂时，火焰体积大大增加，但是在H ₂ O稀释下，火焰体积却大大减少。这种差异被发现从N个特定物理性质主要茎₂，CO ₂，和H ₂ O的CO ₂和H ₂ ö稀释显示在关键中间体物质的地层多种化学影响。此外，用CO稀释₂减弱了所有主要反应，从而产生了最温和的火焰，而H ₂ O则促进了自由基OH和H ₂的形成，从而提高了放热率。最后，检查了含C和不含C（H ₂ -O ₂）反应的整体热贡献，以了解H ₂ -O ₂动力学在氧燃烧中的作用。