Abstract:

In order to study the combustion characteristics of n-heptane under O₂/CO₂ atmosphere, a C-H combustion mechanism based on the detailed reaction paths of CO₂ and H· was proposed. The possible reaction paths of CO₂ and H· were analyzed by using density functional theory, and the calculation grids were established according to the actual size of constant volume combustion chamber. The combustion processes of n-heptane under different atmospheres (air, 53%O₂/47%CO₂, 61%O₂/39%CO₂) were calculated through C-H mechanism. A constant volume incendiary bomb visualization experiment platform was built to measure the combustion process of n-heptane in different atmospheres. The reaction site of CO₂, the reaction energy barrier of CO₂+H·\stackrel{}{\to }CO+·OH, and the flame length were analyzed. The results show that the C-H mechanism can well predict the combustion flame length of n-heptane under O₂/CO₂ atmosphere, and the maximum error and the average error are 9.60% and 2.42% respectively under 50%O₂/50%CO₂. The reactivity of oxygen atom of CO₂ is higher than that of carbon atom, and the average local ionization energy and molecular surface electrostatic potential at the oxygen ends are 297.72 and -13.08 kcal/mol, respectively. H· can combine with carbon atom and oxygen atom of CO₂, the reaction energy barrier are 26.71 and 11.07 kcal/mol, respectively.

Key words: carbon dioxide, computational chemistry, computational fluid dynamics, constant volume combustion chamber, reaction site, flame length

摘要：

为研究正庚烷(n-C₇H₁₆)在O₂/CO₂氛围下的燃烧特性，提出了基于CO₂与H·详细反应路径的C-H燃烧机理。通过密度泛函理论对CO₂与H·可能存在的反应路径进行了分析，根据定容燃烧弹实际尺寸建立了计算网格，利用C-H机理计算了正庚烷在不同氛围(空气、53%O₂/47%CO₂、61%O₂/39%CO₂)下的燃烧过程；搭建了定容燃烧弹可视化实验平台，对正庚烷在不同氛围下的燃烧过程进行了测量；对CO₂的反应位点、CO₂+H·\stackrel{}{\to }CO+·OH的反应能垒、火焰长度进行了分析。结果表明：C-H机理可以很好地预测正庚烷在O₂/CO₂氛围下的燃烧火焰长度，在50%O₂/50%CO₂氛围下的最大误差和平均误差分别为9.60%、2.42%；反应位点分析发现，CO₂氧原子的反应活性大于碳原子，氧端的平均局部离子化能和分子表面静电势分别为297.72 kcal/mol、-13.08 kcal/mol；H·与CO₂的碳原子和氧原子均可发生结合，反应能垒分别为26.71、11.07 kcal/mol。

关键词: 二氧化碳, 计算化学, 计算流体力学, 定容燃烧弹, 反应位点, 火焰长度