Babushok Valeri I, Linteris Gregory T
National Institute of Standards and Technology, Gaithersburg, USA.
Combust Flame. 2024 Apr;262. doi: 10.1016/j.combustflame.2024.113352.
The influence of air humidity on flame propagation in mixtures of hydrofluorocarbons (HFCs) with air was studied through numerical simulations and comparison with measurements from the literature. Water vapor added to the air in mixtures of fluorine rich hydrofluorocarbons (F/H≥1) can be considered as a fuel additive that increases the production of radicals (H, O, OH) and increases the overall reaction rate. The hydrofluorocarbon flame is typically a two-stage reaction proceeding with a relatively fast reaction in the first stage transitioning to a very slow reaction in the second stage which leads to the combustion equilibrium products. The transition to the second stage is determined by the consumption of hydrogen-containing species and formation of HF. Despite a relatively small effect of water on the adiabatic combustion temperature, its influence is significant on the reaction rate and on the temperature increase in the first stage of the combustion leading to the increase in burning velocity. The main reaction for converting HO to hydrogen-containing radicals and promoting combustion is HO+F=HF+OH, as demonstrated by reaction path analyses for the fluorine rich hydrofluorocarbons R-1234yf, R-1234ze(E), and R-134a (F/H = 2). The calculated burning velocity dependence on the equivalence ratio agrees reasonably well with available experimental measurements for R1234yf and R-1234ze(E) with and without the addition of water vapor. In agreement with experimental data, with water vapor, the maximum of burning velocity over is shifted to the lean mixtures (near = 0.8).
通过数值模拟以及与文献中的测量结果进行比较，研究了空气湿度对氢氟烃（HFCs）与空气混合物中火焰传播的影响。在富氟氢氟烃（F/H≥1）混合物中添加到空气中的水蒸气可被视为一种燃料添加剂，它会增加自由基（H、O、OH）的生成并提高整体反应速率。氢氟烃火焰通常是一个两阶段反应，第一阶段反应相对较快，然后过渡到第二阶段非常缓慢的反应，最终生成燃烧平衡产物。向第二阶段的转变由含氢物种的消耗和HF的形成决定。尽管水对绝热燃烧温度的影响相对较小，但其对反应速率以及燃烧第一阶段的温度升高有显著影响，进而导致燃烧速度增加。如对富氟氢氟烃R - 1234yf、R - 1234ze(E)和R - 134a（F/H = 2）的反应路径分析所示，将HO转化为含氢自由基并促进燃烧的主要反应是HO + F = HF + OH。计算得出的燃烧速度与当量比的关系与R1234yf和R - 1234ze(E)在添加和不添加水蒸气情况下的现有实验测量结果相当吻合。与实验数据一致，添加水蒸气后，燃烧速度最大值对应的当量比向贫燃料混合物方向移动（接近 = 0.8）。
