PDF(Pubmed)
Abstract：
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 H2O to hydrogen-containing radicals and promoting combustion is H2O+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 ϕ 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 ϕ is shifted to the lean mixtures (near ϕ = 0.8).
摘要：
通过数值模拟并与文献中的测量结果进行比较，研究了空气湿度对氢氟碳化合物（HFCs）与空气的混合物中火焰传播的影响。在富含氟的氢氟碳化合物（F/H≥1）的混合物中添加到空气中的水蒸气可以被认为是一种燃料添加剂，可以增加自由基的产生（H，O,OH)并提高整体反应速率。氢氟烃火焰通常是两阶段反应,其中第一阶段中的相对快的反应转变为第二阶段中的非常慢的反应,这导致燃烧平衡产物。向第二阶段的转变取决于含氢物质的消耗和HF的形成。尽管水对绝热燃烧温度的影响相对较小，它对反应速率和燃烧第一阶段的温度升高有显著影响，导致燃烧速度增加。将H2O转化为含氢自由基并促进燃烧的主要反应是H2OF=HFOH，如富氟氢氟烃R-1234yf的反应路径分析所示，R-1234ze(E),和R-134a(F/H=2)。计算出的燃烧速度对当量比Φ的依赖性与R1234yf和R-1234ze（E）在添加和不添加水蒸气的情况下的可用实验测量结果相当吻合。与实验数据一致，水蒸气，在Φ上的燃烧速度最大值转移到贫混合物(接近Φ=0.8)。
