This paper presents a numerical investigation of the effects of steam and water mist/spray addition on NO formation in a methane–air counterflow diffusion flame. A detailed chemical mechanism (Glarborg et al. Modeling nitrogen chemistry in combustion, Prog. Energy Combust. Sci. 67 (2018), pp. 31–68) which contains 1397 reactions and 151 species has been employed to investigate the NO formation in a counterflow diffusion flame for a wide range of strain rates (50–400 s${}^{-1}$) in OPPDIF. The water spray/mist evaporation is represented as a first-order dynamic process with Arrhenius type dependence on temperature that can be expressed in a form similar to a first-order chemical reaction. Instead the process is represented as a first-order dynamic process by invoking a hypothetical chemical species ${\mathrm{H}}_2\mathrm{O}\left(\mathrm{L}\right)$ and a surrogate reaction ${\mathrm{H}}_2\mathrm{O}\left(\mathrm{L}\right){\mathrm{H}}_2\mathrm{O}$. This approach allows handling detail chemistry and droplet evaporation at a reasonable computational cost. This model is validated with CFD simulation results where droplets are modelled using the Discrete Phase Modelling approach. The effects of steam and water mist on the flame temperature and NO formation have been examined. It is found that steam/water mist inhibits NO formation by affecting both thermal and prompt pathways. It is seen that the percentage contribution of prompt NO in overall NO production significantly decreases with increasing steam dilution. Water mist causes an additional evaporative heat loss and results in a drop in percentage contribution of thermal NO in overall NO formation.

本文对甲烷和空气逆流扩散火焰中蒸汽和水雾/喷雾添加对NO形成的影响进行了数值研究。详细的化学机理（Glarborg等人，《燃烧中的氮化学模型》，Prog.Energy Combust.Sci.67（2018），pp.31-68）包含1397个反应和151个物种已被用于研究一氧化碳中NO的形成。逆流扩散火焰，应变率范围广（50–400 s${}^{-\mathrm{1个}}$）。喷水/水雾蒸发表示为一阶动态过程，其中阿伦尼乌斯类型取决于温度，可以以类似于一阶化学反应的形式表示。相反，该过程通过调用假设的化学物种表示为一阶动态过程${\mathrm{H}}_{\mathrm{2个}}\mathrm{Ø}（\mathrm{大号}）$ 和替代反应 ${\mathrm{H}}_{\mathrm{2个}}\mathrm{Ø}（\mathrm{大号}）{\mathrm{H}}_{\mathrm{2个}}\mathrm{Ø}$。这种方法允许以合理的计算成本处理详细的化学反应和液滴蒸发。该模型已通过CFD仿真结果验证，其中使用离散相建模方法对液滴进行了建模。已经检查了蒸汽和水雾对火焰温度和NO形成的影响。发现蒸汽/水雾通过影响热通道和快速通道来抑制NO的形成。可以看出，随着蒸汽稀释度的增加，瞬态NO在总NO产生中的百分比贡献显着降低。水雾会导致额外的蒸发热损失，并导致热NO在总NO形成中所占百分比的下降。