Abstract Soret or thermal diffusion is known to impact combustion mixtures by diffusion of species along a temperature gradient. In this numerical modelling study we show that Soret diffusion can cause considerable local changes in the stabilization of H2 enriched premixed flames. First we validate two reduced Soret diffusion models with a more complete multi-component model. One model is able to capture the effect of Soret diffusion in the flame zone while the other model captures the effect in the flame zone as well as in the regions where high temperature gradients might exist e.g., near hot burner, side walls. Using the two reduced models along with conjugate heat transfer, we analyze bluff-body stabilized flames and the effect of Soret diffusion in the flame zone and near hot walls. For such flames, heat transfer between the flame and the burner results in local quenching. This heat is recirculated through the burner towards the unburnt gases creating a temperature gradient in the boundary layer around the burner. Because of Soret diffusion, this gradient drives H2 and even CH4 towards the burner walls in the unburnt mixture thus creating a local stratification (in the mixture approaching the flame base). As a result of this stratification, the burning rate of the flame near the anchoring location is enhanced, which causes more heat to be lost to the burner. The flame stabilizes at a new location where the strain rate is higher in order to neutralize the enhancement in burning rate and a new balance between flame and flow velocity is found. The effect of this local stratification is shown to be profound only when there is considerable heat loss to the burner such as for flames near flashback.

中文翻译：

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热扩散对预混火焰稳定性的影响

摘要 众所周知，Soret 或热扩散会通过物质沿温度梯度的扩散来影响燃烧混合物。在这个数值模拟研究中，我们表明 Soret 扩散会导致富含 H2 的预混火焰的稳定性发生相当大的局部变化。首先，我们使用更完整的多组件模型验证两个简化的 Soret 扩散模型。一个模型能够捕捉火焰区域中 Soret 扩散的影响，而另一个模型捕捉火焰区域以及可能存在高温梯度的区域（例如靠近热燃烧器、侧壁）的影响。使用两个简化模型以及共轭传热，我们分析了钝体稳定火焰以及火焰区和热壁附近的 Soret 扩散的影响。对于这样的火焰，火焰和燃烧器之间的热传递导致局部淬火。该热量通过燃烧器向未燃烧的气体再循环，在燃烧器周围的边界层中产生温度梯度。由于 Soret 扩散，该梯度驱使 H2 甚至 CH4 流向未燃烧混合物中的燃烧器壁，从而产生局部分层（在接近火焰底部的混合物中）。由于这种分层，锚定位置附近火焰的燃烧速度得到提高，从而导致更多的热量散失到燃烧器中。火焰稳定在应变速率较高的新位置，以抵消燃烧速率的增加，并在火焰和流速之间找到新的平衡。