Ammonia (\(\mathrm {NH_3}\)) has attracted interest as a future carbon-free synthetic fuel due to its economic storage and transportation. In this study, quasi direct numerical simulations (quasi-DNS) with detailed-chemistry have been performed in 3-D to examine the flame thickness and assess the validity of Damköhler’s first hypothesis for premixed turbulent planar ammonia/air and methane/air flames under different turbulence levels. The Karlovitz number is systematically changed from 4.26 to 12.06 indicating that all the test conditions are located within the thin reaction zones combustion regime. Results indicate that the ensemble average values of the preheat zone thickness deviate slightly from the thin laminar flamelet assumption, while the reaction zone regions remain relatively intact. Following the balance equation of reaction progress variable gradient, normal strain rate and the tangential diffusion component of flame displacement speed variation in the normal direction to the flame surface are found to be responsible for thickening the flame. However, the sum of reaction and normal diffusion components of flame displacement speed variation in the normal direction to the flame surface is in charge of flame thinning for ammonia/air and methane/air flames. In addition, the validity of Damköhler’s first hypothesis is confirmed by indicating that the ratio of the turbulent burning velocity to the unstrained premixed laminar burning velocity is relatively equal to the ratio of the wrinkled to the unwrinkled flame surface area. Furthermore, the probability density functions of the density-weighted flame displacement speed show that the bulk of flame elements propagate identical to the unstrained premixed laminar flame.

氨 ( \(\mathrm {NH_3}\)) 由于其经济的储存和运输，它作为未来的无碳合成燃料引起了人们的兴趣。在这项研究中，已经在 3-D 中进行了具有详细化学的准直接数值模拟 (quasi-DNS)，以检查火焰厚度并评估 Damköhler 的第一个假设的有效性，即预混湍流平面氨/空气和甲烷/空气火焰不同的湍流水平。卡洛维茨数系统地从 4.26 变为 12.06，表明所有测试条件都位于薄反应区燃烧状态内。结果表明，预热区厚度的整体平均值与薄层流火焰假设略有偏差，而反应区区域保持相对完整。遵循反应进程变量梯度的平衡方程，发现法向应变率和火焰表面法线方向上的火焰位移速度变化的切向扩散分量是导致火焰变厚的原因。然而，火焰位移速度沿火焰表面法线方向变化的反应分量和法向扩散分量之和负责氨/空气和甲烷/空气火焰的火焰变薄。此外，通过表明湍流燃烧速度与无应变预混层流燃烧速度之比相对等于褶皱与未褶皱火焰表面积之比，证实了 Damköhler 的第一个假设的有效性。此外，