The current work assesses the impact of turbulence on flame surface characteristics and scalar dissipation rates (${\chi }_C$) of piloted premixed methane-air flames. This assessment is facilitated via the application of planar Rayleigh scattering (PRS) to a subset of the flames considered in Part I (13 in total), which possess turbulent Karlovitz, Damköhler, and Reynolds numbers in the range of 1.1 $\le K{a}_{T,P}\le$ 144, 0.24 $\le D{a}_{T,P}\le$ 5.79, and 1,200 $\le R{e}_{T,0}\le$ 35,000, respectively. Instantaneous temperature maps are derived from the PRS images with an accuracy that is conservatively estimated to be within $\sim$3%. Additionally, the fidelity of the collected images was enhanced via the application of a combined wavelet-based and edge-preserving guided filtering scheme that allows scales associated with the peak of the dissipation spectra in the modestly turbulent flames considered here to be fully resolved. After such filtering, the temperature images were converted to reaction progress variable maps ($C_T$). Two-dimensional isocontours were extracted from these maps and used to assess the flame surface density (FSD; $\Sigma$) and the in-plane curvature (${\kappa }_{2D}$) of the flames considered here. Furthermore, scalar dissipation rate (${\chi }_{C_T}$), its density weighted average ($\widetilde{{\chi }_{C_T}}$), and other relevant quantities (e.g., the density-weighted variance of $C_T$: $\widetilde{C_T^{″2}}$ and the generalized FSD: $\overline{|\nabla C_T|}$) were derived from the $C_T$-maps. Subsequently, relationships between these quantities were assessed and compared against theoretical models that aim to capture such relationships through simple expressions.

The results indicate that the distribution of ${\kappa }_{2D}$ values broadens with enhanced turbulence, as does the integrated and peak values of FSD. Moreover, each of these parameters exhibit a strong positive correlation with $K{a}_{T,P}$, highlighting the role this non-dimensional parameter plays in dictating flame surface wrinkling/area-generation. Relationships between ${\chi }_{C_T}$, $\widetilde{C_T^{″2}}$, and $\overline{|\nabla C_T|}$, are compared to flamelet-type models proposed by Vervisch et al. as well as by Bray, Swaminathan, Kolla, Chakraborty, and coworkers. Overall, despite the fact that the considered flames exhibit substantial preheat zone broadening and are subjected to extreme levels of turbulence, the proposed theoretical relationships between ${\chi }_{C_T}$, $\widetilde{C_T^{″2}}$, and $\overline{|\nabla C_T|}$ show favorable agreement to the measurements. While differences between the measured and theoretical results are observed, the two can be reconciled with minor adjustments to the various constants in these models (i.e., changing them by no more than a factor of $\sim$2). Ultimately, such observations provide support for utilizing flamelet-type models to simulate premixed flames even when they are subjected to extreme turbulence levels. Moreover, the wealth of information provided here can help guide the development of robust yet efficient numerical tools for simulating highly turbulent premixed flames, which will aid in reducing the cost of and time to produce robust, efficient, and clean-burning combustion engines.

目前的工作评估了湍流对火焰表面特性和标量耗散率的影响（${\chi }_C$) 的预混甲烷-空气火焰。通过将平面瑞利散射 (PRS) 应用到第一部分中考虑的火焰子集（总共 13 个），这些火焰具有 1.1 范围内的湍流 Karlovitz、Damköhler 和 Reynolds 数，从而促进了该评估 $\le 钾{\mathrm{一种}}_{吨,磷}\le$ 144, 0.24 $\le D{\mathrm{一种}}_{吨,磷}\le$ 5.79 和 1,200 $\le \mathrm{电阻}{\mathrm{电子}}_{吨,0}\le$ 35,000，分别。瞬时温度图源自 PRS 图像，其精度保守估计在$～$3%。此外，通过应用组合的基于小波和边缘保留的引导滤波方案来增强所收集图像的保真度，该方案允许与此处考虑的适度湍流火焰中的耗散谱峰值相关联的尺度被完全解析。经过这样的过滤，温度图像被转换为​​反应进程变量图（$C_{吨}$）。从这些图中提取二维等值线并用于评估火焰表面密度（FSD；$\Sigma$) 和面内曲率 (${\kappa }_{2D}$) 这里考虑的火焰。此外，标量耗散率 (${\chi }_{C_{吨}}$)，其密度加权平均值 ($\stackrel{～}{{\chi }_{C_{吨}}}$)，以及其他相关量（例如，密度加权方差 $C_{吨}$： $\stackrel{～}{C_{吨}^{”2}}$ 和广义的 FSD： $\overline{|\nabla C_{吨}|}$) 源自 $C_{吨}$-地图。随后，评估了这些量之间的关系，并将其与旨在通过简单表达式捕捉此类关系的理论模型进行比较。

结果表明，分布 ${\kappa }_{2D}$值随着湍流增强而变宽，FSD 的积分值和峰值也是如此。此外，这些参数中的每一个都与$钾{\mathrm{一种}}_{吨,磷}$，强调了这个无量纲参数在决定火焰表面起皱/区域生成中的作用。之间的关系${\chi }_{C_{吨}}$, $\stackrel{～}{C_{吨}^{”2}}$， 和 $\overline{|\nabla C_{吨}|}$，与 Vervisch 等人提出的小火焰型模型进行了比较。以及 Bray、Swaminathan、Kolla、Chakraborty 和同事的作品。总体而言，尽管所考虑的火焰表现出显着的预热区加宽并受到极端湍流的影响，但提出的理论关系${\chi }_{C_{吨}}$, $\stackrel{～}{C_{吨}^{”2}}$， 和 $\overline{|\nabla C_{吨}|}$显示出与测量值的良好一致性。虽然观察到测量结果和理论结果之间存在差异，但可以通过对这些模型中的各种常数进行微小调整（即，将它们改变不超过$～$2）。最终，这些观察结果为利用火焰模型来模拟预混火焰提供了支持，即使它们受到极端湍流水平的影响。此外，此处提供的大量信息有助于指导开发用于模拟高度湍流预混火焰的稳健而高效的数值工具，这将有助于降低生产稳健、高效和清洁燃烧的内燃机的成本和时间。