Abstract One-dimensional hybrid fs/ps CARS imaging provides single-laser-shot measurements of temperature, oxygen, and hydrogen in a plasma-assisted hydrogen diffusion flame. The coaxial dielectric-barrier-discharge burner collapses the Re ∼50 hydrogen diffusion flame to within ∼5 mm of the burner surface at an applied AC potential of 8.75 kV at 18 kHz, coinciding nicely with the full spatial extent of the 1D CARS measurements. Translating the burner through the measurement volume allowed for measurements at numerous radial locations in increments of 1 mm with a resolution of 140 µm × 30 µm × 600 µm, sufficient to resolve spatial gradients in this unsteady flame. Longer probe delays, required for improved dynamic range in regions of high temperature fluctuations, proved difficult to model as a result of a nontrivial decay in the O2 Raman coherence arising from complexities associated with the triplet ground electronic state of the O2 molecule. Oxygen linewidths were treated empirically using the observed O2 coherence decay in spectra acquired from the product gases of lean, near-adiabatic H2/air flames stabilized on a Hencken flat-flame burner. While still leading to errors up to 10% at worst, the empirically determined Raman linewidth factors eliminated any systematic error in the O2/N2 measurements with probe delay. Temperature measurements in the Hencken Burner flames proved to be insensitive to probe pulse delay, providing robust thermometry. Demonstration of this technique in both the canonical Hencken burner flames and a new DBD burner validates its effectiveness in producing multiple spatially resolved measurements in combustion environments. Measurements in the DBD burner revealed an unsteady, counterflow flattened flame structure near the fuel orifice which became unsteady as the reaction zone curves towards the surface for larger radial positions. Fluctuations in the fuel concentration were largest at the source, as the large, plasma-generated, unsteady external toroidal vortex that dominates the transport in this flame provides enhanced ventilation of the flame surface in close proximity to the fuel tube.

中文翻译：

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介质阻挡放电等离子体辅助氢扩散火焰。第 1 部分：通过一维 fs/ps 旋转 CARS 成像测量温度、氧气和燃料

摘要 一维混合 fs/ps CARS 成像提供了等离子体辅助氢扩散火焰中温度、氧和氢的单次激光射击测量。同轴介质阻挡放电燃烧器在 18 kHz 下施加 8.75 kV 的交流电势时，将 Re~50 氢扩散火焰坍塌到燃烧器表面~5 mm 以内，这与 1D CARS 测量的整个空间范围非常吻合。通过测量体积平移燃烧器允许以 1 mm 的增量在多个径向位置进行测量，分辨率为 140 µm × 30 µm × 600 µm，足以解决这种不稳定火焰中的空间梯度。更长的探头延迟，需要在高温波动区域改善动态范围，由于与 O2 分子的三重基电子态相关的复杂性引起 O2 拉曼相干性的非平凡衰减，因此难以建模。使用从 Hencken 平焰燃烧器上稳定的贫、近绝热 H2/空气火焰的产物气体获得的光谱中观察到的 O2 相干衰减经验性地处理氧线宽。虽然在最坏的情况下仍会导致高达 10% 的误差，但凭经验确定的拉曼线宽因子消除了 O2/N2 测量中的任何系统误差和探头延迟。Hencken Burner 火焰中的温度测量被证明对探头脉冲延迟不敏感，提供了可靠的温度测量。该技术在标准 Hencken 燃烧器火焰和新型 DBD 燃烧器中的演示验证了其在燃烧环境中产生多个空间分辨测量的有效性。DBD 燃烧器中的测量结果表明，燃料孔口附近存在不稳定的逆流扁平火焰结构，随着反应区向表面弯曲以获得更大的径向位置，该结构变得不稳定。燃料浓度的波动在源头最大，因为在该火焰中占主导地位的大的、等离子体生成的、不稳定的外部环形涡流增强了靠近燃料管的火焰表面的通风。靠近燃料孔口的逆流扁平火焰结构随着反应区向表面弯曲以获得更大的径向位置而变得不稳定。燃料浓度的波动在源头最大，因为在该火焰中占主导地位的大的、等离子体生成的、不稳定的外部环形涡流增强了靠近燃料管的火焰表面的通风。靠近燃料孔口的逆流扁平火焰结构随着反应区向表面弯曲以获得更大的径向位置而变得不稳定。燃料浓度的波动在源头最大，因为在该火焰中占主导地位的大的、等离子体生成的、不稳定的外部环形涡流增强了靠近燃料管的火焰表面的通风。