A novel supercontinuum laser absorption spectroscopy (SCLAS) approach combining a planar external Herriott multi-pass cell (HMPC) with fully single-mode fiber (SMF) coupling is presented for broadband multi-scalar combustion measurements in a rapid compression expansion machine (RCEM). For the HMPC, 1-dimensional refractive index gradients occurring in the RCEM combustion chamber are analyzed via ray-tracing with respect to axial and vertical beam steering. The impact of beam steering on the SCLAS signal is compared with the ray-tracing analysis and high-speed flame luminosity images. SCLAS based measurements are presented during compression, auto-ignition and combustion in the RCEM for n-heptane/methane mixtures at varied AFR (air-fuel ratio) and n-heptane/EGR (exhaust gas recirculation) mixtures at temperatures exceeding 1800 K and pressures up to 80 bar. Simultaneous temperature and mole fraction courses of H₂O, CH₄, and CO₂ are inferred from NIR (near-infrared) broadband absorbance spectra detected by a Czerny Turner spectrometer (CTS) in a spectral range of 1374 nm to 1669 nm. The multi-pass approach with SMF coupling, which avoids multi-mode fiber induced noise, allows for high-speed multi-species SCLAS measurements with low standard deviations; for temperature this amounts to about 5 K and partially below at a temporal resolution of 25 µs.

中文翻译：

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通过超连续谱激光吸收光谱在快速压缩膨胀机中进行赫瑞特细胞增强 SMF 耦合多标量燃烧诊断

一种新型超连续谱激光吸收光谱 (SCLAS) 方法将平面外部赫里奥特多通池 (HMPC) 与全单模光纤 (SMF) 耦合相结合，用于快速压缩膨胀机 (RCEM) 中的宽带多标量燃烧测量. 对于 HMPC，RCEM 燃烧室中发生的一维折射率梯度通过相对于轴向和垂直光束控制的光线追踪进行分析。光束转向对 SCLAS 信号的影响与光线追踪分析和高速火焰光度图像进行了比较。在 RCEM 中针对不同AFR 的正庚烷/甲烷混合物在压缩、自燃和燃烧期间提供基于 SCLAS 的测量结果（空燃比）和正庚烷/EGR（废气再循环）混合物，温度超过 1800 K，压力高达 80 bar。H ₂ O、CH ₄和CO _{2 的}同时温度和摩尔分数曲线是从由Czerny Turner 光谱仪(CTS) 在1374 nm 到1669 nm 的光谱范围内检测到的NIR（近红外）宽带吸收光谱推断出来的。采用 SMF 耦合的多通道方法避免了多模光纤引起的噪声，允许以低标准偏差进行高速多物种 SCLAS 测量；对于温度，这相当于约 5 K，部分低于 25 µs 的时间分辨率。