Abstract We have applied chirped-probe-pulse (CPP) femtosecond (fs) coherent anti-Stokes Raman scattering for 5 kHz temperature measurements in turbulent spray flames. The CPP fs CARS technique has previously been used to perform spectroscopic temperature measurements in highly turbulent laboratory burners with excellent accuracy, precision, temporal resolution, and spatial resolution. In this paper, ultrafast CARS measurements in spray flames are presented as part of a larger effort to provide spatially and temporally resolved temperature fields in harsh spray environments. The Sydney Needle Spray Burner (SYNSBURNTM) was used to stabilize turbulent spray flames of acetone and ethanol. The burner features a retractable fuel injector so that the droplet density at the nozzle exit could be systematically varied. Results from selected regions of the turbulent spray flames are discussed in detail to highlight the challenges of CPP fs CARS temperature measurements. Sources of spectral distortion due to interaction with droplets are discussed along with an uncertainty analysis. The passage of fuel through the probe volume caused varying levels of signal degradation and resulted in complete signal loss on approximately 10% of the laser shots for dense spray conditions. The interferences are attributed to two separate phenomena and are categorized based on the probable phase of the fuel – liquid or gas. Interference caused by liquid fuel was unavoidable in certain regions at certain operating conditions, but easily identified and removed. Interference from vapor fuel was more problematic as the nitrogen signal was only moderately corrupted in the high-frequency portion of the spectrum, and the temperature was generally biased to higher values. Rejecting individual signal spectra, based on a fitting error threshold, was shown to be effective in excluding shots with significant interference from fuel droplets, but shots with only minor interference require a more-advanced rejection criterion. Analysis of the temperature fields for a few selected conditions is presented showing trends with the atomization quality of the liquid fuel. Fourier analysis revealed hydrodynamic instabilities in the shear layer and relatively weak thermoacoustic instabilities in the reaction zone.

中文翻译：

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使用啁啾探针脉冲飞秒 CARS 在湍流喷射火焰中进行 5 kHz 温度测量，第 I 部分：处理和干扰分析

摘要 我们已经应用啁啾探针脉冲 (CPP) 飞秒 (fs) 相干反斯托克斯拉曼散射在湍流喷射火焰中进行 5 kHz 温度测量。CPP fs CARS 技术以前曾用于在高度湍流的实验室燃烧器中进行光谱温度测量，具有出色的准确度、精度、时间分辨率和空间分辨率。在本文中，喷雾火焰中的超快 CARS 测量被提出作为在恶劣喷雾环境中提供空间和时间分辨温度场的更大努力的一部分。悉尼针式喷雾燃烧器 (SYNSBURNTM) 用于稳定丙酮和乙醇的湍流喷雾火焰。燃烧器具有可伸缩的燃料喷射器，因此可以系统地改变喷嘴出口处的液滴密度。详细讨论了湍流喷射火焰选定区域的结果，以突出 CPP fs CARS 温度测量的挑战。与不确定性分析一起讨论了由于与液滴相互作用引起的光谱失真的来源。燃料通过探头体积会导致不同程度的信号衰减，并导致在密集喷雾条件下大约 10% 的激光发射信号完全丢失。干扰归因于两种不同的现象，并根据燃料的可能相（液体或气体）进行分类。液体燃料造成的干扰在某些地区在某些运行条件下是不可避免的，但很容易识别和消除。蒸汽燃料的干扰更成问题，因为氮气信号仅在频谱的高频部分受到中度破坏，并且温度通常偏向较高值。事实证明，基于拟合误差阈值拒绝单个信号谱可以有效地排除具有显着燃料液滴干扰的弹丸，但只有轻微干扰的弹丸需要更高级的拒绝标准。对几个选定条件的温度场进行了分析，显示了液体燃料雾化质量的趋势。傅立叶分析揭示了剪切层中的流体动力学不稳定性和反应区中相对较弱的热声不稳定性。事实证明，基于拟合误差阈值拒绝单个信号谱可以有效地排除具有显着燃料液滴干扰的弹丸，但只有轻微干扰的弹丸需要更高级的拒绝标准。对几个选定条件的温度场进行了分析，显示了液体燃料雾化质量的趋势。傅立叶分析揭示了剪切层中的流体动力学不稳定性和反应区中相对较弱的热声不稳定性。事实证明，基于拟合误差阈值拒绝单个信号谱可以有效地排除具有显着燃料液滴干扰的弹丸，但只有轻微干扰的弹丸需要更高级的拒绝标准。对几个选定条件的温度场进行了分析，显示了液体燃料雾化质量的趋势。傅立叶分析揭示了剪切层中的流体动力学不稳定性和反应区中相对较弱的热声不稳定性。对几个选定条件的温度场进行了分析，显示了液体燃料雾化质量的趋势。傅立叶分析揭示了剪切层中的流体动力学不稳定性和反应区中相对较弱的热声不稳定性。对几个选定条件的温度场进行了分析，显示了液体燃料雾化质量的趋势。傅立叶分析揭示了剪切层中的流体动力学不稳定性和反应区中相对较弱的热声不稳定性。