In this article, the application of the FRAME (Frequency Recognition Algorithm for Multiple Exposures) technique is presented for multi-species measurements in symmetric and asymmetric ethylene/air diffusion flames. Laminar Bunsen-type and swirled diffusion flames are investigated to gain a better understanding of sooting combustion. For this purpose, simultaneous imaging is conducted in terms of Laser-Induced Fluorescence (LIF) of Polycyclic Aromatic Hydrocarbons (PAH) and Laser-Induced Incandescence (LII) of soot particles. Subsequently, the approach is utilized for simultaneous imaging of hydroxyl (OH)-LIF and soot-LII. Here, the modulated LIF- and LII-signals are acquired together as a single sub-image—with a single exposure utilizing the full sensor size of a single camera. By employing the frequency-recognition algorithm on the single image, the LIF- and LII-signals are spectrally isolated—generating two individual LIF- and LII-images. The flame luminosity and out-of-focus light such as reflected surrounding laser light are detected as non-modulated signals in the unprocessed image. These unwanted signals are suppressed using the image post-processing, and, therefore, the image contrast of the two resulting images is improved. It is found that PAHs mainly exist in the inner region near the burner and are surrounded by soot. The majority of the OH is distributed on the outer edges of the flame—representing the reaction zone and soot-oxidation region of the flame.

中文翻译：

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单相机在烟灰火焰中同时进行LIF和LII成像的FRAME复制

在本文中，提出了FRAME（多次暴露的频率识别算法）技术在对称和不对称乙烯/空气扩散火焰中进行多物种测量的应用。研究了层流本生型和旋流扩散火焰，以更好地了解烟understanding燃烧。为此，根据多环芳烃（PAH）的激光诱导荧光（LIF）和烟尘颗粒的激光诱导白炽度（LII）进行同步成像。随后，该方法用于羟基（OH）-LIF和烟灰-LII的同时成像。在这里，将调制的LIF和LII信号作为单个子图像一起采集-利用单个摄像机的完整传感器尺寸进行一次曝光。通过对单个图像采用频率识别算法，LIF和LII信号在频谱上是隔离的-生成两个单独的LIF和LII图像。在未处理的图像中，火焰亮度和散焦光（例如反射的周围激光）被检测为未调制信号。使用图像后处理抑制了这些不想要的信号，因此，改善了两个结果图像的图像对比度。发现PAHs主要存在于燃烧器附近的内部区域，并被烟灰包围。大部分OH分布在火焰的外边缘上，代表了火焰的反应区和烟尘氧化区域。在未处理的图像中，火焰亮度和散焦光（例如反射的周围激光）被检测为未调制信号。使用图像后处理抑制了这些不想要的信号，因此，改善了两个结果图像的图像对比度。发现PAHs主要存在于燃烧器附近的内部区域，并被烟灰包围。大部分OH分布在火焰的外边缘上，代表了火焰的反应区和烟尘氧化区域。在未处理的图像中，火焰亮度和散焦光（例如反射的周围激光）被检测为未调制信号。使用图像后处理抑制了这些不想要的信号，因此，改善了两个结果图像的图像对比度。发现PAHs主要存在于燃烧器附近的内部区域，并被烟灰包围。大部分OH分布在火焰的外边缘上，代表了火焰的反应区和烟尘氧化区域。