A laser absorption tomography (LAT) technique was developed for investigating the thermochemical structure of a solid fuel oxidation layer in a hybrid rocket geometry. The measurement strategy utilizes tunable infrared lasers to target rovibrational transitions of three major combustion species: carbon monoxide ( $$\text {CO}$$ ), carbon dioxide ( $${\text{CO}}_{2}$$ ), and water ( $$\text {H}_{2}\text {O}$$ ). Species-specific molecular absorption was measured using a quantum cascade laser (QCL) near 4.98 $$\mu$$ m for $$\text {CO}$$ , an interband cascade laser (ICL) near 4.19 $$\mu$$ m for $$\text {CO}_{2}$$ , and a diode laser near 2.48 $$\mu$$ m for $$\text {H}_{2}\text {O}$$ . Spectrally- and spatially-resolved absorption data was collected by translating collinear laser beams across the exit plane of a fuel cylinder with an oxidizer core flow at various fuel-grain lengths. Under an assumption of azimuthal symmetry, Tikhonov-regularized Abel inversion was performed to yield radially-resolved absorption coefficient, from which a two-line method was used to infer temperature and species mole fraction. Planar measurements at different axial distances were compiled to form two-dimensional images, spatially-resolving the thermochemical structure downstream of the oxygen injector. The method is demonstrated to visualize the oxidation of two fuels, poly(methyl methacrylate) (PMMA) and high-density polyethylene (HDPE), with two injector geometries, highlighting the capability to discern variations in hybrid rocket motor design.

中文翻译：

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通过 $$\text {CO}$$、$$\text {CO}_{2}$$ 和 $$\text {H}_{2 的激光吸收层析成像对混合火箭燃料氧化进行原位热化学分析}\text {O}$$

开发了一种激光吸收断层扫描 (LAT) 技术，用于研究混合火箭几何结构中固体燃料氧化层的热化学结构。测量策略利用可调谐红外激光器来瞄准三种主要燃烧物质的振动跃迁：一氧化碳 ( $$\text {CO}$$ )、二氧化碳 ( $${\text{CO}}_{2}$$ ) ，和水（ $$\text {H}_{2}\text {O}$$ ）。物种特异性分子吸收使用接近 4.98 $$\mu$$ m 的量子级联激光器 (QCL) 测量，用于 $$\text {CO}$$，在 4.19 $$\mu$$ 附近使用带间级联激光器 (ICL) m 表示 $$\text {CO}_{2}$$ ，以及接近 2.48 $$\mu$$ m 的二极管激光器 $$\text {H}_{2}\text {O}$$ 。光谱和空间分辨的吸收数据是通过将共线激光束平移穿过燃料缸的出口平面来收集的，其中氧化剂核心在不同的燃料颗粒长度流动。在方位角对称的假设下，进行了 Tikhonov 正则化阿贝尔反演以产生径向分辨的吸收系数，从中使用两条线方法来推断温度和物种摩尔分数。不同轴向距离的平面测量被编译成二维图像，空间分辨氧气注射器下游的热化学结构。该方法被证明可以可视化两种燃料的氧化，聚甲基丙烯酸甲酯 (PMMA) 和高密度聚乙烯 (HDPE)，具有两种喷射器几何形状，突出了识别混合火箭发动机设计变化的能力。