Lucas Michael, Brotton Stephen J, Min Ahreum, Woodruff Connor, Pantoya Michelle L, Kaiser Ralf I
Department of Chemistry , University of Hawai'i at Manoa , Honolulu , Hawaii 96822 , United States.
Mechanical Engineering Department , Texas Tech University , Lubbock , Texas 79409 , United States.
J Phys Chem A. 2020 Feb 27;124(8):1489-1507. doi: 10.1021/acs.jpca.9b10697. Epub 2020 Feb 17.
Addition of high-energy-density materials such as aluminum (Al) microparticles or nanoparticles to liquid propellants potentially improves performance of the fuel. We report on the effects of untreated, prestressed, and superquenched aluminum particles with diameters of 100 nm, 250 nm, 500 nm, 1.6 μm, and 8.8 μm on the combustion of JP-10 droplets acoustically levitated in an oxygen-argon atmosphere. Ignition was initiated by a carbon dioxide laser, and the resulting oxidation processes were traced by Raman, Fourier-transform infrared (FTIR), and ultraviolet-visible (UV-vis) spectroscopies together with high-speed optical and IR thermal-imaging cameras. The UV-vis emission spectra reveal that the key reactive radical intermediates hydroxyl (OH), methylidyne (CH), dicarbon (C), aluminum monoxide (AlO), and aluminum monohydride (AlH) were formed in addition to atomic aluminum (Al) and the final oxidation products of JP-10, namely, water (HO) and carbon dioxide (CO). The Al particles facilitated ignition of the JP-10 droplets and produced higher temperatures in the combustion process of up to typically 2600 K. The effect of the Al particles on the ignition and maximum flame temperatures increased as the diameters reduced. The different stress treatments did not produce observable changes for the ignition or combustion of the droplets, which indicates that the liquid propellant was not significantly affected by manipulating the mechanical properties of the fuel particle additive. The initiation and enhancement of the combustion were a consequence of forming highly reactive atomic oxygen (O) and aluminum monoxide (AlO) radicals in the reaction of aluminum atoms with molecular oxygen in the gas phase. These radicals initiate the degradation of JP-10 via atomic hydrogen abstraction forming the hydroxyl (OH) and aluminum hydroxide (AlOH) radicals in reactions which are mainly exothermic by up to 68 kJ mol. In contrast, hydrogen abstractions from JP-10 by molecular oxygen or atomic aluminum are strongly endothermic by up to 236 kJ mol, thus making these reactions less competitive. The generation of CH hydrocarbon radicals from the JP-10 initiates successive oxidations and chain reactions with molecular oxygen leading eventually to carbon dioxide and water. These combined experimental results provide insight into how aluminum particles facilitate the oxidation and reaction mechanisms of JP-10 droplets.
向液体推进剂中添加高能密度材料，如铝（Al）微粒或纳米颗粒，可能会提高燃料的性能。我们报告了未经处理、预应力处理和超淬火处理的直径为100纳米、250纳米、500纳米、1.6微米和8.8微米的铝颗粒对在氧氩气氛中声学悬浮的JP - 10液滴燃烧的影响。点火由二氧化碳激光引发，产生的氧化过程通过拉曼光谱、傅里叶变换红外（FTIR）光谱和紫外可见（UV - vis）光谱以及高速光学和红外热成像相机进行追踪。紫外可见发射光谱表明，除了原子铝（Al）以及JP - 10的最终氧化产物水（H₂O）和二氧化碳（CO₂）之外，还形成了关键的活性自由基中间体羟基（OH）、亚甲基（CH）、双碳（C）、一氧化铝（AlO）和一氢化铝（AlH）。铝颗粒促进了JP - 10液滴的点火，并在燃烧过程中产生了高达通常2600 K的更高温度。铝颗粒对点火和最高火焰温度的影响随着直径减小而增大。不同的应力处理对液滴的点火或燃烧没有产生可观察到的变化，这表明通过操纵燃料颗粒添加剂的机械性能，液体推进剂没有受到显著影响。燃烧的引发和增强是铝原子与气相中的分子氧反应形成高活性原子氧（O）和一氧化铝（AlO）自由基的结果。这些自由基通过夺取原子氢引发JP - 10的降解，在主要放热高达68 kJ/mol的反应中形成羟基（OH）和氢氧化铝（AlOH）自由基。相比之下，分子氧或原子铝从JP - 10夺取氢的反应强烈吸热高达236 kJ/mol，因此使这些反应竞争力较弱。JP - 10产生的CH烃自由基引发与分子氧的连续氧化和链反应，最终导致二氧化碳和水。这些综合实验结果深入揭示了铝颗粒如何促进JP - 10液滴的氧化和反应机制。
