Ignition and Combustion of Metals as Fuel of Breathing Propulsion in CO_2 Planet Atmospheres

一种以金属为燃料的吸入二氧化碳的涡轮喷气发动机有可能成为一种可以在火星和金星大气中工作的飞机发动机，这些大气由二氧化碳组成。可能用于此目的的金属有Mg、Li、Al和B，因为它们与CO_2的反应热高。其中，火焰温度较高的Mg和Al比Li和b更具吸引力。根据热力学循环分析，对发动机性能进行评估，以评估发动机的可行性。分析表明，该发动机虽然消耗了大量的金属燃料，但提供了足够的推力值。对金属在撞击式纯二氧化碳气流中的点火和燃烧进行了基础实验研究。发现Li、Mg和Al在t-流中可以自燃。Li和Mg的自燃温度远低于Al的自燃温度。Li的自燃过程分为两个不同的步骤，即表面反应和气相反应。点火后，Li首先以气相燃烧，然后在金属表面燃烧。另一方面，在流中点火时，镁表面被一层保护膜覆盖，以防止进一步氧化。当Mg的初始温度高于临界温度时，反应初期形成的膜变得无保护作用，然后发生气相反应，导致着火。点燃后，Mg始终以气相燃烧。Al的点火过程与Mg的相似。然而，到目前为止，人工智能过程的细节还不清楚。这四种金属中，只有B在C0_2流中不能着火，但在其表面发生了明显的反应，并在其表面出现了熔融的氧化硼。

A carbon dioxide breathing turbojet engine using metals as fuel has potential for an airplane engine which can work in Mars and Venus atmospheres, consisting of CO_2. Several possible metals for this purpose are Mg, Li, Al and B, because of their high heats of reaction with CO_2. In particular, Mg and Al which have higher flame temperatures, are more attractive fuels than Li and B. The feasibility of the engine was assessed by estimating the engine performance according to thermodynamic cycle analysis. The analysis indicates that although the engine consumes a large amount of metal fuel, it gives the sufficient value of thrust.A fundamental study was performed experimentally on the ignition and combustion of the metals in an impinging pure C0_2 gas stream. It was found that Li, Mg and Al could ignite spontaneously in t-he stream. The spontaneous ignition temperatures of Li and Mg were much lower than that of Al. The ignition process of Li had two distinct steps, first a surface reaction and then a gas phase reaction. After,ignition, Li burned in vapor-phase at first and then on the metal surface. On the other hand, at the ignition in the stream, the Mg surface was covered with a protective film against further oxidation. When initial temperatures of Mg were higher than a Critical temperature, the film formed in early reaction stages became non-protective and then gas phase reactions occurred, leading to ignition. After ignition, Mg burned in vapor-phase throughout. The ignition process of Al was found to be similar to that of Mg. However, details of the process of Al have not been made clear so far. Among these four metals, only B could not ignite in the C0_2 stream, but the reactions occurred appreciably on the surface, and the molten boron oxide appeared on its surface.