金屬顆粒高體積能量密度的特性，有利於添加至固體推進劑中以增加整體能量輸出，或在燃煤爐中用金屬顆粒代替煤粉；相較於氣態碳氫化合物火焰，金屬混合火焰具有更高的能量、更高的火焰溫度。本研究旨在探討鐵混合燃燒粒徑對金屬顆粒微爆炸的潛在影響。本實驗使用四種不同的粒徑：2-10μm、50μm、100μm和150μm。預混錐形甲烷-空氣火焰在固定化學計量的條件下，以不同的進料速率摻入鐵顆粒。關於顆粒微爆炸機制，則係氧化劑擴散至鐵顆粒中，並在薄殼中生成氧化鐵。然而，有限的氧在鐵顆粒表面發生異質反應，從而在鐵顆粒表面產生中間產物氧化鐵 (FeO)。氧化鐵的形成，促使鐵顆粒在燃燒過程中有閃爍和收縮的現象。隨後，本研究於實驗中添加一氧化碳 (CO)，使一氧化碳穿透至氧化物殼層內部，並與殼層內之四氧化三鐵 (Fe2O3) 反應。四氧化三鐵將產生氣泡，並促成五羰基鐵 (Fe(CO)5)的形成。在氣泡凝聚過程中，鐵顆粒會逐漸膨脹，終將形成空心的球形顆粒。然而，在某些特殊條件下，五羰基鐵可能會引起鐵顆粒的微爆炸。

Metal particles have a high volumetric energy density, making them attractive to add into solid propellants for increasing overall energy output or replace coal powder with metal particles in the coal-fired furnace. Compared to gaseous hydrocarbon flame, a metal hybrid flame has higher energy and even has a higher flame temperature. In this study, we explored the micro-explosion mechanisms of iron particles in methane-air premixed flames Four different particle sizes were used in this experiment, that is 2-10μm, 50μm, 100μm, and 150μm. A conical methane-air premixed flame was fixed in stoichiometric condition and doped with iron particles at various feeding rates. Regarding the mechanism of the micro-explosion of iron particles, the oxidizer diffuses into iron particles and produces iron oxide in a thin shell. However, limited oxygen heterogeneously reacts over the surface of the iron particles and produces Fe3O4. Fe3O4 comprises FeO and Fe2O3. Fe2O3 is a stable and rigid oxide; however, when CO react Fe3O4, this reaction makes Fe3O4 redox into fresh Fe particles, and when the Fe dominating react with O2 it will lead into FeO. The presence of FeO leads to iron particle blinking and shrinking immediately after these particles have passed the flame front. And when CO was dominate the reaction, it will lead to aforementioned reaction results in the formation of Fe(CO)5 gas bubbles CO, N2, and O2 bubbles. During the agglomeration of the bubbles, the iron particles expand gradually and eventually become hollow spherical particles. However, under special conditions, this condition will induce the micro-explosion of the iron particles.

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