Underground coal fires, which are widely distributed and cause serious resource waste and environmental hazards, have become a common concern of the international community. This paper aims to reveal the mechanism of coal spontaneous combustion and the expansion law of underground coal fires. A void rate model from the goaf to the ground surface and a multi-field coupling model for underground coal fires were established. Based on which, the combustion process from the beginning of oxidation to the formation of large-scale fire of the remaining coal in goaf was analyzed. Furthermore, the evolution law of underground coal fire after nitrogen injection and the influence of different nitrogen injection parameters were analyzed. The results show that the coal spontaneous combustion can be divided into three stages: slow reaction stage (stage Ⅰ), violent combustion stage (stage Ⅱ), and stable combustion stage (stage Ⅲ), and the transformation of different stages is mainly controlled by the oxidation reaction rate of coal. To obtain the optimal parameters for nitrogen injection for fire suppression, the fire extinguishing efficiency concerning nitrogen injection time, nitrogen injection amount and nitrogen injection position, as well as the distribution law of nitrogen in rock strata were analyzed. Through range analysis, it is determined that the most effective fire extinguishing occurs with the injection rate of 0.15 m3/s in stage I, and the injection position has little influence on the fire extinguishing effect. This understanding contributes to a deeper understanding of the multi-field coupling mechanism of underground coal fires and provides a guidance for extinguishing and preventing underground coal fires.

中文翻译：

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煤矿井下燃烧多场耦合特性及喷氮参数优化研究


地下煤火分布广泛，造成严重的资源浪费和环境危害，已成为国际社会的共同关注。本文旨在揭示煤炭自燃机理和地下煤火的扩展规律。建立了采空区至地面的空洞率模型和地下煤火多场耦合模型。在此基础上，分析了采空区剩余煤从开始氧化到形成大规模火灾的燃烧过程。进一步分析了注氮气后井下煤火的演化规律以及不同注氮气参数的影响。结果表明，煤自燃可分为缓慢反应阶段（Ⅰ阶段）、剧烈燃烧阶段（Ⅱ阶段）和稳定燃烧阶段（Ⅲ阶段）3个阶段，不同阶段的转化主要受控于煤的氧化反应速率。为了获得最佳的注氮气灭火参数，对注氮气时间、注氮气量、注氮气位置的灭火效率以及氮气在岩层中的分布规律进行了分析。通过极差分析确定，第一阶段喷射速率为0.15 m3/s时灭火效果最好，且喷射位置对灭火效果影响较小。这一认识有助于加深对地下煤火多场耦合机制的认识，为扑灭和预防地下煤火提供指导。