Coal spontaneous combustion (CSC) is a complex physical and chemical process. Numerical simulation is an efficient method for visualizing and quantifying CSC. However, in previous models, the property parameters of coal are frequently assumed to be constant and hence cannot be used to predict accurately the thermodynamic behaviors during CSC. In this study, a fully coupled porous media model considering water migration, heat transfer, and thermal deformation was developed to investigate the thermal kinetics of CSC. The porosity and thermal strain during CSC in the model were consistent with the experimental results. Moreover, a method based on nuclear magnetic resonance (NMR) was used to calculate the residual saturation of fluids in porous media during heat treatment. The results showed that porosity increased with temperature during CSC, and the NMR transverse relaxation cutoff values of coal depended nonlinearly on temperature. In the initial stage of CSC, moisture was the dominant factor affecting CSC. As time progresses, moisture and temperature exhibited a synergistic effect. Temperature was the leading factor contributing to CSC in the final stage. The temperature increase during CSC exhibited a ‘slow and then fast’ trend. In addition, the deformation of coal during CSC caused thermal shrinkage, and its magnitude depended on the temperature increase rate. The results can be used to identify the thermodynamic behaviors during CSC and contribute to a better understanding of the mechanism of CSC.

煤自燃（CSC）是一个复杂的物理和化学过程。数值模拟是可视化和量化 CSC 的有效方法。然而，在以前的模型中，煤的性质参数经常被假设为常数，因此不能用于准确预测 CSC 期间的热力学行为。在这项研究中，开发了一个考虑水迁移、传热和热变形的全耦合多孔介质模型来研究 CSC 的热动力学。模型中CSC过程中的孔隙率和热应变与实验结果一致。此外，基于核磁共振（NMR）的方法被用于计算热处理过程中多孔介质中流体的残余饱和度。结果表明，在 CSC 过程中，孔隙率随温度的升高而增加，煤的核磁共振横向弛豫截止值与温度呈非线性关系。在CSC初期，水分是影响CSC的主要因素。随着时间的推移，水分和温度表现出协同效应。在最后阶段，温度是导致 CSC 的主要因素。CSC期间的温度升高呈现出“先慢后快”的趋势。此外，煤在CSC过程中的变形引起了热收缩，其大小取决于升温速率。该结果可用于识别 CSC 期间的热力学行为，并有助于更好地理解 CSC 的机制。水分和温度表现出协同效应。在最后阶段，温度是导致 CSC 的主要因素。CSC期间的温度升高呈现出“先慢后快”的趋势。此外，煤在CSC过程中的变形引起了热收缩，其大小取决于升温速率。该结果可用于识别 CSC 期间的热力学行为，并有助于更好地理解 CSC 的机制。水分和温度表现出协同效应。在最后阶段，温度是导致 CSC 的主要因素。CSC期间的温度升高呈现出“先慢后快”的趋势。此外，煤在CSC过程中的变形引起了热收缩，其大小取决于升温速率。该结果可用于识别 CSC 期间的热力学行为，并有助于更好地理解 CSC 的机制。