Study on the Spontaneous Combustion Mechanism and Dynamic Evolution Law of Coal under Low Oxygen Environment

To elucidate the mechanism of coal spontaneous combustion (CSC) and its dynamic evolution under hypoxic conditions, this study employed programmed temperature elevation combined with in situ Fourier-transform infrared spectroscopy (In situ FTIR) to investigate the low-temperature oxidation characteristics of coal under varying oxygen concentrations. The results reveal a distinct two-stage behavior in the low-temperature oxidation process influenced by low oxygen levels, accompanied by an oxygen-temperature competitive mechanism. During the 30-120 °C stage, the accumulation of gas products proceeds at a relatively slow rate and exhibits a significant positive correlation with changes in oxygen concentration; however, beyond 120 °C, gas production rates increase exponentially. Additionally, low oxygen concentration markedly affects the infrared absorption peak intensities of reactive functional groups within the coal matrix, with this influence reaching a turning point at 120 °C. Beyond this temperature, the modulatory effect of oxygen concentration diminishes, and temperature emerges as the primary driving force governing the oxidation progression. Gray relational analysis (GRA) further identifies carboxyl (-COOH) and methylene (-CH₂-) groups as critical participants in the coal low-temperature oxidation process. Variations in oxygen concentration significantly alter the evolution of these functional groups and consequently modulate the oxidation reaction pathways, thereby controlling the generation of gaseous products. These findings uncover the microscopic mechanisms underlying coal spontaneous combustion in low oxygen environments and provide a theoretical foundation for a deeper understanding of coal's low-temperature oxidation behavior.