Multi-scale evolution characteristics of coal low temperature oxidation under varying water content and the promotion-inhibition coupling mechanism of spontaneous combustion

External water significantly influences the spontaneous combustion of goaf residual coal. To clarify the relationship between water content and combustion behavior, coal samples with water contents of 3%, 6.15%, 9.25%, 12.7%, and 16.89% were investigated using microstructural characterization, thermophysical measurements, and temperature-programmed oxidation. Oxygen adsorption capacity, specific surface area (SSA), functional groups, thermophysical properties, and oxidation behavior were systematically analyzed. Oxygen adsorption reached a maximum at 6.15% water content. At 30 °C, SSA decreases from 2.43 m 2 ·g − 1 to 1.35 m 2 ·g − 1 with increasing water content, whereas heating promoted pore development in high water content coal due to water removal. Higher water content increased the contents of –OH, C = O, and –COOH while decreasing C = C and C–O. Increasing water content also enhanced specific heat capacity but reduced thermal diffusivity and thermal conductivity, weakening heat transfer within coal. Gas generation, oxygen consumption, and heat release exhibited bell-shaped trends with maxima at 6.15% moisture. For example, at 160 °C, the oxygen consumption at 6.15% water content is approximately 49.6% higher than that at 16.89%, while the CO and CO 2 yields follow an identical rank order of 6.15%>9.25%>12.7%>3%>16.89% across the oxidation stages. The apparent activation energy reached minimum values of 33.41 and 49.55 kJ·mol − 1 in Stages I and II, respectively, at 6.15% water content, then increased by 21.9% and 22.0% at 16.89%, indicating that excessive water suppresses low-temperature oxidation. These findings provide theoretical support for preventing spontaneous combustion of water-immersed residual coal in goaf.