Abstract
Abstract
Underground coal fire propagation is concealed and difficult to monitor, while the resulting atmospheric pollution poses persistent environmental risks. However, the coupled evolution of the temperature field, oxygen concentration, and pollutant emissions during vertical propagation remains insufficiently understood. In this study, a self-developed physical similarity simulation experimental system was used to conduct a physical similarity simulation experiment from ignition to extinction. The temperature field, oxygen concentration, CO₂, CO, CH₄, C₂H₆, PM₂.₅, PM₁₀, and total suspended particles were monitored continuously. The results showed that thermal–oxygen evolution could be divided into five stages: incubation, rapid heating, intensive reaction, rapid cooling, and burnout. Clear depth-dependent differences were observed: C1–C2 were dominated by burnout, C3–C5 constituted the principal sustained-reaction zone, and C6 exhibited oxygen-limited attenuation. Responses in the overlying strata and at the ground surface lagged behind those within the coal seam. CH₄, C₂H₆, and particulate matter were released mainly during the early stage, whereas CO₂ and CO dominated the middle and later stages. CH₄ and C₂H₆ were concentrated within the first 40–60 h and approached background levels after approximately 80 h. The atmospheric pollution assessment indicated predominantly moderate-to-severe pollution, with CO as the principal contributor. These findings clarify the stage-dependent and depth-dependent coupling among heat transfer, oxygen consumption, and pollutant emissions during the vertical propagation of underground coal fires, providing a basis for monitoring, risk assessment, and mitigation.