Optimization of Nitrogen Injection Parameters for a Partial W‑Type Ventilation Goaf at Duanwang Mine

To optimize nitrogen injection for preventing coal spontaneous combustion in the goaf, closed oxygen consumption tests and field data calibrated the oxygen criterion for the suffocation zone. A numerical model of the 150405 panel goaf with partial "W" ventilation was established to analyze gas drainage and nitrogen injection effects. Increasing the gas drainage volume narrowed the oxidation zone on the conveyor side but expanded it on the track side. Oxidation zone width first decreased and then slightly increased with injection distance and decayed exponentially with higher injection rates. The optimal injection location was identified 40 m from the face on the conveyor side, with a rate of 145.5 m³/h, providing practical guidance for fire prevention.