Sealing tunnel portals is a favorable approach to controlling tunnel fires. This paper experimentally studied the influence of portals-sealing on fire behavior in a small-scale tunnel. A series of characteristic parameters, including fuel burning rate, O₂ and CO₂ volume fraction, and ceiling smoke temperature in the tunnel were measured. Besides, the flame self-extinguishment time, smoke transportation characteristics and gas temperature field at different fire source locations and sealing conditions were systematically investigated. Results indicated that the critical equivalence ratio for methanol fuel converted to ventilation-controlled tunnel fires is within 0.783-0.923. The combustion state is influenced by fire location. Fires occurring near the tunnel entrance are more prone to self-extinguishment than those away from the tunnel entrance. The critical volume fraction of O₂ for flame self-extinguishment ranges from 13.5%-15.3% and decreases with increasing smoke temperature. Moreover, sealing tunnel portals significantly impacts peak smoke temperature values, but hardly changes the longitudinal distribution pattern of temperature. The longitudinal distribution model of gas temperature under the action of the strong plume in a confined space is developed. This study provides guidance for fire risk assessment during the tunnel sealing process and contributes to the scientific development of sealing strategies.

tunnel fire; sealing effect; equivalence ratio; flame self-extinguishment; smoke transportation characteristics