Study on effects of longitudinal ventilation on combustion characteristics and flue gas temperature distribution in full-scale roadway fires

To investigate the influence law of longitudinal ventilation on the fire evolution characteristics of mine roadways, full-scale roadway fire experiments were carried out. The combustion characteristics and flue gas temperature distribution under different ventilation wind speeds (0.5, 1.0, 1.5 and 2.0 m/s) were analyzed. The results show that the flame is slightly inclined driven by thermal buoyancy at low wind speeds. With the increase of wind speed, under the coupling effect of horizontal airflow thrust and thermal buoyancy, the flame evolves into an obviously inclined jet shape, accompanied by the rise of combustion intensity. In the flame core zone, the peak temperature remains stable at 1 200 ℃ under all ventilation wind speeds, whereas the time-history temperature curves differ significantly. The fluctuation range of the temperature curve under the low wind speed of 0.5 m/s is remarkably larger than that under high wind speed conditions. As the wind speed rises, the time required for the volume fraction of CO₂ to reach its peak shortens from 1200 s to 600 s. However, the variation of O₂ volume fraction is not completely synchronized with that of CO₂. At the wind speed of 0.5 m/s, the O₂ volume fraction first drops to the minimum value at 600 s; when the wind speed increases to 1.5 m/s and 2.0 m/s, the time for O₂ volume fraction to reach its minimum is delayed to 1200 s. The volume fraction curve of CO presents a multi-peak distribution characteristic, and its peak value gradually decreases with the rising ventilation wind speed. Meanwhile, the φ(CO)/φ(CO₂) ratio curve exhibits two distinct sharp surges successively at wind speeds of 0.5 m/s and 1.0 m/s, which occur in the initial combustion stage and decay stage respectively. When the wind speed is increased to 1.5 m/s and 2.0 m/s, the peak values of the φ(CO)/φ(CO₂) ratio decrease significantly, which are only 51% and 41% of the corresponding peak value under the wind speed of 0.5 m/s. At different heights, the flue gas temperature drops rapidly at first and then tends to be gentle with the increase of the distance from the fire source, and the fastest temperature attenuation occurs within the area of 15 m. A longitudinal attenuation prediction model for roadway ceiling flue gas temperature considering the influence of ventilation wind speed is established, and the relative error between predicted and measured values is basically controlled within 15%.