Abstract: Experimental and numerical simulations were used to study the variation of critical wind velocity of a dual-fire source fire in a tunnel. The effect of fire power and fire source spacing on the critical wind speed was studied. The results show that: as the spacing between the two fire sources increases, the required critical wind speed of smoke gradually decreases, and when the spacing between the two fire sources reaches the limiting distance, the required critical wind speed of smoke no longer changes; when the power of the fire source on the inlet side is determined, the required critical wind speed increases when the power of the fire source on the outlet side increases within the limiting distance, which means that the fire source on the outlet side has a facilitating effect on the smoke back-flow on the inlet side; within the limiting distance, the critical wind speed decreases quadratically to a stable value with the increase of spacing; the larger the total power of the two fire sources, the more obvious the reduction of the critical wind speed with the increase of the spacing. And the prediction formula of the critical wind speed was obtained.

Key words: tunnel fire, dual fire source, critical wind speed, fire source spacing, fire source heat release rate