Flame dynamics and thermal response in tunnel fires with moving gas fire sources

This study examines flame dynamics and thermal response in tunnel fires with moving gas fire sources through experiments conducted in a naturally ventilated model tunnel. The fire source traveled at steady speeds ranging from 0.3 m/s to 1.2 m/s, enabling evaluation of flame shape evolution, radiation heat flux, and ceiling temperature distribution. Results show that faster fire source movement increases flame inclination, but greater fire intensity counteracts this effect by enhancing buoyancy. A predictive model for flame inclination was developed by correlating the tangent of the flame angle with the Froude number. Flame height decreases by up to 0.023 m as speed rises from 0.3 m/s to 0.5 m/s, and a model incorporating the Richardson number was established to account for movement speed, with prediction deviations controlled within 30%. Flame radiation declines with increasing speed, particularly at lower velocities. The maximum ceiling temperature rise decreases sharply with increasing fire source movement speed. It decreases from 70 K at 5 kW and 110 K at 10 kW at 0.3 m/s to 10.7 K and 28.6 K, respectively, at 1.2 m/s. Although a higher fire power mitigates the decay rate, the fire source movement speed remains the dominant factor. The existing maximum temperature rise model was refined; within the above experimental conditions, the prediction error was reduced by about 20%, improving prediction accuracy for the tested cases.