Effect of ventilation on fire behavior in model tunnel and implications for full-scale

Abstract

This study investigated the effect of tunnel longitudinal ventilation velocity on the actual fire heat release rate (HRR) in a reduced-scale (1:23) tunnel under a constant fuel supply (n-propane, 10–26 L min−1), and longitudinal ventilation (0.2–1.0 m/s). Measurements confirmed the dependency of fire behavior on the change in ventilation velocities, with combustion efficiency changing from 0.63 in low velocity and the smallest fuel flow rate to 0.82 at maximum velocity and the largest fuel flow rate. The longitudinal profile shows the extension of the high gas temperature space downstream with increasing ventilation velocity. The values measured in the model tunnel were lower than those measured in a free-burning. As ventilation velocity increases, the CO2 concentration in the exhaust gases increases, while relative soot production decreases. This indicates the ventilation affects the combustion efficiency towards a more complete combustion regime. Significant differences are observed when the HRR is scaled up to the full scale. Differences between expected and achieved HRR up to 10.84 kW in small scale correspond to 27.49 MW of in full scale. The work reveals the impact of ventilation on the fire HRR as a potential source of uncertainty in extrapolating the small-scale tunnel fire tests.