Tunnel fires: Experiments on critical velocity and burning rate in pool fire during longitudinal ventilation

In this study, the 1/20 reduced-scale experiments using Froude scaling are conducted to investigate the effect of longitudinal ventilation velocity on the burning rate in tunnel fires. The methanol pool fires, acetone pool fires, and n-heptane pool fires with a heat release rate ranging from 2.02 to similar to 6.15 kW, 2.76 to similar to 11.04kW, and 2.23 to similar to 15.6kW, respectively, are used. A load cell is used to measure the mass loss rate of the burning fuel and the temperature distributions are measured by K-type thermocouples in order to investigate smoke movement. The ventilation velocity in the reduced-scale tunnel is controlled by the wind tunnel through an inverter. In the case of a methanol pool fire, the increase in ventilation velocity reduces the burning rate. On the contrary, for acetone and n-heptane pool fires, the increase in ventilation velocity leads to the enhanced burning rate of fuels. The reason is that, for acetone and n-heptane pool fires, the oxygen supply effect prevails rather than the cooling effects as the ventilation velocity increases. However, for a methanol pool fire the cooling effect outweighs the effects of oxygen supply. The relationship between the critical velocity (V-c, m/s) and the heat release rate (Q, MW), for a full tunnel, has been found to be: [GRAPHIC].