| With the rapid development of the transportation industry,tunnels play an important role in the transportation industry.Tunnel fires,as the most dangerous safety accidents in tunnels,have become one of the hotspots in the field of tunnel and fire safety research at home and abroad.When doing experiments about tunnel fires,it was found tunnel fire under natural ventilation condition will self-extinguish.In addition,the tunnel fires with sealing the tunnel portal will also self-extinguish due to under-ventilated.In order to deeply study the mechanism of tunnel fire extinguishment and verify the modeling ability of numerical simulation software FDS for the self-extinction of fires,this paper compares flame shapes and data of experiment and numerical simulation.The main work and results are as follows:Fire Dynamics Simulator(FDS)was used to predict the flame self-extinction phenomenon in a 1:20 reduced-scale tunnel of 20.8 m long.The sensitivity of the grid size to the flame selfextinguishment was studied.The self-extinction does not occur with resolution index of 11 or16,which was in contrast with the experiment result.Then the resolution index was refined to22 ～ 32 in the Z-axis while was kept at 11 ～ 16 in both Y-axis and X-axis.The fire selfextinguish and re-ignition does not occur,which agree with the experiment results.In terms of the predicted maximum temperature rise,no obvious difference was observed between the experiment and simulation results.In the experiment,the maximum temperature rise above the fire source was 750 ℃,and in the numerical simulation,the maximum temperature rise above the fire source was 800 ℃.In the simulation,the predicted oxygen and carbon dioxide concentrations are consistent with the experimental results,while the predicted carbon monoxide concentrations are lower than the experimental results.Further studies with 11.2k W fire in the 10 m long tunnel and 16.8 k W fire in the 20.8 m long tunnel were conducted and compared with experiment,the experiment results agree with the experiment results.For the tunnel fires with sealing the tunnel portal,the greater tunnel entrance sealing ratio,the shorter the fire extinguishing time.In simulation,sealing the tunnel portal will be more likely to cause flame extinction than natural ventilation condition,that is,the limiting oxygen concentration is higher;for the impact of the initial sealing time,the later the initial sealing time,the slower the flame extinguishes.The simulation with a late initial sealing time has a tendency to increase the maximum temperature above the fire source.Therefore,when use the sealing tactics to extinguish the fire,and the initial sealing time should be as early as possible.Tunnel fire with sealing ratio of 75% and above will self-extinguish both experiment and simulation.During the extinguishment,the oxygen concentration is 13.9% ～ 15.1% in both experiment and simulation.The research results are of reference value not only for carrying out more numerical simulations of this type,but also for guiding the application of sealing tactics against tunnel fire. |
