Numerical simulation on turbulent flame propagation in premixed gas deflagration process in a tube will be reported in this paper, aiming at identifying the key factors affecting flame shape and flame velocity. Large eddy simulation with premixed gas combustion model is used to obtain results validated by full-scale experimental data. The effect of flow velocity and turbulence on flame propagation is discussed. The flow velocity of premixed gas is observed to be one of the main factors determining flame shape and affecting flame propagation process. The velocity difference of different parts of the flame front, both in magnitude and direction, will lead to tulip-shaped flame. Turbulence would accelerate the propagation of flame periodically. The cause of flame acceleration of low-intensity turbulence originates from two factors, namely, combustion and flow field, which transfer the heat and mass of chemical reaction from diffusion to vortex transport. As high-intensity turbulence will not affect the chemical reaction and the turbulent burning velocity, flame acceleration is controlled only by the characteristics of the flow field.

An explosion while repairing liquefied petroleum gas (LPG) taxis in a garage located at the ground level of an old residential building constructed in Hong Kong was reported in 2015. Part of the building structures was damaged with the owners staying inside killed. The cause of explosion is still under investigation, but the explosion source can be due to leaking of LPG fuel or flammable clean refrigerants with LPG. A taxi has over 0.5 kg of refrigerant HFC134a (R134a) stored in the air-conditioning unit. A pressure rise exceeding 21 kPa (or 0.21 bar) due to explosion from a small amount of LPG would give damages to the building. As firefighters are always exposing themselves to the risk of explosion when they are carrying out rescue operation in a gas-filled environment, the explosion overpressure has to be more reliably estimated for working out protection schemes during operation. This garage LPG explosion incident was studied numerically using Computational Fluid Dynamics software FLame ACceleration Simulation (FLACS). Three scenarios of different LPG-air mixture volumes and LPG concentrations were investigated. Dispersion of LPG was simulated first with an ignition taken at a position at the garage centre. Overpressure and temperature rise were predicted using a fine grid system with 1 657 600 computing cells was employed. Results were compared with numerical predictions using coarse grids of 207 200 cells. Discussion and conclusions were made with reference to the threshold value of 21 kPa in overpressure.

There are more interests in better understanding kitchen fires with multiple burning sources in this paper because of the demand in the construction industry. Computational Fluid Dynamics (CFD) was applied to study kitchen fires with multiple burning sources using experimental data reported earlier. A room of length 3.6 m, width 2.4 m and height 2.4 m was constructed with a door of width 2.0 m and height 1.9 m to provide natural ventilation. Chinese frying pans of diameter 0.36 m filled with 1000 mL quality soybean oil were used as the burning sources. Three typical fire scenarios with two, four and six burning sources were selected for the numerical study. Numerical experiments were then carried out for justifying the measured transient temperature using the CFD tool Fire Dynamics Simulator (FDS). Grid sensitivity, two boundary conditions and the heat release rate emitted by each burning source were investigated. The results in this paper indicated that for simulations on fire scenarios with high heat release rate and high fire temperature under natural ventilation, thermal radiation heat transfer into the wall surface should be included. The distances between the burning sources and the ventilation vent would affect the burning duration.

Heat release rates of burning gasoline and wood fires in a room were studied by computational fluid dynamics (CFD). Version 5.5.3 of the software Fire Dynamics Simulator (FDS), which is the latest one available, was selected as the CFD simulation tool. Predicted results were compared with two sets of reported data from full-scale burning tests. In the two sets of experiments, the scenarios were set at gasoline pool fire and wood chipboard fire with gasoline respectively. The input heating rate of gasoline pool fire based on experimental measurements was used in the first set of experiments. Three scenarios G1, G2 and G3 with different grid systems were simulated by CFD. The grid system of scenario G2 gave more accurate prediction, which was then used to study the second set of experiments on wood chipboard with gasoline. The combustion model in FDS was used in wood chipboard fire induced by gasoline pool. The wood chipboard was allowed to burn by itself using the pyrolysis model in FDS. The effects of the boundary conditions on free openings for the same set of experiments were studied by three scenarios SOB1, SOB2 and SOB3. Boundary condition SOB2 gave more reliable prediction among the three boundary conditions. Two other scenarios on the effect of moisture content of wood were also studied. The predicted HRR curve was found to agree better with experiment in using SOB2.

Air pumping effect of a fire plume to give higher intake rate through vertical openings in a post- flashover room fire will be discussed in this paper. The thermal balance equation was set up with known fire phenomena in a room. The hydrostatic model was applied to study the air intake rate through vertical openings. An equation relating heat release rate to room air temperature rise with empirical constants was then justified by reported experimental data on post-flashover room fire. The heat release rate was measured by the oxygen consumption method in that experiment. The predicted heat release rate from the empirical equation reported in the literature was observed to be proportional to the room air temperature rise as derived from hydrostatics. However, the proportionality constant is lower than the experimental value. A possible explanation is due to neglecting another fire phenomenon on air pumping action of the fire plume in a real room fire. Higher pressure differences across the door would give higher airflow rates across an opening. This would supply more air to give higher heat release rate as observed in the experiment. In this paper, the pressure due to air pumping of the fire plume is taken as a proportion of the hydrostatic pressure due to temperature differences between the upper hot layer and lower cool layer. Comparing the measured heat release rate with the estimated heat release rate due only to hydrostatics will give the air pumping action. The possible increase in heat release rate in a post-flashover fire can then be estimated accordingly.