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This paper proposes a Laminar Smoke Point (LSP)-based soot model, incorporating (as opposed to previously developed LSP-based models) soot surface growth. The latter is indeed believed to be dominant in soot formation. Simple reactions are also introduced to account for the conversion of fuel and oxygen in soot evolution mechanisms. The proposed and a reference LSP-based soot models have been implemented in OpenFOAM-v2006 and assessed against a wide variety of laminar flames (16 flames). A calibration-evaluation procedure is defined in which some flames are involved in the calibration of the constants, and the majority are utilised in an independent evaluation stage. The results show that the newly added features to the LSP-based soot modelling approach allow for a better agreement over a wider range of conditions, e.g. diluted and highly sooty flames. It is shown that although the proposed model is more accurate for buoyant flames, it performs significantly better than the reference model for non-buoyant flames. [ABSTRACT FROM AUTHOR]

Progress in fire safety science strongly relies on the use of Computational Fluid Dynamics (CFD) to simulate a wide range of scenarios, involving complex geometries, multiple length/time scales and multi-physics (e.g., turbulence, combustion, heat transfer, soot generation, solid pyrolysis, flame spread and liquid evaporation), that could not be studied easily with analytical solutions and zone models. It has been recently well recognised in the fire community that there is need for better modelling of the physics in the near-wall region of boundary layer combustion. Within this context, heat transfer modelling is an important aspect since the fuel gasification rate for solid pyrolysis and liquid evaporation is determined by a heat feedback mechanism that depends on both convection and radiation. The paper focuses on convection and reviews the most commonly used approaches for modelling convective heat transfer with CFD using Large Eddy Simulations (LES) in the context of fire-driven flows. The considered test cases include pool fires and turbulent wall fires. The main assumptions, advantages and disadvantages of each modelling approach are outlined. Finally, a selection of numerical results from the application of the different approaches in pool fire and flame spread cases, is presented in order to demonstrate the impact that convective heat transfer modelling can have in such scenarios. [ABSTRACT FROM AUTHOR]

The paper presents an application of video fire analysis (VFA) to a cable tray fire scenario, a scenario of interest to nuclear power plants where cables constitute a substantial part of the combustible load. Five horizontal trays, each 2.4 m long and 0.45 m wide, are positioned with a 0.3 m spacing (in the vertical direction) and set-up against an insulated wall. Each tray contains 49 power PVC cables of 13 mm outer diameter. Ignition is performed with an 80 kW propane burner centrally positioned at 0.2 m below the first (i.e. lowest) tray. Thanks to a flame detection algorithm, the VFA technique allows a reconstruction of the heat release rate (HRR) profile based on the estimated temporal evolution of flame and extinction fronts at the level of each tray. The obtained profile is generally in good agreement with the HRR measurements (from oxygen depletion calorimetry). However, the time to reach the peak HRR is overestimated by approximately 100 s and the peak HRR of 3 MW is underestimated by 17%. These results are nevertheless encouraging because they provide confidence in the flame spread measurements (which are estimated for the case at hand between 2 mm/s and 5 mm/s). Therefore, a systematic application of VFA to real-scale experiments is believed to generate a valuable set of data (e.g. flame spread rates) for the development of simplified modelling. [ABSTRACT FROM AUTHOR]

In this study, a global soot model was developed and validated in three turbulent jet flames fueled by ethylene, methane, and kerosene, which represent lightly sooting, moderately sooting, and heavily sooting fuels, respectively. In this global soot model, soot chemistry was represented by mixture fraction, and the sooting propensities of different fuels are accounted by their laminar smoke point (LSP) heights, as derived from the flame similarity analysis. Two approaches, conditional moment closure (CMC) and alternative–conditional source-term estimation (A-CSE), for the interaction between soot chemistry and turbulent flow were investigated too. Soot was well predicted by this global soot model for all the three flames compared with the experimental measurements and previous predictions. Compared with complex CMC predictions, the comparable predictions by A-CSE in this study suggest that A-CSE could be a compromising solution for soot prediction in fires. [ABSTRACT FROM AUTHOR]

The paper presents a numerical study on an 18 cm-diameter liquid pool fire in a reduced-scale and mechanically-ventilated enclosure. The enclosure walls are made of a calcium silicate layer and a steel layer on five sides, the remaining sidewall is made of heat-tempered glass. The ventilation system is extracted mechanically with free air inlet. Three air renewal rates (ARR) and open atmosphere conditions are considered in the numerical study. Computational Fluid Dynamics (CFD) simulations are carried out with Fire Dynamics Simulator (FDS 6.7.5). The default evaporation model in FDS (i.e., forced convection approach) is compared to a natural convection approach implemented in the source code. The results show that the oscillatory combustion, occurring at ARR = 15 h−1, is best captured by the natural convection approach. It is also found that prescribing the fuel Auto-Ignition Temperature (AIT) is important to capture the fire oscillations and (local) flame quenching. At ARR = 8 h−1, extinction occurs. It is found that prescribing the fuel AIT allows to prevent spurious oscillatory combustion. At ARR = 22.5 h−1, there is a stable steady-state burning regime for which (as well as for open atmosphere conditions) prescribing the fuel AIT is not crucial. • Fire burning regimes are well predicted in a wide range of ventilation conditions. • Oscillatory combustion is captured by natural convection for evaporation modeling. • Prescribing Auto-Ignition Temperature is important in capturing fire oscillations. • Prescribing AIT prevents spurious fuel re-ignition in under-ventilated conditions. [ABSTRACT FROM AUTHOR]

Having explained the characteristics of a corner fire in the configuration of Single Burning Item (SBI) test in Part I [1], the results of three flame spread experiments conducted with Medium Density Fiberboard (MDF) panels are discussed. The fire growth, in terms of flame heights and spread, is examined from two different angles visually and through Video Fire Analysis (VFA) with a flame detection algorithm. Total Heat Release Rates (HRR) and Smoke Production Rates (SPR), as well as total heat fluxes at several characteristic locations, are presented. Moreover, temperature evolutions are discussed for multiple locations and through the thickness of the panels. Also the backside temperatures, important as boundary condition for numerical simulations, are reported. The corner fire tests with MDF panels yield an average peak HRR of 151 kW and an average total heat flux exceeding 60 kW/m 2 close to the burner, with average flame heights surpassing 1.5 m in about 60 s. [ABSTRACT FROM AUTHOR]

Air cavities and gaps between material layers are common in construction systems, e.g. ventilated façades. Air cavity may provide a pathway for smoke and flame spread in case of fire. Performing physical testing to investigate different systems and fire scenarios is resource demanding. Fire Dynamics Simulator (FDS version 6.7.0) was used to simulate fire driven flow between two parallel vertical walls. Flame heights, thermal impact to the interior wall surface and upward flow velocities were predicted with FDS and compared with experimental results. The fire source was a propane burner with 8 × 391 mm2 gas outlet area. Heat release rates were 6.6 kW and 12.4 kW and the distance between the parallel walls was 40 mm. Two different convective heat transfer coefficient sub grid scale models available in FDS were investigated. In this study the cavity width to mesh cell size ratio was equal or above 10, resulting in good predictions of flame heights, upward flow velocities and wall temperatures. 2 mm grid resulted in 25% lower HRR in locations near the burner gas inlet, compared to 4 mm grid, indicating the importance of well resolved gas outlet boundary. • Cavity width divided by mesh cell size should be greater than 10 in FDS simulations. • Predicted flame heights and flow velocities corresponded well with experiments. • Refining the grid in FDS resulted in lower cumulative HRR in the flame region. • FDS models for heat transfer at surfaces must be revised for transitional flows. [ABSTRACT FROM AUTHOR]

The corner fire characteristics with two inert walls are compared against those with one or two combustible corner walls through a set of standard Single Burning Item (SBI) tests. The study examines how the corner fire behavior is affected by flame spread over one or two walls. In the case of flame spread over one corner wall, the inert side is a Calcium Silicate (CS) panel. As for the combustible wall, two different materials have been tested, namely, plywood and Medium-Density Fiberboard (MDF) panels. The results indicate that the simultaneous burning of two panels in the corner geometry increases the Heat Release Rate (HRR) contribution of each panel by 45–50%. This is because the burning of one corner wall increases the temperatures on the adjacent wall significantly, occasionally by more than 200 °C, and increases the heat fluxes on both corner walls at the same time, sometimes by nearly 20%. The results of HRR, Smoke Production Rate (SPR), flame heights, pyrolysis front propagation, panel temperatures, and total heat fluxes at several characteristic locations are presented. [ABSTRACT FROM AUTHOR]