Wall Fire Research Articles

Large eddy simulation of turbulent vertical wall fires supplied with gaseous fuel through porous burners

This paper presents a large eddy simulation (LES) study of vertical turbulent wall fires, which aims at bringing fundamental insight into the near-wall flame structure and heat transfer characteristics. The LES simulations are wall-resolved, i.e., the simulations are performed with sufficient grid resolution to capture the wall gradients and do not require a wall heat transfer model. The wall fires considered herein correspond to a simplified configuration in which gaseous fuel is supplied from an array of vertical porous burners, featuring a series of meter-scale wall flames with different fuel mass flow rates and different fuel types. Four fuels (methane, ethane, ethylene and propylene) are studied with prescribed fuel flow rates. Simulations are performed using an LES solver called FireFOAM. The Wall-Adapting Local Eddy-viscosity (WALE) model is used for turbulence modeling. The Eddy Dissipation Concept (EDC) model is used for combustion modeling. The thermal radiation model uses the discrete ordinate method with the simplifying assumption of an optically-thin medium characterized by a fixed radiant fraction. In the fuel blowing region, grid convergence is achieved using a 3 mm computational grid; while in the downstream flame preheating region, a 1.5 mm near-wall grid spacing is required to fully resolve the wall convective heat transfer. The change in grid requirement is due to the presence or absence of fuel blowing which affects the thickness of the wall viscous sub-layer. The simulations are in good qualitative and quantitative agreement with experimental data in the turbulent flame region; in particular: the radiative heat flux increases with elevation and with the fuel mass loss rate, while the convective heat flux remains approximately constant with elevation and decreases with the fuel mass loss rate. The present wall-resolved simulations are considered a first step on the route to developing accurate wall models needed for engineering simulations of wall fires.

Friendly fire: Engineering a fort wall in the Iron Age

There is widespread evidence that the walls of Iron Age forts across Europe were set on fire, causing partial melting of the stonework followed by either recrystallization or glass formation on cooling – a process termed “vitrification”. The motivation for fort wall firing has remained speculative since its first description in 1777. Since the suggestion of MacKie (1969) that fort vitrification might destabilize fort walls, the debate as to motives has focused on combative or destructive intentions. Here, a multidisciplinary analysis of experimental fort wall samples shows that in fact vitrification results in strengthening, not weakening. The strengthening involves diffusive and viscous sintering of material aggregates and size-dependent heat transfer. These new results support a long-since-dismissed idea that Iron Age fort walls were intentionally set ablaze in order to fortify the walls.

Experimental study on the burning behaviors of three typical thermoplastic materials liquid pool fire with different mass feeding rates

Nowadays, thermoplastic materials, which represent a risk of the high melt flow fire spread, are widely used in construction industry. The flow of thermoplastic’s melt drips will accelerate the downward flame spread and fall into the pool fires which appears at the foot of the wall fires. Fire will develop to larger and larger soon because of the wall fires and pool fires mutual enhancement mechanism. In this paper, a new experimental setup is used to quantitatively analyze the burning characteristics of pool fires at different steady mass feeding rates. PP (polypropylene), PE (polyethylene) and PS (polystyrene) thermoplastic polymers are selected as test materials and were heated to be the molten phase by electric heater. N2 gas is continuously injected into the chamber to avoid a sudden ignition. The characteristics parameters including dripping rate, flowing rate of hot molten liquids, burning rate and radiant flux of flowing pool fires are analyzed. The experiment results preliminarily suggest that the hot molten liquids induced by PP polymers are easier to drop and flow than that by PE and PS. Therefore, PP materials may be more dangerous for their faster pool fires flowing rate on the floor. Meanwhile, the burning rate of pool fires induced by PS is higher than that by PE and PP, although the dripping rate and flowing rate of PS is the slowest for its large viscosity. For larger mass feeding rates, the dripping rate of three hot molten drips becomes faster. It also indicates that the experimental process of surface tension flow and the flame front of pool fires do not coincide with melt flow front for PP and PE at different mass feeding rates. Specifically, the flame front of pool fires induced by molten PP or PE polymers is slower than the forward movement of the hot molten liquids. The reason for these combustion characteristics of molten thermoplastic polymers that mentioned above may be related to viscosity and structures of thermoplastics, as well as the pyrolysis process of different thermoplastics.

Effects of altitude and inclination on the flame structure over the insulation material PS based on heat and mass transfer

Experiments were conducted on the insulation materials of EPS and XPS in a small-scale flame spread experimental bench in the Tibetan plateau area of Lhasa (with an altitude of 3658m) and the plain area of Hefei (with an altitude of 50m), respectively. The detailed flame structure including flame angle, flame length and maximum length of pool fire over EPS and XPS with thicknesses of 2cm, 3cm, 4cm and 5cm inclined at the angles of −30° to 30° was investigated. It is found that for the same thickness of EPS and XPS inclined at the same angle, the flame length is longer and the flame angle is smaller in Hefei than those in Lhasa in the wall fire zone, which is in good agreement with the predictions. The preheating length δf is correspondingly longer in plain due to smaller flame angle and longer flame length and the flame heat flux q̇f″ increases with air pressure, which make the flame convective and radiative heat (q̇f″)2δf larger leading to promote flame spread. For the horizontal flame spread over EPS and XPS, the maximum length of pool fire is significantly smaller than that in other incline angles in Lhasa, which can be attributed to the smallest heat transfer to the residue pool fire zone during flame spread making PS in the residue pool fire zone extinguish more easily.

A Novel Method of Mobile Robot Fire Detection and Tracing Using Proportional Derivative (PD) Algorithm

One of the problems in intelligent mobile robot fire fighting contest is how the robot can find and can extinguish a fire without alot of sensors. The fire is located in a white circle area at one of the corner in room with random combinations. The way to solve this problems is conventional method-called-wall tracing. The robot uses wall tracing method to navigate, when entering the room this method still in used by the robot until its find the fire spot then uses one additional sensor to detect the white circle area where the fire located at. After detecting the white circle area, the robot will extinguishes the fire. This paper proposed a new method as optimization of conventional method. The proposed method is implementation of current algorithm (proportional derivatives algorithm) not only to wall tracing but also to TPA81 sensor (fire tracing) -called-wall and fire tracing method. Furthermore, this method is combination method between wall tracing and fire tracing. The robot will approach directly to the fire without wall tracing and without detecting white circle area. Then, the robot extinguishes the fire quickly. The robot uses only TPA81 sensor that can be used to detects the fire spot and its position in the room. Test result shows that 50% of the fire position variation on Indonesian Intelligent Robot Contest can be optimized using this method.

Numerical Simulation for Predicting Fire Behavior of Axially Loaded Circular Concrete Filled Steel Tubular Columns

The present study investigates the behavior of axial loaded circular concrete filled hollow steel section (CFHSS) columns. A nonlinear finite element model using ABAQUS program was developed to investigate the fire behavior of the inspected columns from previous fire tests. The study variables include column dimensions, steel section wall thickness, concrete strength, concrete types (plain or reinforced), and fire protection thickness. The comparison indicated that the results obtained from the model were within acceptable limit of accuracy of 15%. A sensitivity study was carried out to investigate the influence of the output of the numerical model including the Poisson’s ratio of concrete, thermal conductance at the steel-concrete interface, frictional contact at steel-concrete interface, and imperfection buckling of columns. Based on the sensitivity analysis, several modelling suggestions were given in this paper which will be beneficial for further study.

Experimental study of non-monotonous sidewall effect on flame characteristics and burning rate of n-heptane pool fires

To study the influence of sidewall effect on flame characteristics and burning rate, a series of experiments with heptane pools was conducted. The results showed that as the fires were placed close to the sidewall, the flames inclined to the sidewall due to the restriction on air entrainment, and the burning rate increased on the whole, which could be mainly due to the enhanced radiation from the heated sidewall and ceiling flame. However, regardless of fuel pool shape, the burning rate obtained the peak value when the fire was near the sidewall, rather than attached to the sidewall, resulting from less flame radiation from the vertical flame part to the fuel in the latter case. The ratio of longitudinal ceiling flame length to transverse length tended to decrease with the fire moving close to the sidewall. For cases with the largest length and wall fires, the ratio was nearly 0.5, which could be explained according to the theory of mirror effect. Also, due to the non-monotonous sidewall effect, a higher burning rate did not necessarily lead to a larger ceiling flame length.

Review and Prospect of Study on External Vertical Fire Spread up High Rise Buildings in China

In recent years, a large number of incidents of external fire spread up high rise buildings happened in the world. One of main reasons is that combustible organic materials, EPS, Polyurethane, etc, are used in external thermal insulation system (ETIS) for energy conservation purpose. In some incidents, fire spread in combustible organic materials couple with that from window to window make it impossible for fire fighters to prevent the external vertical fire spread up high rise buildings and caused severe damage to structures and loss of life and property. In this paper, some typical external wall fire hazards in China are described briefly, and then relative research progresses are presented. Furthermore, some research needs and possible directions of future research are proposed.

Simulation of Ethylene Wall Fires Using the Spatially-Evolving One-Dimensional Turbulence Model

The mechanism of flame propagation in fuel beds of wildland fires is important to understand in order to quantify fire spread rates. Fires spread by radiative and convective heating and in some cases require direct flame contact to achieve ignition. The flame in an advancing fire is unsteady and turbulent, making study of intermittent flames in complex fuels difficult. A 1.83 m tall, 0.61 m wide vertical wall fire, in which ethylene fuel is slowly fed through a porous ceramic, is modeled to investigate unsteady turbulent flames in a controlled environment. Three fuel flow rates of 235, 390, and 470 L/min are considered. Simulations of this configuration are performed using a spatial formulation of the one-dimensional turbulence (ODT) model which is able to resolve individual flames (a key property of this model) and has been shown to provide turbulent statistics that compare well with experimental data for a number of flow configurations including wall fires. In the ODT model diffusion–reaction equations are solved along a notional line of sight perpendicular to the wall that is advanced vertically. Turbulent advection is modeled through stochastic domain mapping processes. A new Darrieus–Landau combustion instability model is incorporated in the ODT eddy selection process. The ODT model is shown to capture the evolution of the flame and describe the intermittent properties at the flame/air interface. Simulations include radiation and soot effects and are compared to experimental temperature measurements. Simulated mean temperatures differ from the experiments by an average of 63 K over all measurement points for the three fuel flow rates. Predicted root mean square temperature fluctuations capture the trends in the experimental data, but overestimate the raw experimental values by a factor of two. This difference is discussed using thermocouple response and heat transfer correction models. Simulated velocity, soot, and radiation properties are also reported.

Experimental Research on High Temperature Corrosion Prevention Technology for Water Wall of Opposed Wall Fired Ultra Supercritical Boiler

In order to solve the problem of high temperature corrosion to water wall of opposed wall fired ultra supercritical boiler, comprehensive study is carried out by combining theoretical analysis and experimental research, obtaining the variation of flue gas composition before and after introduction of near wall wind and effect of primary air velocity, central air opening, swirl intensity of outer secondary air and inner secondary air opening on composition of flue gas in near wall region. The results show that 1) the introduction of near wall wind significantly improves reducing atmosphere in near wall region; 2) among the four parameters listed above, swirl intensity of outer secondary air and inner secondary air opening have greater influence on composition of near wall flue gas; 3) under the comprehensive effect of swirl intensity of outer secondary air and inner secondary air opening, the volume fraction of CO in near wall flue gas can be controlled below 1500ppm, which effectively disturbs the condition for high temperature corrosion.

Heat flux profile upon building facade with side walls due to window ejected fire plume: An experimental investigation and global correlation

This paper investigates the heat flux profile upon building facade with side wall constraints due to ejected fire plumes from a window of an under-ventilated compartment fire. A reduced-scale model (1:8), consisting of a cubic fire compartment with a facade wall attached and two side walls located symmetrically at both sides of the window is developed. The window dimensions and the side wall distances are changed in experiments, representing different ventilations and constraints on fire plume entrainment. Five heat flux gauges are employed in measurement of vertical heat flux profile upon the facade wall. Results show that with the decrease in separation distance of side walls, the heat flux increases for small windows where dimensionless excess heat release rate Q̇ex⁎≥1.3 (“(half) axisymmetric fire” regime), meanwhile shows weak dependency on side wall separation distance for large windows where Q̇ex⁎<1.3 (“wall fire” regime). A new global formula is proposed to characterize the vertical profile of heat flux based on Lee’s model without side walls as further modified by a parameter K in relation to the separation distance of side walls and characteristic length scales of the window. Experimental data for different windows and side wall separation distances are well collapsed by the proposed formula.

Numerical case studies of vertical wall fire protection using water spray

Studies of vertical wall fire protection are evaluated with numerical method. Typical fire cases such as heated dry wall and upward flame spread have been validated. Results predicted by simulations are found to agree with experiment results. The combustion behavior and flame development of vertical polymethylmethacrylate slabs with different water flow rates are explored and discussed. Water spray is found to be capable of strengthening the fire resistance of combustible even under high heat flux radiation. Provided result and data are expected to provide reference for fire protection methods design and development of modern buildings.

Experimental investigation on window ejected facade flame heights with different constraint side wall lengths and global correlation

This paper presents an experimental investigation on the effect of side wall length (normal to the facade direction) on the ejected facade flame height from a window of an under-ventilated compartment fire. The ejected facade flames are recorded by a CCD camera with various side wall lengths L at different side wall separation distances D. Results show that, as the length of the side wall increases, the change in behavior of the flame height can be categorized into two regimes: (1) the flame-entrainment-controlled regime in which flame height increases with side wall length for “(half) axisymmetric fire” but independent of side wall length for “wall fire”; and (2) the combustion-efficiency-controlled regime where the flame heights for both these two fire types decrease with side wall length due to decrease of the combustion efficiency inside the fire room, for L=3D or greater. A global parameter K is then proposed based on scaling analysis for the air entrainment of the flame with side wall length, in relation to characteristic length scales ℓ1 and ℓ2 of the window, which well collapse the experimental data for different window dimensions, side wall lengths and separation distances.

Acoustic Pyrometry System for Environmental Protection in Power Plant Boilers

On-line monitoring of the distribution of the temperature field in a boiler furnace is important to reduce emissions that cause pollution and damage to the environment in power plants. Acoustic pyrometry, which is best suited for high temperature and dusty conditions, has been a very active research area recently. The present study provides a reconstruction technique of a two-dimensional temperature field through the measurements of multiple paths, which is used to monitor the combustion process in the boiler furnace. The geometric pixel division and the regularization algorithm were used to solve the reconstruction problem of temperature profile in many cases. Then, adopting this method, a temperature field monitoring system with multiple paths was developed and applied to a 330 MW unit (opposed wall firing). Through the long-term operations, it was proved that the acoustic pyrometer system could realize the visualization of temperature profile in the furnace.

Fire Resistance of High-Rise Building External Wall Using Water Spray Curtain: An Exploration of Fire Protection Design

To find out practical design of high-rise building external wall fire protection, a preliminary study of water spray curtain was performed. The characteristic of the spray was analyzed through experiments. Basic characteristics such as exponential relationship between discharge rate and working pressure of the nozzle were obtained. The spread behavior of water film on the wall, such as spread width, was tested and analyzed. Feasible design and apply layout of the spray system on external wall was presented. The probable design was proved to be much more energy-saving than traditional sprinklers. In the end, a workable pattern of application was presented and further explained how the design worked and reduced construction energy.

An experimental study of an LPG tank at low filling level heated by a remote wall fire

This paper describes an experimental study of 2300 L pressure vessels exposed to remote fire heating by a natural gas fuelled wall fire simulator. The tanks were filled to 15% capacity with commercial liquid propane. The flame intensity and distance were varied to study the effect of different heating levels on the tank and its lading.The fire simulator is first characterized with tests including fire thermocouples, radiative flux meters and thermal imaging. With the appropriate positioning of a target tank it is possible to get very realistic fire heat fluxes at the tank surface.Three tests were conducted with the 2300 L tanks filled to 15% capacity with propane. The tanks were positioned at three different distances from the wall fire resulting in measured average peak heat flux at the tank surfaces ranging between 24 and 43 kW m−2. The data shows rapid rise in vapour space wall temperatures, significant temperature stratification in the vapour space, and moderate rate of pressure rise. These results provide excellent data for the validation of computer models used to predict the response of pressure vessels exposed to moderate heating from a remote fire.

Effects of Air Staging Conditions on the Combustion and NOx Emission Characteristics in a 600 MW Wall Fired Utility Boiler Using Lean Coal

A three-dimensional numerical investigation is presented on the coal combustion and NOx emission in a supercritical 600 MW wall fired utility boiler fed with lean coal. The distributions of velocity, temperature, and species were obtained using a finite volume method and some validated submodels. The influence of air staging condition, i.e., overfire air (OFA) ratio and OFA port position, on combustion and especially on NOx emission was studied. The temperature of the burner zone and the carbon content in fly ash increased with increasing OFA ratio, while the NOx emission decreased with increasing OFA ratio. An increase of the OFA port position resulted in a decrease of NOx emission and an increase of carbon content in fly ash. In addition, high burnout rate of pulverized coal and low NOx emission can be achieved in the present boiler, in which OFA was injected from Port 3 with a ratio of 34.2%. This study provides new insights into the physical and chemical processes in a wall fired utility boiler fed with lean coal and also illustrates a method to reduce NOx emission.

A multi-component dataset framework for validation of CFD flame spread models

A review of the literature has shown the need for a comprehensive flame spread dataset framework for computational fluid dynamics model validation purposes. To develop this framework, the flame spread process was viewed as having four key components: turbulent fluid dynamics, gas phase kinetics, flame heat transfer, and condensed-phase pyrolysis. A series of extensively instrumented inter-related experiments based on the four components was conducted under different source fire permutations. This series of three progressively more complex experiments, from free plume, to inert wall fires, to combustible wall flame spread were carried out to enable collection of data relevant to each component of flame spread. Measurements made include heat release rate, plume centerline temperature and velocity, heat flux to wall, near-wall temperature, flame height, flame spread progression, mass loss, and burn pattern. The combustible wall test data in the current research may not be enough to validate a complex real-wo...

Large Eddy Simulation of Vertical Turbulent Wall Fires

The objective of the present study is to evaluate the ability of wall-resolved large eddy simulations (LES) to accurately simulate wall fires. The boundary layer combustion configuration is a simplified vertical wall flame configuration in which gaseous fuel (propylene) is supplied across a porous wall and the fuel mass flow rate is prescribed. The focus of the study is on the flame-to-wall heat transfer. The LES performance is evaluated via comparisons with a previously developed experimental database.LES simulations are performed using FireFOAM (FireFOAM is an advanced fire modeling software developed by FM Global). The FireFOAM simulations use: a carefully-designed block-structured computational grid; the k-equation eddy viscosity model for turbulence; the Eddy Dissipation Concept (EDC) model for combustion; and the discrete ordinate method for thermal radiation transport. A number of modifications are introduced in the baseline FireFOAM modeling capability: the original turbulent eddy viscosity model is replaced by the wall-adapting local eddy-viscosity model – WALE – that provides correct near-wall behavior; the EDC combustion model is also enhanced to include laminar flame conditions.The wall flame configuration features low Reynolds number conditions and a transitional laminar-to-turbulent combustion regime; while these low Reynolds number conditions are believed to be representative of meter-scale wall fires, they represent a difficult challenge for LES simulations. The simulations are in good qualitative comparison with experimental data; quantitative agreement is fair. The main source of discrepancy is an overestimate of the size of the laminar flame base region and a reduced accuracy of LES combustion and radiation models under laminar-like conditions.

Fire hazards of exterior wall assemblies containing combustible components

The Fire Protection Research Foundation has funded a research project on “fire hazards of exterior wall assemblies containing combustible composites”. This paper presents preliminary findings from the project. In particular, statistics relating to exterior wall fires have been reviewed. Exterior wall fires appear to account for somewhere between 1.3% and 3% of structure fires in the selected property types investigated. Fires involving combustible exterior wall assemblies are low frequency events however the resulting consequences in terms of extent of fire spread and injuries and fatalities can be large as demonstrated by selected fire incident case studies. An overview of this project and it's further work is provided.