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Reaction to fire performance
Published in Andrew Buchanan, Birgit Östman, Fire Safe Use of Wood in Buildings, 2023
When a combustible material is exposed to the heat flux from an external heat source (radiative, convective or a combination), its temperature will rise. If the net heat flux into the material is sufficiently high, the surface temperature will eventually reach a level at which the material starts to pyrolyse. The fuel vapours generated emerge from the exposed surface and mix with air in the gas phase. This mixture may ignite when the fuel vapour concentration exceeds the lower flammability limit. Sustained flaming initiated by a local heat source in the gas phase, such as a small flame or a hot spark, is referred to as piloted ignition. Auto-ignition occurs if there is no pilot present, and flaming is initiated at the hot surface of the heated solid.
A review of thermodynamic concepts
Published in Ronald L. Fournier, Basic Transport Phenomena in Biomedical Engineering, 2017
These flammability limits are provided as the lower and upper flammability (or explosion) limits. The upper (UFL) and lower flammability limit (LFL) is stated as the volume percent (which is the same as the mole percent) of the flammable chemical in air. If the flammable compound’s volume percent or mole percent in air at a given T and P lies within the LFL to UFL range, then that mixture is ignitable or explosive. If the volume percent or mole percent of the flammable chemical in air is less than the LFL, or greater than the UFL, then that mixture is not ignitable or explosive.
Physical Hazard Characterization
Published in George G. Lowry, Robert C. Lowry, Handbook of Hazard Communication and OSHA Requirements, 2017
George G. Lowry, Robert C. Lowry
A flammable gas is defined in two different ways: (1) it is a gas whose lower flammability limit (LFL) is less than 13% by volume in air; or (2) it is a gas whose upper flammability limit (UFL) is more than 12% higher than its LFL, regardless of the value of the latter.
Small World Network Model Validation. Case Study of Suartone Historical Fire in Corsica
Published in Combustion Science and Technology, 2022
N. Hamamousse, A. Kaiss, F. Giroud, N. Bozabalian, J-P. Clerc, N. Zekri
The packing ratio is defined as the ratio of the volume of the solid particles to that of the fuel bed for the same mass. The effective volume submitted to the heating process is thus. The model uses the ignition process defined by Koo et al. (Koo et al. 2005), where the receptive fuel cell is heated in three steps: i) its temperature is raised by the absorbed heat flux up to the boiling point of water (), ii) at the boiling point, the whole water content of the fuel is evaporated, and the wet fine fuel particles (WFF) are dried turning into dried fine fuel particles (DFF), iii) the temperature of the dried fuel increases then steadily until it reaches ignition temperature . Ignition occurs when the mixture of air and Volatile Organic Compounds (VOCs) emitted during the fuel cell pyrolysis attains the lower flammability limit at ignition temperature. The emission of VOCs is not included explicitly in the model, but the ignition temperature corresponds to the lower flammability limit. The energy conservation condition for a receptive cell exposed to fire (with burning cells) is given by the following equations for the three above mentioned steps:
Polydispersity Effects in Low-order Ignition Modeling of Jet Fuel Sprays
Published in Combustion Science and Technology, 2022
Pedro M. de Oliveira, M. Philip Sitte, Epaminondas Mastorakos
The effect of the cell size and droplet size distribution on the pdfs of is shown in Figure 2, with the line color scheme shown according to the distributions of droplet size in Figure 1a. For this given condition, was set just above the lower flammability limit (dashed vertical line). The effect on the local equivalence ratio caused by the polydispersity can be clearly noticed: coarse atomization conditions (high ) resulted in high probability for values below , with leaner conditions than the average cell equivalence ratio being more likely to occur. As decreases and the spray becomes closer to monodisperse condition this effect disappears. Evidently, the size of the domain cell also determines the magnitude of the fluctuations in this model. Thus, must be chosen according to physical criteria (e.g. chemical, turbulent, and evaporation time/length scales) in addition to those given in Neophytou, Richardson, Mastorakos (2012) to satisfy the assumption of turbulent transport of the flame particles by the eddies.
NOx Minimization in Staged Combustion Using Rich Premixed Flame in Porous Media
Published in Combustion Science and Technology, 2020
Abhisek Banerjee, Prithwish Kundu, Vitaliy Gnatenko, Serguei Zelepouga, John Wagner, Yaroslav Chudnovsky, Alexei Saveliev
Cooling down the exhaust of the porous flame to 1000 K before reburning in the secondary flame, leads to a reduction in maximum flame temperature approximately by 400 K. This decrease hinders in thermal NOx generation for the nonpremixed flame, causing EI NOx to reduce from a value ranging between 0.8 g/kg–1.18 g/kg to 0.40 g/kg–0.55 g/kg when compared for the same equivalence ratio. However, cooling the exhaust of the porous flame changes the lower flammability limit to φ = 1.4. Thus, cooling down the porous flame exhaust result in approximately 54% drop in the EI NOx. The variation of EI NOx as a function of equivalence ratio shows similar trends. The numerical results obtained in the research shows good agreement with the experimental data.