Lower flammable limit flame propagation

The autoignition temperature is the minimum temperature required for self-sustained combustion in the absence of an external ignition source. The value depends on specified test conditions. Tht flammable (explosive) limits specify the range of concentration of the vapor in air (in percent by volume) for which a flame can propagate. Below the lower flammable limit, the gas mixture is too lean to burn above the flammable limit, the mixture is too rich. Additional compounds can be found in National Fire Protection Association, National Fire Protection Handbook, 14th ed., 1991. 

The lower flammable limit (LEL) or lower explosive limit (LEL) is the minimum concentration of vapor in air below which a flame is not propagated when an ignition source is present (61—64). Below this concentration, the mixture is considered too lean to bum. The lower flammable limit and the flash point of a flammable Hquid are closely related by the Hquid s vapor pressure characteristics. 

Let s now mm attention back to the flammability limit itself. When small increments of a combustible gas are successively mixed with air, a concentration is finally attained in which a flame will propagate if a source of ignition is present. This is referred to as the Lower Flammable Limit (LFL or lower explosion limit) of the gas in air. As further increments of the gas are added, a higher concentration of flammable gas in air will finally be attained in which... 

Flammable Limits The minimum and maximum concentration of fuel vapor or gas in a fuel vapor or gas/gaseous oxidant mixture (usually expressed in percent hy volume) defining the concentration range (flammable or explosive range) over which propagation of flame will occur on contact with an ignition source. See also Lower Flammable Limit and Upper Flammable Limit. 

Using the assumption of a minimum flame temperature needed for ignition of the mixture, determine the minimum fuel mass loss rate per unit surface area (m l) to cause flame propagation through the boundary layer. The heat of combustion that the volatile wood produces (Ahc) is 15 kJ/g. (Hint the adiabatic flame temperature at the lower flammable limit for the mixture in the boundary layer must be at least 1300 °C.)... 

Lower Flammable Limit - The lowest mixture of fuel in air that will support flame propagation. 

Most liquids respond to a temperature rise through a thermodynamic phase change to gas. For ignition to occur, the fuel concentration in air must be in a range that defines a flammable mixture. These bounding limits are commonly referred to as the lower flammability limit (LFL) and upper flammable limit (UFL). These are the lowest and highest fuel concentrations in air (by volume) that will support flame propagation. Fuel concentrations below the LFL or above the UFL are too lean or rich, respectively, and will not support combustion. 

Flammable limits—The minimum (lower flammable limit, FFF) and maximum (upper flammable limit, UFF) concentration of combustible vapor in air that will propagate a flame. 

Lower flammability limits of vapors may be predicted quickly, including the effects of initial temperature and inert diluents such as N2 and CO2. The limiting oxygen content necessary for flame propagation can... 

LFL Lower Flammability Limit the minimum concentration of a chemical in air at which flame propagation occurs. 

Eggleston, Herrera, and Pish 1976 To provide needed data about the use of air entrained by a water spray to dilute flammable vapor releases below the lower flammability limit. Absorption/adsorption effects are insignificant in the case of ethylene and vinyl chloride. Sprinklers and water-spray nozzles vary widely in their efficiency as air movers. Flame quenching was not affected in any of the experiments Water sprays increased the rate of flame propagation. The air-pumping action of a water curtain can be used to set up a barrier to the horizontal flow of vapors. 

Flammability limits. The range of flammable vapor-air or gas-air mixtures between the upper and lower flammable limits. Flammability limits are usually expressed in volume percent. Flammability limits are affected by pressure, temperature, direction of flame propagation, oxygen content, type of inerts, and other factors. The precise values depend on the test method. 

Additional physical phenomena influence rates of horizontal spread of flames over surfaces of liquid fuels [111]-[120]. If the equilibrium vapor pressure of the liquid fuel at its initial temperature is high enough for the fuel concentration in the gas mixture at the liquid surface to lie above the lower flammability limit, then premixed flame propagation occurs in the gas above the liquid, and flame spread is rapid. If the liquid is cold and... 

The lower and upper flammabihty limits are the boundary-line equilibrium mixtures of vapor or gas with air, which if ignited will just propagate a flame away from the ignition sonrce. Each of these limits has a temperature at which the flammabihty Emits are reached. The lower flammability limit temperature corresponds approximately to the flash point, but since the flash point is determined with downward flame propagation and nonnniform mixtnres and the lower flammability temperature is determined with npward flame propagation and nnifrom vapor mixtures, the measured lower flammability temperature is often somewhat lower than the flash point. 

The upper and lower flammability limits are the boundary-line mixtures of vapor or gas with air, which, if ignited, will just propagate flame and are given in terms of percent by volume of gas or vapor in the air. Each of these limits also has a temperature at which the flammability limits are reached. The temperature corresponding to the lower-limit partial vapor pressure should equal the flash point. The... 

In Fig. 14.3, the upper boundary of the premixed flame propagation mode corresponds to the point where fuel vapor concentration becomes equal to the lower flammability limit at the mid-point between neighboring droplets. Since... 

Two limits of solvent flammability exist. The lower flammability limit is the minimum eon-centration of solvent vapor in oxidizing gas (air) that is capable of propagating a flame through a homogeneous mixture of the oxidizer and the solvent vapor. Below the lower flammability limit the mixture is too lean to bum or explode. The upper flammability limit is the maximum concentration of solvent vapor in an oxidizing gas (air) above which propagation of flame does not occur. Mixtures with solvent vapor concentrations above the upper flammability limit are too rich in solvent or too lean in oxidizer to bum or explode. 

Flammable Limits The mixture of fuel and standard air necessary for combustion of fuel vapors must be within certain limits. The lower flammable limit (LFL) is the minimum concentration of vapor-to-air, below which propagation of a flame will not occur in the presence of an ignition source. The upper flammable limit (UFL) is the maximum vapor-to-air mixture above which propagation will not occur. Mixtures below the lower flammable limit are too lean, with too little fuel. Those above the upper flammable limit are too rich, with too much fuel. The term lower explosive limit is equivalent to LFL. The upper explosive limit is equivalent to UFL. Flammable limits vary somewhat with temperature and pressure. The flammable range is the mixture of fuel and air between LFL and UFL. Table 16-4 includes LFL and UFL values. 

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