Flammability limits mechanism

Provide damper mechanical position stop to prevent complete closure of damper Eliminate flammables or combustibles Provide inert atmosphere Design ventilation system to keep flammable concentration below lower flammable limit Install on-line flammable gas detection system that activates an inerting system Provide automatic sprinkler protection Use deflagration vents... 

When a flammable liquid is sprayed as fine droplets into the air, a flammable mixture can result, which may burn or explode. The mist or spray may be formed by condensation of saturated vapors or by mechanical means [40]. As the particle sizes of the liquid become greater than 0.01 mm diameter, the lower flammability limit of the material becomes lower while above 0.01 mm, the LEL is about the same as the vapor. Mechanical engine crankcase explosions of oil mist in air are hazardous, and current practice is to apply explosion relief valves to the crankcase. 

Laminar flame speed is one of the fundamental properties characterizing the global combustion rate of a fuel/ oxidizer mixture. Therefore, it frequently serves as the reference quantity in the study of the phenomena involving premixed flames, such as flammability limits, flame stabilization, blowoff, blowout, extinction, and turbulent combustion. Furthermore, it contains the information on the reaction mechanism in the high-temperature regime, in the presence of diffusive transport. Hence, at the global level, laminar flame-speed data have been widely used to validate a proposed chemical reaction mechanism. 

The tendency of premixed flames to detach from the flame holder to stabilize further downstream has also been reported close to the flammability limit in a two-dimensional sudden expansion flow [27]. The change in flame position in the present annular flow arrangement was a consequence of flow oscillations associated with rough combustion, and the flame can be particularly susceptible to detachment and possible extinction, especially at values of equivalence ratio close to the lean flammability limit. Measurements of extinction in opposed jet flames subject to pressure oscillations [28] show that a number of cycles of local flame extinction and relight were required before the flame finally blew off. The number of cycles over which the extinction process occurred depended on the frequency and amplitude of the oscillated input and the equivalence ratios in the opposed jets. Thus the onset of large amplitudes of oscillations in the lean combustor is not likely to lead to instantaneous blow-off, and the availability of a control mechanism to respond to the naturally occurring oscillations at their onset can slow down the progress towards total extinction and restore a stable flame. 

Use laminar premixed free-flame calculations with a detailed reaction mechanism for hydrocarbon oxidation (e.g., GRI-Mech (GRIM30. mec)) to estimate the lean flammability limit for this gas composition in air, assuming that the mixture is flammable if the predicted flame speed is equal to or above 5 cm/s. For comparison, the lean flammability limits for methane and ethane are fuel-air equivalence ratios of 0.46 and 0.50, respectively. 

The flash point, denoted PP or jp, expressed in K( C), is the temperature at which a pool of a flammable liquid will generate sufficient vapors to form an ignitable vapor/air mixture. It can also be seen as the temperature at which a liquid will reach its lower flammabihty limit (LFL) in air. However, flammable liquids can also ignite below their flash point if the surface area is increased either by dispersion (e.g., aerosol) or by mechanical activation (e.g., spraying) that raises the concentration of vapor in air above the lower flammability limit. In practice the flash point of a liquid is measured following standardized laboratory test protocols such as the Continuously Closed Cup Test (ASTM D6450), the Pensky-Martens Closed Cup Test (ASTM D93) or by the Tag Closed Cup Test (ASTM D56). 

Explosions Explosions occur in flammable mixtures which are within the flammable limits and there are two types a deflagration and a detonation. In a deflagration flame propagation occurs where the flame front travels at about 1 m/s through the mixture while in a detonation the flame velocity is sonic, i.e. about 300 m/s. The mechanism of a detonation relies on the fact that heat can be generated by compressing a gas. One of the... 

Adequate natural or mechanical ventilation shall be provided to maintain the concentration of flammable vapor at or below 10 percent of the lower flammable limit. 

A theory of diffusion flame propagation under isothermal conditions has been proposed [145]. It has been found that in a simple case the reaction kinetics corresponds to second-order autocatalysis accompanied by first order-consumption of active species. Recently, the burning rate and the flammability limits of a cool carbon suHide flame have been computed [14] making use of the mechanism and rate constants given in a review [233, 234]. The ideas stated in this review apparently provide an explanation for the experimental facts observed the shift of... 

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