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Reactivity of Product Gases Generated in Idealized Enclosure Fire Environments.


pdf icon Reactivity of Product Gases Generated in Idealized Enclosure Fire Environments. (4085 K)
Pitts, W. M.

Combustion Institute, Symposium (International) on Combustion, 24th. July 5-10, 1992, Sydney, Australia, 1737-1746 pp, 1992.

Keywords:

enclosures; experiments; temperature; predictive models; global equivalence ratio; free radicals

Abstract:

Previous experiments have demonstrated that the mole fractions of major product gases trapped in a hood located above a fire can be correlated in terms of the global equivalence ratio. Temperatures in the hood experiments have generally been low. Full-kinetic calculations are employed to characterize the reactivity and reaction behavior for the product gases observed in a hood experiment burning natural gas as fuel. A range of temperatures (700-1300 K) typical of enclosure fires is considered. Mixing is assumed to be infinitely fast (perfectly-stirred reactor) or infinitely slow (plug-flow reactor). Both isothermal and adiabatic cases are treated. Calculations are reported for a range of residence times (0-20 s) and global equivalence ratios (0.5-2.83). The dominant variable for reaction behavior is found to be temperature. Effects due to mixing and heat transfer assumptions are less important. The results indicate that the hood product gases are reactive for temperatures greater than 800 K. For rich mixtures, reaction generates primarily carbon monoxide as opposed to carbon dioxide. At higher temperatures the formation of hydrogen is favored over water while water is favored in the 800-1000 K range. In the lower temperature range HO2 is the dominant free radical. Uncertainties in rates for reactions involving this specie introduce considerable uncertainty into the calculated behaviors. At higher temperatures (1100-1300 K) the important free radicals are H atom and OH. Reactions involving these radicals are better characterized than those involving HO2. The findings suggest that the results of the hood experiments cannot be used directly for the modeling of species production in enclosure fires.