Reactivity of Product Gases Generated in Idealized Enclosure Fire Environments.
Reactivity of Product Gases Generated in Idealized
Enclosure Fire Environments.
Pitts, W. M.
Combustion Institute, Symposium (International) on
Combustion, 24th. July 5-10, 1992, Sydney, Australia,
1737-1746 pp, 1992.
enclosures; experiments; temperature; predictive models;
global equivalence ratio; free radicals
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.