Critical Mass Pyrolysis Rates for Extinction in Fires Over Solid Materials.
Critical Mass Pyrolysis Rates for Extinction in Fires
Over Solid Materials.
Delichatsios, M. A.
NIST GCR 98-746; FMRC J.I. 0Y1J0.RU/0Y1N3.RU; 44 p.
Sponsor:National Institute of Standards and Technology,
Available from: National Technical Information Service
Order number: PB98-146137
solids; pyrolysis rate; extinction; charring; solid
fuels; heat flux; inert gases; nitrogen
New flame extinction conditions for the critical mass
pyrolysis rate are developed when extinction occurs by
interaction of flames with the pyrolyzing surface of a
condensed material. The extinction conditions provide
the critical mass pyrolysis rate and the corresponding
convective heat flux to the surface. A novel chemistry
based formulation for extinction is provided which shows
that the sum of fuel mass fraction near the surface and
the ambient oxygen mass fraction (correctedfor
stoichiometry and combustion efficiency) is constant.
The extinction conditions are derived from simple
anslysis of combustion and heat transfer, and they are
shown to be applicable for various experimental
conditions such as fuel dilution by inert gas, oxygen
dilution by inert gas, effects of external heat flux,
material preheating, transient (charring) pyrolysis,
including geometric effects which influence the critical
mass pyrolysis rate through an effective heat transfer
coefficient. Additional validation of the proposed
extinction conditions is provided by numerical
simulation reported in literature in the regime of low
straining rates for a stagnation flow on a cylinder.
The present approach can be used to measure critical
extinction conditions in a flammability apparatus and
allow them to be applied in other conditions such as in
microgravity. The critical extinction conditions are
needed to calculate transient decay pyrolysis of solids
after an extinguishment agent is applied.