Measurements of Heat and Combustion Products in Reduced-Scale Ventilation-Limited Compartment Fires.
Measurements of Heat and Combustion Products in
Reduced-Scale Ventilation-Limited Compartment Fires.
(11069 K)
Bundy, M.; Hamins, A.; Johnsson, E. L.; Kim, S. C.; Ko,
G. W.; Lenhert, D. B.
NIST Technical Note 1483; NIST TN 1483; 154 p. July
2007.
Keywords:
compartment fires; heat products; combustion products;
ventilation; enclosures; burners; heat release rate;
temperature; velocity; soot; heat flux; fuels; fire
spread; doors; construction materials; carbon balance
method; combustion efficiency; chemical analysis;
thermocouples; probes; gas chromatography
Abstract:
A series of new reduced-scale compartment fire
experiments were conducted, which included local
measurements of temperature and species composition.
The measurements are unique to the compartment fire
literature. By design, the experiments provided a
comprehensive and quantitative assessment of major and
minor carbonaceous gaseous species and soot at two
locations in the upper layer of fire in a 2/5 scale
International Organization for Standards (ISO) 9705
room. The enclosure defined in the international
standard ISO 9705 "Full-scale room test for surface
products" is an important structure in which to conduct
fire research. Many dozens of research projects and
journal articles have focused on this enclosure and the
standard describing its use. It is a common reference
point for studies of many fire-related phenomena as well
as fire modeling efforts. While some previous studies
have considered the mixture fraction to analyze
experimental compartment fire data, few have considered
minor hydrocarbon species and none have considered soot.
In tandem, accurate measurements of temperature at
these same locations allowed analysis of thermal effects
on species concentrations. A wide range of fuel types
were considered, including aliphatic hydrocarbons
(natural gas and heptane), aromatic hydrocarbons
(toluene and polystyrene) and alcohols (methanol and
ethanol). Field models, such as the National Institute
of Standards and Technology (NIST) Fire Dynamics
Simulator (FDS), are widely used by fire protection
engineers to predict fire growth and smoke transport for
practical engineering applications. Field models
numerically solve the conservation equations of mass,
momentum and energy that govern low-speed,
thermally-driven flows with an emphasis on smoke and
heat transport from fires. All field models have
strengths and weaknesses. Among the various assumptions
used in the development of previous versions of FDS, all
chemical species were tied to the mixture fraction state
relations. A single mixture fraction variable cannot be
used for the prediction of carbon monoxide and soot, and
the yield of these species was prescribed in FDS 4,
rather than predicted. In fact, the yield of these
species is usually not constant, but a complex function
of their time-temperature history. In practice, an
engineer using FDS 4 would choose combustion product
yields directly from literature values for
well-ventilated burning, using data from a bench-scale
apparatus. Using this approach, the carbon monoxide
(CO) volume fraction for pool fire burning in an
under-ventilated compartment can be underestimated by as
much as a factor of ten. A new version of FDS (version
5) is currently being tested which implements a
predictive model of CO production. The experimental
results provided in this report are the first step of a
long-term NIST project to generate the data necessary to
test our understanding of fire phenomena in enclosures
and to guide the development and validation of field
models by providing high quality experimental data. The
experimental plan was designed in cooperation with
developers of the NIST FDS model to assure that the
measurements would be of maximum value. Advanced
development of FDS and other field models is extremely
important, since it will lead to improved accuracy in
the prediction of underventilated burning, typical of
fire conditions that occur in structures. Improving
models for under-ventilated burning will foster improved
prediction of important life safety and fire dynamic
phenomena, including fire spread, backdraft, flashover,
and egress (involving the presence of toxic gases and
smoke), which are critically important for application
of fire models for fire safety. In summary, the main
objective of this project is to provide an improved
understanding of the physics, chemistry, and structure
of underventilated compartment fires, and to provide
experimental measurements to guide the development of
fire chemistry sub-models.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899