Flame Base Structure of Small-Scale Pool Fires.
Flame Base Structure of Small-Scale Pool Fires.
(481 K)
Venkatesh, S.; Ito, A.; Saito, K.; Wichman, I. S.
NIST GCR 96-704; 22 p. December 1996.
Combustion Institute, Symposium (International) on
Combustion, 26th. Proceedings. Volume 1. July
28-August 2, 1996, Napoli, Italy, Combustion Institute,
Pittsburgh, PA, 1437-1443 pp, 1996.
Sponsor:
National Institute of Standards and Technology,
Gaithersburg, MD
Available from:
National Technical Information Service
Order number: PB97-137574
Keywords:
pool fires; air entrainment; diffusion flames; flame
spread; flow visualization; small scale fire tests;
temperature profiles
Abstract:
This paper attempts to answer the question, "Why are
small scale pool fires anchored?" by providing and
interpreting a new set of experimental data. For
momentum-controlled, high Reynolds (Re) number
turbulent-jet diffusion flames, the formation of a
premixing zone is suggested as the primary reason for
the flame anchoring. For buoyancy-controlled pool
fires, however, the existence of the premixing zone at
the flame base is not clear because both Re and Fr
(Froude number) are low. To improve our understanding
of the flame anchoring mechanism and structure of
buoyancy-controlled liquid pool fires, we employed small
scale pool fires whose diameters range between 1.5 - 30
cm. Our measurements include flow visualization by a
particle-track laser-sheet technique (PTLS) combined
with a high speed video camera and temperature profiles
by a fine thermocouple. We found from those
measurements that major air entrainment occurred through
the primary anchoring zone, PAZ, which consists of a
small area covering approximately 1 cm high and around
the circumference just above the dark zone; while air
entrainment through the quenching zone (a dark zone
formed between the visible flame edge and the burner
port) was negligible. The structure of the PAZ was
found to be premixed flame (another interpretation may
be it is similar to counter-diffusion flame). This
enables the pool fires to anchor at the burner port. In
addition, we visualized the existence of a vortex ring
at a stagnation zone in the fuel vapor phase for both
propanol and hexane pool fires, in agreement with
qualitative observation by other workers.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899