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 ( Rc ) 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-unchoring mechanism and structure of buoyancy-controlled liquid pool fires, we employed small-scale pool fires whose diameters range between 1.5–20 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, PA, 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 PA was found to be premixed flame (another interpretation may be that 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.
[1]
B. Mccaffrey.
Momentum implications for buoyant diffusion flames
,
1983
.
[2]
H. Tsuji.
Counterflow diffusion flames
,
1982
.
[3]
Jay P. Gore,et al.
Air entrainment flow field induced by a pool fire
,
1995
.
[4]
I. Wichman.
On the Quenching of a Diffusion Flame Near a Cold Wall
,
1989
.
[5]
F. Williams,et al.
Asymptotic analysis of the structure and extinction of spherically symmetrical n-heptane diffusion flames
,
1992
.
[6]
J. Dold.
Flame propagation in a nonuniform mixture: Analysis of a slowly varying Triple Flame
,
1989
.
[7]
I. Glassman,et al.
Pyrolysis Zone Structure of Allene, 1,3 Butadiene and Benzene Smoke Point Diffusion Flames*
,
1992
.
[8]
S. Chung,et al.
On the characteristics of laminar lifted flames in a nonpremixed jet
,
1991
.
[9]
R. Chitty,et al.
A study of the deterministic properties of unbounded fire plumes
,
1980
.