Experiments on the periodic instability of buoyant plumes and pool fires

Journal Article · Thu Apr 01 00:00:00 EST 1993 · Combustion and Flame; (United States)

DOI:https://doi.org/10.1016/0010-2180(93)90090-P· OSTI ID:6537545

Cetegen, B M; Ahmed, T A ^[1]

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1. Univ. of Connecticut, Storrs (United States)

An experimental study of buoyant propane diffusion flames was undertaken to identify the mechanism responsible for the periodic oscillations near the source of these flames. This phenomenon, often referred to as puffing in the literature, exhibits itself as quasi-periodic oscillations of the diffusion flame front near the axisymmetric source of a fire with formation of large scale flaming vortical structures. First, the behavior of buoyant, noncombusting plumes originating from 1.10- and 0.30-m-diameter sources was investigated with either isothermal helium or high temperature combustion products as the buoyant fluid. It was found that the helium plumes exhibited puffing at both scales with puffing frequencies similar to the flames scaling with D[sup [minus]1/2]. Second, effects of heat release were studied by dilution of fuel with a noncombustible gas. It was found that puffing persisted as long as a diffusion flame was sustained by the fuel stream although its intensity diminished with increasing dilution. Third, effects of disturbances both internal and external to the flame were studied. Based on the reported experiments, a puffing mechanism is suggested. The puffing mechanism involves (1) acceleration of buoyant plume gas in stagnant surroundings resulting in formation of a toroidal vortical structure within one burner diameter above its surface, (2) the decaying influence of the toroidal vortex on the flame surface near the burner lip as it connects upward, and (3) the accumulation of buoyant gas inside the flame envelope and its buoyant acceleration to form the next vortical structure. The scaling of puffing frequency with the burner diameter is connected to the convection speed of toroidal vortices within one diameter height above the burner surface as it was shown with the use of a simple kinematic model.

• OSTI ID: 6537545
• Journal Information: Combustion and Flame; (United States), Vol. 93:1-2; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
FLAMES
OSCILLATIONS
PROPANE
COMBUSTION KINETICS
ACCIDENTS
COMBUSTION PRODUCTS
DIFFUSION
DILUTION
FIRES
HAZARDOUS MATERIALS SPILLS
VORTICES
ALKANES
CHEMICAL REACTION KINETICS
HYDROCARBONS
KINETICS
ORGANIC COMPOUNDS
REACTION KINETICS
400800* - Combustion
Pyrolysis
& High-Temperature Chemistry