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Fire Interactions and Pulsation - Theoretical and Physical Modeling


The study of fire behavior has numerous applications, from the control of destructive wildfires to the design of more efficient combustion engines. Two phenomena of freely burning flames, fire pulsation and flame interaction, have significant consequences for the understanding and control of fire.

Fire pulsation is a feature of freely burning flames, and is characterized by periodic, large scale fluctuations in flame structure which appear to be only dependent on the scale of the fire. To help understand the origins of these pulsations, both laminar and turbulent pool fires were filmed using a high speed camera. Fluctuations in image intensity, which occur throughout the pulsation cycle, were quantitatively analyzed to identify the existence of dominant pulsation frequencies. The measured pulsation frequencies agreed well with existing experiments from the literature. The imagery was also used to support a new theoretical model which proposes that pulsation is initially triggered by thermals, discrete convective instabilities which develop at the base of the flame before rising and disturbing the flame structure.

Fire interactions occur when two or more flames are placed adjacent to each other. Flame height, angle of tilt, burning intensity, and rate of spread have all been observed to increase as proximate fires converge. To explain the flame tilting phenomena, a model based on the conservation of linear momentum is developed, and it is shown that entrainment in the inner region between flames is restricted as a result of flame configuration. The model is validated by using cross-correlation image analysis to analyze the behavior of passive tracer smoke placed in the entrainment field of two stationary pool fires. In addition, the heat transfer aspects of flame merging are discussed in detail, and modifications to existing fire spread models to accommodate an adjacent flame front are proposed.

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