Abstract
The purpose of this study was to investigate the merging behavior of small-scale buoyant flames that might be representative of flames from a leaf in a shrub. Zirconia felt pads soaked in n-heptane were suspended on thin rods and spaced both horizontally and vertically. Time-dependent video images from flames from two-pad and three-pad configurations were analyzed to determine merging probability, combined flame characteristics (height, area, and width), and changes in burn time. Correlations of these combined flame characteristics were developed based on horizontal and vertical spacing between the pads. Merging probability correlated with an exponential function that was quadratic in horizontal and/or vertical spacing. Flame heights corrected for vertical inter-pad spacing showed a maximum increase of 50% over single flame heights, and were correlated with an exponential decay function. Flame areas increased by a maximum of 34%, but on average were relatively constant. Corrected flame widths for the merged flames increased by as much as 55% in some configurations, but decreased by up to 73% in other configurations. Burn times for upper pads decreased when there was no horizontal spacing. The limited flame growth observed in these non-overlapping configurations in the horizontal dimension imply that overlapping configurations seem to be necessary for significant flame growth.
Highlights
The prevalence of wildland fires in recent years in the western United States illustrates the need for improved understanding and management of fire behavior
The probability of flame merging based on horizontal and vertical spacing for both the two-pad and three-pad experiments was correlated with the same model form that consisted of an exponential decay function, which may prove useful for other flame merging configurations
Flame merging experiments were conducted successfully with zirconia felt pads soaked in n-heptane and suspended on thin ceramic rods
Summary
The prevalence of wildland fires in recent years in the western United States illustrates the need for improved understanding and management of fire behavior. Attempts to model shrub combustion that utilize more informed geometries of shrubs, but without the complicated computational fluid dynamics, have been performed [11,12] Such reduced order shrub combustion models use empirical descriptions of flame geometry to describe leaf-to-leaf flame propagation, and have attempted to use flame merging behavior equations developed from horizontally spaced pool fires or wood cribs. One of the main needs for accurate shrub combustion modeling is the complicated flame growth pattern caused by the merging of flames from multiple leaves and small branches in three dimensions. Such descriptions of flame merging behavior will be useful in detailed descriptions of fires in other fuels, including trees. Other examples include flame merging in back fires and fire complexes
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