A study on the maximum temperature of ceiling jet induced by rectangular-source fires in a tunnel using ceiling smoke extraction

Fire behavior and effects in forests and woodlands are influenced by surface fuels and senesced leaf litter in particular. We have known that species exhibit differential flammability for some time, but isolated efforts have often attributed differences to disparate mechanisms. Recent research has expanded the diversity of species evaluated, clarified patterns at the fuelbed level, and provided evidence that the physical and chemical traits of litter or fuelbeds drive flammability. To date, little effort has focused on uniting methods, clarifying the awkward terminology, or, perhaps most importantly, comparing laboratory findings to field observations of fire behavior. Here, we review recent literature and synthesize findings on what we know about the flammability of litter and propose future research directions.

https://link.springer.com/content/pdf/10.1007%2Fs40725-015-0012-x.pdf

The Flammability of Forest and Woodland Litter: a Synthesis

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2020EF001671

Causes of the Widespread 2019–2020 Australian Bushfire Season

Experimental study on the characteristics of flame merging and tilt angle from twin propane burners under cross wind

This paper investigates the flame interaction of two parallel rectangular fires. Multiple propane burners were used to produce parallel fires for experiments. Experimental observations combined with analytical analysis provide a physical interpretation on the mechanism of flame interaction. Three types of flame interaction regimes, namely the “Independent regime”, “Intermittent regime” and “Consistent regime”, are quantitatively identified in terms of the flame merging probability (Pm) extracted from image analysis. These three regimes are further divided into five distinct interaction states including (a) State I, independent flames with no interaction, (b) State II, independent flames that have interaction, (c) State III, flames that have intermittent touch with each other, (d) State IV, partly merged flames, and (e) State V, completely merged flames. It is found that for a given fuel size parameter, the data of Pm in different interaction states versus the dimensionless flame spacing s/zc (s: flame spacing, zc: a characteristic length) cluster well and can be well fitted by Boltzmann function, and the function parameters have definite physical significance. For different interaction states, the dimensionless flame height Zf/Zf0 (Zf0: the flame height of one single fire) is correlated with s/zc. Especially, it is found that when s/zc falls into State II, Zf/Zf0 declines to be a constant due to the competition of two distinct effects induced by flame interaction. The dependence of Zf/Zf0 upon s/zc in different interaction states is fully illustrated. Finally, another dimensionless flame height Zf/D (D: a characteristic size of fuel bed by regarding the two flames as a whole) is formulated as a function of heat release rate for different interaction states.

Interaction of two parallel rectangular fires

Experimental study on flame characteristics of propane fire array

A fact often overlooked is that large-scale wildfires, although occurring infrequently, are responsible for the overwhelming majority of fire-related suppression costs, economic losses, and natural resources damages. Fortunately, the increasingly severe problems of large-scale wildfires worldwide have been receiving ever-growing academic attention. The high-intensity burning behaviors in wildfires stem from the significant interaction of combustion with heat transfer and atmospheric flow under complicated fuel, meteorology, and topography conditions. Therefore, mitigating measures against large-scale wildfire disasters have grown into a challenging research focus for combustion scientists. Research over the past century has resulted in incrementally enhanced insights into the mechanisms of combustion dynamics underlying the various erratic behaviors in large-scale wildfires, with theories and models of fire accelerations developed and validated. These advances are expected to improve the efficacy of large-scale wildfire predictions significantly. Nevertheless, the physical interpretation of the acceleration of large-scale wildfires is far from adequate and complete. This paper intends not to make a comprehensive review of the entire wildfire research field, but to depict an overall pattern of the essential factors that lead an initial small-scale spreading flame to a large-scale wildfire beyond control. It is outlined that the complicated transformation of fuel preheating mechanisms determines the growth of surface fire spread, while varied large-size flame fronts and unique spread modes induced in specific fire environments play an essential role in fire spread acceleration. Additionally, multiple fires burning and merging often act as crucial steps for accelerating surface fire spread, generating large-size flames, and triggering unique spread modes. These major potential factors strike the energy balance of a low-intensity wildfire and push it to a high-intensity state. Several issues regarding intensely burning behaviors in large-scale wildfires are selected for in-depth discussions, for which an overview of the progress and challenges in research is presented. It is concluded that the fundamental exploration targeted at developing application tools capable of dealing with large-scale wildfires remains at its early stages. Opportunities for innovation are abundant, yet systematic and long-term research programs are required.

Combustion dynamics of large-scale wildfires

This work intends to interpret the fire interaction mechanisms of multiple pool fires (MPF). A series of n-heptane and ethanol MPF tests with fuel pan diameters D of 0.2 m, 0.15 m, 0.05 m and different S/D (S: fire spacing) are performed. It is revealed that the air entrainment and convection of the center fire, and the leaning of the outer fire depend on the difference of the burning rates between the center and outer fires. Besides, it is indicated that the fire merging criterion depends on fuel type. For the typical fuels used in this work, compared to ethanol MPF, n-heptane MPF has a larger critical S/D attributed to its higher burning rate and flame height. The results also indicate that for MPF with no air entrainment restriction, the mass burning flux and heat feedbacks of the center fire monotonically increase with decreasing S/D. However, if air entrainment is restricted, the heat feedback rates and fractions non-monotonically depend on S/D. Furthermore, an under-ventilated burning phenomenon of MPF is found and illustrated as a result of air entrainment restriction. It is indicated that the under-ventilated burning induces the spill of excess unconsumed fuel vapors, influences the near-field radial velocity profile of MPF, and weakens the conduction heat feedback of the center fire. Finally, for the center fire of convection-dominated MPF, a modified mass burning flux correlation is derived based on the stagnant layer theory, which is verified to reasonably agree well with the experimental data.

Interpretation on fire interaction mechanisms of multiple pool fires

This paper experimentally evaluates the effect of slope on spread of a linear flame front over a pine needle fuel bed in still air. The slope angle of the fuel bed varied from 0 to 32°. The fuel mass consumption in flaming fire spread, temperature over the fuel bed, velocities of the flow around the flame front and heat fluxes (total and radiant) near the end of the fuel bed were measured. The mass loss rate and rate of fire spread both increased with increasing slope, whereas the fuel consumption efficiency varied in the opposite way. It was shown that a weak reverse inflow and an upslope wind (induced by the flame itself) exist respectively ahead of and behind the flame front, and their significant difference in velocity (causing a pressure difference) plays an essential role in the forward tilting of the flame front. This mechanism promotes burning, especially on higher slopes. Natural convective cooling has a remarkable effect on the fuel pre-heating in the spread of linear flame fronts under slope conditions. A fire spread model for a linear flame front was developed to consider the natural convective cooling and the fuel consumption efficiency. The model agrees well with the experimental data on fire spread rate. Its reliability, especially for higher slopes, was verified by comparison with other models.

Xiaodong Xie

Papers

Interaction of two parallel rectangular fires

Experimental study on flame characteristics of propane fire array

Combustion dynamics of large-scale wildfires

Interpretation on fire interaction mechanisms of multiple pool fires

Effect of slope on spread of a linear flame front over a pine needle fuel bed: experiments and modelling