Numerical study of an experimental high-intensity prescribed fire across Corsican Genista salzmannii vegetation

This article presents a first attempt of implementation of a lab scale methodology proposed to describe the thermal decomposition behavior of vegetative fuels, by using thermogravimetric (TG) methods, with respect to forest fire. Experiments within this method include testing the usual grinded form of samples compared to a continues fuel layer (intact form), which can render reliable and useful information to improve the understanding of the ignitability and combustibility of forest fuels along with predicting fire propagation. Moreover, slow (20 and 40 Â°C/min) and fast (60, 80 and 100 Â°C/min) heating rate were chosen to get close from the actual conditions of wildland fires (preheating/smoldering and flame region, respectively). In this work, we report the thermal decomposition behavior under inert (N2) and oxidative (air) atmospheres of Genista Salzmannii Needles (GSN) involved in fires of Mediterranean forests. TG analyses were performed to assess thermal reactivity and combustion indices (ignition, devolatilization, combustion and burnout indices) of grinded and cut GSN samples at fives heating rates of 20, 40, 60, 80 and 100 Â°C/min. The use of the set of thermal indices practical investigation, ignitability, combustibility and sustainability of forest fuels are important properties to be determined when talking to efficient wildland fire management. Moreover, Activation energy was calculated by means of two iso-conversional methods. The results showed that the cut GSN was characterized by a higher mass loss rate compared to grinded samples. As the heating rate increases, reactivity and combustion indices increase linearly. At low heating rates (20 and 40 Â°C/min), these parameters are quite similar for both samples, while the gap becomes more and more significant at elevated heating rates (60, 80 and 100 Â°C/min). High correlation coefficients (R2 > 0.96) were obtained, which indicate a good degree of fitting reliability between combustion characteristics and the tested heating rates. Furthermore, the variation of activation energy (Ea) with the conversion rate has exhibited a quite similar behavior during the whole pyrolysis and combustion process. Char formation, at the end of an intense devolatilization, was the most complex process. The oxidation of the remaining char was characterized by a significant decrease of Ea, which is not considered as a major event in the combustion process. Finally, the obtained data provide systematic knowledge for understanding the thermal decomposition of forest fuels (considered as the first stage in fire process), while the developed methodology can be used for comparison and classification of vegetative fuels related to fire risk potential.

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“…Fayad et al (2022) highlight the high-intensity of wildland fire generate by this vegetation specie.…”

mentioning

confidence: 90%

Comprehensive Characterization of Pyrolysis and Combustion of Genista Salzmannii Needles (GSN) for Fire Hazard Analysis

Rahib¹,

Leroy-Cancellieri²,

Cancellieri³

et al. 2022

Advances in Forest Fire Research 2022

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“…The focus of these experiments was on determining the behavior and impact of the high intensity fires. A brief description of this protocol will be presented next, while detailed information can be found in a previous article [35].…”

Section: Experimental Protocolmentioning

confidence: 99%

“…This permits to assess the radiative and total heat fluxes (equal to the sum of radiative and convective heat fluxes) recorded during the experiment by the fluxmeters located at the end of the plot. The details concerning the numerical evaluation of these heat transfer modes are presented in previous papers [35,37].…”

Section: Heat Fluxesmentioning

confidence: 99%

A Study of Two High Intensity Fires across Corsican Shrubland

Fayad¹,

Morandini²,

Accary³

et al. 2023

Atmosphere

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This paper reports two experimental fires conducted at field-scale in Corsica, across a particular mountain shrubland. The orientation of the experimental plots was chosen in such a way that the wind was aligned along the main slope direction in order to obtain a high intensity fire. The first objective was to study the high intensity fire behavior by evaluating the propagation conditions related to its speed and intensity, as well as the geometry of the fire front and its impact on different targets. Therefore, an experimental protocol was designed to determine the properties of the fire spread using UAV cameras and its impact using heat flux gauges. Another objective was to study these experiments numerically using a fully physical fire model, namely FireStar3D. Numerical results concerning the fire dynamics, particularly the ROS, were also compared to other predictions of the FireStar2D model. The comparison with experimental measurements showed the robustness of the 3D approach with a maximum difference of 5.2% for the head fire ROS. The fire intensities obtained revealed that these experiments are representative of high intensity fires, which are very difficult to control in the case of real wildfires. Other parameters investigated numerically (flame geometry and heat fluxes) were also in fairly good agreement with the experimental measurements and confirm the capacity of FireStar3D to predict surface fires of high intensity.

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“…These windows have a spectral transmission range of 0.2-5.5 µm compared with 0.2-50 µm for the un-windowed gauges, which may result in a slight underestimate of the incident radiant flux. Sapphire windows were used in several previous wildland flame spread studies (Anderson 1969;Silvani and Morandini 2009;Silvani et al 2012Silvani et al , 2018Frankman et al 2013;Tihay et al 2014;Morandini et al 2019;Fayad et al 2022). Heat flux measurements were recorded at a minimum of 5 Hz (25 out of 29 experiments at 10 Hz).…”

Section: Heat Fluxesmentioning

confidence: 99%

Effects of fuel bed structure on heat transfer mechanisms within and above porous fuel beds in quiescent flame spread scenarios

Campbell-Lochrie

Walker-Rávena²,

Gallagher³

et al. 2023

Int. J. Wildland Fire

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Background. Further understanding of the effect of fuel structure on underlying physical phenomena controlling flame spread is required given the lack of a coherent porous flame spread theory. Aims. To systematically investigate the effect of fuel structure on the heat transfer mechanisms within and above porous fuel beds. Methods. Radiant and total heat fluxes were measured in two extended series of laboratory-based quiescent flame spread experiments in pine needle beds across a range of structural conditions (various fuel loadings, bulk densities, and fuel depths). Key results. Peak radiant heat fluxes from the in-bed combustion region were greater than peak radiant heat fluxes from the above-bed flame front for all of the studied fuel conditions. However, the magnitude and duration of radiant heating from the above-bed flame increased with fuel loading (where bulk density was held constant and fuel depth allowed to vary). Conclusions. Our study highlighted the important role of fuel structure on heat transfer mechanisms, and the relevance of development of semi-empirical and simplified physics-based models. Implications. The interdependent effects of fuel bed properties on the underlying heat transfer mechanisms must be considered in the further development of coherent, flame spread theories.

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Numerical study of an experimental high-intensity prescribed fire across Corsican Genista salzmannii vegetation

Cited by 11 publications

References 42 publications

Comprehensive Characterization of Pyrolysis and Combustion of Genista Salzmannii Needles (GSN) for Fire Hazard Analysis

Comprehensive Characterization of Pyrolysis and Combustion of Genista Salzmannii Needles (GSN) for Fire Hazard Analysis

A Study of Two High Intensity Fires across Corsican Shrubland

Effects of fuel bed structure on heat transfer mechanisms within and above porous fuel beds in quiescent flame spread scenarios

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