New experimental diagnostics in combustion of forest fuels: microscale appreciation for a macroscale approach

In modelling the wildfire behaviour, good knowledge of the mechanisms and the kinetic parameters controlling the thermal decomposition of forest fuel is of great importance. The kinetic modelling is based on the mass-loss rate, which defines the mass-source term of combustible gases that supply the flames and influences the propagation of wildland fires. In this work, we investigated the thermal degradation of three different fuels using a multi-scale approach.Lab-scale experimental diagnostics such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), use of the cone calorimeter (CC) or Fire Propagation Apparatus (FPA) led to valuable results for modelling the thermal degradation of vegetal fuels and allowed several upgrades of pyrolysis models.However, this work remains beyond large-scale conditions of a wildland or forest fire. In an effort to elaborate on the kinetic models under realistic natural fire conditions, a mass-loss device specifically designed for the field scale has been developed. The paper presents primary results gained using this new device, during large-scale experiments of controlled fires. The mass-loss records obtained on a field scale highlight the influence of the chemical composition and the structure of plants. Indeed, two species with similar chemical and morphological characteristics exhibit similar mass-loss rates, whereas the third presents different thermal behaviour.The experimental data collected at a field scale led to a new insight about thermal degradation processes of natural fuel when compared to the kinetic laws established in TGA. These new results provide a global description of the kinetics of degradation of Mediterranean forest fuels. The results led to a proposed thermal degradation mechanism that has also been validated on a larger scale.</p

An analytical model based on radiative heating for the determination of safety distances for wildland fires

International audienceThe radiative heat transfer is often the main thermal impact of a wildfire on people fighting the fire or on structures. Thus, the estimation of the radiation coming from the fire font and hitting a target is of primary importance for forest and urban managers. A new flame model based on the solid flame assumption is developed by considering a finite fire front width. The realistic description of finite fire front widths allows proposing a new criterion for the estimation of the radiative impact of the fire, which is based on the ratio fire front width/ flame length, opposed to the classical approach of considering only the flame length. The new model needs to be solved numerically so an analytical approximation is proposed to obtain a simple and useful formulation of the acceptable safety distance. A sensivity analysis is conducted on the different physical and geometrical parameters used to define the flame front. This analysis shows that the flame temperature is the most sensitive parameter. The results of the analytical model are compared with the numerical solution of the flame model and previous approaches based only on flame length. The results show that the analytical model is a good approximation of the numerical approach and displays realistic estimations of the acceptable safety distance for different fire front characteristics

Comparative Study To Evaluate the Drying Kinetics of Boreal Peats from Micro to Macro Scales

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Energetic potential and kinetic behavior of peats

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Fuel types and potential fire behaviour in Sardinia and Corsica islands: a pilot study.

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