A convective–radiative propagation model for wildland fires

Abstract

The ‘Balbi model’ is a simplified steady-state physical propagation model for surface fires that considers radiative heat transfer from the surface area of burning fuel particles as well as from the flame body. In this work, a completely new version of this propagation model for wildand fires is proposed. Even if, in the present work, this model is confined to laboratory experiments, its purpose is to be used at a larger scale in the field under operational conditions. This model was constructed from a radiative propagation model with the addition of a convective heat transfer term resulting from the impingement of packets of hot reacting gases on unburnt fuel elements located at the base of the flame. The flame inside the fuel bed is seen as the ‘fingers of fire’ described in the literature. The proposed model is physics-based, faster than real time and fully predictive, which means that model parameters do not change from one experiment to another. The predicted rate of spread is applied to a large set of laboratory experiments (through homogeneous pine needles and excelsior fuel beds) and is compared with the predictions of both a very simple empirical model (Catchpole) and a detailed physical model (FireStar2D).

Interaction between two parallel fire fronts under different wind conditions

“…9, we present a physical interpretation of the fire spread properties for the three values of the flow velocity (U 0 = 0, 2 and 5 m s −1 ) corresponding to the three fire As shown in each case, the flame geometry and size change during the fire fronts' advance in a way that depends on the flow velocity. These changes are associated with the role of horizontal and vertical forces that change the flame geometry (Morvan 2007;Balbi et al 2020;Viegas et al 2021) and, consequently, the ROS between the two parallel fire lines.…”

Fuelbreak effectiveness against wind-driven and plume-dominated fires: A 3D numerical study

“…Unlike the curves shown in Fig. 16 for DIMZAL, in this case the tilt angle was not imposed to an arbitrary defined value (0 • and 45 • ), but was calculated from an estimated ratio between the horizontal component of the gas velocity due to the wind and the vertical component due to buoyancy [22,42]. In this case the best fit (minimizing root square error) was obtained for an incident heat flux equal to 10 kW m − 2 .…”

Fuel moisture content threshold leading to fire extinction under marginal conditions

“…In order to evaluate the FMC threshold that determines fire propagation success under marginal fire conditions, simulations were performed using the simplified physical surface fire model developed at the University of Corsica [23,[25][26][27][28], the FIRESTAR2D computational fluid dynamics software [2,24,29,30] and an empirical criterion. These three methods are described in this section.…”

“…Where ∆H is the fuel heat of combustion of the pyrolysis gases (assumed equal to 17.4 × 10 3 kJ/kg for any fuels) [23,28], χo is the radiant heat fraction (assumed equal to 0.3), st is the stoichiometric coefficient (assumed equal to 9), Cpa is the specific heat of ambient air and n is related to the expression of extinction length, following the definition of optical depth given in [35] :…”

“…The aim of this work is to identify the FMC threshold for homogeneous surface fuel that leads to fire extinction under weak wind conditions. This aim was achieved by applying numerical simulations performed with two fire behavior models: a simplified-physical surface fire spread model [20][21][22][23] and a detailed fire physical model [24]. An empirical criterion was also applied [14].…”