Thierry Marcelli

A 3D PHYSICAL REAL-TIME MODEL OF SURFACE FIRES ACROSS FUEL BEDS

Abstract This work presents a new modelling approach to the elaboration of a simple model of surface fire spread. This model runs faster than real-time and will be integrated in management tools. Until now, models used in such tools have been based on an empirical relationship. These tools may be efficient for conditions that are comparable to those of test-fires but the absence of a physical description makes them inapplicable to other situations. This paper proposes a physical 3D model of surface fire able to predict fire behaviour faster than real-time. This model is tested on experiments carried out across fuel beds under slope and wind conditions.

Fire spread across pine needle fuel beds: characterization of temperature and velocity distributions within the fire plume

The aim of this article is twofold. First, it concerns the improvement of knowledge on the fundamental physical mechanisms that control the propagation of forest fires. To proceed, an experimental apparatus was designed to study, in laboratory conditions, the flame of a fire spreading across a pine needle fuel bed. Characterization of temperature was managed by using a reconstruction method based on a double thermocouple probe technique developed recently. The vertical gas velocity distribution was derived from the previous reconstructed signals by measuring the transit time of a thermal fluctuation between two points of the flow. Second, the experimental data were used for the testing of a physical two-phase model of forest fire behavior in which the decomposition of solid fuel constituting a forest fuel bed as well as the multiple interactions with the gas phase are represented.

Measurement of fluctuating temperatures in a continuous flame spreading across a fuel bed using a double thermocouple probe

Abstract Although the modeling of the spread of a forest fire has made considerable progress recently, there remains a lack of reliable measurements of such fluctuating scalar quantities as temperature for the validation of the different existing models. This led us to use double thermocouples to measure fluctuating temperatures in the continuous flame region of a fire plume. An enthalpy balance to model the temperature of a thermocouple-junction immersed in a flame was written. Then a linearized first-order model was derived and a method for identifying the model’s parameters, i.e., the time constant and gain coefficient, was provided. This model was tested with a clean, diffusion flame of ethanol to compensate for the gas temperature. These measurements agree with the model for the temperature of a thermocouple’s hot junction. Finally, the compensated gas temperature for the turbulent flame of a fire spreading across a bed of pine needles was investigated.

Physical Modeling of Surface Fire Under Nonparallel Wind and Slope Conditions

The physical model we developed in a previous work (J. H. Balbi et al., 2007) predicts fire behavior with a computational time that is faster than real time. However, it has the inconvenient of introducing an empirical law (B. J. McCaffrey, 1979), which provides flame height according to heat release rate. The authors introduce two improvements of this model: the triangular flame hypothesis and a modification taking into account the air cooling on the rear fire front. To test this variant of their simplified model, it was compared with important experimental results (D. X. Viegas, 2004b). The experiments were performed in homogeneous and plane fuel beds made with dead Pinus pinaster needles under high values of wind and slope. In spite of these high values this physical model provides a good approximation of the fire front perimeter.

Discrete-event modelling of fire spreading

We deal here with the application of discrete-event System Specification (DEVS) formalism to implement a semi-physical fire spread model. Currently, models from physics finely representing forest fires are not efficient and still under development. If current softwares are devoted to the simulation of simple models of fire spread, nowadays there is no environment allowing us to model and simulate complex physical models of fire spread. Simulation models of such a type of models require being easily designed, modified and efficient in terms of execution time. DEVS formalism can be used to deal with these problems. This formalism enables the association of object-oriented hierarchical modelling with discrete-event techniques. Object-oriented hierarchical programming facilitates construction, maintenance and reusability of the simulation model. Discrete-events reduce the calculation domain to the active cells of the propagation domain (the heated ones).