An improved non-equilibrium model for the ignition of living fuel

Abstract

This paper deals with the modelling of living fuel ignition, suggesting that an accurate description using a multiphase formulation requires consideration of a thermal disequilibrium within the vegetation particle, between the solid (wood) and the liquid (sap). A simple model at particle scale is studied to evaluate the flux distribution between phases in order to split the net flux on the particles into the two sub-phases. An analytical solution for the split function is obtained from this model and is implemented in ForestFireFOAM, a computational fluid dynamics (CFD) solver dedicated to vegetation fire simulations, based on FireFOAM. Using this multiphase formulation, simulations are run and compared with existing data on living fuel flammability. The following aspects were considered: fuel surface temperature, ignition, flaming combustion time, mean and peak heat release rate (HRR). Acceptable results were obtained, suggesting that the thermal equilibrium might not be an acceptable assumption to properly model ignition of living fuel.

Modelling the fire propagation from the fuel bed to the lower canopy of ornamental species used in wildland–urban interfaces

“…Consequently, the most important point would be to improve the modelling for moisture content higher than 60% (i.e. live plants) in adopting a multiphase model for live plants such as suggested in Lamorlette et al (2018).…”

Clarifying the meaning of mantras in wildland fire behaviour modelling: reply to Cruz et al. (2017)

“…Cruz et al (2017) give an incomplete picture of the advances made and the state of activity (including new experiments) in pursuit of improvements to these models (e.g. Anand et al 2017;Mueller 2017;Lamorlette et al 2018).…”

Fuel moisture content threshold leading to fire extinction under marginal conditions

“…For future works, it will be of primary interest to study the correlation between wind and slope on the ignition potential of grasses and more complex fuels like shrub. Physical properties of the experimental fuel bed (Excelsior) [39,40].…”

“…The concept of fire extinction is used by several wildland surface fire models [39]. For instance, Rothermel's model uses the concept of extinction as the limiting case of spread rate [40]: "the fuel moisture at which the fire ceases to spread".…”