## 1 Introduction  
Charring materials (timber and composite materials) are widely used in many civil [1] and aeronautical [2] applications. On the one hand this leads to a sustainable development with lower energy requirements and less pollution, but on the other hand, this may lead to fire hazards. These materials have a flammable nature, and this makes necessary the prediction of a fire potential with the consequent loss of stiffness, strength and resistance of a structure [3]. In the recent few decades, different studies approached the topic and aimed to characterize the performance of charred materials under combustion. Fire retardancy [4], flammability properties [5] and gaseous emissions [6] are just a few examples of the main properties that have been studied. The main strength of this fire community lies in its ability to describe how a fire behaves for a given material, including the description of ignition, fire growing, propagation and extinction processes [7]. Different numerical simulation programs have been developed for such purposes. One of the most successful is fireFoam [8], an opensource code to simulate and visualize the fire behavior in a defined geometry. Different application cases can be found in the literature [9, 10, 11]. In a numerical simulation, modeling the flame is not enough. A description of the charred material degradation process in the absence of oxygen (the pyrolysis), as well as the coupling between material and environment, are fundamental aspects that need to be captured. Pyrolysis leads to the production of a large variety of chemical species: water, methane, propane, carbon monoxide and dioxide, phenol, cresol, hydrogen, etc. The production of these species and their concentration is strongly affected by the imposed conditions [12; 13]. This would not affect only the material, but even the combustion process. The gaseous species, once produced, will percolate in the material and eventually reach the external environment. Many of these species are fuels, therefore the correct prediction of their formation could change the outcome of the simulation. Different pyrolysis models have been developed during the years, each characterized by a different level of accuracy in the description of the chemical reactions. The simplest one is the single reaction mechanism [14] in which only a single decomposition reaction is considered. A next step is done with the multi-component single reaction model [15] where the description becomes sensible to the feed-stock. With an increase in complexity, there is the competitive model [16] that introduces competitive reactions to predict different product distributions depending on the conversion conditions, such as heating rate and pressure. Finally, there are the competitive multi-component models [17; 18] which represent efficiently the dependence on the feed-stock as well as the temperature effect on the yields. Pyrolysis is not the only process to model in charring materials. Mass, momentum and energy of the material need to be conserved, and the transport of gaseous species also need to be taken also into account. A generic combustion problem with a charring material is schematized in Figure 1.  
The problem may be split in two regions: the environment, where combustion happens, and the material, characterized by a thermal degradation process, the pyrolysis. Two different models are required for the numerical resolution. We chose to couple fireFoam with a detailed pyrolysis model. The latter enters in the type-3 models classification proposed by [PERSON] et al., 2011 [19], and it has already been applied to different applications, like ablative heat-shield design and pyrolysis of lignocellulosic biomass [20; 21; 22]. The main objective of this paper is to propose for the first time a numerical framework that couples a detailed three-dimensional pyrolysis model and fireFoam.