Numerical study of the combustion regimes in naturally-vented compartment fires

Numerical simulations are performed to investigate the classical compartment fire problem involving a single door opening. Three different configurations were considered, namely a full-scale (ISO 9705), an intermediate and a small-scale enclosure with various opening heights and widths. A large number of numerical simulations was carried out using the CFD code Fire Dynamics Simulator (FDS)(version 6.7.0). Based on the variation of the average temperature inside the compartment, three combustion regimes were identified namely well-ventilated, transitional and under-ventilated regime. This variation also allowed us to identify the boundaries between regimes. Furthermore, by adopting a non-dimensional representation of the fire heat release rate inside the compartment as a function of the Global Equivalence Ratio (GER), a clear demarcation between these combustion regimes was obtained. A linear correlation has been established between the maximum heat release rate inside the compartment and the ventilation factor. The latter is expressed as <(Q)over dot>(max)(in) = 850 A root H. A linear relation between the maximum air flow rate <(m)over dot>(in) and the ventilation factor A root H was found, i.e. <(m)over dot>(max)(in)= 0.46 A root H where A is the door surface area and H its height.