Effect of environmental conditions on fire combustion regimes in mechanically-ventilated compartments

Abstract This publication deals with under-ventilated combustion regimes in case of pool fire in a confined- and mechanically-ventilated enclosure. The objective is to improve the understanding of combustion regimes in a ventilated compartment focusing on the effect of fire size and the ventilation rate. It is based on dodecane pool fire tests conducted on a reduced scale (1.875 m3) enclosure and considering two varying parameters, the pool diameter and the ventilation air flow rate prior to ignition. Three combustion regimes were identified: two steady burning regimes with extinction by lack of fuel or oxygen (fuel burnout) and a transient burning regime with extinction by lack of oxygen. A representation of these regimes is proposed with two scaling parameters: the reference global equivalence ratio, ϕo, and the volumetric fire heat release rate. Results demonstrate that increasing ϕo reduces the burning rate in comparison to its value in an open atmosphere. While for a low volumetric fire heat release rate (HRR), the reduction in burning rate is mainly due to oxygen depletion, gas temperature has an additional effect at higher volumetric HRR (about 16 kW/m3). The effect of gas temperature compensates for the effect of oxygen depletion and increases the burning rate. The conditions leading to the highest gas temperature inside the enclosure were obtained in fire scenarios with high volumetric fire HRR and moderate ϕo.