Effect of environmental conditions on fire combustion régimes in mechanically ventilated compartments

International audienceThis publication deals with under-ventilated combustion regimes in case of pool fire in aconfined- and mechanically-ventilated enclosure. The objective is to improve the understanding ofcombustion regimes in a ventilated compartment focusing on the effect of fire size and theventilation 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 flowrate prior to ignition. Three combustion regimes were identified: two steady burning regimes withextinction by lack of fuel or oxygen (fuel burnout) and a transient burning regime with extinctionby lack of oxygen. A representation ofthese regimes is proposed with two scaling parameters: thereference global equivalence ratio, ^o, and the volumetric fire heat release rate. Results demonstratethat increasing ^o reduces the burning rate in comparison to its value in an open atmosphere. Whilefor a low volumetric fire heat release rate (HRR), the reduction in burning rate is mainly due tooxygen depletion, gas temperature has an additional effect at higher volumetric HRR (about16 kW/m3). The effect of gas temperature compensates for the effect of oxygen depletion andincreases the burning rate. The conditions leading to the highest gas temperature inside theenclosure were obtained in fire scenarios with high volumetric fire HRR and moderate ^o