Multi-scale analysis of the under-ventilated combustion regime for the case of a fire event in a confined and mechanically ventilated compartment

Abstract

This work deals with under-ventilated pool fires in confined and mechanically ventilated enclosures. The objective is to demonstrate the suitability of reduced-scale experiments to investigate under-ventilated combustion regimes in the case of a mechanically ventilated enclosure, by analysing combustion regimes at two different scales. The fire scenario consists in a dodecane liquid pool fire located in a mechanically ventilated room. Reduced-scale experiments concern a 0.031 m2 pool size inside a 1.875 m3 enclosure and large-scale experiments concern a 0.4 m2 pool size inside a 120 m3 enclosure. The varying parameter is the ventilation flow rate, which allows the fire behaviour to be investigated, from free-burning to confined situations. At both scales, results show that the burning rate decreases with the ventilation flow rate and a linear relationship between oxygen concentration and fuel mass loss rate is revealed. Comparison between the well-stirred reactor model and the experimental results shows good agreement for both scales. The work demonstrates the suitability of the reduced-scale approach to reproduce the combustion process in a vitiated environment, provided that appropriate dimensionless parameters are used: a reduced heat-release rate, a thermal ratio parameter and the global equivalence ratio.