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Local Extinction of Diffusion Flames in Fires

Lecoustre V., Narayanan P., Baum, H.R. and Trouve, A., 2011. Local Extinction of Diffusion Flames in Fires. Fire Safety Science 10: 583-595. 10.3801/IAFSS.FSS.10-583


The objective of the present study is to use large activation energy asymptotic (AEA) theory to bring basic information on the extinction limits of non-premixed flames. The AEA analysis leads to an explicit expression that predicts the occurrence of flame extinction in the form of a critical Damköhler number criterion; the criterion provides a unified framework to explain the different extinction limits that are observed in non-premixed combustion (i.e., aerodynamic quenching, thermal quenching, and dilution quenching). The critical Damköhler number criterion is then formulated in terms of six input variables; these variables characterize the magnitude of flame stretch, the magnitude of the flame heat losses, and the composition and heat content of the fuel and oxidizer supply streams; these input variables thereby contain information on (laminar or turbulent) flow-induced perturbations, deviations from adiabatic combustion, and air and fuel vitiation. Different two-dimensional flammability maps are then presented using different assumptions aimed at reducing the dimension of the parameter space from six to two. While providing a limited view point, these flammability maps provide valuable insights; it is found for instance that diffusion flames are more sensitive to air vitiation than fuel vitiation.

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