Abstract
Extinction in a turbulent non-premixed flame can lead to a local state or eddy where the fuel, oxidizer and combustion products are mixed together. The process of quenching and re-ignition of these eddies in turbulent non-premixed flames is analyzed. The corresponding critical conditions are first related to the eddy Damköhler number, and then, through the spectrum of the mixed eddy sizes, to the turbulent Karlovitz number of the flow and the properties of the stoichiometric pre-mixture in the eddy. It is shown that the mixed eddies at the reaction length scale are the most reactive, and there is a continuous range of reaction completeness between the overall quenching and re-ignition. Based on the spectrum of eddy sizes in the flow, a local volume fraction of reactive eddies is defined that can be used as a factor in the expression of the reaction rate in turbulent non-premixed combustion models. Representative chemical kinetic properties necessary to implement this approach in fire modeling are introduced. The model predictions are compared with test data on quenching by dilution, blow-off extinction limit, and extinction strain rate as a function of diluent type and concentration.
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