Extended EDC local extinction model accounting finite-rate chemistry for MILD combustion

Abstract

An extended Eddy Dissipation Concept (EDC) local extinction model is proposed to take into account the effects of finite-rate chemistry, normally occurring in Moderate to Intense Low oxygen Dilution (MILD) combustion, on the extinction limits. Local extinction is predicted when the local fine structure residence time is below a local critical value that is determined theoretically in the present study. The proposed model has been evaluated against experimental data reported for CH4/H2 jet-in-hot and diluted coflow flames. Comparison with the standard EDC extinction model is also presented. Results show that prediction of extinction threshold in MILD combustion conditions is attainable only through the application of the extended EDC extinction model on a well-resolved turbulence–chemistry interaction field. The effect of penetrating surrounding air into the reaction zone with subsequent flame cooling at downstream is also captured by the proposed extinction model. Despite its simplicity, the extended EDC extinction model is able to describe many features of localized extinction under MILD combustion as well as conventional combustion conditions.