Effects of Damkِhler number on flame extinction and reignition in turbulent non-premixed flames using DNS

Results from a parametric study of flame extinction and reignition with varying Damkِhler number using direct numerical simulation are presented. Three planar, non-premixed ethylene jet flames were simulated at a constant Reynolds number of 5120. The fuel and oxidizer stream compositions were varied to adjust the steady laminar extinction scalar dissipation rate, while maintaining constant flow and geometric conditions. Peak flame extinction varies from approximately 40% to nearly global blowout as the Damkِhler number decreases. The degree of extinction significantly affects the development of the jets and the degree of mixing of fuel, oxidizer, and combustion products prior to reignition. The global characteristics of the flames are presented along with an analysis of the modes of reignition. It is found that the initially non-premixed flame undergoing nearly global extinction reignites through premixed flame propagation in a highly stratified mixture. A progress variable is defined and a budget of key terms in its transport equation is presented.