Effects of Damkoehler number on flame extinction and reignition in turbulent nonpremixed flames using DNS

摘要

Results from a parametric study of flame extinction and reignition with varying Damkohler number using direct numerical simulation are presented. Three planar, nonpremixed ethy-lene jet flames were simulated at a constant Reynolds number of 5,120. 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 Dahmkohler 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 nonpremixed flame undergoing nearly global extinction reignites through premixed flame propagation in a highly stratified mixture.