Direct numerical simulation of extinction and reignition in a nonpremixed turbulent ethylene jet flame

Direct numerical simulation of a nonpremixed, turbulent, ethylene jet flame is performed to investigate fundamental mechanisms of extinction and reignition processes. A reduced ethylene mechanism consisting of nineteen transported and ten quasi-steady state species, with 167 reactions was used, along with mixture averaged transport properties. The flow configuration is a temporally-evolving slot jet at a Reynolds number of 5,120. Extreme extinction of the nonpremixed flame occurs, followed by a period of intense turbulent scalar mixing between reactants and quenched products in which less than 2stratified mixture with nonhomogeneous composition and temperature. Various modes of reignition are analyzed-autoignition, edge flame propagation, and premixed flame propagation-by monitoring Takeno's flame index [H. Yamashitia, M. Shimada, and T. Takeno, Proc. Combust. Inst., 26 (1996) 27-34], homogeneous ignition delay times by sampling the mixture prior to reignition, and the turbulent displacement speed of the reaction front. The dominant reignition mechanism is found to be premixed flame propagation commencing from a few high temperature flame kernels which survive near global extinction.