Direct Numerical Simulation Study of an Experimental Lifted H2/N2 Flame. Part 2: Flame Stabilization

The stabilization of an experimental lifted turbulent flame is studied using direct numerical simulation. An eighth-order central spatial difference scheme and a fourth-order explicit Runge-Kutta time integration method are employed to solve the fully compressible N-S equations. A 9-species and 19-step mechanism for hydrogen/air combustion is used. The interactions between the flame islands and large eddies are examined. Two modes of the interactions are identified. On the one hand, large eddies may exert extensive strains and high dissipation rates on the flame, resulting in local extinction. On the other hand, large eddies may modify the flow field to connect the flame islands with the flame base. The flame base and ignition kernels are found on the lean-fuel side and in locations with low scalar dissipation rate. A new coordinate conditioned on the stabilization point is adopted to perform averaging. The averaged quantities obtained under the new coordinate reflect the characteristics in the vicinity of the flame base. Finally, statistics of the stabilization point are analyzed in terms of time evolution and probability density function. It is speculated that the flame is stabilized by a competition of autoignition and large-scale structures.