DNS of auto-ignition in turbulent diffusion H₂/air flames

Direct numerical simulation (DNS) is used to study auto-ignition of turbulent diffusion ames. A novel, all-Mach number algorithm developed by Doom et al¹ is used. The chemical mechanism is a nine species, nineteen reaction mechanism for H₂ and Air from Mueller at el.² Simulations of three dimensional turbulent diffusion ames are performed. Isotropic turbulence is superimposed on an unstrained diffusion ame where diluted H₂ at ambient temperature interacts with hot air. Both, unity and non{unity Lewis number are studied. The results are contrasted to the homogeneous mixture problem and laminar diffusion ames. Results show that auto-ignition occurs in fuel lean, low vorticity, high temperature regions with low scalar dissipation around a most reactive mixture fraction, ζMR (Mastorakos et al.³). However, unlike the laminar ame where auto-ignition occurs at ζMR, the turbulent flame auto-ignites over a very broad range of ζ around ζMR, which cannot completely predict the onset of ignition. The simulations also study the effects of three-dimensionality. Past two-dimensional simulations (Mastorakos et al.³) show that when ame fronts collide, extinction occurs. However, our three dimensional results show that when ame fronts collide; they can either increase in intensity, combine without any appreciable change in intensity or extinguish. This behavior is due to the three-dimensionality of the flow.