Dynamical System Analysis of a Turbulent Premixed Planar Hydrogen Flame in the Corrugated Flamelets Combustion Regime

A direct numerical simulation (DNS) database for hydrogen premixed turbulent flames representative of the corrugated flamelets combustion regime is analysed using the computational singular perturbation (CSP) by incorporating the tangential stretch rate (TSR) approach. It is shown that turbulent flame can be divided roughly into 3 regions: a frozen, explosive, and dissipative state in the direction of the reaction progress. The analysis shows that the flame front can be divided into 2 subregions: a diffusion-dominant zone followed by the kinetically controlled zone. In all cases, the dominant processes (reaction and diffusion) are identified: (i) in the preheat region, reactions H2 + OH → H2O + H and H + O2 (+M) → HO2 (+M) play significant role, (ii) in the flame front region, initially the diffusivity of H and later the chain branching reaction H + O2 → O + OH provide major contributions to the explosive character of the system, (iii) in the downstream region, initially the diffusivities of H and H2 and later reaction H + O2 (+M) → HO2 (+M) contribute the most to the dissipation of the system. At all time steps, the flame front is successfully tracked as the region where the TSR variable turns positive. Finally, the effect of preferential diffusion is highlighted. In particular, the mixture becomes leaner and
richer behind the cusps and the concave parts of the flame fronts, respectively and these features
become more pronounced as turbulence increases.