EQUIVALENCE RATIO GOVERNS THE MULTI-STAGE NONLINEAR EVOLUTION OF PREMIXED HYDROGEN FLAMES

Lean hydrogen–air flames exhibit strong thermodiffusive instabilities due to preferential diffusion effects at low Lewis numbers (Le$<$1). In this work, Direct Numerical Simulations (DNS) are used to investigate the non-linear evolution of premixed flames under lean, stoichiometric and rich conditions. Results reveal a three-stage evolution: an initial flow-induced regime with similar behaviour across mixtures, followed by a transitional stage where differences emerge, and a final regime where lean flames become curvature-dominated, enhancing reactivity in convex regions. In contrast, stoichiometric and rich flames remain primarily governed by strain, leading to smoother and more stable flame structures.