Coupling effects of instability mechanisms on the destabilization of hydrogen–oxygen premixed flames near the lean limit

This study investigates the instability of spherically expanding hydrogen–oxygen premixed flames through experiments and theoretical analysis over hydrogen concentrations of 5–14% at 298 K and 1 atm. It is found that mixtures below 6% cannot sustain combustion under 0.2 J ignition. As hydrogen concentration increases, flame propagation accelerates and instability develops at smaller radii. Near the lean limit, buoyancy plays an important role, leading to faster upward propagation and noticeable flame drifting. Moreover, theoretical analysis indicates that flame behavior results from the combined effects of hydrodynamic, thermo-diffusive, and buoyancy mechanisms. While hydrodynamic effects remain destabilizing, thermo-diffusive effects become more pronounced with increasing hydrogen content. Buoyancy tends to stabilize long-wavelength disturbances at low concentrations, but its influence gradually weakens as hydrogen concentration increases.