Modelling unconfined hydrogen-air detonation: Influence of equivalence ratio, ignition height, and concentration gradients validated against large-scale experiments

Assessing hydrogen-air detonation hazards is critical for safe hydrogen use across various applications. Past studies have mainly focused on uniform mixtures with limited concentration ranges in unconfined detonations. This study develops a validated numerical model incorporating detailed chemical kinetics, an embedded large eddy simulation approach, and finite-rate chemistry to investigate the effects of hydrogen concentration, ignition location, and concentration distribution on detonation characteristics. The experimental configuration comprised a 5.09 m 3 cylindrical hydrogen-air mixture, two reflected walls, and six pressure sensors. Detonation occurred within 21.5% to 66.6% hydrogen concentration. Central ignition produced 28% higher near-field overpressure than bottom ignition, while far-field measurements showed negligible dependence on ignition height. The highest detonation intensity among uniform mixtures occurred at an equivalence ratio of 1.5. The uniform mixture produced higher detonation intensity than mixtures with steep concentration gradients. The findings provide guidance for infrastructure design and safety assessment against accidental hydrogen detonation events. • ELES with detailed finite-rate chemistry validated for unconfined hydrogen-air detonation. • Detonation limits of 21.5%–66.6% H 2 identified for cylindrical geometry. • Maximum detonation strength observed at equivalence ratio ϕ = 1.5. • Central ignition produces 28% higher near-field overpressure than bottom ignition. • Concentration gradients inhibit detonation strength and introduce blast asymmetry.