The influence of fuel concentration on the explosion dynamics characteristics of hydrogen/air premixed gas in confined spaces

Hydrogen energy, as a zero-carbon energy source, holds broad application prospects in critical defense systems due to its high energy density and zero carbon emissions. To enhance energy utilization efficiency and ensure operational safety, an integrated approach combining experimental and numerical simulations was adopted to systematically examine the effects of hydrogen concentration on explosion dynamics within a confined environment. Experiments were carried out in a cylindrical chamber equipped with high-frequency pressure sensors and a high-speed camera to record transient overpressure and track flame development. Complementing the experimental setup, computational fluid dynamics (CFD) simulations were implemented using a detailed 19-step hydrogen/air chemical reaction mechanism to accurately reproduce the spatiotemporal evolution of flow field velocity during the premixed gas explosion process. Results indicate that the maximum explosion pressure occurred at a hydrogen concentration of 30 vol.%, peaking at 0.62394 MPa. The peak flame area was largest at both 30 vol.% and 45 vol.%, exceeding results at 15 vol.% and 60 vol.% by 14.6% and 6.3%, respectively. The 30 vol.% condition also achieved the peak flame area in the shortest time, at 8.2 ms. Furthermore, geometric constraints at the junction of the cylindrical sidewall and the endwall led to accumulation of unburned hydrogen, causing localized increases in density and pressure and resulting in four clearly discernible high-velocity regions within the flow field. At 9 ms, the flow velocity profile along the centerline exhibited symmetry with a dual-peak structure appearing unilaterally. While the 45 vol.% condition showed an early transient velocity advantage due to intensified local heat release, the 30 vol.% condition demonstrated superior late-stage velocity recovery owing to more stable and sustained combustion near the stoichiometric ratio. These findings underscore the high combustion efficiency and stability achievable near stoichiometric conditions, providing a scientific foundation for the design and optimization of high-efficiency hydrogen combustion systems.