Enhancing safety in hydrogen storage: Understanding the dynamic process in hydrogen-methane mixtures during the pressurized leakage

Using natural gas pipelines for hydrogen-doped transportation represents a cost-effective solution for large-scale and long-distance hydrogen transport. However, concerns have been raised regarding the potential for leakage under high-pressure conditions, which could result in the spontaneous combustion of the leaking hydrogen. It is, therefore, imperative to understand the gas dynamics involved in methane-hydrogen mixtures during high-pressure leaks to ensure the safety of hydrogen storage. In the present work, the release process and the spontaneous ignition of hydrogen/methane mixtures with a hydrogen blending ratio from 0.1 to 1.0 from pressurized storage containers (20 MPa) have been numerically studied upon validated models. The findings indicate that spontaneous ignition occurs in the mixtures with any hydrogen blending ratios under the releasing pressure of 20 MPa, but the methane component is not involved in the initial combustion if the hydrogen blending ratio is less than 0.5. As the hydrogen blending ratio increases, more combustible components are involved in the initial ignition, and the location of the initial ignition turns closer to the leakage port. Meanwhile, as the hydrogen blending ratio rises from 0.1 to 1.0, the shockwave propagation is accelerated with the moment the shockwave first reflects is advanced from 58 to 60 μs to 22–24 μs, and the maximum temperature in the early leakage will exceed 3000 K. Furthermore, a higher hydrogen blending ratio leads to a more rapid pressure rise in the external space (reaching peak pressure at 191 μs for pure hydrogen) and forming a Mach disk structure with higher Mach numbers (around 7). These findings provide critical insights for understanding the combustion behavior of hydrogen/methane mixtures in high-pressure pipelines and offer valuable guidance for developing safety protocols and infrastructure designs.