Assessment and Optimization of hydrogen Injection Conformance in Natural Gas Pipeline Systems for Enhanced Energy Transition

Abstract The integration of hydrogen into natural gas pipelines is a promising pathway toward decarbonizing existing energy infrastructure, but achieving uniform mixing and conformance remains a critical challenge for safety, efficiency, and end-user performance. This study presents a comprehensive computational fluid dynamics (CFD) analysis of hydrogen injection and dispersion in a natural gas transmission pipeline using ANSYS Fluent. A main pipeline (25 m length, 1 m diameter) with a T-junction hydrogen injection (0.2 m diameter, 3 m length) was modelled under operating conditions of 0.3 MPa and 300 K. Methane flowed at 1.0 m/s, while hydrogen was injected at varying inlet velocities corresponding to volume fractions of 2%, 5%, 10%, 15%, 20%, 30%, 40%, and 60%. The simulations employed a realizable k-ε turbulence model, species transport, and the energy equation to capture flow dynamics and hydrogen–methane mixing. Mesh dependency analysis was performed across coarse (0.5 m), medium (0.1 m), and fine (0.02 m) grids to ensure numerical reliability. Mixing efficiency was evaluated using the coefficient of variation (COV) of hydrogen mass fraction along the pipeline. Results reveal that hydrogen mixing improves progressively downstream, with COV reductions exceeding 70% within 20 diameters of the injection point. At lower fractions (≤20%), conformance was achieved more rapidly, while higher fractions (≥40%) exhibited persistent inhomogeneities and delayed stabilization. Mesh independence was confirmed, with the fine mesh deviating by less than 3% from the medium mesh. This study provides novel quantitative insights into hydrogen–natural gas conformance across a wide blending range, offering a robust framework to optimize injection strategies for safer pipeline integration and advancing the energy transition.