Effects of H₂ blended ratio and N₂/CO₂ dilution fraction on the deflagration shock wave of H₂NG in slender closed pipelines

To reveal the deflagration hazard and propagation law of hydrogen-enriched natural gas (H₂NG) in closed spaces, this paper studied the deflagration characteristic parameters under different H₂ blended ratio (λ) and inert gas dilution fraction (X_dilution) in slender closed pipelines with steel circular hole obstacles. The results indicate that the positive feedback mechanism's sustained effect, failure, and re-action leads to a “three-zone” distribution of H₂NG explosion overpressure along the pipeline, namely the acceleration, attenuation, and rebound zones. The maximum explosion overpressure (P_max), maximum pressure rise rate ((dP/dt)_max), and peak shock wave propagation velocity (V_p) all increase with the increase of λ. The rise of λ has the most significant enhancement effect on (dP/dt) _max, while the enhancement effect on V_p is the smallest. This is because the main reasons affecting their increase are different. P_max, (dP/dt)_max, and V_p exhibit exponential decay with increased N₂ and CO₂. However, CO₂ has a more significant inhibitory effect on the H₂NG deflagration process. When X_CO2 = 25% and X_CO2 = 30%, the deflagration process of H₂NG with λ = 20% and λ = 80% can be inhibited entirely, respectively, which has important guiding significance for the safe application of H₂NG.