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 (lambda) and inert gas dilution fraction (Xdilution) 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 (Pmax), maximum pressure rise rate ((dP/dt)max), and peak shock wave propagation velocity (Vp) all increase with the increase of lambda. The rise of lambda has the most significant enhancement effect on (dP/dt) max, while the enhancement effect on Vp is the smallest. This is because the main reasons affecting their increase are different. Pmax, (dP/dt)max, and Vp exhibit exponential decay with increased N2 and CO2. However, CO2 has a more significant inhibitory effect on the H2NG deflagration process. When XCO2 = 25% and XCO2 = 30%, the deflagration process of H2NG with lambda = 20% and lambda = 80% can be inhibited entirely, respectively, which has important guiding significance for the safe application of H2NG.