Effects of Hydrogen Blending Ratio and Equivalence Ratio on the Dynamic Characteristics of Deflagration Shock Waves of CH₄/H₂ Mixtures

To evaluate the explosion hazard of CH₄/H₂ mixtures, experiments were conducted in a long and closed pipeline with a length-to-diameter ratio of 51 and built-in obstacles, and the characteristic parameters of deflagration shock waves were analyzed under different hydrogen blending ratios (0 ≤ λ ≤ 100%) and equivalence ratios (0.5 ≤ Φ ≤ 3). The results indicate that within the range of Φ = 0.8-1.2, the explosion overpressure (P_P) exhibits a “two-zone” structure distribution. When 0 ≤ λ ≤ 80%, P_P shows an initial increase and then a decrease in both regions, while deflagration to detonation transition (DDT) occurs in the second evolution region when λ = 100%, which is caused by the different strengths of the positive feedback mechanism coupled with flames and shock waves. The P_max, (dP/dt)_max, and V_a show a trend of first increasing and then decreasing and monotonically increasing with the increase of the equivalence ratio and hydrogen blending ratio, respectively, and reach their maximum values at Φ = 1.0 and λ = 100%. For CH₄/H₂ mixtures with low hydrogen blending ratios (λ = 0 and 20%), the P_max and (dP/dt)_max in the fuel-lean conditions (Φ = 0.9 and 0.8) are higher than those in the fuel-rich conditions (Φ = 1.1 and 1.2), while the CH₄/H₂ mixtures under high hydrogen blending ratios (λ = 80 and 100%) are the opposite. Overall, the increase in H₂ at a high hydrogen blending ratio and the increase in the equivalence ratio at a fuel-lean condition significantly enhance the average V_a. In addition, chemical kinetics analysis found that R38 and R52 elementary reactions are the dominant elementary reactions that promote and inhibit temperature increase, respectively. Their temperature sensitivity coefficients are negatively correlated with the hydrogen blending ratio and positively correlated with the equivalence ratio. The research results provide vital information for evaluating the explosion hazards of CH₄/H₂ mixtures and developing safety protection measures.