Effect of hydrogen addition on explosion characteristics of premixed methane/air mixture under different equivalence ratio distributions

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

“…It is worth noting that the H and CH 3 (+M) radicals that maintain the R38 and R52 elementary reactions are mainly provided by CH 4 in the mixed gas. 24 Therefore, for CH 4 /H 2 mixtures with a hydrogen blending ratio of 40%, as the equivalence ratio increases from 0.8 to 1.0 and 1.2, the volume fraction of CH 4 also increases, leading to an increase in the sensitivity coefficient of the R38 and R52 elementary reactions. As shown in Figure 8 b, when the equivalence ratio is 1.0, the sensitivity coefficients of R38 and R52 elementary reactions decrease with the increase of the hydrogen blending ratio from 0 to 20, 40, and 60%.…”

“…This indicates that the deflagration consequences of CH 4 /H 2 mixtures with low hydrogen blending ratios are more severe under fuel-lean conditions, while those with high hydrogen blending ratios are more severe under fuel-rich conditions. The continuous addition of H 2 provides CH 4 /H 2 mixtures with more high-energy free radicals such as H, OH, and O, , so the improvement of the flame combustion rate by H 2 is essentially dominated by the chemical reaction rate. However, the influence of CH 4 on the flame combustion rate is mainly through the thermal effect, as the heat generated during CH 4 combustion is higher than that of H 2 .…”

“…In the R52 elementary reaction, the highly reactive H radical collides with the CH 3 (+M) radical to generate a low reactive CH 4 (+M) radical, significantly suppressing the combustion reaction. It is worth noting that the H and CH 3 (+M) radicals that maintain the R38 and R52 elementary reactions are mainly provided by CH 4 in the mixed gas . Therefore, for CH 4 /H 2 mixtures with a hydrogen blending ratio of 40%, as the equivalence ratio increases from 0.8 to 1.0 and 1.2, the volume fraction of CH 4 also increases, leading to an increase in the sensitivity coefficient of the R38 and R52 elementary reactions.…”

“…The results showed that the sensitivity of CH 4 /H 2 mixtures was improved after adding hydrogen, which is related to the decrease in the explosion time and the increase in the pressure rise rate. Liu et al 24 conducted explosion characteristic experiments on CH 4 /H 2 mixtures with different hydrogen blending ratios in a 1 m pipeline and found that the addition of H 2 can accelerate the evolution of flame structure in the steady-state stage, and the pressure also changes from bimodal distribution to unimodal distribution. Zhang et al 25 simulated the explosion process of CH 4 /H 2 mixtures in urban utility tunnels, showing that with the increase of the proportion of H 2 , a vapor cloud with the same volume leads to higher overpressure, which increases 16% in 10% H 2 and 32% in 20% H 2 , averagely.…”