Experimental and molecular dynamics study on the concentration distribution characteristics of methane-hydrogen mixtures under static conditions

The methane-hydrogen mixture is an important clean energy, but whether the two gases stratify remains controversial. This paper explores it via full-scale closed pipeline experiments and molecular dynamics simulations (MD). MD simulations show methane-hydrogen mixture has significant stratification only with a drop of at least 100 km, and weak stratification with a 10-km drop. Lower temperatures boost stratification, but at 250 K, the normalized partial pressure difference is only 24.13 %, and stratification is hard to see above 250 K. Experiments find that even after long standing, stratification in 160-mm pipelines is mild. After 312 days, the concentration deviation is 3.4 % for SF₆–H₂ and 1.68 % for CH₄–H₂, indicating lateral diffusion and turbulent mixing can suppress stratification. Stratification is more obvious in 63-mm pipelines (26.82 % for SF₆–H₂ and 13.44 % for CH₄–H₂). Inclined pipelines reduce stratification more than vertical ones. This study helps understand the stability and safe transport of hydrogen-enriched natural gas in pipelines.