Abstract:

The lower flammability limits of H₂/CH₄ mixtures over a wide range of H₂ fractions are systematic experimentally studied at various initial temperatures. The effect of initial temperatures on the near?limit flames of H₂/CH₄ mixtures is insightfully discussed. In addition， the estimations of the lower flammability limits of H₂/CH₄ mixtures is also calculated using Le Chatelier rule and Kondo’s correlation. The results show that the lower flammability limits of H₂/CH₄ mixtures decrease with the growth of H₂ fractions under all measured initial temperatures. The greater declines of lower flammability limits are presented at higher initial temperatures. Moreover， the lower flammability limits of H₂/CH₄ mixtures almost linearly decrease with the increase of initial temperatures. Under the higher initial temperatures， the dominant promotion of H+O₂=O+OH on the near-limit flames of H₂/CH₄ mixtures is enhanced by the significant increase of H radicals. The comparison between the experimental data and calculation results shows that Le Chatelier rule presents satisfactory applications on estimating lower flammability limits of H₂/CH₄ mixtures based on the accurate measurements. Kondo’s correlation provides the greater accurate predictions on the linear temperature dependence of the lower flammability limits of mixtures with lower H₂ fractions. However， the considerable distinctions between experimental data and calculation results using Kondo’s correlation at higher H₂ fractions under elevated initial temperatures are attributed to the significant variation of the sensitivity of dominant reactions and the mole fractions of vital radicals.

Key words: lower flammable limit, initial temperature, hydrogen fraction, vital radical, Le Chatelier rule