Hydrogen　enriched　natural　gas　represents　an　important　pathway　for　achieving　low-carbon　and　green　transformation　in　the　domestic　gas　sector.　However,　the　flame　tends　to　become　unstable　when　a　large　proportion　of　hydrogen　is　blended.　To　investigate　the　flame　instability　mechanisms,　a　model　for　the　diffusion　combustion　of　hydrogen-enriched　natural　gas　in　porous　media　has　been　established　based　on　a　simplified　reaction　mechanism.　Model　validation　through　temperature　and　oxygen　mole　fraction　comparisons　demonstrated　maximum　and　average　errors　of　4.1　%　and　1.5　%,　respectively.　These　error　ranges　were　confirmed　to　be　within　acceptable　accuracy　limits,　indicating　that　the　established　numerical　model　effectively　represents　the　actual　combustion　processes.　Additionally,　a　novel　flashback　identification　method　was　proposed　based　on　flashback　classification.　Numerical　analyses　were　conducted　to　investigate　the　mechanisms　of　flashback　occurrence　during　the　combustion　process　of　hydrogen-enriched　natural　gas　under　critical　hydrogen　blending　ratios.　The　results　indicate　that　the　flashback　mode　within　the　burner　is　characterized　as　boundary　layer　flashback.　Consequently,　the　peak　temperature　judgment　method　can　be　effectively　employed　to　detect　the　occurrence　of　flashback　within　the　burner.　When　the　hydrogen　blending　ratio　reaches　40　%,　some　reactions　will　occur　within　the　porous　medium,　leading　to　a　sharp　increase　in　OH　radical　concentrations,　which　ultimately　results　in　flashback　phenomena.　Additionally,　the　transition　in　combustion　modes　can　cause　insufficient　oxygen　replenishment　in　certain　areas,　thereby　causing　a　dramatic　increase　in　CO　production.　This　study　provides　theoretical　guidance　and　technical　support　for　the　application　and　promotion　of　hydrogen　enriched　natural　gas　in　household　gas　appliances.　©　2025