In　this　study,　three　typical　tube　bundle　structures　with　1.5　m　in　length　are　adopted　to　investigate　the　effect　of　different　geometries　on　the　detonation　propagation　behaviors　in　hydrogen-air　mixtures　with　six　different　equivalence　ratios　(Φ　=　0.65,　0.8,　1.0,　1.25,　1.5,　2.0).　The　tube　bundle　section　is　created　by　inserting　several　smaller　diameter　pipes　(d　=　20　mm)　into　a　big　tube　with　6.0　m　long　and　an　inner　diameter　of　90　mm.　Various　tube　bundle　structures　can　be　obtained　by　varying　the　number　of　small　pipes.　The　results　obtained　from　a　smooth　tube　are　also　given　for　comparison.　Four　piezoelectric　pressure　transducers　(PCB102B06)　are　employed　to　record　the　time-of-arrival　of　the　detonation　wave,　from　which　the　averaged　velocity　can　be　obtained.　Smoked　foil　technique　is　also　used　to　register　the　detonation　cellular　structure　in　the　smooth　tube.　The　experimental　results　indicate　that,　in　the　smooth　tube,　the　detonation　can　sustain　a　steady　velocity　when　the　P0　is　greater　than　Pc,　in　which　P0　and　Pc　represent　the　initial　pressure　and　the　critical　pressure.　Near　the　critical　pressure,　the　velocity　deficit　increases　sharply.　Below　the　critical　pressure,　no　stable　velocity　and　cellular　pattern　can　be　obtained.　In　the　tube　bundle　section,　the　critical　pressure　and　velocity　deficit　are　elevated　obviously.　Near　the　critical　condition,　the　velocity　deficit　is　about　30%　of　the　CJ　values.　Below　the　critical　pressure,　the　decoupled　flame　still　can　sustain　a　steady　velocity　at　about　0.5VCJ　where　VCJ　is　the　theoretical　CJ　detonation　velocity.　Finally,　the　critical　condition　analysis　of　the　detonation　propagation　are　conducted.　The　critical　conditions　can　be　quantified　as　DH/λ　＞　1,　where　DH　is　the　hydraulic　diameter　and　λ　is　the　experimental　measured　detonation　cell　size.　©　2018