CO2　dilution　is　an　effective　strategy　for　combustion　control.　To　understand　the　detailed　dilution　effects　of　CO2　(including　physical　effects　and　chemical　effects)　on　CH4　and　H-2　combustion,　an　open-source　CFD　package　laminarSMOKE　was　utilized　to　simulate　the　transient　one-dimensional　outwardly　spherical　flame　combustion　process　in　a　closed　chamber　under　0-15%　CO2　dilution　mole　fraction　(alpha),　at　293　K,　1　bar,　stoichiometric　ratio.　The　overall　CO2　dilution　effects　decrease　the　unstretched/stretched　flame　propagation　speed,　maximum　combustion　pressure　and　prolong　the　combustion　duration.　In　most　conditions,　physical　effects　play　a　dominant　role　and　chemical　effects　amplify　the　dilution　effects.　Typically,　the　maximum　combustion　pressure　of　CH4-CO2-air　flame　at　alpha　=　15%　reduces　1.15　bar　compared　with　the　undiluted　case,　the　reduction　percentage　caused　by　physical　and　chemical　effects　is　12%　and　1.5%,　respectively.　In　addition,　opposite　overall　effects　of　CO2　dilution　on　Markstein　length　(L-b)　of　CH4　flames　and　H-2　flame　are　performed.　The　physical　effects　of　CO2　dilution　increase　the　L-b　of　CH4　flames　but　decrease　that　of　H-2　flames.　Chemical　effects　are　similar　to　physical　effects　for　CH4　flames,　but　nonmonotonic　behavior　is　performed　for　H-2　flame　due　to　the　combined　effects　of　density　ratio　and　mixture　reactivity　changes.　(C)　2019　Elsevier　Ltd.　All　rights　reserved.