A　numerical　study　on　CH4　and　air　premixed　combustion　inside　a　small　tube　with　a　temperature　gradient　at　the　wall　was　undertaken　to　investigate　the　effects　of　inlet　velocity,　equivalence　ratio　and　combustor　size　on　combustion　characteristics.　The　simulation　results　show　that　the　inlet　velocity　has　a　significant　influence　on　the　reaction　zone,　and　the　flame　front　shifts　downstream　as　the　inlet　velocity　increases.　The　results　also　show　that,　the　inlet　velocity　has　no　obvious　effects　on　the　flame　temperature.　The　highest　flame　temperature　is　obtained　if　the　equivalence　ratio　is　set　to　1.　It　is　disclosed　that　the　combustor　size　strongly　influences　the　combustion　characteristics.　The　smaller　the　combustor　size　is,　the　more　difficult　it　is　to　maintain　the　steady　combustion.　The　smallest　combustor　size　that　the　stable　flame　can　be　sustained　is　determined　mainly　by　the　wall　temperature　of　the　micro-combustor　under　the　given　conditions.　The　higher　the　wall　temperature　is,　the　smaller　the　smallest　combustor　size.　Therefore　increasing　wall　temperature　is　an　effective　way　to　realize　flame　stabilization　for　a　given　combustor　size.　(C)　2010　Elsevier　Ltd.　All　rights　reserved.