Experiments　were　conducted　to　study　the　effects　of　H-2,　overall　equivalence　ratio,　and　airside　oxygen　concentration　on　the　structure　and　reaction　zone　of　an　LPG　circumferential　inverse　diffusion　flame　(CIDF)　with　various　hydrogen　additions.　Planar　laser-induced　fluorescence　(PLIF)　technique　was　used　to　diagnose　distribution　and　concentration　of　hydroxyl　radical　(OH)　inside　the　flame.　The　result　shows　that　hydrogen　addition　can　significantly　improve　combustion　of　the　LPG　IDF.　Although　100%H-2　IDF　contains　double　flame　structure,　LPG-H-2　IDF　seldom　shows　the　structure　even　when　H2　percentage　is　as　high　as　90%.　Under　the　low　air　jet　velocity　and　high　overall　equivalence　ratio　condition,　LPG　IDF　shows　a　large　and　intense　reaction　zone,　which　is　similar　to　that　found　in　a　turbulent　premixed　flame.　Oxygen　enhancement　on　the　oxidizer　side　could　significantly　improve　the　combustion　without　changing　the　overall　equivalence　ratio.　(C)　2016　Hydrogen　Energy　Publications　LLC.　Published　by　Elsevier　Ltd.　All　rights　reserved.