Dimethyl　ether　(DME),　as　a　sustainable　fuel,　could　be　used　as　an　ignition　improver　in　spark　ignition　engines　to　improve　the　performance　under　lean　conditions.　Direct　injection　engines　could　gain　higher　thermal　efficiency　than　the　port　fuel　injection　engines.　To　study　the　effects　of　second　injection　(SOI2)　timing　on　the　engine　combustion　characteristics,　experiments　were　conducted　on　an　engine　with　independent　DME　port　injection　and　gasoline　direct　injection　systems.　Tests　were　performed　at　a　constant　engine　speed　of　1400　rpm　and　manifolds　absolute　pressure　of　60　kPa　under　excess　air　ratios　of　1.2　and　1.3.　The　start　of　injection　during　intake　was　kept　constant　at　300　degrees　CA　BTDC　and　the　SOI2　timing　was　varied　from　90　to　150　degrees　CA　BTDC.　Split　injection　ratio　was　1:1.　Results　showed　that　a　higher　brake　thermal　efficiency　(BM),　lower　cyclic　variation,　HC　and　particle　emissions　were　obtained　for　DME-gasoline　blends　engines.　Moreover,　the　ideal　S012　timing　could　make　the　heat　release　more　concentrated　and　ease　the　cyclic　variation,　which　enhance　BTE　and　reduce　HC,　NOx　and　particle　number　emissions.　In　addition,　when　more　fuel　was　obtained,　the　combustion　temperature　was　increased,　improving　BTE　and　reducing　HC　emissions　under　lean　combustion　conditions.　(C)　2019　Elsevier　Ltd.　All　rights　reserved.