Dimethyl　ether　(DME)　is　thought　to　be　one　of　the　most　favorable　alternative　fuels　or　additives　for　internal　combustion　(IC)　engines　in　the　future.　Because　spark-ignited　(SI)　ethanol　engines　have　the　poor　performance　at　cold　start　and　low　operating　conditions　caused　by　negative　properties　of　ethanol　such　as　the　high　latent　heat,　DME　is　introduced　aiming　at　improving　the　engine　economical　and　emissions　performance.　The　experiments　were　carried　out　on　a　modified　4-cylinder　gasoline　engine　under　a　typical　city　driving　speed　of　1400　rpm　and　an　intake　manifold　absolute　pressure　(MAP)　of　61.5　kPa.　In　this　paper,　the　effect　of　DME　blending　on　the　engine　performance　at　different　excess　air　ratios　and　two　DME　volume　fractions　of　1%　and　2%　was　experimentally　investigated.　The　engine　manifold　was　modified　so　that　ethanol　and　DME　can　be　injected　and　mixed　with　air　simultaneously　in　the　intake　ports.　A　hybrid　electronic　control　unit　(HECU)　was　specially　developed　to　control　the　injection　timings　and　durations　of　ethanol　and　DME,　accomplishing　specified　excess　air　ratios　and　DME　volume　fractions　in　the　intake.　The　experimental　results　indicated　that,　DME　addition　benefits　enhancing　the　indicated　thermal　efficiency,　which　is　increased　by　about　10%　at)　lambda　=　1.25　compared　with　the　original　ethanol　engine.　And　the　maximum　reduction　of　COVimep　is　about　50%　after　DME　addition.　Besides,　the　HC　emissions　from　the　DME-enriched　ethanol　engine　at　the　DME　volume　fraction　of　2%　are　averagely　reduced　by　45%　compared　with　those　from　the　original　ethanol　engine.　But　the　NOx　emissions　slightly　increase　with　the　increase　of　DME　volume　fraction　in　the　intake.　Consequently,　DME　addition　can　be　considered　as　a　potentially　applicable　approach　for　improving　the　overall　performance　of　SI　ethanol　engines.　(C)　2012　Elsevier　Ltd.　All　rights　reserved.