Dimethyl　ether　(DME)　and　methanol　are　thought　to　be　one　of　the　most　promising　alternative　fuels　for　IC　engines.　Meanwhile,　previous　investigations　also　have　pointed　out　the　good　prospects　for　adopting　DME　and　methanol　in　IC　engines.　The　experiments　in　this　paper　were　carried　out　at　idle　condition　to　investigate　the　effect　of　applying　the　methanol/DME　blended　fuel　in　a　SI　engine.　The　engine　was　modified　to　be　fueled　with　the　mixture　of　methanol　and　DME　which　were　injected　into　the　engine　intake　ports　simultaneously.　Various　DME　fractions　were　selected　to　investigate　the　effect　of　DME　addition　on　engine　performance.　The　experimental　results　showed　that　indicated　thermal　efficiency　was　increased　by　25%　and　coefficient　of　cyclic　variation　in　engine　speed　was　decreased　by　29.2%　at　the　DME　energy　fraction　of　85.2%　in　the　total　fuel.　In　addition,　both　flame　development　and　propagation　durations　were　shortened　with　the　increase　of　DME　enrichment　level　at　idle　condition.　Meanwhile,　the　largest　drop　of　HC　emissions　was　nearly　50%　compared　with　the　original　methanol　engine　at　stoichiometric　condition.　However,　CO　and　NOx　emissions　increase　with　the　addition　of　DME.　(C)　2011　Elsevier　Ltd.　All　rights　reserved.