Dimethyl　ether　(DME)　and　ethanol　are　thought　to　be　alternative　fuels　for　future　internal　combustion　(IC)　engines.　The　experiments　in　this　paper　were　carried　out　at　idle　and　stoichiometric　conditions　to　investigate　the　effect　of　DME　addition　on　the　idle　performance　of　a　spark-ignited　(SI)　ethanol　engine.　The　engine　was　modified　to　be　fueled　with　the　mixture　of　DME　and　ethanol　which　were　injected　into　the　engine　intake　ports　simultaneously.　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　addition　fractions　in　the　total　ethanol-DME　fuel　mixture.　The　experimental　results　demonstrated　that,　the　indicated　thermal　efficiency　was　increased　by　over　20%　after　DME　blending　and　the　flame　development　and　propagation　durations　were　shortened　with　the　increase　of　DME　addition　fraction.　Meanwhile,　HC　emissions　were　obviously　decreased　with　the　increasing　fraction　of　DME　addition,　while　NOx　emissions　were　slightly　increased.　Therefore,　DME　addition　is　a　potentially　applicable　method　to　improve　the　idle　performance　of　SI　ethanol　engines.　(C)　2011　Elsevier　B.V.　All　rights　reserved.