A　Model　2102QB　diesel　engine　was　retrofitted　to　run　fueled　with　dimethyl　ether　(DME,　CH3OCH3)　in　various　EGR　rates　and　to　investigate　EGR　rate　effect　on　unregulated　emissions　characteristics　including　CH3OCH3,　formaldehyde　(HCHO)　and　methyl　formate　(HCOOCH3)　with　gas　chromatography.　Experimental　results　show　that　unburnt　CH3OCH3　emission　is　the　largest　in　amount　in　the　three　pollutants,　max.　concentration　reaches　0.75　g/(kW·h),　and　specific　HCHO　and　HCOOCH3　emissions　are　one　magnitude　lower　than　that　of　CH3OCH3,　max.　concentration　are　of　around　0.091　g/(kW·h)　and　0.061　g/(kW·h)　respectively.　With　engine　speed　increasing,　CH3OCH3　emission　decreases　while　HCHO　exhibits　increase-decrease　variation　trend;　and　with　engine　load　increasing,　CH3OCH3,　HCHO　&　HCOOCH3　emissions　are　all　decrease.　After　introducing　EGR,　CH3OCH3　emission　increases　and　the　increment　decreases　with　engine　load　increasing;　HCHO　emission　still　exhibits　increase-decrease　variation　trend　and　the　variation　is　obvious　while　load　lower　than　40%.　However,　HCOOCH3　emission　exhibits　typical　features　of　low　temperature　oxidation　reaction　products,　i.e.　exhibits　increase-decrease　variation　trend　with　EGR　rate　increasing.　©,　2015,　Chinese　Society　for　Internal　Combustion　Engines.　All　right　reserved.