Ignition　delays　of　lean　dimethyl　ether　(DME)/hydrogen　mixtures　with　hydrogen　mole　fraction　ranging　from　0　to　85%　were　measured　using　a　rapid　compression　machine　with　equivalence　ratios　from　0.3　to　0.5,　temperatures　from　621　to　852　K　and　pressures　from　7　to　22　bar.　Numerical　analysis　was　performed　based　on　the　NUI　Aramco　Mech　2.0　and,　in　general,　good　agreement　between　measurements　and　predictions　was　demonstrated.　Both　measurements　and　predictions　show　that　H-2　addition　increases　the　ignition　delay　of　DME/H-2　mixtures　nonlinearly.　Moreover,　the　effect　of　H-2　addition　on　ignition　delay　becomes　more　pronounced　at　H-2　mole　fraction　above　70%　and　lower　pressure.　The　dilution　and　chemical　effects　of　H-2　addition　were　quantified,　and　the　dilution　effect　decreases　whereas　the　chemical　effect　increases　with　the　increase　of　H-2　mole　fraction.　It　is　also　found　that　DME/H-2　mixtures　show　a　three-stage　heat　release　behavior　at　very　lean　condition　(phi　=　0.3),　namely,　a　low　temperature　heat　release　(LTHR)　stage　followed　by　two　high　temperature　heat　release　(HTHR)　stages.　The　first-　and　second-stage　HTHR　are　caused　by　the　conversion　of　HCHO　to　CO　and　the　production　of　final　reaction　products　CO2　and　H2O　respectively.　Overall,　DME　is　mainly　consumed　during　the　LTHR　and　first-stage　HTHR　whereas　H-2　is　mainly　consumed　during　the　second-stage　HTHR.　The　two-stage　HTHR　behavior　of　DME/H-2　mixtures　occurs　when　H-2　and　HCHO　produced　during　DME＇s　LTHR　stage　are　present　in　a　proper　proportion　prior　to　high-temperature　ignition　and　the　temperature　after　LTHR　has　reached　a　proper　level.