Dimethyl　ether　(DME)/n-butane　mixtures　are　ideal　fuel　for　homogeneous　charge　compression　ignition　(HCCI)　engine.　Fundamental　ignition　delay　data　under　engine-related　conditions　are　essential　to　better　understand　HCCI　combustion　and　to　validate　DME/n-butane　models.　However,　there　is　a　significant　lack　of　ignition　delay　data　of　DME/n-butane　mixtures　under　high-pressure　and　low-temperature　conditions.　Therefore,　ignition　delays　of　DME/n-butane　mixtures　at　equivalence　ratio　of　0.5　were　measured　at　different　DME　blending　ratios　(0,　20,　40,　60,　80　and　100%),　pressures　(12,　16,　24　and　30　bar),　temperatures　(622-929　K)　and　fuel　concentrations　(1.6　and　2.2%)　using　a　rapid　compression　machine　(RCM).　A　numerical　analysis　was　performed　using　the　NUI　Aramco　Mech　2.0,　and　a　good　agreement　to　experimental　data　was　obtained.　The　results　well　indicate　the　two-stage　ignition　and　negative　temperature　coefficient　(NTC)　behavior　of　DME/n-butane　mixtures.　With　DME　addition,　system　reactivity　is　enhanced　and　air-fuel　mixtures　can　be　ignited　at　lower　temperatures.　Meanwhile,　DME　addition　promotes　both　the　first-stage　and　total　ignition,　and　the　total　ignition　delay　as　a　function　of　DME　blending　ratio　decreases　nonlinearly,　especially　at　low　pressures.　In　addition,　the　DME/n-butane　mixtures　ignite　faster　at　higher　fuel　concentration　and　pressure　conditions,　which　is　more　prominent　in　the　NTC　region.　Kinetic　analysis　indicates　that　compared　with　slower　internal　H-atom　isomerization　rate　of　n-butane,　DME　has　a　more　active　chain　branching　path,　which　promotes　the　low-temperature　oxidation　of　n-butane　and　overall　fuel,　thus　faster　development　of　total　radical　pool,　increased　concentration　of　radicals　and　decreased　ignition　delay.　The　addition　of　20%　DME　results　in　a　significant　increase　of　free　radicals　and　heat　release　rate　while　the　DME　chemistry　becomes　the　most　ignition-sensitive　one　in　DME/n-butane　mixtures　when　the　DME　blending　ratio　reaches　60%.