Autoignition of dimethyl ether in air was studied in a turbulent flow-reactor with optical access, at conditions relevant to micro gas turbine combustors. The ignition process was visualized using OH*-chemiluminescence imaging, showing the formation of multiple autoignition kernels along the central axis of the reactor. Ignition delays in the range of tau = 112-310 ms were measured at temperatures of T = 739-902 K, pressures of P = 0.2-0.4 MPa, equivalence ratios of phi = 0.225-0.675, and initial flow velocities of U-i = 8-46 m/s. The effect of adding nitrogen to the reactants as a diluent was investigated for mole fractions of additional nitrogen ranging from 0 < X-N2 < 0.1. The experimental ignition delays were compared with homogeneous gas-phase chemical kinetic modeling. Comparison between the modeling and experiments showed significant discrepancies, but agreement was improved when heat transfer in the reactor was taken into account in the modeling.