Development of a large-entrainment-ratio axisymmetric supersonic ejector for micro butane combustor

A large-entrainment-ratio micro ejector has been developed to supply fuel–air mixture for a micro butane combustor. As a key component of the ejector, an axisymmetric convergent–divergent supersonic nozzle having a throat diameter of 42 µm is fabricated with high-precision electro-discharge machining. Operating conditions and geometric parameters of the ejector are systematically changed, and their effects on volume–flow-rate ratio are investigated in a series of experiments. Experimental data are compared with analytic solutions and CFD results. It is found that the present micro ejector achieves a maximum air-to-butane volume–flow-rate ratio of 43 when the back pressure is 11.6 Pa. It is also found that the present ejector can produce larger volume–flow-rate ratio than the previous MEMS 2D ejector at small back pressure.