Micro-ejector to supply fuel-air mixture to a micro-combustor

Micro-ejectors to supply fuel-air mixture to micro-combustors were fabricated and tested. The ejector sucks air using the jet of vaporized liquid gas ejected from a nozzle by its own vapor pressure, and needs no moving part and electric power supply. A tapered nozzle and a Laval nozzle were fabricated by the deep reactive ion etching of silicon. Using the Laval nozzle, which produces supersonic flow, the performance of the ejector becomes high, and the maximum entrainment ratio, which is defined as the volumetric ratio between ejected fuel flow and sucked air flow, reached 36.8. This entrainment ratio is stoichiometrically enough for the complete combustion of butane (>31). At this time, the flow rate of fuel-air mixture was 394 sccm. We investigated several characteristics of the prototyped ejectors. The most important problem that we found is that entrainment ratio considerably drops, when several tens Pa pressure is applied at the exit of the ejector by the pressure loss of a combustor. However, the performance of the ejector will be improved by optimizing the design of the Laval nozzle according to the supplied pressure of fuel.