An assessment of the aerodynamic, thermodynamic, and manufacturing issues for the design, development, and microfabrication of a demonstration micro engine

Abstract

Silicon microfabrication is an established technology for the manufacture of integrated circuits and microelectromechanical systems (MEMS) devices such as pressure transducers and accelerometers. Recent advances in silicon microfabrication technology allow the possibility of designing high-precision mechanical devices for power conversion. Micro gas turbine engines (microengines) are one particular application of this technology. These tiny jet engines have immediate application as propulsion systems for Micro UAVs Other envisioned applications include portable electrical power generation for commercial, consumer, and military uses A microengine-based power or propulsion system could offer more than 10x the performance of a battery of the same weight. This would make it an enabling technology for longduration portable computers, high-power mobile phones, and other portable power applications. This thesis describes an assessment of the aerodynamic, thermodynamic, and manufacturing issues associated with the design, development, and microfabrication of an all-silicon demonstration microengine. The design goal is the simplest feasible engine that can demonstrate the micro gas turbine engine concept. This demo microengine integrates high-speed, low Reynold's number turbomachinery, high-speed micro gas bearings, a compact hydrogen combustor, and an innovative turbine cooling scheme into a quartersized turbojet engine with a target thrust of 10 grams. Due to the scale of the device and the nature of the microfabrication process, the engine components are tightly coupled and the design involved a number of system trades not normally encountered in conventional engines. This thesis addresses several of these key design trades and identifies thermo-structural design and manufacturing constraints as the two principal limitations on current microengine design. The thesis also discusses the fabrication development effort and results culminating in a micro turbocharger that has been tested to speeds of up to 30,000 RPM. Rotor imbalance was identified as the probable limit on current operation. Recommendations for future work include development of advanced turbine cooling schemes to improve device efficiency and development improved fabrication capabilities to reduce rotor imbalance.