This work describes the development of both miniature-scale and micro-scale rotary internal combustion engines. This work is part of a project to develop a portable, high specific energy, liquid hydrocarbon-fueled power supply. A Wankel-type rotary engine was chosen for development because of its self-valving operation, planar geometry, and the ability to extract either mechanical or electrical power. To investigate engine behavior and design issues, larger-scale "mini-rotary'' engines have been fabricated from 4 steel. Mini-rotary engine chambers are approximately 1000 mm3 to 1 700 mm3 in size and their displacements range from 78 mm3 to 348 mm3. The smallest commercially available rotary engine is a 5000 mm3 displacement engine used for remote controlled airplanes.
An engine tea bench for the mini-rotary engine was developed and experiments conducted with Hz-air fueled mini-rotary engines to examine the effects of sealing, ignition, design, and thermal management. As part of the engine test stand development, the smallest dynamometer found in the literature was developed. Testing of the 348 mm3 displacement mini-rotary engine resulted in 3.7 W of net power output at 9,300 RPM. The success of the mini-engine shows that there are no fundamental phenomena that would prevent the operation of the micro-engine. However, heat loss and sealing are key issues for the efficient operation of the micro-engine, and they must be taken into account in the design and fabrication of the micro-rotary engine.
Fabrication of a "micro-rotary" engine began after the validation of the mini-engine. The first generation micro-rotary engine has an engine chamber total volume of approximately 1 rnm3 and a displacement of 0.06 mm3. The micro-rotary engine was fabricated at the UC Berkeley Microfabrication Laboratory using a Si deep reactive ion etching process. High precision, high aspect ratio structures are necessary to provide adequate sealing for high compression ratios. Novel design and fabrication processes were developed and analyzed as part of the fabrication process. Effects such as footing and lateral to vertical etch rates were minimized for proper engine operation. Analysis of the fabricated housing, rotor, and shaft have indicated that the micro-rotary engine can be fabricated using MEMS techniques to the required tolerance.