Design and Test of Small-Scale Rotary Engine Power System

Abstract

In order to develop a portable, autonomous power generation system with a magnitude improvement in energy density over alkaline or lithium-ion batteries, the liquid hydrocarbons fueled small-scale rotary (Wankel-type) internal combustion engines project is directed toward the development of a practical small-scale power generator. Micro combustion and seal are two of the most prominent questions of the design of small-scale rotary engine. As a result, the mathematical model of the micro combustion is proposed and some simulations are implemented. In addition, a combustion experiment is made in a micro combustion vessel to confirm the lower limit of the combustor size and quench distance. Based on an epitrochoidal-shaped housing the small-scale rotary engine is designed. For its planar construction, the rotary engine is available to the MEMS manufacturing techniques such as DRIE, LIGA, DEM, EDM, and is also suitable for micromation. While in the experiment, it is founded that with the housing of the engine with epitrochoidal-shape expanding, the engine couldn’t work steadily. Thus the analysis and simulation of heat transfer and thermal-stress are made to modify the contour of the epitrochoidal-shaped housing. Besides, the single-rotor construction, oil film face seals, and springs apex seals are adopted in the design. A series of small-scale rotary engines (including M2.4, M1.5 and M0.75 rotary engine) have been designed and fabricated from steel by using electro discharge machining (EDM). Test platforms for small-scale rotary engines have been developed and experiments have been conducted respectively, in which liquid hydrocarbons fueled small-scale rotary engines and high-pressure air driven small scale rotary engines to examine the effects of sealing, ignition, design, and thermal management on efficiency. The preliminary test of the M2.4 rotary engine (compressed chambers is 166 mm3, swept displacements is 2600 mm3) fueled by liquid hydrocarbons has shown steady 150 W net power output at 15000 RPM. The preliminary test of the M0.75 rotary engine (compressed chambers is 9 mm3, swept displacements is 143 mm3) can output 1.5W net power at 14000 RPM with high-pressure-air driven. Testing of the small-scale rotary engine has verified the feasibility of the micro-engine. However, heat loss and sealing issues are the key points for efficient operation of the micro-engine, and they must be taken into account in its design and fabrication to improve the design of sealing and micro combustion chamber.