Micro internal combustion swing engine (MICSE) for portable power generation systems

Recent progress is summarized in development of a palm-sized portable power generation system based on the micro internal combustion swing engine (MICSE). A swing engine is a rotationally oscillating free-piston engine in which combustion occurs in four chambers separated by a single rotating swing-arm, with virtually no other moving parts. The swing-arm creates four distinct combustion chambers in a single base structure; the resulting efficient use of both chamber space and system mass permits lower weight and smaller size at the same power than linear free-piston engines. The rotating swing-arm also produces less vibration than a linearly translating piston. The swing engine is unique among internal combustion systems in that it does not have any "dead point" in its operating cycle, and thus does not require an external starter. Mechanical-to-electrical power conversion is via a shaft-coupled inductive alternator outside the combustion chamber. The oscillating swing arrangement maintains a constant optimal separation between the magnets and inductive coil to provide more efficient coupling of mechanical power to electrical power. The swing motion produces excellent load-following characteristics; the system fully adjusts to large step changes in power demand in less than four swing cycles (0.05 sec). Load changes affect the swing angle more than the swing frequency, permitting system components to operate over a narrow range of frequencies for additional weight savings and increased reliability. Engine control requires only simple four-state bit logic based on threshold values of angular velocity obtained from the alternator output, and can be implemented without any mechanical linkage. Since timing is based on the swing-arm position, the system automatically adjusts to changes in external load, ambient temperature, and equivalence ratio. The engine currently under development is sized for 20W average electrical power output on butane fuel.