Structural Design and Porting Parameters Calculation of a Micro Piston Engine for Power Generation

In this paper, a new type micro piston internal combustion engine is reported. The micro engine can be used to provide mechanical energy for micro electric power generation system. It is consisted of three or four planar plate structure. This micro engine has special advantages in structure which are more suitable to minimize whole engine to MEMS dimensions than traditional engines. Compared with traditional or other existing micro piston engines, there is a sliding chute and crank mechanism rather than a crank and connecting rod mechanism to improve the space utilization ratio. The crank is fixed on the plate next to the main body plate of the engine. A free piston micro engine without the crank and connecting rod mechanism is given too. Scheme of structure, operation and characters of the micro engine are described in detail. The displacement, velocity and acceleration functions of piston are deduced to understand the rules of piston motion. Calculating formulas of porting parameters are deduced too. Finally, an example of the micro engine with specific design parameters is given. Mathematic modeling of the porting parameters is built. The calculation results show that the phase angles of the inlet, scavenging port and the exhaust port of the example engine are respectively of 21.78°, 156.27° and 158.39° under following conditions. Compression ratio is 5; working volume is 5mm³; length of stroke is 2mm; the sectional dimension of the piston is 2mm×1mm; and the value of revolution is 9000RPM. When the width of gas ports are all 1mm, the heights of inlet, scavenging port and exhaust port corresponding to the port phase angles above are respectively 72μm, 85μm, and 70μm. According to the assembly testing on computer, it is shown that the micro piston engine presented here is workable, controllable and suitable for MEMS fabrication in structure. It can be used as device to provide mechanical energy for micro electric power generation system.