Study on high specific power micro-Stirling engine

In this paper we describe the new design methods of micro-Stirling engines. By setting the phase angle of two engines at 90 degrees instead of 180 degrees, the engines, which we named TF4 (torque flattening four-cylinder) engines, generate continuous positive and smooth torque, so they do not need a flywheel to supplement negative torque. Although raising the buffer pressure effectively improves the power of the Stirling engines, it is difficult to apply mechanical seals to micro-Stirling engines. Instead of mechanical seals, we suggest the use of magnetic clutches that transmit engine torque without contact. Using magnetic clutches, it is possible to avoid the use of rotary seal parts and decrease friction loss. Based on the proposed methods, we fabricated high specific power miniaturized alpha-type Stirling engines of 0.074 cc swept volume, whose maximum frequency is 317 Hz. We also demonstrate the efficiency of the engines and magnetic clutches.