Performance Evaluation of an Electromagnetic Free Piston Compressor Without Permanent Magnets

The performance of a linear free piston gas compressor is investigated in this study. Two compressor pistons are mounted on a robust reciprocating cage mover, which is driven by a double-stator linear induction machine. Since the beginning of the 21st century, many permanent-magnet machines were investigated due to their high power density and efficiency. Less attention has been paid to linear induction machines (LIMs) that stand out through the fact that they do not require expensive rare-earth magnets, and moreover, they are insensitive to strong magnetic fields, high temperatures, and harsh working conditions. This enables them to be used with corrosive media, e.g., for a hydrogen compressor. Therefore, a prototype of a potentially more robust electromagnetic free piston gas compressor was built. It is evaluated on two test benches: First, the LIM is tested with a load motor that enables the measurement of the mechanical output power, and second, the free piston gas compressor is tested with ambient air and the discharge pressure and output flow rate are measured. The electrical power consumption, the mechanical output power of the linear motor, and the pneumatic output power of the free piston compressor are determined for various operating conditions. The measurement results are presented and the average cycle efficiencies are calculated. Moreover, the average cycle power losses of the LIM are analyzed.