Characteristic analysis and energy efficiency of an oil-free dual-piston linear compressor for household refrigeration with various conditions

The presence of piston offset in a linear compressor reduce the volume efficiency and motor efficiency. To counteract the piston offset, the dual-piston linear compressor prototype is proposed and developed. A mathematical model has been built to analyze the piston offset characteristics of the dual-piston linear compressor. And a real-time test bench is established to verify the piston offset characteristics and evaluate the compressor efficiency and refrigeration performance. Meanwhile, the dynamic behavior of the dual-piston linear compressor is also discussed. The results suggests that the dual-piston linear compressor can effectively reduce the datum position drift of piston because the integral average value of gas force in a cycle is close to zero. The maximum piston offset is only 4.1% of stroke. The current and displacement curves of dual-piston linear compressor (8.65%) have a relative low distortion compared with the single piston structure (73.69%), due to close to the sine curve of gas force acting on the piston for the dual-piston compressor, which can contribute to the elevation of motor efficiency. For the same pressure ratio (2–4), the compressor efficiency with the different condensing pressure cases is almost in agreement with the different evaporating pressure cases when the working temperature range is from −3.9 °C to 51 °C, which shows that when the linear compressor operates in resonance, the compressor efficiency can almost identical under the same pressure ratio. The relative Carnot efficiency ranges from 47.5% to 58.7%, which is almost 11% higher than that of linear compressor in the literature (40.3%). And it verified that the dual-piston structure can effectively improve the linear compressor.