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 degrees C to 51 degrees 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.