Piston trajectory optimization of a reciprocating compressor

• Published in: International journal of refrigeration Vol. 121; pp. 159 - 167
• Main Authors: Silva, Ernane, Dutra, Thiago
• Format: Journal Article
• Language: English
• Published: Paris Elsevier Ltd 01.01.2021; Elsevier Science Ltd
• Subjects: Compresseur alternatif; Compresseur à piston libre; Compressors; Conservation equations; Efficacité thermodynamique; Free-piston compressor; Fuite; Heat transfer; Leakage; Optimization; Piston rings; Piston trajectory; Pressure ratio; Reciprocating compressor; Reciprocating compressors; Suction; Thermodynamic efficiency; Thermodynamics; Trajectoire du piston; Trajectory optimization; Transfert de chaleur; Volumetric analysis; Volumetric efficiency; Piston trajectory; Leakage; Reciprocating compressor; Trajectoire du piston; Thermodynamic efficiency; Transfert de chaleur; Compresseur alternatif; Fuite; Free-piston compressor; Compresseur à piston libre; Heat transfer; Efficacité thermodynamique
• ISSN: 0140-7007; 1879-2081
• DOI: 10.1016/j.ijrefrig.2020.09.021

•The piston trajectory that maximizes the thermodynamic efficiency is found.•The expansion and the discharge processes are shortened.•Thermodynamic losses due to leakage and heat transfer are reduced.•The volumetric efficiency is increased with respect to a baseline compressor.•The optimized compressor is less affected by the pressure ratio. Energetic efficiency is one of the main drivers in the design of hermetic reciprocating compressors. Although many studies have been conducted on this subject, there is still room for further improvement, mainly by mitigating thermodynamic losses. This study applies a simulation model based on an unsteady lumped formulation of the mass and energy conservation equations to predict the piston trajectory that provides the highest thermodynamic efficiency for a reciprocating compressor, disregarding the constraints associated with the driving mechanism. The optimum piston trajectory (OPT) is described by four constant-speed stages of the piston and brings about shorter times for the expansion, suction and discharge processes, but a longer time for the compression process with respect to a baseline crank-rod compressor. The OPT resulted in the improvement of the thermodynamic efficiency from 88.3% to 92.1%, and the volumetric efficiency from 70.9% to 72.0%, mainly by reductions of the heat transfer and leakage losses. Furthermore, the performance of the optimized compressor was evaluated for other conditions of the operating envelope. It was found that the optimized compressor is more efficient than the baseline for all conditions assessed and is less affected by the pressure ratio.