Parametric Analysis of Gas Leakage in the Piston-Cylinder Clearance of Reciprocating Compressors

Gas leakage is one of the main sources of inefficiencies in low-capacity reciprocating compressors, undermining the compressor performance by reducing the mass flow rate and increasing the energy consumption. In reciprocating compressors, leakage in the piston-cylinder clearance is driven by the piston motion and pressure difference between the compression chamber and the internal environment of the shell. This paper reports a parametric numerical analysis of leakage in the piston-cylinder clearance of a low-capacity reciprocating compressor. A simulation model based on the Reynolds equation is applied throughout the compression cycle to assess the effect of the compressor operating conditions, clearance geometry, piston velocity and piston secondary motion on the leakage and compressor performance. A 3D CFD model is also developed to validate the Reynolds leakage model and to evaluate the effect of the piston secondary motion on leakage, assuming the piston is fixed with predetermined eccentricities. The results show that the compressibility effects are very relevant to estimate the gas leakage. The simulations also revealed that leakage is more detrimental to the compressor performance when it is operating in low back-pressure conditions. Additionally, the piston secondary motion can intensify the gas leakage in the piston-cylinder clearance by up to 90%. On the other hand, the piston velocity only plays a minor role in assessing the leakage.