Dynamic Analysis of Gas Lubricated Reciprocating Ringless Pistons—Basic Modeling

Abstract

A mathematical model is developed for analyzing the dynamics of gas lubricated ringless pistons. It takes into account the effects of piston-cylinder geometry, dynamic properties of piston and connecting rod, and operating conditions. A corresponding computer program is described which enables to obtain the piston trajectory and evaluate its stability. Preliminary results are presented for a reference case of a cryocooler which uses a stirling cycle design where helium gas is compressed by a motor driven piston. It is found that the connecting rod inertia plays an important role in stabilizing the piston motion. It is also found that the stability of piston motion strongly depends on the thermohydrodynamic condition of operation. Under isothermal condition the piston can be stable while under adiabatic condition its dynamic equilibrium may be unstable.