Numerical analysis for irreversible processes in a piston-cylinder system

A numerical analysis for the irreversible process in an adiabatic piston-cylinder system has been conducted. Axisymmetric compressible momentum and energy equations were solved numerically to obtain the state quantities of the system using the laminar flow model. The numerical method is based on the combined Implicit Continuous-fluid Eulerian technique and the Arbitrary-Lagrangian-Eulerian method. The computations were performed for a single compression process and a single expansion process with the piston velocities of ±1 m/s, ±2 m/s, ±4 m/s, ±6 m/s, ±8 m/s and ± 10 m/s and for cyclic compression and expansion processes with sinusoidal velocity variation. It is found that the piston velocity has effects on the state quantities of the piston-cylinder system and it experienced an irreversible process when the piston moved with an infinite velocity. However, the process can be treated as a polytropic process and the polytropic exponent is approximately equal to the adiabatic exponent, n ≈ γ when the piston velocity is less than ±10 m/s. In the cyclic process of 10,000 rpm, the internal energy increases 0.037% of the compression work in each cycle.