Dynamics Analysis of Reciprocating Compressor Crankshafts

Abstract

Reciprocating compressors are used in several types of applications, such as gas distribution and refrigeration systems. One of the main causes of failure of these machines are high loads, which leads to large stresses in the crankshaft. In order to study effects of these loads, the dynamic model of a two-stage reciprocating compressor driven by asynchronous and synchronous electric motor was developed. This model is described by a rigid system composed of piston, rod, crosshead, connecting rod and crankshaft. Based on the Newton and Euler equations, the resistive loads acting on the crankshaft are calculated. The mass and the inertia of these components as well as the thermodynamic cycle are parameters for this model. The thermodynamic cycle assumed ideal gas for an isotropic system, a thermal insulation between the gas and cylinder and an instant behavior of the valves. These assumptions are reasonable because the simulated reciprocating compressor operates with compression ratio below two, resulting in the absence of large temperature rates and gradients. Since the resistive forces are cyclic, the torque applied by the drive will also oscillate cyclically, resulting in an oscillation of the angular velocity. The simulation results show that there are great amplitudes of torque due to the high pressure of the compressed gas. In the permanent regime, the loads had a good agreement with experimental data. The study proved to be important in the design and operation of the reciprocating compressor, in order to prevent failure of the crankshaft.