Dynamic Analysis of Piston Secondary Motion for Small Reciprocating Compressors

Abstract

Piston dynamics plays a fundamental role in two critical processes related to fluid flow in reciprocating compressors. The first is the gas leakage through the radial clearance, which may cause considerable loss in the pumping efficiency of the compressor. The second process is the viscous friction associated with the lubricant film in the radial clearance. In the present contribution a numerical simulation is performed for a ringless piston inside the cylinder of a reciprocating compressor, including both the axial and the radial piston motion. The compressor considered here is a small hermetic compressor employed in domestic refrigerators, with the radial clearance between piston and cylinder filled with lubricant oil. In operation, the piston moves up and down along the axis of the cylinder, but the radial oscillatory motion in the cylinder bore, despite being usually small, plays a very important role on the compressor performance and reliability. The compromise between oil leakage through the piston-cylinder clearance and the friction losses requires a detailed analysis of the oscillatory motion for a good design. All corresponding forces and moments are included in the problem formulation of the piston dynamics in order to determine the piston trajectory, velocity and acceleration at each time step. The hydrodynamic force is obtained from the integration of the pressure distribution on the piston skirt, which, in turn, is determined from a finite volume solution of the time dependent equation that governs the oil flow. A Newton-Raphson procedure was employed in solving the equations of the piston dynamics. The results explored the effects of some design parameters and operating conditions on the stability of the piston, the oil leakage, and friction losses. Emphasis was placed on investigating the influence of the pin location, radial clearance and oil viscosity on the piston dynamics. [S0742-4787(11)00301-8]

A new and efficient mechanism for spark ignition engines

“…Scientists have been also made great efforts on reducing sound pollution resulting from piston dis-alignment in cylinder, which originates from asymmetry of crank and slider mechanism [25][26][27][28][29][30]. Researches have also come to focus on very complicated mechanisms that diminish vibrations and internal friction in these facilities.…”

Role of the Thermodynamics, Heat Transfer, and Fluid Mechanics of Lubricant Oil in Hermetic Reciprocating Compressors

“…The axial and radial bearings are usually designed considering the load-carrying capacity together with the well-established methodology based on the solution of the lubrication equation [59,60]. Piston analysis solutions have also been reported for the secondary piston motion [61][62][63][64][65]. However, very few studies have considered that the bearings are interconnected and that the system dynamics should be considered incorporating the bearing performances operating together [64].…”

“…To perform a numerical solution for an entire cycle of the crankshaft system encompassing both suction and discharge strokes, the computation starts at a given crankshaft angle (zero, for example) with all eccentricity ratios between journal and bearings equal to zero and proceeds advancing in time until a periodic regime is established. For radial bearings a periodic regime is usually reached after two to three cycles, whereas for the piston between 20 and 30 cycles are required for the periodic regime to be reached [58,62,64].…”

Modeling for Design Optimization of Piston Crown Geometry Through Structural Strength and Lubrication Performance Correlation Analysis

“…Rest of this fuel energy is wasted either because of friction or emission or pumping loss (Smedley, 2004). Because of many connecting and contacting action within engine, parasitic loss due to friction is significant (Dursunkaya et al, 1994;Prata et al, 2000). Along with the friction forces due to ring-liner, skirt-liner, ring-ring groove land contact, the combustion gas force, inertia force, secondary dynamic forces of piston and pin, connecting rod force acts on the reciprocating piston subsystem of a running engine (Akalin and Newaz, 2001a;Mishra et al, 2008;Chong et al, 2012;Shahmohamadi et al, 2013).…”