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An analytical method is presented in this paper for simulating piston secondary dynamics and piston-bore contact for an asymmetric half piston model including elastohydrodynamic (EHD) lubrication at the bore-skirt interface. A piston EHD analysis is used based on a finite-difference formulation. The oil film is discretized using a two-dimensional mesh. For improved computational efficiency without loss of accuracy, the Reynolds’ equation is solved using a perturbation approach which utilizes an “influence zone” concept, and a successive over-relaxation solver. The analysis includes several important physical attributes such as bore distortion effects due to mechanical and thermal deformation, inertia loading and piston barrelity and ovality. A Newmark-Beta time integration scheme combined with a Newton-Raphson linearization, calculates the piston secondary motion.

The side-load capacity of an unlubricated ringless piston assembly was calculated for a four-stroke I.C. engine for possible application to a Low-Heat-Rejection engine. A compressible flow analysis for an ideal gas was used to calculate the flow at the piston-cylinder interface. The analysis accounts for the gas inertia effect and possible choked flow. The piston side-load capacity is compared with the actual side thrust on the piston, generated through the combination of piston inertia, cylinder pressure, and connecting rod angularity. It was found that a carefully designed ringless piston can support the side load of a slider-crank mechanism during the power stroke of a four-stroke engine. However, during the remaining strokes, the load can be supported only partially.

A theoretical analysis is presented for calculating the trajectory of a ringless piston within the cylinder clearance of an I.C. engine with a crosshead design. The flexible polytope unconstrained minimization method is used to find the equilibrium between the piston rod structural elasticity and the gas-film hydrodynamics at the piston-cylinder interface. It was found that even when the crosshead bearing is not concentric with the cylinder (i.e., there is an initial eccentricity between the piston and cylinder centerlines), the piston does not touch the cylinder wall during an engine cycle. However, this happens only when a carefully designed piston skirt profile and piston rod length and diameter are used.