Search

Lubrication of a wrist pin journal can become a limiting factor in the performance of internal combustion engines. A wrist pin journal is a hydrodynamic bearing with a radial clearance of only a few micrometers that is filled with a mixture of oil and air. Moreover, the radial clearance changes periodically with the piston motion and according to the working cycle of the internal combustion engine. Hence, a numerical study of the flow and oil transport inside a wrist pin journal requires an unsteady 3D two-phase model. Furthermore, the numerical model must include gravity and centrifugal forces, the unsteady rotation of the piston pin, and the oil feed on both sides of the piston pin boss. Presently, neither the oil feed surrounding the piston pin boss nor the mechanism transporting the oil into the gap between the piston and piston pin are fully understood. This study presents a numerical approach describing the lubrication inside the wrist pin journal. A particular aspect of the modeling is combining a structured mesh of hexahedron cells for the narrow gap and unstructured meshing in the surrounding geometry due to the difference in length scale of several orders of magnitude. The numerical model has been validated on test cases and experimental oil transport data obtained from a piston model experiment. The numerical results include images of complex 3D structures of oil and air fractions inside the oil film and in the regions surrounding the piston boss. [ABSTRACT FROM AUTHOR]

This work describes a 3D computational fluid dynamic model, which characterizes the hydrodynamic behavior of a mixing strategy applied to egg-shaped reactors that lack a mechanical stirring device. The model is based on Navier-Stokes and material balance equations without a chemical reaction. To describe the behavior of mixing, initial water feed flows of 6, 7.5 and 9 mL s−1were used. An experimental validation was subsequently carried out using a pulse technique, with NaCl as a tracer. The residence time distributions were quantitatively determined. Then, the degradation process of the wastewater sludge was characterized by studying the time dependence of the dynamic viscosity, the concentration of volatile solids and the density of wastewater sludge. The data resulting were introduced into the validated model, and five feed flows from 9 to 13 mL s−1, the best performance found was with feed flow of 11 mL s−1. [ABSTRACT FROM PUBLISHER]