Research on the influence of key structural parameters on piston secondary motion

Piston secondary motion not only influences the side knocking of piston and frictional loss, but also influence the in-cylinder oil consumption and gas blow-by. An inline four-cylinder common rail diesel engine was chosen as the research object. Dynamic simulation model of piston assembly was built based on the piston and cylinder liner temperature field test. The impacts of pinhole offset, liner clearance and piston skirt ovality on piston secondary motion were researched. Based on the surface response method, the influence of multiple factors on friction power loss and slapping energy is estimated. The results indicate that: in-cylinder stress condition of piston will change with its structural parameters, then the secondary motion of piston will be affected as a result. Pinhole offset, liner clearance, piston skirt ovality and the interaction of the latter two all have significant effects on the friction power loss, while the slapping energy is significantly affected by liner clearance. Therefore, the parameters can be designed based on the significance level to optimize the secondary motion characteristics of the piston.

Generation of Surfaces with Isotropic and Anisotropic Wetting Properties by Curved Water Jet Guided Laser Micro-Machining

This experimental work utilizes a newly developed method, curved water jet guided laser micro-machining, to generate micro features on metallic surfaces. During the process, material is removed by a high-power nanosecond laser beam which is transmitted through a high-pressure micro water jet via total internal reflection. To achieve intricate texturing patterns, a secondary motion component is superimposed on the XY motion of the workpiece provided by the motion stage. The secondary motion is generated by deflecting the water jet trajectory by a controllable dielectrophoretic force. The induced secondary motion of the water jet cuts the processing time to one half when generating texture patterns for isotropic wetting as compared to processes with only XY motion. The ability to alter the water jet's trajectory by tens of microns at high frequencies, which is beyond the capability of conventional CNC machines, allows a wide range of different micro patterns to be generated, profoundly increasing the flexibility and efficiency of the process as compared to conventional approaches. As a demonstration, surface textures for isotropic and anisotropic behaviors are generated on stainless steel surfaces. The influence of feature spacing, motion speed (frequency) and texturing patterns on surface wettability are studied.

Numerical study on thoracic aortic aneurysms : the aneurysms aggravation effects on the seconda rythme flows motion

It is Well know that there is a strong correlation between artery wall diseases and the flow structure disturbance. Aneurysms are enlargements situated at different but specifics parts of the vascular system; it is a silent diseas that evolves in time. The thoracic aortic aneurysms (T. A. A) remains relatively unstudied and therefore the present study aimis is to clarify the effects of the (T . A. A) evolution and the geometrical variations on both hydrodynamic instabilities inside the aortic bulge especially the vortex ring phenomenon and the secondary motion (Dean and lyne vortices) downsream the aneurysms. Two different cases of asymmetric enlargements in the ascending part of the aortic are studied for both newtonien and the shear-thinning model to mimic the blood rheology inside the aneurysms bulge in order to investigate both parameters impact on the vortex ring behavior. Results schowed that the blood rheoligy effects the propagation velocity while the aneurysms size influences the vortex ring rupture, the motion of the ring interaction with an inclined wall phenomenon. Results also showed that vortex ring disturbs the boundary layer and therefore the secondary motion in the rest of the aorta.

Generation of Surfaces With Isotropic and Anisotropic Wetting Properties by Curved Water Jet Guided Laser Micro-Machining

This experimental work utilizes a newly developed method, curved water jet guided laser micro-machining, to generate micro features on metallic surfaces. During the process, material is removed by a high-power nanosecond laser beam which is transmitted through a high-pressure micro water jet via total internal reflection. To achieve intricate texturing patterns, a secondary motion component is superimposed on the XY motion of the workpiece provided by the motion stage. The secondary motion is generated by deflecting the water jet trajectory by a controllable dielectrophoretic force. The induced secondary motion of the water jet cuts the processing time to one half when generating texture patterns for isotropic wetting as compared to processes with only XY motion. The ability to alter the water jet’s trajectory by tens of microns at high frequencies, which is beyond the capability of conventional CNC machines, allows a wide range of different micro patterns to be generated, profoundly increasing the flexibility and efficiency of the process as compared to conventional approaches. As a demonstration, surface textures for isotropic and anisotropic behaviors are generated on stainless steel surfaces. The influence of feature spacing, motion speed (frequency) and texturing patterns on surface wettability are studied.

Effect of piston clearance on the lubrication performance in axial piston pump

Purpose This paper aims to provide a reliable and efficient numerical piston–cylinder design method and assess the effect of clearance on the piston-cylinder lubrication. Design/methodology/approach Numerical analyses of lubrication characteristics were performed for the piston–cylinder interface. The axial piston was numerically modeled, and the film pressure was calculated using the unsteady two-dimensional Reynolds equation. The behavior of the piston was analyzed by calculating the eccentricity satisfying the force and moment balance. Findings The secondary motion of the piston included numerically simulated several cycles until the piston behavior converged, and contact with the inner wall of the cylinder and friction region was estimated. Results showed that the piston–cylinder clearance affected the contact force, length of the contact region and leakage flow rate. Originality/value This result improves the understanding of the piston–cylinder lubrication and suggests considerations in terms of lubrication in clearance design.