Antoni Iskra

Geometric shape of the support surface of the piston

Geometry of the slot between piston bearing surface and cylinder bore affects the friction losses of the IC engine to the far extent. It appears that these losses depend more on the area covered with oil than the thickness of oil layer separating collaborating parts. Barrel-shaped or stepwise piston bearing surface is the way to reduce the oil-covered area. The first concept has been used for years while the stepwise profile has not been applied for various reasons, although this idea providing higher load capacity of oil layer in stepwise slot was published in literature in the fifties of twentieth century. The stepwise profile can be obtained covering the cylindrical or tapered piston-bearing surface with a thin layer graphite. This paper presents the results of simulation leading to the reduction in friction losses and abrasive wear of piston bearing surface and cylinder bore. Covering the piston bearing surface with a thin layer of graphite one can get an extremely advantageous tribological properties of the piston assembly which means the expected parameters of oil film and in a case of film rupture – an ignorable abrasive wear of the graphite layer and/or cylinder bore.

[i][/i]THE IMPACT OF MICROGEOMETRY BEARING SURFACE OF THE PISTON ON THE PARAMETERS OF OIL FILM

The formation of oil film is possible under certain parameters of microgeometry cooperating components the main node of the internal combustion engine, which is a piston-pin-piston rings. In addition, this node is primarily responsible for the formation of mechanical losses. It is advisable to reduce friction losses in the piston-cylinder group lead to an increase in the overall efficiency of the engine and thus reduce the fuel consumption. One way of achieving these objectives is modification of microgeometry of the piston-bearing surface, which cooperates with the cylinder wall. The geometry of the gap between the piston skirt and the cylinder liner greatly affects the friction loss inside the engine. This means that the friction loss is much more affected by the area covered by the oil film separating the mating elements than its thickness. The method to reduce the area covered by the oil film is a modification of the bearing surface of the piston by adjusting the profile. The supporting surface, which performs a reciprocating motion relative to the strokes of the cylinder liner ensure the continuity of the oil film with the smallest possible value of the friction losses at the node piston-cylinder. This paper presents the results of simulation leading which aim to determining the parameters oil film on the friction loss for the modified bearing surface of the piston.

The problems of piston skirt microgeometry in combustion engines

Geometry of the slot between piston bearing surface and cylinder bore affects the friction losses of the IC engine to the far extent. It appears that these losses depend more on the area covered with oil than the thickness of oil layer separating collaborating parts. Barrel-shaped or stepwise piston bearing surface is the way to reduce the oil covered area. Turns out that the referred to friction losses contributes more to area covered by the oil film than the film thickness of the separation elements cooperating. The method to reduce the area covered by the oil film is a modification of the bearing surface of the piston by adjusting the profile. This paper presents the results of simulation leading to the reduction in friction losses and abrasive wear of piston bearing surface and cylinder bore. Covering the piston bearing surface with a thin layer of graphite one can get an extremely advantageous tribological properties of the piston assembly which means the expected parameters of oil film and in a case of film rupture-an ignorable abrasive wear of the graphite layer and/or cylinder bore.

Comparing the resistance to motion of pistons coated with a layer of nanotubes with standard pistons

The paper presents preliminary results of testing the resistance to motion of pistons coated with a layer of carbon nanotubes (CNTs). A significant part of this paper was devoted to the problems of putting a layer of nanotubes on the surface of an aluminum alloy. Obtaining a layer of nanotubes of a very narrow margin of tolerance was a difficult technological problem to overcome. A standard process of growing a layer of nanotubes leads to a corrosion damage of the side surface of pistons; therefore, new technologies were developed allowing for obtaining a permanent layer of nanotubes less than 5 microns thick. Pistons whose side surfaces were coated with a layer of nanotubes were mounted to an engine with an external drive, and then measurements of the moment of momentary resistance to motion were performed, which enables capturing these phases of the engine work cycles in which the layer of nanotubes gives the best results. At present, long-term research is being carried out in order to determine the degree of the risk of exfoliation of the layer of nanotubes under the conditions of large mechanical and thermal loads. The special nanotechnology method cold nanosphere lithography has been invested to control the structural properties sand growth of multiwalled carbon nanotubes. The preliminary analysis of dismantled pistons revealed that nanotubes layers were partially worn off at the peaks of micro roughness but in the valleys, the nanotubes accurately adhered to the piston lateral surface.