Ported engine constructions with low-tension compression seals
View Patent ↗In ported engine constructions, cooling of piston crowns and cylinder liners results in reduction or elimination of bore/liner distortions, thus ensuring circularity of the bore/piston interface throughout engine operation. Consequently, the need for heavily-tensioned piston rings is eliminated. Such engine constructions incorporate annular low-tension compression seals on the pistons, which substantially reduce port bridge wear during all phases of engine operation while also limiting blow-by during combustion.
1. A method for operating an opposed piston engine in which a pair of pistons is disposed in opposition in the bore of a cylinder, the cylinder including inlet and exhaust ports opening through the bore, each piston including a crown with a front face, a circumferential groove having a floor, and an annular compression seal mounted in the groove, each compression seal including an annular bearing surface and an annular inner peripheral surface spaced from the floor of the groove in which the compression seal is mounted, the method comprising:
operating the opposed-piston engine with a two-stroke cycle;
cooling the cylinder and the crown of each piston to maintain circularity of the interface between the bore and each piston;
contacting the bore with the annular bearing surface of each compression seal;
combusting a mixture of air and fuel in the bore, between the front faces, as the pistons move through respective top dead center (TDC) positions;
the annular bearing surface of each compression seal contacting the bore, with no clearance between the annular bearing surface and the bore, in response to a high level of compression seal tension in the direction of the bore resulting from combustion pressure acting against the inner peripheral surface as the piston moves away from a TDC position;
reducing the compression seal tension resulting from combustion pressure of each compression seal as the piston on which it is mounted moves toward a BDC position;
the annular bearing surface of each compression seal contacting the bore, with no clearance between the annular bearing surface and the bore, in response to a residual low level of compression seal tension in the direction of the bore as the piston traverses a port.
2. The method of claim 1 , further comprising:
forming a space between front faces for compressing the air as the pistons move through the TDC positions;
forming an annular squish zone around the space; and
injecting the fuel into the space through an opening through the squish zone.
3. The method of claim 2 , further comprising maintaining alignment of a gap in each compression seal with a respective port bridge as the piston on which the compression seal is mounted traverses a port.
4. The method of claim 3 , wherein the residual low level of compression seal tension is about 3 Newtons.