Piston thermal management in an opposed-piston engine
An opposed-piston engine includes pistons, each piston having an annular cavity in the piston's sidewall and positioned between its crown and ring grooves to block transfer of heat from the crown to the piston body.
1. An internal combustion engine comprising:
at least one cylinder with longitudinally-separated exhaust and intake ports and a pair of pistons disposed in opposition to one another in a bore of the cylinder, each piston including a piston body with a crown at one end, an end surface on the crown, and a bowl formed in the end surface, in which a combustion chamber has a cavity defined between the end surface bowls when the pistons are near respective top dead center positions in the cylinder; wherein:
each piston includes at least one ring groove in a piston sidewall near the crown, and a thermal resistor for reducing or blocking heat transfer from the crown to the at least one ring groove, the thermal resistor comprising:
an annular cavity in the piston sidewall along a circumference of the piston body and positioned between the end surface and the at least one ring groove, the annular cavity having a mouth that opens through the piston sidewall; and
a low thermal conductivity material contained in the annular cavity, in which a sleeve is seated on an outer circumferential surface of the crown with an upper flange held against a shoulder of the crown and a lower flange covering the mouth of the annular cavity, the upper flange extending in a radial direction of the piston and the lower flange extending downwardly in an axial direction of the piston.
2. The internal combustion engine of claim 1 , in which each piston further includes one or more cooling galleries within the piston body under the crown.
3. The internal combustion engine of claim 1 , wherein the annular cavity has a shape of a wedge in cross section, with the mouth that opens through the piston sidewall and tapers to an inner notch.
4. The internal combustion engine of claim 1 , wherein the crown of each piston is manufactured out of a material with a higher oxidizing temperature than the piston body.
5. The internal combustion engine of claim 4 , wherein the material with the higher oxidizing temperature comprises stainless steel or a nickel alloy.
6. The internal combustion engine of claim 1 , wherein each piston further comprises a surface treatment, the surface treatment increasing a surface oxidation temperature of a material of the crown of each piston.
7. The internal combustion engine of claim 1 , wherein in each piston, the piston sidewall and crown are formed as a single unitary piece by forging, casting, and/or machining.
8. The internal combustion engine of claim 7 , wherein in each piston, when the sleeve is seated and fixed in place, the sleeve and the annular cavity form a chamber that is substantially airtight.
9. A piston for a two-stroke internal combustion engine, comprising:
a piston body with a crown and a sidewall;
an end surface formed on the crown;
the end surface including an elongated bowl that defines a combustion chamber with an opposing piston end surface;
at least one ring groove in the piston sidewall near the crown; a thermal resistor for reducing or blocking heat transfer from the crown to the at least one ring groove, the thermal resistor comprising:
an annular cavity in the piston sidewall along a circumference of the piston body and positioned between the end surface and the at least one ring groove, the annular cavity having a mouth that opens through the piston sidewall;
a low thermal conductivity material contained in the annular cavity; and
a sleeve seated on an outer circumferential surface of the crown, the sleeve comprising an upper flange held against a shoulder of the crown and a lower flange covering the mouth of the annular cavity, the upper flange extending in a radial direction of the piston and the lower flange extending downwardly in an axial direction of the piston.
10. The piston of claim 9 , further including one or more cooling galleries within the piston body under the crown.
11. The piston of claim 9 , wherein the annular cavity has a shape of a wedge in cross section, with the mouth that opens through the piston sidewall and further wherein the wedge further tapers to an inner notch.
12. The piston of claim 9 , wherein the crown is manufactured out of a material with a higher oxidizing temperature than the piston body.
13. The piston of claim 12 , wherein the material with the higher oxidizing temperature comprises stainless steel or a nickel alloy.
14. The piston of claim 9 , further comprising a surface treatment, the surface treatment increasing a surface oxidation temperature of a material of the crown of each piston.
15. The piston of claim 9 , wherein the piston sidewall and crown are formed as a single unitary piece by forging, casting, and/or machining.
16. The piston of claim 15 , wherein when the sleeve is seated and fixed in place, the sleeve and the annular cavity form a chamber that is substantially airtight.