Methods and systems for managing a clearance gap in a piston engine

1. An assembly comprising:

a cylinder comprising:

a bore, and

a section within the bore of the cylinder capable of containing a fluid, wherein the fluid comprises a gas; and

a free piston configured to translate axially within the bore along an axis of the bore, wherein blow-by gas from the section flows axially away from the section through a clearance gap between the free piston and the cylinder, and wherein the free piston comprises a feature or a component configured to provide self-centering using flow of the blow-by gas, wherein the assembly is configured for oil-less operation.

2. The assembly of claim 1 , wherein the feature is selected from the group consisting of one or more slotted pockets, a step, a tapered portion, and any combination thereof.

3. The assembly of claim 1 , wherein the free piston further comprises one or more additional features or components that aid in equalizing pressure.

4. The assembly of claim 3 , wherein the one or more additional features comprise a plurality of circumferential grooves positioned behind the self-centering feature relative to the section.

5. The assembly of claim 1 , wherein the free piston further comprises one or more passages configured to route the flow of the blow-by gas away from a portion of the clearance gap.

6. The assembly of claim 1 , wherein the section comprises at least one of a combustion section and a gas driver section.

7. The assembly of claim 1 , further comprising a bearing element configured to provide a flow of a bearing fluid into the clearance gap.

8. The assembly of claim 7 , wherein the feature is a feature of the bearing element.

9. The assembly of claim 7 , wherein the bearing element is affixed to the free piston assembly, and wherein the free piston assembly further comprises a feed passage configured to receive a bearing fluid from a fluid source and to provide the bearing fluid to the bearing element.

10. The assembly of claim 7 , wherein the bearing fluid comprises air.

11. The assembly of claim 7 , wherein the bearing element comprises at least one of a graphite element, a metal element with machined features, a sintered metal element, a porous ceramic element, and a nonporous ceramic element.

12. The assembly of claim 7 , wherein the flow of bearing fluid is configured to form a fluid layer in the clearance gap that aids in centering the free piston assembly about an axis of the bore.

13. An assembly comprising:

a free piston comprising a piston face configured to contact a section of a free-piston engine, the section capable of containing a fluid; and

a feature or a component configured to provide self-centering of the assembly in a bore of the free-piston engine, wherein the assembly is configured for oil-less operation.

14. The assembly of claim 13 , wherein the feature is selected from the group consisting of one or more slotted pockets, a step, a tapered portion, and any combination thereof.

15. The assembly of claim 13 , wherein the fluid contained in the section comprises a gas, and wherein the section comprises at least one of a gas driver section and a combustion section.

16. The assembly of claim 13 , further comprising one or more additional features or components that aid in equalizing pressure.

17. The assembly of claim 16 , wherein the one or more additional features comprise a plurality of circumferential grooves positioned behind the self-centering feature or component relative to the piston face.

18. The assembly of claim 13 , wherein the fluid contained in the section comprises a gas, and wherein the feature or the component is further configured to use a flow of blowby gas from the section to provide the self-centering.

19. The assembly of claim 13 , further comprising one or more passages configured to route a flow of blow-by gas from the section.

20. The assembly of claim 13 , further comprising a bearing element, wherein the bearing element is configured to provide a flow of bearing fluid into a clearance gap between the free piston and the bore of the free-piston engine.

21. The assembly of claim 20 , wherein the feature is a feature of the bearing element.

22. The assembly of claim 20 , further comprising a feed passage configured to receive a bearing fluid from a fluid source and to provide the bearing fluid to the bearing element.

23. The assembly of claim 20 , wherein the bearing fluid comprises air.

24. The assembly of claim 20 , wherein the bearing element comprises at least one of a graphite element, a metal element with machined features, a sintered metal element, a porous ceramic element, and a nonporous ceramic element.

25. The assembly of claim 20 , wherein the flow of the bearing fluid is configured to form a fluid layer in the clearance gap that aids in centering the piston free-piston assembly about an axis of the bore.

26. An assembly comprising:

a cylinder comprising:

a bore, and

a section within the bore of the cylinder, the section capable of containing a fluid, wherein the fluid comprises a gas; and

a free piston configured to translate axially along an axis of the bore, wherein blow-by gas from the section flows axially away from the section through a clearance gap between the free piston and the cylinder, and wherein the free piston comprises a feature or a component that aids in equalizing pressure, wherein the assembly is configured for oil-less operation.

27. The assembly of claim 26 , wherein the feature that aids in equalizing the pressure comprises a labyrinth seal configured to affect the flow of the blow-by gas.

28. The assembly of claim 26 , wherein the section comprises at least one of a combustion section and a gas driver section.