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

Abstract

A piston engine may include a clearance gap between a piston assembly and a cylinder. The piston may be configured to translate in a bore of the cylinder. The clearance gap between the piston assembly and the bore may be actively or passively controlled. A control system may provide one or more adjustments based on, for example, a detected temperature, pressure, flow rate, work metric, and/or other indicator. The adjustments may include, for example, adjusting a cylinder liner, adjusting a flow through a bearing element, adjusting a coolant flow, adjusting a heat pipe property, and/or other adjustments. One or more auxiliary systems may be used to provide the adjustments.

What is claimed is: 
     
       1. A method of controlling a clearance gap between a piston assembly and a cylinder of a free-piston engine, the method comprising:
 detecting at least one indicator of the clearance gap; 
 determining a control response based at least in part on the indicator; 
 generating a control signal based at least in part on the control response; and 
 causing the clearance gap to be adjusted based at least in part on the control signal, wherein:
 the piston assembly comprises at least one feature or component that interacts with blow-by gas from a compression section of the free-piston engine to aid in centering the piston assembly, wherein the at least one feature or component is selected from the group consisting of a step, a slotted pocket, a labyrinth, and any combination thereof. 
 
 
     
     
       2. The method of  claim 1 , wherein the at least one indicator comprises a temperature. 
     
     
       3. The method of  claim 1 , wherein the at least one indicator comprises a thickness of the clearance gap. 
     
     
       4. The method of  claim 1 , wherein the at least one indicator comprises a pressure. 
     
     
       5. The method of  claim 1 , wherein the at least one indicator comprises a gas flow rate. 
     
     
       6. The method of  claim 1 , wherein the at least one indicator comprises a work interaction of the free-piston engine. 
     
     
       7. The method of  claim 1 , wherein the at least one indicator comprises a velocity. 
     
     
       8. The method of  claim 1 , wherein the at least one indicator comprises an acceleration. 
     
     
       9. The method of  claim 1 , wherein causing the clearance gap to be adjusted comprises causing a pressure to be adjusted to a cylinder liner positioned coaxial in the cylinder. 
     
     
       10. The method of  claim 1 , wherein causing the clearance gap to be adjusted comprises causing a flow of a bearing fluid through a bearing element of the free-piston engine to be adjusted. 
     
     
       11. The method of  claim 1 , wherein causing the clearance gap to be adjusted comprises providing a coolant to at least one of the piston assembly and the cylinder to control a temperature of the free-piston engine. 
     
     
       12. The method of  claim 1 , wherein causing the clearance gap to be adjusted comprises causing a property of a heat pipe of the free-piston engine to be adjusted. 
     
     
       13. The method of  claim 1 , wherein causing the clearance gap to be adjusted comprises causing a force applied to a piston assembly of the free-piston engine to be adjusted. 
     
     
       14. The method of  claim 1 , wherein causing the clearance gap to be adjusted comprises causing a pressure of a gas flow to the inside of the cylinder to be adjusted. 
     
     
       15. A system configured to control a clearance gap between a piston assembly and a cylinder of a free-piston engine, the system comprising:
 at least one sensor configured to detect at least one indicator of the clearance gap; 
 processing equipment configured to determine a control response based at least in part on the at least one indicator; and 
 a control interface configured to provide a control signal based at least in part on the control response, wherein:
 the piston assembly comprises at least one feature or component that interacts with blow-by gas from a compression section of the free-piston engine to aid in centering the piston assembly, wherein the at least one feature or component is selected from the group consisting of a step, a slotted pocket, a labyrinth, and any combination thereof. 
 
 
     
     
       16. The system of  claim 15 , wherein the at least one sensor is configured to detect a temperature. 
     
     
       17. The system of  claim 15 , wherein the at least one sensor is configured to detect a thickness of the clearance gap. 
     
     
       18. The system of  claim 15 , wherein the at least one sensor is configured to detect a pressure. 
     
     
       19. The system of  claim 15 , wherein the at least one sensor is configured to detect a fluid flow rate. 
     
     
       20. The system of  claim 15 , wherein the at least one sensor is configured to detect a work output of the free-piston engine or work input to the free-piston engine. 
     
     
       21. The system of  claim 15 , wherein the at least one sensor is configured to detect a velocity. 
     
     
       22. The system of  claim 15 , further comprising at least one auxiliary system configured to adjust the clearance gap based at least in part on the control signal. 
     
     
       23. The system of  claim 22 , wherein the at least one auxiliary system is configured to adjust the clearance gap by adjusting a pressure to the outside of a cylinder liner positioned coaxial in the cylinder to reduce or increase the clearance gap in response to the control signal. 
     
     
       24. The system of  claim 22 , wherein the at least one auxiliary system is configured to adjust the clearance gap by increasing or decreasing a gas flow through a bearing element of the free-piston engine in response to the control signal. 
     
     
       25. The system of  claim 22 , wherein the at least one auxiliary system is configured to adjust the clearance gap by providing a coolant to at least one of the piston assembly and the cylinder to control a temperature of the free-piston engine in response to the control signal. 
     
     
       26. The system of  claim 22 , wherein the at least one auxiliary system is configured to adjust the clearance gap by adjusting a property of a heat pipe of the free-piston engine in response to the control signal. 
     
     
       27. The system of  claim 22 , wherein the at least one auxiliary system is configured to adjust a force applied to a piston assembly of the free-piston engine in response to the control signal. 
     
     
       28. The system of  claim 22 , wherein the at least one auxiliary system is configured to adjust a pressure of a gas flow to the inside of the cylinder in response to the control signal. 
     
     
       29. A method of controlling a clearance gap between a piston assembly and a cylinder of a free-piston engine, the method comprising:
 causing the clearance gap to be adjusted based at least in part on a control signal, wherein:   the piston assembly comprises at least one feature or component that interacts with blow-by gas from a compression section of the free-piston engine to aid in centering the piston assembly, wherein the at least one feature or component is selected from the group consisting of a step, a slotted pocket, a labyrinth, and any combination thereof.   
     
     
       30. The method of claim 29, further comprising:
 generating a control signal based at least in part on a control response corresponding to at least one indicator of the clear gap, wherein the at least one indicator comprises a temperature.   
     
     
       31. The method of claim 29, further comprising:
 generating a control signal based at least in part on a control response corresponding to at least one indicator of the clear gap, wherein the at least one indicator comprises a thickness of the clearance gap.   
     
     
       32. The method of claim 29, further comprising:
 generating a control signal based at least in part on a control response corresponding to at least one indicator of the clear gap, wherein the at least one indicator comprises a pressure.   
     
     
       33. The method of claim 29, further comprising:
 generating a control signal based at least in part on a control response corresponding to at least one indicator of the clear gap, wherein the at least one indicator comprises a gas flow rate.   
     
     
       34. The method of claim 29, further comprising:
 generating a control signal based at least in part on a control response corresponding to at least one indicator of the clear gap, wherein the at least one indicator comprises a work interaction of the piston engine.   
     
     
       35. The method of claim 29, further comprising:
 generating a control signal based at least in part on a control response corresponding to at least one indicator of the clear gap, wherein the at least one indicator comprises a force.   
     
     
       36. The method of claim 29, wherein causing the clearance gap to be adjusted comprises causing a fuel flow to the piston engine to be adjusted. 
     
     
       37. The method of claim 29, wherein causing the clearance gap to be adjusted comprises causing a flow of a bearing fluid through a bearing element of the piston engine to be adjusted. 
     
     
       38. The method of claim 29, wherein causing the clearance gap to be adjusted comprises providing a coolant to the piston engine. 
     
     
       39. The method of claim 29, wherein the piston assembly comprises a piston rod coupled to a piston comprising a circumferential groove configured to receive a piston ring or piston ring assembly. 
     
     
       40. A free-piston piston assembly comprising at least one feature or component that interacts with blow-by gas from a compression section of a free-piston machine in which the free-piston assembly reciprocates to aid in centering the piston assembly, wherein the at least one feature or component is selected from the group consisting of a step, a slotted pocket, a labyrinth, and any combination thereof.