Free-piston internal combustion engine

• US 6,035,637 A
• Filed: 02/25/1998
• Issued: 03/14/2000
• Est. Priority Date: 07/01/1997
• Status: Expired due to Term

• Current Assignee: Sunpower Corporation (Totalenergies Se)
• Original Assignee: Sunpower Corporation (Totalenergies Se)
• Inventors: Kopko, William L., Beale, William T.
• Primary Examiner(s): NGUYEN, HOANG M
• Application Number:
  US09/030,067
• Time in Patent Office: 748 Days
• Field of Search: 60/595, 60/653, 60/679, 417/364
• US Class Current: 60/595
• CPC Class Codes: F02B 2075/025 two
• CPC Class Codes: F02B 63/041 Linear electric generators
• CPC Class Codes: F02B 71/00 Free-piston engines; Engines without rotary main shaft
• CPC Class Codes: F02B 71/04 Adaptations of such engines for special use; Combinations of such engines with apparatus driven thereby
• CPC Class Codes: F02B 75/04 Engines with variable distances between pistons at top dead-centre positions and cylinder heads
• CPC Class Codes: F02D 13/0203 Variable control of intake and exhaust valves
• CPC Class Codes: F02D 13/0215 changing the valve timing only
• CPC Class Codes: F02G 1/0435 the engine being of the free piston type
• CPC Class Codes: F02G 2244/50 Double acting piston machines
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

This invention is an efficient free-piston internal-combustion engine having an expansion ratio greater than the compression ratio and preferably with gas bearings supporting the piston. The use of gas bearings in combination with high-temperature ceramic materials allows the engine to be nearly adiabatic and with exhaust temperatures in excess of 600° C. These high exhaust temperatures in turn allow the engine to operate as a topping cycle for gas turbines, Stirling engines, steam engines, etc. An improved valving system for flexible control of the engine may include the use of a valve actuator in a piston. In one embodiment, a pair of oppositely disposed combustion chamber passageways extending between the combustion chamber and the earth'"'"'s atmosphere, each have a combustion-chamber valve for controlling the passage of gas through the passageways. The combustion-chamber valves are essentially simultaneously opened and closed to permit independent variation and control of the compression ratio, expansion ratio, and stroke of the engine. When the valves are opened, the combustion chamber is purged or supercharged with combustion supporting air, and closed to initiate compression. Variable control of the piston positions at which the valves are opened and closed permits the engine to operate at a high efficiency over a broad range of power output loading conditions. In another embodiment the combustion chamber and a gas compressor are combined in the same cylinder.

Claims

1. A free-piston internal-combustion engine, comprising:

a cylinder;

a piston that is slidingly reciprocatable in said cylinder;

a combustion chamber within said cylinder and which has a boundary defined by said piston wherein the motion of said piston compresses gas in said chamber during a compression stroke of said piston and expands gas in said chamber during an expansion stroke of said piston;

a driver for driving said piston in direction that compresses gas in said chamber;

intake means for drawing gas from a source into said chamber;

means for adding fuel to said chamber;

exhaust means for venting products of combustion from said chamber; and

means for controlling said intake and exhaust means so that the expansion stroke of said piston following ignition of fuel in said combustion chamber is greater than the compression stroke before ignition.

2. A free-piston internal-combustion engine as set forth in claim 1, further comprising a gas bearing for supporting said piston within said cylinder.

3. The free-piston internal-combustion engine of claim 2 wherein total heat transferred through the walls of said cylinder is less than 20 percent of the lower heating value of the fuel combusted in said engine.

4. The free-piston internal-combustion engine of claim 3 that further comprises a heat engine that uses the exhaust gasses as a heat source.

5. The free-piston internal-combustion engine system of claim 4 wherein said heat engine is a Stirling engine.

6. The free-piston internal-combustion engine system of claim 4 wherein said heat engine is a steam engine.

7. The free-piston internal-combustion engine of claim 1 wherein

said intake means comprises a flow path between said source of gas that can support combustion and the end of the combustion chamber opposite said piston and at least one check valve located in said flow path,

said exhaust means comprises at least one check valve located in the cylinder wall,

said control means comprises a means for preventing flow through said exhaust valve during the expansion stroke of said piston, and

said means for adding fuel to said chamber comprises a fuel injector that injects fuel into said chamber.

8. The free-piston internal-combustion engine of claim 7 wherein said return means comprises a second combustion chamber located on the opposite side of said piston from the first combustion chamber.

9. The free-piston internal-combustion engine of claim 7 wherein said return means comprises a gas spring.

10. The free-piston internal-combustion engine of claim 7 wherein the pressure of gasses after they exit said exhaust check valve is higher than the pressure of said source of gas so that said engine also acts as a compressor.

11. The free-piston internal-combustion engine of claim 10, further comprising a turbine located in a flow path between said exhaust means and the atmosphere.

12. The free-piston internal-combustion engine of claim 11 wherein said means for preventing flow through said exhaust valve comprises a slide valve that is actuated by the pressure inside said combustion chamber.

13. The free-piston internal-combustion engine of claim 1 where said exhaust means comprises a valve in a flow path between said chamber and the atmosphere with a valve actuator that controls the position of said valve.

14. The free-piston internal-combustion engine of claim 13 where said intake means comprises a flow path between said source of gas and said chamber and an intake valve in said flow path.

15. The free-piston internal-combustion engine of claim 14 where said intake means further comprises a blower for pressurizing said gas above atmospheric pressure and said intake valve comprises a check valve.

16. The free-piston internal-combustion engine of claim 15 further comprising a piston-position sensor and means for controlling the operation of said exhaust valve and said means for adding fuel in response to piston position.

17. The free-piston internal-combustion engine of claim 1 further comprising a spark ignition means located in said combustion chamber.

18. An internal-combustion engine, comprising:

a cylinder;

a piston slidingly movable in said cylinder in first and second opposite directions;

a combustion chamber within said cylinder having a boundary defined by said piston, wherein said piston compresses gas in said chamber during a compression stroke of said piston in said first direction, and expands gas in said chamber during an expansion stroke of said piston in said second direction;

means for adding fuel to said chamber;

a driver for driving said piston in a direction that compresses gas in said chamber;

an intake port located in a wall of said cylinder for admitting gas into said chamber from a source;

an exhaust port located in a wall of said cylinder for venting gaseous products of combustion from said chamber;

an auxiliary port located in a wall of said cylinder;

pressure-activated valve means for closing said auxiliary port in response to a second predetermined pressure lower than a first predetermined pressure created at the end of said expansion stroke;

wherein said piston uncovers said intake and exhaust ports at the end of said expansion stroke to allow said gaseous products to be vented from said combustion chamber and to allow fresh gas to be admitted to said combustion chamber, and said piston begins its compression stroke only upon covering said auxiliary port during motion in said first direction, such that said expansion stroke following ignition of said fuel in said chamber is longer than said compression stroke.

19. A free-piston internal-combustion engine as set forth in claim 18, said engine further comprising gas bearing that supports said piston within said cylinder.

20. A means for controlling output power from a free-piston internal-combustion engine with pneumatic output comprising:

a compressor that supplies air to the inlet to the engine,

a turbine that receives a higher-pressure gas output from the engine and which drives said compressor and which is connected to a shaft output,

means for controlling the amount of fuel entering said engine so that the amount of fuel to said engine increases when increased power output is required, which increases the pressure and flow of gas exiting said engine which increases the speed of said turbine and said compressor so that there is a corresponding increase in air supplied to said engine.

21. The means for controlling output power from a free-piston internal-combustion engine of claim 20, further comprising:

epicyclic gears with a first input that is connected to said shaft output from said turbine,

a variable-speed motor-generator that is connected to a second input to said epicyclic gears,

a shaft output from said gears so that the speed of the variable-speed motor-generator can compensate for changes in turbine speed to maintain close to a constant output speed from said epicyclic gears.

22. A power plant including a gas turbine with a shaft output, a first compressor that is driven by said gas turbine for supplying a stream of compressed air, and a free-piston internal-combustion engine utilizing compressed air from said compressor to generate power in addition to power generated by said gas turbine, and providing exhaust gases to said stream of compressed air, said free-piston internal-combustion engine comprising:

a cylinder;

a piston that is slidingly reciprocatable in said cylinder;

a combustion chamber within said cylinder and which has a boundary defined by said piston wherein the motion of said piston compresses gas in said chamber during a compression stroke of said piston and expands gas in said chamber during an expansion stroke of said piston;

a driver for driving said piston in direction that compresses gas in said chamber;

intake port into said chamber that received compressed air from said first compressor;

means for adding fuel to said chamber;

exhaust port for venting products of combustion from said chamber into the inlet of said gas turbine; and

a gas bearing that supports said piston in said cylinder so as to allow the power plant to operate at high temperatures without thermal decomposition of lubricant.

23. The power plant of claim 22 where said free-piston internal combustion engine further comprises a second compressor that is driven by said piston and which is located in a flow path between said first compressor and said inlet port so as to further raise the pressure of air entering said cylinder.

24. The power plant of claim 22 further comprising a check valve in said intake port.

25. The power plant of claim 24 further comprising means for controlling flow through said exhaust port.

26. The power plant of claim 24 wherein the pressure of gases exiting said exhaust means is higher than the pressure of gases leaving said first compressor so that said engine acts as a compressor.

27. The power plant of claim 22 wherein at least 80% of the waste heat generated by said free-piston internal combustion engine goes into heating the gases leaving said engine.