Free-piston engine

• US 6,199,519 B1
• Filed: 06/25/1998
• Issued: 03/13/2001
• Est. Priority Date: 06/25/1998
• Status: Expired due to Term

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Van Blarigan, Peter
• Primary Examiner(s): Wolfe, Willis R.
• Assistant Examiner(s): Benton, Jason
• Application Number:
  US09/104,895
• Time in Patent Office: 992 Days
• Field of Search: 123/46.R, 123/46.A
• US Class Current: 123/46.00R
• CPC Class Codes: B60L 2200/26 Rail vehicles
• CPC Class Codes: B60L 2200/32 Waterborne vessels
• CPC Class Codes: B60L 2240/36 Temperature of vehicle components or parts
• CPC Class Codes: B60L 2270/145 Structure borne vibrations
• CPC Class Codes: B60L 50/62 charged by low-power generators primarily intended to support the batteries, e.g. range extenders
• CPC Class Codes: F02B 2075/025 two
• CPC Class Codes: F02B 63/041 Linear electric generators
• 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: Y02T 10/62 Hybrid vehicles
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries
• CPC Class Codes: Y02T 10/7072 Electromobility specific charging systems or methods for batteries, ultracapacitors, supercapacitors or double-layer capacitors

Abstract

A combustion system which can utilize high compression ratios, short burn durations, and homogeneous fuel/air mixtures in conjunction with low equivalence ratios. In particular, a free-piston, two-stroke autoignition internal combustion engine including an electrical generator having a linear alternator with a double-ended free piston that oscillates inside a closed cylinder is provided. Fuel and air are introduced in a two-stroke cycle fashion on each end, where the cylinder charge is compressed to the point of autoignition without spark plugs. The piston is driven in an oscillating motion as combustion occurs successively on each end. This leads to rapid combustion at almost constant volume for any fuel/air equivalence ratio mixture at very high compression ratios. The engine is characterized by high thermal efficiency and low NO_x emissions. The engine is particularly suited for generating electrical current in a hybrid automobile.

Claims

1. A free-piston, two-stroke, autoignition internal combustion engine that emits near zero NO_x emissions of less than about 20 ppm comprising:

a housing including a cylinder having first and second combustion chambers at opposite ends thereof, wherein each combustion chamber includes an inlet and outlet;

a double-ended piston that is displaceable between the first and second combustion chambers;

a linear alternator means operable with the piston for converting kinetic energy of the piston into electrical energy;

a source of fuel and air that supplies a fuel and air mixture into each combustion chamber through the inlets;

means for controlling the compression ratio to cause autoignition of the fuel and air mixture in each combustion chamber at a compression ratio of at least about 16;

1; and

means for causing the fuel and air mixture to react following autoignition at a combustion rate so that at least 95% of the fuel is combusted in less than about 80 μ

sec wherein the engine is characterized by a thermal efficiency of at least about 48%.

2. The free-piston engine of claim 1 wherein the source of the fuel and air supplies a fuel and air mixture that has an equivalence ratio that ranges from 0.25 to 0.55.

3. The free-piston engine of claim 1 wherein the means for controlling the compression ratio causes autoignition of the fuel and air mixture in each combustion chamber at a compression ratio of about 25:

1 to 35;

1.

4. The free-piston engine of claim 1 wherein the linear alternator means comprises an electrical stator and a permanent magnet, with one of said stator or magnet being secured to the free-piston and the another being secured to the housing adjacent the free-piston.

5. The free-piston engine of claim 1 wherein the means for controlling the compression ratio causes autoignition of the fuel and air mixture in each combustion chamber at a compression ratio ranges from 20:

1 to 40;

1.

6. The free-piston engine of claim 5 wherein the engine is characterized by a thermal efficiency of greater than about 52%.

7. The free-piston engine of claim 1 wherein the means for causing the fuel and air mixture to react causes at least 95% of the fuel to be combusted in less than about 50 μ

sec following autoignition.

8. The free-piston engine of claim 1 wherein the source of fuel and air comprises fuel that includes hydrogen, hydrocarbons and mixtures thereof.

9. The free-piston engine of claim 4 wherein the electrical stator is secured to the housing and the permanent magnet is secured to the free-piston.

10. The free-piston engine of claim 1 comprising means for synchronously opening and closing the inlets and outlets to produce a pressure-volume relationship in each of the combustion chambers.

11. A method for generating electrical current that comprises the steps of:

(a) providing a free-piston, two-stroke autoignition internal combustion engine that emits near zero NO_x emissions of less than about 20 ppm comprising;

(i) a housing including a cylinder having first and second combustion chambers at opposite ends thereof, wherein each combustion chamber includes an inlet and outlet;

(ii) a double-ended piston that is displaceable between the first and second combustion chambers;

(iii) a linear alternator means operable with the piston for converting kinetic energy of the piston into electrical energy;

(iv) a source of fuel and air that supplies a fuel and air mixture into each combustion chamber through the inlets;

(v) means for controlling the compression ratio to cause autoignition of the fuel and air mixture in each combustion chamber at a compression ratio of at least about 16;

1; and

(vi) means for causing the fuel and air mixture to react following autoignition at a combustion rate so that at least 95% of the fuel is combusted in less than about 80 μ

sec;

(b) operating the engine to generate electric energy wherein the engine emits near zero NO_x emissions of less than about 20 ppm and wherein the engine is characterized by a thermal efficiency of at least about 48%.

12. The method of claim 11 wherein the engine emits near zero NO_x emissions of less than about 5 ppm.

13. The method of claim 11 wherein the source of the fuel and air supplies a fuel and air mixture that has an equivalence ratio that ranges from 0.25 to 0.55.

14. The method of claim 11 wherein the means for controlling the compression ratio causes autoignition of the fuel and air mixture in each combustion chamber at a compression ration of about 25:

1 to 35;

1.

15. The method of claim 11 wherein the linear alternator means comprises an electrical stator and a permanent magnet, with one of said stator or magnet being secured to the free-piston and the another being secured to the housing adjacent the free-piston.

16. The method of claim 11 wherein the engine is operated at a compression ratio that ranges from 20:

1 to 40;

1.

17. The method of claim 16 wherein the engine is operated at a thermal efficiency that is greater than about 52%.

18. The method of claim 11 wherein the engine is operated at a combustion rate whereby at least 95% of the fuel is combusted in less than about 50 μ

sec following autoignition.

19. The method of claim 11 wherein the engine uses fuel that includes hydrogen, hydrocarbons and mixtures thereof.

20. The method of claim 15 wherein the electrical stator is secured to the housing and the permanent magnet is secured to the free-piston.

21. The method of claim 11 wherein step (b) comprises synchronously opening and closing the inlets and outlets to produce a pressure-volume relationship in each of the combustion chambers.

22. In a hybrid vehicle including a frame, wheels, electric motors for driving the wheels, a storage battery for receiving electric current and for energizing the motors, and control means for operating the vehicle and components thereof, the improvement comprises of employing a free-piston engine-alternator for charging the battery, said free-piston engine-alternator emits near zero NO_x emissions of less than about 20 ppm comprising:

a housing including a cylinder having first and second combustion chambers at opposite ends thereof, wherein each combustion chamber includes an inlet and outlet;

a double-ended piston that is displaceable between the first and second combustion chambers;

a linear alternator means operable with the piston for converting kinetic energy of the piston into electrical energy;

a source of fuel and air that supplies a fuel and air mixture into each combustion chamber through the inlets;

means for controlling the compression ratio to cause autoignition of the fuel and air mixture in each combustion chamber at a compression ratio of at least about 16;

1; and

means for causing the fuel and air mixture to react following autoignition at a combustion rate so that at least 95% of the fuel is combusted in less than about 80 μ

sec wherein the engine is characterized by a thermal efficiency of at least about 48%.

23. The hybrid vehicle of claim 22 wherein the source of the fuel and air supplies a fuel and air mixture that has an equivalence ratio that ranges from 0.25 to 0.55.

24. The hybrid vehicle of claim 22 wherein the means for controlling the compression ratio causes autoignition of the fuel and air mixture in each combustion chamber at a compression ratio of about 25:

1 to 35;

1.

25. The hybrid vehicle of claim 22 wherein the linear alternator means comprises an electrical stator and a permanent magnet, with one of the stator and magnet being secured to the free-piston and the another being secured to the housing adjacent the free-piston.

26. The hybrid vehicle of claim 22 wherein the means for controlling the compression ratio causes autoignition of the fuel and air mixture in each combustion chamber at a compression ratio ranges from 20:

1 to 40;

1.

27. The hybrid vehicle of claim 26 wherein the engine is characterized by a thermal efficiency of greater than about 52%.

28. The hybrid vehicle of claim 22 wherein the means for causing the fuel and air mixture to react causes at least 95% of the fuel to be combusted in less than about 50 μ

sec following autoignition.

29. The hybrid vehicle of claim 22 wherein the source of fuel and air comprises fuel that includes hydrogen, hydrocarbons and mixtures thereof.

30. The hybrid vehicle of claim 25 wherein the electrical stator is secured to the housing and the permanent magnet is secured to the free-piston.

31. The hybrid vehicle of claim 22 wherein the free-piston engine-alternator comprises means for synchronously opening and closing the inlets and outlets to produce a pressure-volume relationship in each of the combustion chambers.