Stirling engine comprising metal foam regenerator

Abstract

A Stirling engine comprising: a crank case (1) with a crank shaft (2) arranged therein, a displacer cylinder (3) with a reciprocatingly arranged displacer piston (4) therein, said displacer piston (4) being connected to said crank shaft (2) via a connecting rod (5) extending through a first end of said displacer cylinder (3), and wherein the displacer cylinder (3) defines a hot chamber (6) and a cool chamber (7) separated by the displacer piston (4), a working cylinder (8) defining a working cylinder chamber (11) with a reciprocatingly arranged working piston (9) therein, said working piston (9) being connected to said crank shaft (2) via a connecting rod (10) extending through a first end of the working cylinder (8), a heater device (14), arranged at a second end of said displacer cylinder (3) opposite to said first end and configured to heat a working gas which is present in the hot chamber (6) of the displacer cylinder (3) and in fluid communication with the working cylinder chamber (11) through a working gas channel which comprises a first heat exchanger (16) extending from a head (19) of the displacer cylinder (3) into the heater device (14), and a second heat exchanger (17) formed by a regenerator arranged outside the heater device (14). The regenerator (17) comprises a regenerator element (17) formed by metal foam that has an open porosity.

Claims

1. A stirling engine comprising: a crank case with a crank shaft arranged therein, a displacer cylinder with a reciprocatingly arranged displacer piston therein, said displacer piston being connected to said crank shaft via a connecting rod extending through a first end of said displacer cylinder, and wherein the displacer cylinder defines a hot chamber and a cool chamber separated by the displacer piston, a working cylinder defining a working cylinder chamber with a reciprocatingly arranged working piston therein, said working piston being connected to said crank shaft via a connecting rod extending through a first end of the working cylinder, a heater device, arranged at a second end of said displacer cylinder opposite to said first end and configured to heat a working gas which is present in the hot chamber of the displacer cylinder and in fluid communication with the working cylinder chamber through a working gas channel which comprises a first heat exchanger extending from a head of the displacer cylinder into the heater device, and a second heat exchanger formed by a regenerator arranged outside the heater device, wherein the regenerator comprises a regenerator formed by metal foam that has an open porosity, wherein the metal foam is comprised by a matrix, and wherein the matrix material in itself is at least partly hollow.

2. The stirling engine according to claim 1, wherein hydraulic porosity of the regenerator is at least 10% of the total volume of the metal foam.

3. The stirling engine according to claim 2, wherein the hydraulic porosity is within the range of 70-95% of the total volume of the metal foam.

4. The stirling engine according to claim 1, wherein the porosity inside the matrix material is 1-50% of the total volume of the matrix.

5. The stirling engine according to claim 1, wherein the porosity inside the matrix material is 25-50% of the total volume of the matrix.

6. The stirling engine according to claim 1, wherein the regenerator comprises at least two sub elements arranged in alignment with each other and one after the other as seen in a longitudinal direction of the working gas flow channel.

7. The stirling engine according to claim 6, wherein the regenerator has lower hydraulic porosity in an end thereof turned towards the displacer cylinder than in an end thereof turned towards the working cylinder.

8. The stirling engine according to claim 1, wherein the regenerator has lower matrix porosity in an end thereof turned towards the displacer cylinder than in an end thereof turned towards the working cylinder.

9. The stirling engine according to claim 1, wherein the regenerator has an annular cross-section and it is arranged outside and surrounding an outer periphery of the displacer cylinder.

10. The stirling engine according to claim 1, wherein the regenerator is clamped between an inner cylinder and an outer cylinder.

11. The stirling engine according to claim 10, wherein said inner cylinder is the displacer cylinder.

12. The stirling engine according to claim 6, wherein the regenerator has lower matrix porosity in an end thereof turned towards the displacer cylinder than in an end thereof turned towards the working cylinder.

13. The stirling engine according to claim 7, wherein the regenerator has lower matrix porosity in an end thereof turned towards the displacer cylinder than in an end thereof turned towards the working cylinder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For fuller understanding of the present disclosure and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which:

(2) FIG. 1 is a view from above of a Stirling engine according to an example provided with a schematically shown heater device,

(3) FIG. 2 is a view corresponding to FIG. 1, but with the heater device removed from the rest of the engine,

(4) FIG. 3 is a cross-section according to in FIG. 1, still with the heater device shown schematically,

(5) FIG. 4 is a cross-section of a part of the regenerator element, and

(6) FIG. 5 is an end view showing the regenerator element as clamped between an inner and an outer cylinder.

DETAILED DESCRIPTION

(7) FIGS. 1-3 show an example of a Stirling engine according to the present disclosure. The Stirling engine shown is of gamma type and comprises a crank case 1 with a crank shaft 2 arranged therein, and a displacer cylinder 3 with a reciprocatingly arranged displacer piston 4 therein. The displacer piston 4 is connected to the crank shaft 2 via a connecting rod 5 extending through a first end of said displacer cylinder 3. During operation of the Stirling engine, the displacer cylinder 3 defines a hot chamber 6 and a cool chamber 7 separated by the displacer piston 4.

(8) The Stirling engine further comprises a working cylinder 8 with a reciprocatingly arranged working piston 9 therein, said working piston 9 being connected to the crank shaft 2 via a connecting rod 10 extending through a first end of the working cylinder 8. A working cylinder chamber 11 defined by the working cylinder 8 is divided by the working piston 9 into a first part 12, through which said connecting rod 10 extends, and a second part 13 configured to house a working gas during operation of the Stirling engine. The second part 13 of the working cylinder chamber 11 is in fluid communication with the hot chamber 6 of the displacer cylinder 3 for the transportation of the working gas between said second part 13 of the working chamber 11 and the hot chamber 6 of the displacer cylinder 3 during operation of the engine. A heater device 14 is arranged at a second end of the displacer cylinder opposite to said first end and configured to heat a working gas which is present in the hot chamber 6 of the displacer cylinder 3 and which is in fluid communication with the second part 13 of the working cylinder chamber 11. In the example shown the heater device 14 comprises a combustion chamber 15 which is arranged at the second end of said displacer cylinder 3 opposite to said first end. Furthermore, the Stirling engine comprises a first heat exchanger 16 and a second heat exchanger 17. The first heat exchanger 16 comprises plurality of tubes 23 that extend from a displacer cylinder head 19 provided at said second end of the displacer cylinder 3 into the combustion chamber 15 and out of the combustion chamber 15 to the second heat exchanger 17. The second heat exchanger 17 is comprised by a regenerator provided outside the combustion chamber 15 and outside the displacer cylinder 3. In the example shown the engine also comprises a third heat exchanger 20 formed by a cooler arranged between the regenerator 17 and the working cylinder chamber 11, a first transition flow element 21 provided between said first and second heat exchangers 16, 17, and a second transition flow element 22 provided between the third heat exchanger 20 and the working cylinder 8. The cooler 20 comprises a body with channels 46 for the conduction of the working gas therethrough and with further channels 47 which form part of a cooling medium circuit.

(9) The hot chamber 6 defined by the displacer cylinder 3 is in fluid communication with a second end, i.e. the above-defined second part 13, of the working cylinder chamber 11 through a channel comprising the first heat exchanger 16, the second heat exchanger 17, the third heat exchanger 20, the first transition flow element 21 and the second transition flow element 22.

(10) The regenerator 17 comprises a regenerator element formed by metal foam that has an open porosity, thereby enabling the working gas to flow through the regenerator element while at the same time exchanging heat therewith. The hydraulic porosity of the regenerator element, referred to as the porosity available for a working fluid, in this case a working gas, to flow through on its way through the regenerator element, is within the range of 70-95% of the total volume of the metal foam. The metal may be any metal or metal alloy suitable for use in a high temperature application, such as a ferro chrome alloy or a nickel steel alloy.

(11) The metal foam of the regenerator 17 is comprised by a matrix, wherein the matrix material in itself is at least partly hollow. The porosity inside the matrix material is 25-50% of the total volume of the matrix and forms part of a closed porosity in the metal foam, excluded from what is defined as hydraulic porosity hereinabove.

(12) The regenerator element 17 comprises a plurality of sub elements 17a, 17b, 17c, arranged in alignment with each other and one after the other as seen in a longitudinal direction of the working gas flow channel. The regenerator element has lower hydraulic porosity in an end thereof turned towards the displacer cylinder 3 than in an end thereof turned towards the working cylinder 8. This is accomplished as the sub element 17a most adjacent the displacer cylinder 3 has lower hydraulic porosity than the sub element 17c most adjacent the working cylinder 8.

(13) The regenerator element 17 has lower matrix porosity in an end thereof turned towards the displacer cylinder 3 than in an end thereof turned towards the working cylinder 8. This is accomplished as the sub element 17a most adjacent the displacer cylinder 3 has lower matrix porosity than the sub element 17c most adjacent the working cylinder 8.

(14) The regenerator element 17 has an annular cross-section and is arranged outside and surrounding an outer periphery of the displacer cylinder 3. Each sub element 17, 17b, 17c has an annular shape and is subdivided in two halves, thereby enabling easy assembly thereof onto the outer periphery of displacer cylinder 3. An outer cylinder 18 formed by an annular element subdivided in two halves is arranged on the outer periphery of the regenerator element 17 and clamps the latter against the displacer cylinder 3.

(15) The foregoing description of the examples has been furnished for illustrative and descriptive purposes. It is not intended to be exhaustive, or to limit the examples to the variants described. Many modifications and variations will obviously be apparent to one skilled in the art. The examples have been chosen and described in order to best explicate principles and practical applications, and to thereby enable one skilled in the art to understand the examples in terms of its various examples and with the various modifications that are applicable to its intended use. The components and features specified above may, within the framework of the examples, be combined between different examples specified.