Free-piston linear apparatus

Abstract

The present invention relates to a free-piston linear apparatus, comprising a piston arranged within a cylinder, said piston being configured for linear displacement within the cylinder; a combustion chamber arranged on one side of said piston and a gas expansion chamber arranged on an opposite side of said piston, wherein said piston is drivable under the action of a fuel medium expanding in the combustion chamber; an exhaust vent arranged to release exhaust gas from the combustion chamber to an exhaust system, wherein said exhaust system comprises a heat exchanger configured to transfer residual heat from said exhaust gas to said gas expansion chamber in order to heat the gas expansion chamber; and wherein said gas expansion chamber comprises at least one gas port for injecting and/or releasing gas into/from the gas expansion chamber.

Claims

1. A free-piston linear apparatus, comprising: a piston arranged within a cylinder, said piston being configured for linear displacement within the cylinder; a combustion chamber arranged on one side of said piston and a gas expansion chamber arranged on an opposite side of said piston, wherein said piston is drivable under the action of a fuel medium expanding in the combustion chamber; an exhaust vent arranged to release exhaust gas from the combustion chamber to an exhaust system, wherein said exhaust system comprises a heat exchanger configured to transfer residual heat from said exhaust gas to said gas expansion chamber in order to heat the gas expansion chamber; and wherein said gas expansion chamber comprises at least one gas port for injecting and/or releasing gas into/from the gas expansion chamber wherein said free-piston linear apparatus further comprises a hydrogen storage tank connected to said gas expansion chamber, wherein said gas expansion chamber comprises a gas inlet and a gas outlet for supplying and releasing gas into/from the gas expansion chamber, wherein said gas expansion chamber is connected to: said hydrogen storage tank via said gas inlet, and said combustion chamber via said gas outlet; wherein said free-piston linear apparatus is arranged such that hydrogen is transported into said heated gas expansion chamber, in which the hydrogen expands, and wherein said hydrogen is subsequently transported into said combustion chamber, in which the hydrogen is combusted.

2. The free-piston linear apparatus according to claim 1, wherein said piston comprises a piston rod, and wherein said free-piston linear apparatus further comprises: a linear generator arrangement comprising: a set of stator windings arranged around the path of linear displacement, and at least one magnetic element mounted to said piston rod in order to induce a current into said stator windings during said linear displacement of said piston.

3. The free-piston linear apparatus according to claim 1, further comprising a by-pass path from said gas inlet to said gas outlet such that hydrogen gas can be transported directly from said hydrogen tank to said combustion chamber and thereby bypass the gas expansion chamber.

4. The free-piston linear apparatus according to claim 1, wherein each of said gas outlet and said gas inlet comprises a control valve for directing a flow of hydrogen gas.

5. The free-piston linear apparatus according to claim 1, further comprising: a temperature sensor configured to determine a temperature of said gas expansion chamber; and a control unit configured to control an injection of hydrogen gas from said hydrogen storage tank into the gas expansion chamber based on at least one of an input from a user, the temperature of the gas expansion chamber, and a position of the piston.

6. The free-piston linear apparatus according to claim 5, wherein said control unit is configured to control an injection of hydrogen gas into the gas expansion chamber from the hydrogen storage tank once the temperature of the gas expansion chamber is above a predetermined threshold value.

7. The free-piston linear apparatus according to claim 1, further comprising a liquid fuel tank, wherein said liquid fuel tank is connected to said combustion chamber.

8. The free-piston linear apparatus according to claim 1, wherein said heat exchanger is arranged adjacent to the gas expansion chamber and configured to transfer heat to at least one wall of said gas expansion chamber.

9. The free-piston linear apparatus according to claim 1, further comprising cooling means arranged to cool hydrogen gas exiting said gas expansion chamber.

10. Method for operating a free piston linear apparatus according to claim 1, said method comprising: injecting a fuel medium into the combustion chamber and causing the fuel medium to expand in a combustion reaction within the combustion chamber in order to drive said piston toward said gas expansion chamber; releasing residual exhaust gas from said combustion chamber via said exhaust system; injecting hydrogen gas into said gas expansion chamber whereby the hydrogen gas is heated by the residual exhaust gas via the heat exchanger of the exhaust system and caused to expand within the gas expansion chamber in order to drive said piston back toward said combustion chamber; and transporting hydrogen gas from said gas expansion chamber into the combustion chamber and causing the hydrogen gas to expand in a combustion reaction within the combustion chamber in order to drive said piston toward the gas expansion chamber.

11. The method according to claim 10, wherein the step of injecting hydrogen gas into the gas expansion chamber is performed once a temperature of the gas expansion chamber reaches a threshold value.

12. The method according to claim 10, further comprising the step: cooling the hydrogen gas as it is transported from the gas expansion chamber to the combustion chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments of the present invention, with reference to the appended drawing, wherein:

(2) FIG. 1 is a schematic view of a free-piston linear apparatus according to one exemplary embodiment of the present invention,

(3) FIG. 2 is a schematic view of the free-piston linear apparatus of FIG. 1 illustrating a step of the combustion cycle,

(4) FIG. 3 is a schematic view of the free-piston linear apparatus of FIG. 1 illustrating a step of the combustion cycle,

(5) FIG. 4 is a schematic view of the free-piston linear apparatus of FIG. 1 illustrating a step of the combustion cycle,

(6) FIG. 5 is a schematic view of a free-piston linear apparatus according to one exemplary embodiment of the present invention,

(7) FIG. 6 is a flow-chart describing a method for operating a free piston linear apparatus according to one exemplary embodiment of the present invention.

DETAILED DESCRIPTION

(8) In the following detailed description, embodiments of the present invention will be described. However, it is to be understood that features of the different embodiments are exchangeable between the embodiments and may be combined in different ways, unless anything else is specifically indicated. Even though in the following description, numerous specific details are set forth to provide a more thorough understanding of the present invention, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well known constructions or functions are not described in detail, so as not to obscure the present invention. In illustrations containing a large number of identical or equivalent elements or devices, only a few of the elements/devices will be provided with a reference mark in order to reduce clogging of the figures.

(9) FIG. 1 shows a free-piston linear apparatus 1 according to an embodiment of the present invention. The free-piston linear apparatus 1 of FIG. 1 is mirror symmetric over a plane of symmetry dividing the combustion chamber 13 in half (separating the two pistons 3, 3). The following description should be understood as describing one half of the mirror symmetric free-piston linear apparatus 1, however, the skilled person realizes that the description is analogously applicable to the other half of the free-piston linear apparatus 1. The free-piston linear apparatus 1 comprises a piston 3 arranged within a cylinder 5. The piston 3 comprises a first piston head 7, a second piston head 9, and a rod connecting the two piston heads 11. The cylinder 5 is arranged around the piston 3 such that the piston 3 is held within and at least partly enclosed by the cylinder 5. The free-piston linear apparatus 1 further comprises a combustion chamber 13 arranged on one side of said piston and a gas expansion chamber 15 arranged on an opposite side of said piston 3. With reference to the abovementioned mirror symmetry, the free-piston linear apparatus 1 is to be understood as preferably having two cylinders 5, two pistons 3, two gas expansion chambers 15 and one combustion chamber 13 arranged between the two halves of the apparatus 1.

(10) The cross-sectional shape of the first and second piston head 7, 9 is the same as the cross-sectional shape of the inner wall 17 of the cylinder 5, with the size of the piston heads 7, 9 being chosen to ensure a tight fit between the piston heads 7, 9 and the inner walls 17 of the cylinder 5. This ensures that little or no fuel, combustion gas or air escapes the combustion chamber 13 and/or the gas expansion chamber 15 during operation of the free-piston linear apparatus 1. The cylinder 5 and piston 3 are configured to allow linear movement of the piston 3 inside the cylinder 5, in a direction parallel with the longitudinal axis of the piston rod 11. In other words, the piston 3 is drivable under the action of a fuel medium expanding in the combustion chamber 13. The piston 3 may move between two end positions (shown in FIG. 1 and FIG. 2), one being defined by a combustion chamber wall 19 provided with a through hole 21 for the piston rod 11, and the other being defined by a gas expansion chamber wall 23 also provided with a through hole 25 for the piston rod 11. When the piston 3 approaches either one of its two end positions, its speed is reduced by the pressure exerted on the respective piston head 7, 9 from the gas in the two respective chambers 13, 15. As the gas inside the chambers 13, 15 is compressed by the piston heads 7, 9, the pressure increases and the braking effect of the gas on the piston 3 is increased. In other words, when the piston 3 approaches either one of its end positions, the gas in either the combustion chamber 13 or the gas expansion chamber 15 is compressed and exerts a pressure on the piston head 7, 9 arranged therein, whereby said pressure stops the piston 3 from moving any further. The two gas expansion chambers 15 of the mirror imaged free-piston linear apparatus 1 is provided with a pressure equalization channel 27 which connects the two gas expansion chambers 15.

(11) The free-piston linear apparatus 1 further comprises an exhaust vent 29 arranged to release exhaust gas from the combustion chamber 15 to an exhaust system 31. The exhaust vent 29 is a one-way controllable valve connecting the combustion chamber 13 to an exhaust channel 33 forming part of the exhaust system 31. The exhaust vent 29 is configured to open once the pistons 3 have been pushed apart as a result of the expanding gas inside the combustion chamber 13. Thus, the pressure from the expanding gas inside the combustion chamber 13 is first harnessed to displace the pistons 3, after which it is guided out through the exhaust vent 29. The exhaust system 31 further comprises a heat exchanger 35 configured to transfer residual heat from the exhaust gas to the gas expansion chamber 15. This is done in order to heat the gas expansion chamber 15 and reuse any waste heat from the combustion process. The heat exchanger 35 comprises a channel for guiding the exhaust gas (not shown) and preferably also means for improving the heat transfer rate between the exhaust gas and the heat exchanger (not shown). The heat exchanger 35 is connected to the outer wall 37 of the gas expansion chamber 15 and arranged such that heat may be transferred from the exhaust gas to the inner wall 39 of the gas expansion chamber 15.

(12) The gas expansion chamber 15 comprises a gas inlet 41 for injecting gas into the gas expansion chamber 15 and a gas outlet 43 for releasing gas from the gas expansion chamber 15.

(13) The free-piston linear apparatus 1 further comprises a linear generator arrangement 45 comprising a set of stator windings 47 arranged around the path of linear displacement, and one or more magnetic elements 49 mounted to said piston rod 11 in order to induce a current into said stator windings 47 during said linear displacement of said piston 3. The stator windings 47 are part of the inside wall 17 of the cylinder 5. The magnetic element 49 extends around the piston rod 11. For example, the magnetic element 49 can be a cylindrical magnet with a central through-hole 51 in which the piston rod 11 is arranged. The magnetic element 49 is firmly connected to the piston rod 11 such that when the piston 3 moves, the magnetic element 49 moves with it. Thus, when the piston heads 7, 9 are driven by a combustion in the combustion chamber 13 or by a gas spring effect from the gas expansion chamber 15, the magnetic element 49 moves back and forth in relation to the set of stator windings 47, thereby inducing a current therein.

(14) The free-piston linear apparatus 1 further comprises a hydrogen storage tank 53. The hydrogen storage tank 53 is connected to the gas inlet 41 of the gas expansion chamber 15 via a first channel 55 and the gas outlet 43 of the gas expansion chamber 15 is connected to the combustion chamber 13 via a second channel 57. Hydrogen from the hydrogen storage tank 53 may also be transported to the combustion chamber 13 by means of a bypass channel 59 connecting the first channel 55 and the second channel 57. At the intersection between the first channel 55, the gas inlet 41, and the bypass channel 59, a T-port and a control valve 61 are provided. This T-port and this control valve 61 are configured to direct the flow of hydrogen from said first channel 55 and to either said gas inlet 41 or to said bypass channel 59. At the intersection between the bypass channel 59, the gas outlet 43, and the second channel 57, a T-port and a control valve 63 are provided. This T-port and this control valve 63 are configured to direct the flow of hydrogen from either said first gas outlet 43 or said bypass channel 59 and to said second channel 57.

(15) In said gas expansion chamber 15, there is provided a temperature sensor 65 configured to determine a temperature of said gas expansion chamber 15. The temperature sensor is arranged on an inner wall 39 of the gas expansion chamber 15. By being able to measure the temperature of the gas expansion chamber 15, it is possible to control the flow of hydrogen so that hydrogen is directed into the gas expansion chamber 15 only once the gas expansion chamber 15 has reached a predetermined temperature. Thus, it is ensured that the hydrogen entering the gas expansion chamber 15 expands as much as is desired. Furthermore, the free-piston linear apparatus 1 comprises a control unit (not shown) configured to control an injection of hydrogen gas from said hydrogen storage tank 53 into the gas expansion chamber 15 and/or into the combustion chamber 13 based on input from a user, the temperature of the gas expansion chamber 15, and a position of the piston 3.

(16) The free-piston linear apparatus 1 further comprises a liquid fuel tank 67. The liquid fuel tank 67 is connected to the combustion chamber 13. At the intersection between a channel 69 leading from the liquid fuel tank 67, the second channel 57, and the fuel inlet 71 of the combustion chamber 15, there is provided a T-port and a control valve 73. This T-port and this control valve 73 is configured to control what fuel enters the combustion chamber 13. Either hydrogen is taken from the second channel 57, or liquid fuel is taken from the liquid fuel tank 67. The control valve 73 is also configured to control the amount of fuel entering the combustion chamber 13. The combustion chamber 13 further comprises an air inlet 72 arrange to allow air to be injected into the combustion chamber 13, thus providing a mixture between fuel and oxygen which is beneficial for the combustion.

(17) The second channel 57 is provided with a cooling element 75 arranged so that hydrogen exiting the gas expansion chamber 15 may be cooled before entering the combustion chamber 13.

(18) FIG. 1-5 show an exemplary operating cycle of the free-piston linear apparatus 1. FIGS. 1 and 2 show hydrogen gas exiting the hydrogen gas tank 53 through, in order, the first channel 55, the bypass channel 59, the second channel 57 and into the combustion chamber 13 via the inlet 71 of the combustion chamber 13. Once the hydrogen gas is inside the combustion chamber 13, a spark plug 77 ignites the air/fuel mixture, thus causing the two pistons 3 of the free-piston linear apparatus 1 to move away from each other. In FIG. 2, the pistons 3 have moved to their most distal position, and the exhaust vent 29 has consequently been opened. The exhaust gas is guided through the exhaust system 31 to the heat exchangers 35 arranged in connection with either gas expansion chamber 15. As the exhaust gas passes the heat exchangers 35, the gas expansion chambers 15 are heated. The process described herein in relation to FIGS. 1 and 2 is repeated until the temperature sensors 65 senses that the gas expansion chambers 15 have reached a desired temperature.

(19) FIGS. 3-4 show the hydrogen gas exiting the hydrogen tank 53 and entering gas expansion chambers 15, due to the T-ports 61 being arranged to guide the hydrogen away from the bypass channel 59 and to the inlet 41 of the gas expansion chamber 15 instead. While in the gas expansion chamber 15, the temperature of the inner walls 39 causes the hydrogen to expand. As the hydrogen expands, the outlet 43 of the gas expansion chamber 15 is kept closed and the pistons 3 are driven towards each other. The pressure equalization channel 27 ensures that the two pistons 3 are subjected to equal amounts of pressure. This enables synchronization of the movement of either piston 3, thus preventing undue imbalance of the movement of the free-piston linear arrangement 1. Once the pistons 3 have been driven to their most proximal position, the outlet 43 of the gas expansion chamber 15 is opened and the heated hydrogen gas is allowed to exit therethrough. As the heated hydrogen passes the cooling means 75, heat is dissipated and the hydrogen is cooled. After this, the hydrogen enters the combustion chamber 13 where it is combusted according to the process described in relation to FIG. 2 above. After combusting the hydrogen inside the combustion chamber 13, the steps described in relation to FIGS. 3-4 are repeated until the temperature of the gas expansion chamber 15 drops below a predetermined threshold. Once the temperature drops below this threshold, the steps described in relation to FIGS. 1-2 are repeated until the temperature rises above said threshold. In the embodiment described above, the temperature threshold for the gas expansion chamber is 350 C.

(20) FIG. 5 shows another exemplary embodiment of the present invention. Here, a schematic view of a free-piston linear apparatus 1 is shown. The free-piston linear apparatus 1 of FIG. 5 is similar to the free-piston linear apparatus 1 of FIGS. 1-4, with one exception being that the gas expansion chambers 15 of FIGS. 1-4 have changed place with the combustion chamber 13. Consequently, the free-piston linear apparatus 1 of FIG. 5 comprises two combustion chambers 13, one gas expansion chamber 15, two pistons 3 arranged between the gas expansion chamber 15 and the two combustion chambers 13, and one heat exchanger 35 arranged in connection with the gas expansion chamber. Further, during operation of the free-piston linear apparatus 1 of FIG. 5, the hydrogen gas exits the hydrogen gas tank 53 through, in order, the first channel 55, the second channel 56, and into the combustion chamber 13 via the inlet 71 of the combustion chamber 13. Once the hydrogen gas is inside the combustion chamber 13, a spark plug 77 ignites the air/fuel mixture, thus causing the two pistons 3 of the free-piston linear apparatus 1 to move towards each other. The pressure equalization channel 27 ensures that the two pistons 3 are subjected to equal amounts of pressure from the combustion in the combustion chambers 13. This enables synchronization of the movement of either piston 3, thus preventing undue imbalance of the movement of the free-piston linear arrangement 1 during its operation. After the pistons 3 have been moved towards each other, the pistons 3 are in their most proximal position, and the exhaust vents 29 are opened. The exhaust gas is then guided through the exhaust channels 33 to the heat exchanger 35 arranged in connection with the gas expansion chamber 15. As the exhaust gas passes the heat exchangers 35, the gas expansion chambers 15 are heated. This process is repeated until the temperature sensor 65 senses that the gas expansion chamber 15 has reached a desired temperature.

(21) After a predetermined temperature has been sensed by the temperature sensor 65, the hydrogen gas exiting the hydrogen tank 53 instead enters the central gas expansion chamber 15. The hydrogen gas is guided there by means of T-ports and control valves similar to those discussed in relation to FIGS. 1-4. In other words, hydrogen gas exits the hydrogen gas tank 53, moves through the first channel 55, the second channel 56, the third channel 57 and into the gas expansion chamber 15 through the inlet 41. While in the gas expansion chamber 15, the temperature of the gas expansion chamber 15 causes the hydrogen to expand. As the hydrogen expands, the outlets 43 of the gas expansion chamber 15 are kept closed and the pistons 3 are driven away from each other. Once the pistons 3 have been driven to their most distal position, the outlets 43 of the gas expansion chamber 15 are opened and the heated hydrogen gas is allowed to exit therethrough. As the heated hydrogen passes the cooling means 75, heat is dissipated and the hydrogen is cooled. After this, the hydrogen enters the combustion chambers 13 where it is combusted according to the process described above. After combusting the hydrogen inside the combustion chambers 13, the steps of heating the hydrogen gas in the gas expansion chamber 15, cooling it with the cooling means 75 and combusting it in the combustion chambers 13 are repeated until the temperature of the gas expansion chamber 15 drops below a predetermined threshold. Once the temperature drops below this threshold, the steps of directly guiding the hydrogen gas from the hydrogen gas tank 53 to the combustion chambers 13 and guiding the exhaust gas from the combustion chambers 13 to the heat exchanger 35 are repeated until the temperature rises above said threshold. In the embodiment described above, this temperature threshold for the gas expansion chamber is 350 C.

(22) FIG. 6 is a flow-chart describing a method for operating a free piston linear apparatus according to one exemplary embodiment of the present invention. The method comprises the steps of:

(23) injecting 101 a fuel medium into the combustion chamber and causing 102 the fuel medium to expand in a combustion reaction within the combustion chamber in order to drive said piston toward said gas expansion chamber;

(24) releasing 103 residual exhaust gas from said combustion chamber via said exhaust system;

(25) once a temperature of the gas expansion chamber reaches a threshold value, injecting 104 hydrogen gas into said gas expansion chamber whereby the hydrogen gas is heated 105 by the residual exhaust gas via the heat exchanger of the exhaust system and caused 106 to expand within the gas expansion chamber in order to drive said piston back toward said combustion chamber;

(26) transporting 107 hydrogen gas from said gas expansion chamber into the combustion chamber;

(27) cooling 108 the hydrogen gas as it is transported from the gas expansion chamber to the combustion chamber; and

(28) causing 109 the hydrogen gas to expand in a combustion reaction within the combustion chamber in order to drive said piston toward the gas expansion chamber.

(29) Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. Variations to the disclosed embodiments can be understood and effected by the skilled addressee in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. Furthermore, in the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality.