Internal combustion engine system

Abstract

An internal combustion engine system includes a reciprocating compressor for pressurizing a fluid medium and having a compressor cylinder for accommodating a compressor piston. The compressor cylinder has a main cylinder volume and a secondary adjustable volume in fluid communication with the main cylinder volume so as to provide a variable geometrical compression ratio.

Claims

1. An internal combustion engine system comprising a reciprocating compressor for pressurizing a fluid medium and having a compressor cylinder for accommodating a compressor piston, said compressor cylinder having a main cylinder volume and a secondary adjustable volume in fluid communication with the main cylinder volume so as to provide a variable geometrical compression ratio, wherein the secondary adjustable volume comprises at least a plurality of volume compartment portions which are capable of separation by at least one valve, and wherein each of the plurality of volume compartment portions are individually arranged in fluid communication with the main cylinder volume via the at least one valve.

2. The internal combustion engine system according to claim 1, wherein the secondary adjustable volume is configured to provide for a geometrical compression ratio control of the compressor cylinder by adjusting the volume of the secondary adjustable volume into a number of defined volumes.

3. The internal combustion engine system according to claim 1, wherein the plurality of volume compartment portions are different sizes.

4. The internal combustion engine system according to claim 1, wherein the plurality of volume compartment portions are of fixed size.

5. The internal combustion engine system according claim 3, wherein a total dead volume is provided by at least two volume compartment portions of different size, each one of the two volume compartment portions of different size being individually arranged in fluid communication with the main cylinder volume by the at least one valve.

6. The internal combustion engine system according to claim 5, wherein the at least one valve is a rotatable valve assembly arranged to open and close an entrance to the at least two volume compartment portions of different size, respectively, by a rotation of the rotatable valve around its center axis.

7. The internal combustion engine system according to claim 1, wherein the volume of the secondary adjustable volume is adjusted in response to an engine load of the ICE system.

8. The internal combustion engine system according to claim 1, wherein the volume of the secondary adjustable volume is adjusted in response to a position of the compressor piston in the compressor cylinder so as to adjust the volume of the secondary adjustable volume based on the engine load.

9. The internal combustion engine system according to claim 1, wherein ICE system is operable such that the fluid communication between the main cylinder and the secondary adjustable volume is always open during a compression stroke.

10. The internal combustion engine system according to claim 1, wherein the ICE system comprises a control unit for controlling the secondary adjustable volume.

11. The internal combustion engine system according to claim 1, wherein the reciprocating compressor is operable by a crankshaft of an internal combustion engine.

12. The internal combustion engine system according to claim 1, further comprising at least one combustion cylinder housing a combustion piston, said combustion cylinder being configured to be energized by forces of combustion; said compressor cylinder being configured to compress a volume of; an expander cylinder housing an expander piston, said expander cylinder being in fluid communication with the at least one combustion piston.

13. A vehicle comprising an internal combustion engine system according to claim 1.

14. A method for controlling a geometrical compression ratio of a reciprocating compressor of an internal combustion engine system, said reciprocating compressor is configured to pressurize a fluid medium and having a compressor cylinder for accommodating a compressor piston, said compressor cylinder having a main cylinder volume and a secondary adjustable volume in fluid communication with the main cylinder volume so as to provide a variable geometrical compression ratio wherein the secondary adjustable volume comprises at least a plurality of volume compartment portions which are capable of separation by at least one valve, and wherein each of the plurality of volume compartment portions are individually arranged in fluid communication with the main cylinder volume via the at least one valve, wherein the method comprising the steps of: adjusting the volume of the secondary adjustable volume to a first adjusted volume; and pressurizing said fluid medium to a first geometrical compression ratio by a displacement of the compressor piston from a bottom dead center to top dead center.

15. The method according to claim 14, further comprising the steps of: determining an engine load of the ICE system; and adjusting the volume of the secondary adjustable volume in response to the determined engine load.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 is a side view of a vehicle comprising an internal combustion engine (ICE) system according to an example embodiment of the present disclosure;

(3) FIG. 2 is a side view of a reciprocating compressor of an ICE system according to an example embodiment of the present disclosure;

(4) FIGS. 3a to 3f illustrate additional parts of the reciprocating compressor of FIG. 2 according to an example embodiment of the present disclosure;

(5) FIG. 4 is a perspective view of the ICE system according to an example embodiment of the present disclosure;

(6) FIG. 5 is a flow-chart of a method according to an example embodiment of the present disclosure, in which the method comprises a number of steps for controlling a geometrical compression ratio of a reciprocating compressor of an ICE system in FIG. 1;

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE DISCLOSURE

(7) The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which an exemplary embodiment of the disclosure is shown. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein; rather, the embodiment is provided for thoroughness and completeness. Like reference character refer to like elements throughout the description.

(8) With particular reference to FIG. 1, there is provided a vehicle 1 with an internal combustion engine (ICE) system 100 according to the present disclosure. The vehicle 1 depicted in FIG. 1 is a truck for which the internal combustion engine system 100, which will be described in detail below, is particularly suitable for. The internal combustion engine system comprises at least a reciprocating compressor, as will be further described in relation to FIGS. 2 to 5. Moreover, the internal combustion engine system 100 includes an internal combustion engine (ICE). In this example, the ICE system is a hydrogen piston internal combustion engine system.

(9) The combustion in such hydrogen ICE system is based on a combustion of air and hydrogen, as is commonly known in the art.

(10) The ICE system further typically comprises a control unit 180, as illustrated in FIG. 1. As will be further described in relation to FIG. 5, the control unit 180 is configured to perform any one of a number of steps of a method for controlling the reciprocating compressor of the ICE system. The control unit 180 is here a part of a main electronic control unit for controlling the vehicle and various parts of the vehicle. In particular, the control unit 180 is arranged in communication with the reciprocating compressor and the other components of the ICE.

(11) One example embodiment of a reciprocating compressor according to an example embodiment of the present disclosure will now be described in relation to FIG. 2 and FIGS. 3a to 3f, while further components of the ICE system will subsequently be described in relation to FIG. 4.

(12) Turning to FIG. 2, there is depicted a reciprocating compressor 120 according to an example embodiment of the present disclosure for use in the ICE system 100 of FIG. 1. The reciprocating compressor 120 extends along a compression axis CA, typically corresponding to a longitudinal direction of the reciprocating compressor 120, as illustrated in FIG. 2. In this context, it should be noted that the term cylinder generally refers to a component having an interior space for accommodating a reciprocating piston, as is commonly known in the art. Further, it should be noted that the reciprocating compressor may sometimes be denoted as the compressor.

(13) The reciprocating compressor 120 comprises a compressor cylinder 121 housing a compressor piston 122. The compressor piston is connected to a connecting rod 154. The compressor piston connecting rod 154 connects the compressor piston 122 to a crankshaft 140, as also illustrated in FIG. 4. As is commonly known in the art, the compressor cylinder 120 is configured to draw a volume of ambient air, compress the air, and transfer the compressed air to a suitable combustor of the ICE system. One example of a suitable combustor arrangement will be further described below in relation to FIG. 4, which depicts a combustor having first and second combustion cylinders 111, 114.

(14) The reciprocating compressor is configured to compress air by a displacement of the compressor piston from a bottom dead center (BDC) to top dead center (TDC), as is commonly known in the art. In other words, the compressor cylinder 121 is design so as to accommodate the compressor piston 122. That is, the compressor cylinder 121 is configured to compress a volume of air by the compressor piston and subsequently transfer the compressed air to the combustor. To this end, the compressor cylinder comprises a main cylinder volume 124. The main cylinder volume is generally defined at the cylinder head of the compressor cylinder. Further, the main cylinder volume is generally defined by the interior surfaces of the cylinder head in combination with the compressor piston 122, as is illustrated in FIG. 2, which also corresponds to a conventional cylinder- and piston-arrangement. Accordingly, the main cylinder volume defines a first space for compressing the air.

(15) Moreover, the reciprocating compressor 120 comprises a secondary adjustable volume 126, as illustrated in FIG. 2, and further in FIGS. 3a to 3f. The secondary adjustable volume 126 is arranged in fluid communication with the main cylinder volume 124. As will be evident from the below description of the reciprocating compressor 120, the secondary adjustable volume 126 provides for adjusting the total volume (interior space) of the reciprocating compressor 120. In this manner, it becomes possible to provide a variable geometrical compression ratio during operation of the reciprocating compressor 120, and the ICE system 100.

(16) By way of example, as illustrated in FIG. 2, and more particularly in FIGS. 3a to 3f, the secondary adjustable volume 126 is defined by a number of sub-compartments 127 and 128. The sub-compartment 127 provides a first dead volume of a first size. Analogously, the sub-compartment 128 provides a second dead volume of a second size. Each one of the two sub-compartments 127 and 128, defining fixed dead volumes of different size, can be set in fluid communication with the main cylinder volume. Generally, the secondary adjustable volume 126 is set in fluid communication with the main cylinder volume 124 by means of a valve, such as the valve 170 in FIG. 2. In other words, each one of the two sub-compartments 127 and 128 can be set in fluid communication with the main cylinder volume 124 by means of the valve 170, which will be further described below.

(17) As such, the secondary adjustable volume 126 is configured to provide for a geometrical compression ratio control of the compressor cylinder 121 by adjusting the volume of the secondary adjustable volume 126 into a number of defined dead volumes. The secondary adjacent volume here comprises a first sub-compartment 127 and a second sub-compartment 128. Moreover, the first sub-compartment 127 and the second sub-compartment 128 are here of different sizes, as illustrated in FIG. 2, and also further in FIGS. 3a to 3f. However, it should be noted that although the secondary adjustable volume here merely comprises the first sub-compartment 127 and the second sub-compartment 128 of different sizes, there is provided a secondary adjustable volume that can be adjusted into four different dead volumes. One example of such configuration of the secondary adjustable volume is now described in relation to FIGS. 3c to 3f.

(18) As mentioned above, and as shown in e.g. FIG. 3c, the reciprocating compressor 120 comprises the valve 170. In this example embodiment, the valve is a rotatable valve assembly arranged to rotate e.g. in a clockwise rotation in relation to its center axis. As illustrated in FIGS. 3c to 3f, the valve can open and close the entrance to the sub-compartments 127 and 128, respectively, by a rotation around its center axis. In the example illustrated in FIGS. 3a to 3f, the geometrical compression ratio control is provided by the two fixed dead volumes (defined by the compartments 127 and 128) of different size. The two sub-compartments 127 and 128 can be set in fluid communication with the main cylinder volume 124 of the compressor 120 by controlling the valve 170.

(19) In the example embodiment as illustrated in FIGS. 3a to 3f, the size of the first sub-compartment 127 is smaller than the size of the second sub-compartment 128. Moreover, as mentioned above, the valve 170 can regulate the fluid medium passage between each one of the sub-compartments 127 and 128 and the main cylinder volume 124.

(20) As illustrated in FIG. 3c, the valve 170 is set in a position to block the entrances to each one of the two sub-compartments 127 and 128. In this configuration of the secondary adjustable volume 170, no additional dead volume is provided. Therefore, the compression of air in the compressor 120 occurs solely in the main cylinder volume 124.

(21) As illustrated in FIG. 3d, the valve 170 is set in a position to block the entrance to the larger one of the sub-compartments, i.e. the sub-compartment 128, while providing a fluid communication between the main cylinder volume 124 and the other one of the sub-compartments, i.e. the sub-compartment 127 (which is the smaller one of the sub-compartments). Hence, in this configuration of the secondary adjustable volume 170, a first dead volume of a first size is provided. To this end, the compression of air in the compressor 120 occurs in the main cylinder volume 124 and in the sub-compartment 127 of the secondary adjustable volume 126.

(22) As illustrated in FIG. 3e, the valve 170 is set in a position to block the entrance to the smaller one of the sub-compartments, i.e. the sub-compartment 127, while providing a fluid communication between the main cylinder volume 124 and the other one of the sub-compartments, i.e. the sub-compartment 128 (which is the larger one of the sub-compartments). Hence, in this configuration of the secondary adjustable volume 170, a second dead volume of a second size is provided. To this end, the compression of air in the compressor 120 occurs in the main cylinder volume 124 and in the sub-compartment 128 of the secondary adjustable volume 126.

(23) Finally, as illustrated in FIG. 3f, the valve 170 is set in a position to provide passages to both sub-compartments. In other words, the valve 170 is controlled to set the sub-compartment 127 and the sub-compartment 128 in fluid communication with the main cylinder volume 124. Hence, in this configuration of the secondary adjustable volume 170, a third dead volume of a third size is provided. To this end, the compression of air in the compressor 120 occurs in the main cylinder volume 124 together with volume defined by the sub-compartments 127 and 128 of the secondary adjustable volume 126.

(24) Accordingly, it becomes possible to provide a plurality of different dead volume portions of different size. Since the volumes described above in relation to FIGS. 3c to 3f are different in size, it is possible to provide four different geometrical compression ratios.

(25) It should also be noted that the two sub-compartments 127 and 128 may be of the same size. In such example, there is provided a secondary adjustable volume with two different dead volumes, one dead volume defined by one of the sub-compartments, and another dead volume defined by the combined size of the two sub-compartments.

(26) It should be noted that a plurality of dead volume portions of different size can also be provided by other types of arrangement of sub-compartments in combination with other types of valves. In another example, the secondary adjustable volume can be provided by conventional on/off valves, slide valves, reed valves or any other types of valves suitable for being arranged in a compressor environment. By way of example (although not illustrated), the secondary adjustable volume may also be provided by a design where a slide valve is pressed against a port to a sub-compartment for sealing by means of the compression pressure in the compressor working chamber. In such example, a movement of the slide valve may occur at a similar pressure between the main cylinder volume and the secondary adjustable volume.

(27) In another example embodiment (although not shown), each one of the two fixed dead volumes of different size is individually arranged in fluid communication with the main cylinder volume by a first and second valves, respectively.

(28) Optionally, the reciprocating compressor 120 also comprises 172 and 174, as illustrated in FIGS. 3a to 3f. That is, the reciprocating compressor 120 generally comprises the inlet valve 172 for controlling inflow of air into the compressor. The inlet valve may e.g. be a conventional reed valve. Further, the reciprocating compressor 120 comprises an outlet valve 174 for exhaust of the compressed air.

(29) Moreover, the valve 170 is generally controllable by means of the control unit 180, as mentioned above.

(30) In order to control the compression of the air in relation to the operation of the ICE system, in particular the combustion reaction, and the operation of the vehicle, the geometrical compression ratio control as described above is generally based on an engine characteristic of the ICE system. Hence, although strictly not required, the volume of the secondary adjustable volume 126 is adjusted in response to the engine load of the ICE system.

(31) The operation of the engine, i.e. the engine load, can be determined in several different ways. By way of example, the engine load of the ICE system is determined based on an actuation of a vehicle acceleration device, such as an acceleration pedal. The requested propulsion torque may e.g. be determined based on the position of the acceleration pedal, as manipulated by a driver. Typically, the ICE system comprises a sensor arranged to gather data indicating the engine load. The sensor may be arranged in communication with the control unit of the ICE system or the vehicle. The sensor (although not shown) may be arranged to detect a change in engine load and/or determine the engine load of the ICE for a given operational state. Subsequently, a value of the engine load, or an indication of a change in engine load, is transferred to the control unit 180 for further processing. To this end, the control unit 180 is configured to determine the engine load of the ICE system based on the gathered data and further to adjust the volume of the secondary adjustable volume in response to the determined engine load.

(32) In another example embodiment, the ICE system comprises a sensor device (although not shown) for detecting the position of the compressor piston 122 in the compressor cylinder 121. Moreover, the volume of the secondary adjustable volume 126 is adjusted in response to the detected position of the compressor piston 122 in the compressor cylinder 121 so as to adjust the volume of the secondary adjustable volume 126 based on a working point of the compressor 120.

(33) Generally, the valve 170 is regulated (adjusted) by a applying a force on the valve so as to rotate the valve into an open position. Likely, the valve 170 is rotated from one position to another position when the pressure in the cylinder is reduced to certain level, as may be set by the control unit or the function of the valve.

(34) Accordingly, the engine load as well as a change in engine load can be monitored and determined in several different ways.

(35) Optionally, the ICE system is operable such that the fluid communication between the main cylinder volume 121 and the secondary adjustable volume 126 is always open during a compression stroke. If the secondary adjustable volume is regulated in response to the engine load, the ICE system is generally operable such that the fluid communication between the main cylinder and the secondary adjustable volume is always open during a compression stroke and until there is a change in engine load. However, it should be readily appreciated that in other situations, the fluid communication between the main cylinder volume 121 and the secondary adjustable volume 126 may be controlled to be closed during the compression stroke.

(36) Turning now to FIG. 4, which is a perspective view of some additional components of the example embodiment of the ICE system 100 in FIG. 1. Firstly, it should be noted a that full illustration of the cylinders housing the respective pistons have been omitted from FIG. 4 for simplicity of understanding the disclosure and the piston configurations.

(37) Hence, while it should be noted that the ICE system may include several cylinders, the internal combustion engine system 100 here comprises at least a piston combustor assembly 110 having at least one combustion cylinder 111 housing a first combustion piston 112, and a second combustion cylinder 114 housing a second combustion piston 116. As mentioned above, the internal combustion engine system 100 further comprises the compressor 120 having the compressor cylinder 121 housing the compressor piston 122. Also, as depicted in FIG. 4, the ICE system 100 comprises an expander 130 in the form of a two-stroke machine. The expander 130 comprises an expander cylinder 131 housing an expander piston 132.

(38) Turning again to the combustor assembly 110, it should be understood that the first and second combustion pistons 112, 116 are individually arranged inside the first and second combustion cylinders 111, 114, respectively, and are adapted for reciprocating motion therein. Correspondingly, the compressor piston 122 and the expander piston 132 are arranged inside the compressor cylinder 121 and the expander cylinder 131, respectively, and are adapted for reciprocating motion therein.

(39) Moreover, as shown in e.g. FIG. 4, the ICE system 100 comprises a crankshaft 140. The crankshaft is rotatable around an axis of rotation, generally corresponding to a longitudinal axis LA of the crankshaft. The rotatable crankshaft is generally arranged in the ICE system so as to rotate by means of the power pistons and also effect a linear movement of the other piston(s) of the ICE system, as further described in more detail below.

(40) As mentioned above, the ICE system 100 comprises the compressor piston connecting rod 154 connecting the compressor piston 122 to the crankshaft 140, as illustrated in FIG. 4. Further, in FIG. 4, the expander piston 132 is connected to the compressor piston 122 by a connecting element assembly 150. Alternatively, although not shown, the ICE system comprises an expander piston connecting rod connecting the expander piston 132 to the crankshaft 140. In this example, the expander piston 132 may still also be connected to the compressor piston 122 by a similar connecting element assembly.

(41) Correspondingly, as illustrated in FIG. 4, a first combustion piston connecting rod 163 connects the first combustion piston 112 to the crankshaft 140, and a second combustion piston connecting rod 164 connects the second combustion piston 114 to the crankshaft 140. Thus, the above-mentioned reciprocating motions of the pistons can be transferred into a rotational motion of the crankshaft 140.

(42) By way of example, as illustrated in e.g. FIG. 4, the expander piston 132 is connected to the compressor piston 122 by a connecting element assembly 150 in the form of two connecting arms arranged in a respective periphery portion of the expander and compressor cylinders 132, 122. Each one of the connecting arms typically extends from the expander piston 132 to the compressor piston 122. Even though two connecting arms are shown in FIG. 4, it should be understood that other number of connecting arms, or only one connecting arm, may be used within the concept of the disclosure. Moreover, the connecting element assembly 150 may be arranged with no connecting arms, but instead as e.g. a connecting envelope extending from the expander piston 132 to the compressor piston 122, such that the expander piston 132 and the compressor piston 122 move in unison. The connecting element assembly 150 should be rigidly connected the expander piston 132 to the compressor piston 122, such that the expander piston 132 and the compressor piston 122 move in unison. By way of example, the connecting element assembly 150 rigidly connects the expander piston 132 with the compressor piston 122 such that when the compressor piston 122 moves in a downstroke (i.e. in order to compress the air in the compressor cylinder 121), the expander piston 132 moves in a stroke following the motion of the compressor piston 122. Correspondingly, as the expander piston 132 moves in an upstroke, the compressor piston 122 moves in a stroke following the motion of the expander piston 132.

(43) As shown in FIG. 4, the compressor cylinder 121 and the expander cylinder 132 are positioned on opposite sides of, and in close proximity to, the crankshaft 140. Stated differently, a substantial portion of the crankshaft 140 is generally arranged in between the expander piston 132 and the compressor piston 122, such that the substantial portion of crankshaft is arranged between respective crankshaft facing surfaces of the compressor piston and the expander piston, as illustrated in e.g. FIG. 4. In other words, the compressor piston 122, the expander piston 132 and the substantial portion of the crankshaft 140 are arranged along a geometrical axis GA, and the substantial portion of the crankshaft 140 is arranged along the geometrical axis GA in between the compressor piston 122 and the expander piston 132. In this manner, there is provided a so-called compressor-expander arrangement enclosing a substantial portion of the crankshaft 140. The internal position of the components in the ICE system 100 may be described in a different manner.

(44) In at least a third way of describing the internal position of the components in the ICE system 100, the expander piston 132 has a circular, or round, cross section extending in a first geometrical plane, and the compressor piston 122 has a circular, or round, cross section extending in a second geometrical plane, the first and second geometrical planes being positioned in a parallel configuration on opposite sides of the longitudinal axis LA of the crankshaft 140.

(45) As seen in FIG. 4, the expander piston 132 is configured for a reciprocating motion inside of the expander cylinder 131 along the expander axis EA. Correspondingly, the compressor piston 122 is configured for a reciprocating motion inside of the compressor cylinder 121 along a compressor axis CA. Correspondingly, the first combustion piston 112 is configured for a reciprocating motion inside of the first combustion cylinder 111 along a combustion axis CoA1, and the second combustion piston 116 is configured for a reciprocating motion inside of the second combustion cylinder 114 along a combustion axis CoA2. As seen in e.g. FIG. 4, the expander cylinder 130 and the compressor cylinder 120 are co-axially arranged, i.e. the expander axis EA and the compressor axis CA are aligned.

(46) Turning back to FIG. 4, it is shown that the first combustion cylinder 111 and the second combustion cylinder 114 may be described as protruding laterally from the crankshaft 140 compared to the expander cylinder 130. Thus, the expander cylinder 130, and the first and second combustion cylinders 111, 114 are arranged inside the ICE system 100 in such way that the expander axis EA is angled in relation to each one of the combustion axis CoA1, CoA2 by between 40 degrees and 90 degrees, preferably between 50 degrees and 75 degrees, and more preferably between 55 degrees and 65 degrees, such as e.g. about 60 degrees.

(47) The function of the ICE system 100 will now be further elucidated with reference FIG. 4. The compressor cylinder 120 is configured to draw a volume of ambient air, compress the air, and transfer the compressed air to the first and second combustion cylinders 111, 114. The first and second combustion cylinders 111, 114 are configured to be energized by forces of combustion, e.g. by ignition of the fuel by means of a spark plug (e.g. as for a petrol or gasoline driven engine) or heat originating from compression (e.g. as for a diesel driven engine). The expander cylinder 130 is configured to receive exhaust gases from the first and second combustion pistons 112, 116. Transportation of air, fuel and gases are carried out by means of corresponding inlet valves 136, transfer ports, and outlet valves 136 known by the skilled person in the art, and which fluidly interconnects the compressor cylinder 121, the first and second combustion cylinders 111, 114 and the expander cylinder 131.

(48) In one example, the crankshaft is driven by at least one of the combustion pistons by means of a corresponding combustion piston connecting rod, and is driven by the expander piston by means of a corresponding expander piston connecting rod, wherein the compressor piston is driven by the crankshaft by means of the expander piston.

(49) However, a slightly opposite arrangement may also be possible, which is also illustrated in the ICE system in FIG. 4. That is, the expander piston 132 is not directly connected to the crankshaft 140, via its own connecting rod, but is instead connected to the crankshaft 140 via the connecting element assembly 150, the compressor piston 122 and the compressor piston connecting rod 154. Hereby, the rotational motion of the crankshaft 140 is transferred into a reciprocating motion of the expander piston 132 via the compressor piston connecting rod 154. Thus, the crankshaft 140 is driven by the first and second combustion pistons 112, 116 by means of the respective combustion piston connecting rods and is driven by the compressor piston by means of the compressor piston connecting rod 154, but the crankshaft 140 drives the expander piston 132 by means of the compressor piston 122 and the compressor piston connecting rod 154.

(50) In FIG. 5, there is depicted a method 300 for controlling a geometrical compression ratio of the reciprocating compressor 120, as described above in relation to FIG. 1 and further in FIGS. 3a to 3f and FIG. 4. The method is generally performed by the control unit 180 during operation of the ICE system 100. Optionally, as a first step, the method comprises the step of determining 105 an engine load of the ICE system 100. The engine load may generally be determined as previously described herein. Subsequently, in step 310, the volume of the secondary adjustable volume 126 is adjusted to a first adjusted volume. That is, the volume of the secondary adjustable volume 126 is adjusted in response to the determined engine load. Thereafter, in step 320, the reciprocating compressor pressurizes the air to a first geometrical compression ratio. Subsequently, the compressed air is transferred to the combustion cylinder(s), as mentioned above in relation to FIG. 4.

(51) It is to be understood that the present disclosure is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.