COMPRESSION-END PRESSURE CONTROL DEVICE AND ENGINE SYSTEM

Abstract

 A compression-end pressure control device (300) is disclosed for controlling a supply amount of a pressurized working fluid for a variable compression device, the variable compression device that increases a compression ratio of a combustion chamber (R1) by supplying the working fluid to a fluid chamber (R3), the compression-end pressure control device (300) including: a compression ratio-setting device (305) that decreases a compression ratio of the combustion chamber (R1) by controlling the variable compression device in the case where a compression end pressure acquired in the combustion chamber (R1) is higher than a reference range determined in advance; and a variable compression device adjusting device (306) that controls a supply amount of the working fluid based on the compression ratio determined by the compression ratio-setting device (305).

Description

[Technical Field]

[0001] The present disclosure relates to a compression-end pressure control device and an engine system. Priority is claimed on Japanese Patent Application No. 2017-243275, filed December 19, 2017, the content of which is incorporated herein by reference.

[Background Art]

[0002] For example, Patent Document 1 discloses a large reciprocating piston combustion engine including a crosshead. The large reciprocating piston combustion engine of Patent Document 1 is a dual fuel engine capable of operating with both a liquid fuel such as heavy oil and a gaseous fuel such as natural gas. The large reciprocating piston combustion engine of Patent Document 1 copes with both a compression ratio suitable for operation with a liquid fuel and a compression ratio suitable for operation with a gaseous fuel. Therefore, an adjustment mechanism for changing a compression ratio by moving a piston rod by a hydraulic pressure is provided in the crosshead.

[Citation List]

[Patent Document]

[0003] [Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. 2014-020375

[Summary of Invention]

[Technical Problem]

[0004] In a multi-cylinder engine, in order to suppress variation of a compression-end pressure of each cylinder (a combustion chamber pressure at a top dead center), a valve-closing timing of an exhaust valve is changed and thus a compression-end pressure is adjusted. In an engine system including a variable compression device, a valve-closing timing of the exhaust valve is changed and thus a compression-end pressure between a plurality of cylinders is adjusted. However, if a valve-closing timing of the exhaust valve is delayed in order to decrease a compression-end pressure, a large amount of air is discharged from a combustion chamber. Therefore, an air filling amount in the combustion chamber decreases, and a concentration of fuel gas relative to gas in the combustion chamber increases. As a result, abnormal combustion may occur in the combustion chamber.

[0005] The present disclosure has been made in view of the above-described problems, and an object thereof is to prevent abnormal combustion when controlling a compression-end pressure.

[Solution to Problem]

[0006] The present disclosure employs, as a first aspect for solving the above-described problem, means of a compression-end pressure control device for controlling a supply amount of a pressurized working fluid of a variable compression device, the variable compression device that increases a compression ratio of a combustion chamber by supplying the working fluid to a fluid chamber, including a compression ratio-setting device that sets a compression ratio so as to decrease a compression ratio of the combustion chamber by controlling the acquired variable compression device in the case where a compression-end pressure acquired in the combustion chamber is higher than a reference range determined in advance, and a variable compression device adjusting device that controls a supply amount of the working fluid based on the compression ratio determined by the compression ratio-setting device.

[0007] The present disclosure employs, as a second aspect, means of the compression-end pressure control device according to the first aspect, further including an exhaust valve-adjusting device that makes a valve-closing timing of an exhaust valve device that opens and closes an exhaust port in the combustion chamber earlier than a current valve-closing timing, in the case where the compression-end pressure is lower than the reference range.

[0008] The present disclosure employs, as a third aspect, means of the compression-end pressure control device according to the first or second aspect, further including an abnormal combustion-estimating device that estimates whether or not abnormal combustion is occurring under the compression-end pressure, based on a composition of fuel to be supplied to the combustion chamber, in the case where the compression-end pressure in the combustion chamber is higher than the reference range determined in advance, wherein compression ratio-setting device determines the compression ratio based on an estimation result of abnormal combustion-estimating means.

[0009] The present disclosure employs, as a fourth aspect, means of an engine system including a plurality of cylinders each one of which includes a combustion chamber, a variable compression device including a fluid chamber in which a piston rod is moved in a direction to increase a compression ratio of the combustion chamber by supplying a pressurized working fluid, and the compression-end pressure control device according to any one of first to third aspects.

[Advantageous Effects of Invention]

[0010] According to the present disclosure, in the case where a compression-end pressure is higher than a reference range determined in advance, a compression-end pressure is decreased by lowering a compression ratio of the combustion chamber. Therefore, a discharge amount of gas in the combustion chamber does not change, and thus it is possible to decrease a compression-end pressure without reducing the amount of air charged into the combustion chamber. Therefore, it is possible to prevent abnormal combustion without increasing the concentration of gaseous fuel in the combustion chamber.

[Brief Description of Drawings]

[0011] 

FIG. 1 is a sectional view of an engine system according to an embodiment of the present disclosure.

FIG. 2 is a schematic sectional view showing a part of the engine system according to the embodiment of the present disclosure.

FIG. 3 is a block diagram of a controller of the engine system according to the embodiment of the present disclosure.

FIG. 4 is a flowchart of compression-end pressure control of the controller according to the embodiment of the present disclosure.

FIG. 5 is a flowchart of a compression ratio changing control of the controller according to the embodiment of the present disclosure.

[Description of Embodiments]

[0012] Hereinafter, an embodiment of an engine system 100 according to the present disclosure will be described with reference to the drawings.

[0013] An engine system 100 of the present embodiment is mounted on a ship such as a large tanker, for example, and includes an engine 1, a supercharger 200, a controller 300 (a compression-end pressure control device), an in-cylinder pressure sensor 400, and a gas chromatography instrument 500, as shown in FIG. 1. Note that, in the present embodiment, the engine 1 is regarded as a main machine and the supercharger 200 is regarded as an auxiliary machine, and the engine 1 (the main engine) and the supercharger 200 (the auxiliary machine) are described as separate bodies. However, the supercharger 200 can be configured as a part of the engine 1.

[0014] The engine 1 is a multi-cylinder diesel engine of a uniflow scavenging type, and can operate in a gas operation mode in which a gaseous fuel such as natural gas is burned together with a liquid fuel such as heavy oil, and a diesel operation mode in which a liquid fuel such as heavy oil is burned. Note that, in the gas operation mode, only a gaseous fuel may be burned. The engine 1 includes a frame 2, a cylinder unit 3, a piston 4, an exhaust valve unit 5, a piston rod 6, a crosshead 7, a hydraulic unit 8 (a pressure-increasing mechanism), a connecting rod 9, a crank angle sensor 10, a crank shaft 11, a scavenging reservoir 12, an exhaust reservoir 13, and an air cooler 14. In addition, the cylinder unit 3, the piston 4, the exhaust valve unit 5, and the piston rod 6 constitute a cylinder. Note that, in FIG. 1, a side on which the exhaust valve unit 5 is provided may be referred to as an upper side, and the side on which the crank shaft 11 described later is provided may be referred to as a lower side. The view seen in the center axis direction of the piston rod 6 may be referred to as a plan view.

[0015] The frame 2 is a strength member that supports the entire engine 1, and accommodates the crosshead 7, the hydraulic unit 8, and the connecting rod 9. Further, in the frame 2, a crosshead pin 7a of the crosshead 7 described later is provided to be capable of reciprocation.

[0016] The cylinder unit 3 includes a cylindrical cylinder liner 3a, a cylinder head 3b, and a cylinder jacket 3c. The cylinder liner 3a is a cylindrical member, and a sliding surface on which the piston 4 slides is formed on an inner side thereof. A space surrounded by an inner peripheral surface of the cylinder liner 3a and the piston 4 is a combustion chamber R1. In addition, a plurality of scavenging ports S arranged along a circumferential direction are formed at a lower portion of the cylinder liner 3a. Each scavenging port S has an opening that opens on an inner peripheral surface and an outer peripheral surface of the cylinder liner 3a, and allows a scavenging chamber R2 in the cylinder jacket 3c and an inside of the cylinder liner 3a to communicate with each other. The cylinder head 3b is a lid member, and is provided at upper end of the cylinder liner 3a. The cylinder head 3b includes an exhaust port H formed at a center in plan view, and is coupled to the exhaust reservoir 13. In addition, a fuel injection valve (not shown) is provided in the cylinder head 3b. Further, an in-cylinder pressure sensor (not shown) is provided near the fuel injection valve of the cylinder head 3b. The in-cylinder pressure sensor detects the pressure in the combustion chamber R1 and sends the detected pressure to the controller 300. The cylinder jacket 3c is a cylindrical member, is provided between the frame 2 and the cylinder liner 3a, a lower end of the cylinder liner 3a is inserted thereinto, and the scavenging chamber R2 is formed therein. In addition, the scavenging chamber R2 of the cylinder jacket 3c is coupled to the scavenging reservoir 12.

[0017] The piston 4 is a substantially columnar member, is coupled to the piston rod 6 described later, and is disposed inside the cylinder liner 3a. In addition, a piston ring (not shown) is provided on an outer peripheral surface of the piston 4, and a gap between the piston 4 and the cylinder liner 3a is sealed with the piston ring. The piston 4 slides in the cylinder liner 3a with the piston rod 6 due to fluctuation of the pressure in the combustion chamber R1.

[0018] The exhaust valve unit 5 includes an exhaust valve 5a, an exhaust valve housing 5b, and an exhaust valve driving unit 5c. The exhaust valve 5a is provided inside the cylinder head 3b, and closes the exhaust port H in the cylinder unit 3 according to the exhaust valve driving unit 5c. The exhaust valve housing 5b is a cylindrical housing, and accommodates an end of the exhaust valve 5a far from the cylinder unit 3. The exhaust valve driving unit 5c is an actuator that moves the exhaust valve 5a in a direction along a stroke direction of the piston 4.

[0019]  The piston rod 6 is a long member having one end coupled to the piston 4 and the other end connected to the crosshead pin 7a. The other end of the piston rod 6 is inserted into the crosshead pin 7a, and the connecting rod 9 is rotatably connected to the crosshead pin 7a. Further, the piston rod 6 includes a large diameter portion in which a diameter of a part of the other end is larger than each diameter in other parts of the piston rod 6.

[0020] The crosshead 7 includes the crosshead pin 7a, a guide shoe 7b, and a lid member 7c. As shown in FIG. 2, the crosshead pin 7a is a columnar member, and movably connects the piston rod 6 and the connecting rod 9 to each other. The crosshead pin 7a has an insertion space into which the other end of the piston rod 6 is inserted. In this insertion space, a hydraulic chamber R3 (a fluid chamber) through which supply and discharge of hydraulic oil (working fluid) are performed is formed between the large diameter portion of the piston rod 6 and the crosshead pin. A lower surface of a flange of the piston rod 6 and a bottom surface of the insertion space that is a bottom surface of the hydraulic chamber R3 are parallel with each other. An outlet hole O is formed in the crosshead pin 7a below a center thereof and penetrates the crosshead pin 7a along an axial direction thereof. The outlet hole O is an opening through which cooling oil (lubricating fluid) that has passed through a cooling passage (not shown) of the piston rod 6 flows and is discharged. The crosshead pin 7a is provided with therein a supply flow path R4 coupling the hydraulic chamber R3 and a plunger pump 8c described later to each other, and a relief flow path R5 coupling the hydraulic chamber R3 and a relief valve 8f described later to each other.

[0021]  The guide shoe 7b is a member that rotatably supports the crosshead pin 7a, and moves on a guide rail (not shown) along a stroke direction of the piston 4 with the crosshead pin 7a. As the guide shoe 7b moves along the guide rail, rotational movement of the crosshead pin 7a is restricted, and movement of the crosshead pin 7a in directions other than a linear direction along a stroke direction of the piston 4 is also restricted. The lid member 7c is an annular member, is fixed to an upper portion of the crosshead pin 7a, and an end of the piston rod 6 far from the cylinder unit 3 is inserted thereinto. The crosshead 7 transmits linear movement of the piston 4 to the connecting rod 9.

[0022] As shown in FIG. 2, the hydraulic unit 8 includes a supply pump 8a, an oscillating pipe 8b, a plunger pump 8c, a first check valve 8d and a second check valve 8e of the plunger pump 8c, and a relief valve 8f. Further, the piston rod 6, the crosshead 7, the hydraulic unit 8, and the controller 300 function as a variable compression device according to the present disclosure.

[0023] The supply pump 8a is a pump that increases the pressure of hydraulic oil supplied from a hydraulic oil tank (not shown) and supplies the hydraulic oil to the plunger pump 8c based on an instruction received from the controller 300. The supply pump 8a is driven with the electric power of a battery of a ship, and can operate before a liquid fuel is supplied to the combustion chamber R1. The oscillating pipe 8b is a pipe coupling the supply pump 8a and the plunger pump 8c of each cylinder to each other, and is provided to oscillate between the plunger pump 8c moving with the crosshead pin 7a and the supply pump 8a fixed and not moving.

[0024] The plunger pump 8c is fixed to the crosshead pin 7a, and includes a rod-shaped plunger 8c1, a cylindrical cylinder 8c2 that slidably accommodates a plunger 8c1, and a plunger driving unit 8c3. The plunger pump 8c slides in the cylinder 8c2 by the plunger 8c1 being coupled to a driving unit (not shown), and increases the pressure of hydraulic oil to supply the hydraulic oil to the hydraulic chamber R3. Further, the first check valve 8d is provided at an opening for discharging hydraulic oil, provided at an end of the cylinder 8c2 close to the supply flow path R4. Further, the second check valve 8e is provided at an opening for sucking hydraulic oil, provided on a side peripheral surface of the cylinder 8c2. The plunger driving unit 8c3 is coupled to the plunger 8c1, and reciprocates the plunger 8c1 based on an instruction received from the controller 300.

[0025] The first check valve 8d is configured to be closed by a valve body being biased toward an inside of the cylinder 8c2, and prevents the hydraulic oil supplied to the hydraulic chamber R3 from flowing back to the cylinder 8c2. Further, when the pressure of the hydraulic oil in the cylinder 8c2 becomes larger than a biasing force (a valve opening pressure) of a biasing member for biasing the valve body of the first check valve 8d, the first check valve 8d is opened by the valve body being pushed with the hydraulic oil in the cylinder 8c2. The second check valve 8e is configured to be closed by a valve body being biased toward an outside of the cylinder 8c2, and prevents the hydraulic oil supplied to the cylinder 8c2 from flowing back to the supply pump 8a. Further, when the pressure of the hydraulic oil supplied from the supply pump 8a becomes larger than a biasing force (a valve opening pressure) of a biasing member for biasing the valve body of the second check valve 8e, the second check valve 8e is opened by the valve body being pushed with the hydraulic oil supplied from the supply pump 8a. Note that, the first check valve 8d has a valve opening pressure higher than a valve opening pressure of the second check valve 8e. Therefore, during a steady operation in which the engine system is operated at a preset compression ratio, the valve is not opened by the pressure of the hydraulic oil supplied from the supply pump 8a.

[0026] The relief valve 8f is provided in the crosshead pin 7a, and includes a main body portion 8f1 and a relief valve driving unit 8f2. The main body portion 8f1 is a valve body coupled to the hydraulic chamber R3 and a hydraulic oil tank (not shown). The relief valve driving unit 8f2 is coupled to the main body portion 8f1, and opens and closes the main body portion 8f1 based on an instruction received from the controller 300. When the relief valve 8f is opened by the relief valve driving unit 8f2, the hydraulic oil stored in the hydraulic chamber R3 is returned to the hydraulic oil tank.

[0027] As shown in FIG. 1, the connecting rod 9 is a long member having one end connected to the crosshead pin 7a and the other end connected to the crank shaft 11. The connecting rod 9 converts linear movement of the piston 4 transmitted to the crosshead pin 7a into rotational movement. The crank angle sensor 10 is a sensor for measuring a crank angle of the crank shaft 11, and transmits a crank pulse signal for calculating the crank angle to the controller 300.

[0028] The crank shaft 11 is a long member, is coupled to a connecting rod 9 provided in each cylinder, and rotates with rotational movement transmitted by the connecting rod 9. Thereby, for example, power is transmitted to a screw or the like. The scavenging reservoir 12 is provided between the cylinder jacket 3c and the supercharger 200, and air pressurized by the supercharger 200 flows therein. Further, the scavenging reservoir 12 is provided with an air cooler 14 therein. The exhaust reservoir 13 is a tubular member, and is coupled to the exhaust port H of each cylinder and is coupled to the supercharger 200. The gas discharged from the exhaust port H is temporarily stored in the exhaust reservoir 13 and thus is supplied to the supercharger 200 in a state where pulsation is suppressed. The air cooler 14 cools air in the scavenging reservoir 12.

[0029] The supercharger 200 pressurizes air sucked from an intake port (not shown) by a turbine rotated with gas discharged from an exhaust port H and supplies the pressurized air to a combustion chamber R1 via a scavenging port S.

[0030] The controller 300 is a computer that controls a fuel supply amount and the like of each cylinder based on an operation performed by an operator of a ship. The controller 300 includes a central processing unit (CPU), a memory such as a random-access memory (RAM) and a read-only memory (ROM), storage device such as a solid-state drive (SSD) and a hard disk drive (HDD), and the like. Further, the controller 300 changes a compression ratio in the combustion chamber R1 by controlling the hydraulic unit 8.

[0031] Specifically, as shown in FIG. 3, the controller 300 includes a compression-end pressure-determining unit 301, a self-ignition timing calculating unit 302, an abnormal combustion-estimating unit 303 (an abnormal combustion-estimating device), and an exhaust valve-adjusting unit 304 (an exhaust valve-adjusting device), a compression ratio-setting unit 305 (a compression ratio-setting device), and a hydraulic pressure-adjusting unit 306 (a variable compression device adjusting device). The compression-end pressure-determining unit 301 compares a compression-end pressure acquired from the in-cylinder pressure sensor 400 with a reference range stored in advance. The reference range stored in advance is determined from, for example, a map based on an engine speed, an engine load, and a compression-end pressure.

[0032] The self-ignition timing calculating unit 302 calculates a self-ignition timing (information on abnormal combustion) with reference to a self-ignition timing map stored in advance, based on information including a composition of a gaseous fuel acquired by the gas chromatography instrument 500. The self-ignition timing map stores a time from start of fuel injection to self-ignition in a plurality of patterns of combinations of content ratios of respective components of a gaseous fuel. That is, the self-ignition timing calculating unit 302 calculates a self-ignition timing from a time from start of fuel injection to self-ignition in patterns of combinations of content ratios of respective components of a gaseous fuel closest to a detected fuel composition, with reference to the self-ignition timing map.

[0033] The abnormal combustion-estimating unit 303 calculates a distribution of combustion gas of a gaseous fuel in the combustion chamber R1 and calculates a timing of the combustion gas spreading to the combustion chamber R1 (a combustion completion timing), based on an injection amount of a gaseous fuel and the acquired compression-end pressure. Then, the abnormal combustion-estimating unit 303 determines whether or not abnormal combustion is occurring by comparing the combustion completion timing with the self-ignition timing and determining whether or not the self-ignition timing is earlier than the combustion completion timing. In the case where the self-ignition timing is earlier than the combustion completion timing, it is determined that there is a high possibility that abnormal combustion occurs, and in the case where the self-ignition timing is the same as the combustion completion timing and in the case where the self-ignition timing is later than the combustion completion timing, it is determined that there is a high possibility that abnormal combustion does not occur.

[0034] The exhaust valve-adjusting unit 304 opens and closes the exhaust valve 5a by controlling the exhaust valve driving unit 5c. In addition, the exhaust valve-adjusting unit 304 controls the exhaust valve driving unit 5c such that a valve-closing timing of the exhaust valve 5a advances (is made earlier) in the case where a compression-end pressure is lower than a reference range, based on a determination result of the compression-end pressure-determining unit 301.

[0035] The compression ratio-setting unit 305 calculates an optimal compression ratio according to the type of fuel, based on an external input. Further, the compression ratio-setting unit 305 determines a compression ratio so as to be maximum in a range in which a gaseous fuel self-ignites at a compression end with reference to a compression ratio-setting map stored in advance, based on the self-ignition timing calculated by the self-ignition timing calculating unit 302. The compression ratio is also termed a compression ratio-setting value. A correlation between the self-ignition timing and the compression ratio is stored in the compression ratio-setting map.

[0036]  The hydraulic pressure-adjusting unit 306 adjusts a supply amount of hydraulic oil with respect to the hydraulic chamber R3 by controlling the plunger pump 8c and the relief valve 8f of the hydraulic unit 8, based on the compression ratio (the compression ratio-setting value) acquired from the compression ratio-setting unit 305.

[0037] The in-cylinder pressure sensor 400 is a sensor that measures the pressure in the combustion chamber R1, and is provided on an inner wall of the combustion chamber R1. The gas chromatography instrument 500 acquires a composition of a gaseous fuel to be supplied to the combustion chamber R1 when a gaseous fuel is supplied to the combustion chamber R1, and detects a distribution for each composition of a gaseous fuel. The gas chromatography instrument 500 detects a composition distribution of a gaseous fuel at a frequency of, for example, about once a day or about once an hour.

[0038] In the engine system 100, the fuel injected into the combustion chamber R1 from a fuel injection valve (not shown) is ignited and exploded, the piston 4 is slid in the cylinder liner 3a, and the crank shaft 11 is rotated. More specifically, the fuel supplied to the combustion chamber R1 is compressed, rises in temperature, and spontaneously ignites by being mixed with the pressurized air flowing-in from the scavenging port S and then by moving the piston 4 in a direction toward the top dead center in a stroke direction. In addition, in the case where the fuel is a liquid fuel, a liquid fuel rises in temperature, evaporates, and spontaneously ignites in the combustion chamber R1.

[0039] Then, the fuel in the combustion chamber R1 spontaneously ignites and rapidly expands, so that the pressure is applied to the piston 4 in a direction toward a bottom dead center in a stroke direction. Thereby, the piston 4 moves in a direction toward the bottom dead center with the piston rod 6, and the crank shaft 11 is rotated via the connecting rod 9. Further, when the piston 4 is moved to the bottom dead center, the pressurized air flows from the scavenging port S into the combustion chamber R1. The exhaust port H is opened by driving the exhaust valve unit 5. Thereby, exhaust gas in the combustion chamber R1 is pushed out to the exhaust reservoir 13 through the exhaust port H with the pressurized air.

[0040] In the case of increasing the compression ratio in order to use a gaseous fuel, the compression ratio-setting unit 305 of the controller 300 calculates an optimum compression ratio, the hydraulic pressure-adjusting unit 306 drives the supply pump 8a, and hydraulic oil is supplied to the plunger pump 8c. Then, the hydraulic pressure-adjusting unit 306 of the controller 300 drives the plunger pump 8c, pressurizes the hydraulic oil until the pressure reaches a pressure at which the piston rod 6 can be lifted, and supplies the hydraulic oil to the hydraulic chamber R3. Due to the pressure of the hydraulic oil supplied to the hydraulic chamber R3, the end (the large diameter portion) of the piston rod 6 is lifted from the bottom surface of the hydraulic chamber R3. Accordingly, the piston rod 6 is moved upward, and the top dead center of the piston 4 is moved upward (that is, near the exhaust port H).

[0041] In the case of decreasing the compression ratio in order to use a liquid fuel, the compression ratio-setting unit 305 of the controller 300 calculates an optimum compression ratio, the hydraulic pressure-adjusting unit 306 drives the relief valve 8f, and the hydraulic chamber R3 and a hydraulic oil tank (not shown) are in a communication state with each other. Then, the weight of the piston rod 6 is applied to the hydraulic oil in the hydraulic chamber R3, and the hydraulic oil in the hydraulic chamber R3 is pushed out to the hydraulic oil tank via the relief valve 8f. Thereby, the hydraulic oil in the hydraulic chamber R3 decreases, and the piston rod 6 moves downward (that is, near the crank shaft 11). Accordingly, the top dead center of the piston 4 is moved downward.

[0042] Adjustment of the compression-end pressure will be described with reference to FIGs. 4 and 5. After an operation of changing the compression ratio according to the type of fuel (liquid fuel or gaseous fuel) is completed, the controller 300 causes the compression-end pressure-determining unit 301 to acquire the compression-end pressure (step S1) and to compare the acquired compression-end pressure with a reference range determined in advance (step S2). In the case where the acquired compression-end pressure is lower than the reference range, the controller 300 causes the exhaust valve-adjusting unit 304 to control the exhaust valve driving unit 5c and to advance the valve-closing timing of the exhaust valve 5a (step S3). Further, in the case where the acquired compression-end pressure is within the reference range, the controller 300 ends flow. Further, in the case where the acquired compression-end pressure is higher than the reference range, the controller 300 causes the variable compression device to change the compression ratio (step S4). By making the compression-end pressures of all the cylinders within the reference range by such control, variations in the compression-end pressures of the respective cylinders are prevented.

[0043] An operation of step S4 will be described in detail with reference to FIG. 5. First, when a gaseous fuel is supplied to the combustion chamber R1, the controller 300 acquires a composition of a gaseous fuel to be supplied to the combustion chamber R1 from the gas chromatography instrument 500 (step S11), and causes the self-ignition timing calculating unit 302 to calculate the self-ignition timing with the self-ignition timing map (step S12).

[0044] Then, the controller 300 causes the abnormal combustion-estimating unit 303 to calculate the combustion completion timing based on the injection amount and a combustion speed of a gaseous fuel (step S13). Next, the controller 300 causes the abnormal combustion-estimating unit 303 to determine whether or not the calculated self-ignition timing is earlier than the calculated combustion completion timing under the compression-end pressure acquired (step S14).

[0045] In the case where the determination in step S14 is YES, that is, in the case where the self-ignition timing is earlier than the combustion completion timing, there is a high possibility that the air-fuel mixture self-ignites earlier than the combustion gas spreads to the combustion chamber R1 and abnormal combustion occurs. Therefore, the controller 300 causes the compression ratio-setting unit 305 to determine the compression ratio with the compression ratio-setting map so that the compression ratio is lower than a current compression ratio of the combustion chamber R1 (step S15). Then, in order to lower the compression ratio so as to match the determined compression ratio (the compression ratio-setting value), the controller 300 causes the hydraulic pressure-adjusting unit 306 to reduce the supply amount of the hydraulic oil to be supplied to the hydraulic chamber R3 (Step S16).

[0046] Further, in the case where the determination in step S14 is NO, that is, in the case where the self-ignition timing is later than the combustion completion timing, or the combustion completion timing and the self-ignition timing are simultaneous, the flow ends.

[0047] Note that, the amount of movement of the piston rod 6 with the change in the compression ratio depending on the type of fuel is much larger than the amount of movement of the piston rod 6 with the change in the compression ratio due to adjustment of the compression-end pressure. Therefore, by changing the compression ratio due to adjustment of the compression-end pressure after changing the compression ratio depending on the type of fuel, the optimum compression ratio for each fuel can be obtained.

[0048] According to the present embodiment, in the case where the acquired compression-end pressure is higher than the reference range determined in advance, the compression-end pressure is decreased by lowering the compression ratio of the combustion chamber R1. Therefore, the discharge amount of gas in the combustion chamber R1 does not change, and thus it is possible to decrease the compression-end pressure without reducing the amount of air charged into the combustion chamber R1. Therefore, it is possible to prevent abnormal combustion without increasing the concentration of gaseous fuel in the combustion chamber R1.

[0049] Further, according to the present embodiment, in the case where the acquired compression-end pressure is lower than the reference range determined in advance, the compression-end pressure is increased by making a valve-closing timing of the exhaust valve 5a earlier. Therefore, it is possible to increase the compression-end pressure without reducing the amount of air charged into the combustion chamber R1. Therefore, it is possible to prevent abnormal combustion without increasing the concentration of gaseous fuel in the combustion chamber R1.

[0050] Further, according to the present embodiment, the self-ignition timing calculating unit 302 can calculate the self-ignition timing based on the composition of the fuel, and the compression ratio-setting unit 305 can determine the compression ratio of the combustion chamber R1 based on the self-ignition timing such that abnormal combustion does not occur. Therefore, it is possible to prevent abnormal combustion by determining the compression ratio based on the probability of occurrence of abnormal combustion that differs depending on the composition of a gaseous fuel.

[0051] In the above, the preferred embodiment of the present disclosure has been described with reference to the drawings, but the present disclosure is not limited to the above embodiment. The shapes, combinations, and the like of the constituent members shown in the above-described embodiments are merely examples, and can be variously changed based on design requirements and the like without departing from the spirit of the present disclosure.

[0052] Further, in the above-described embodiment, the engine system 100 is configured to include the gas chromatography instrument 500, but the present invention is not limited to this. In the case where a composition of a gaseous fuel is known in advance, the gas chromatography instrument 500 may not be provided. Further, a composition acquisition device may have a configuration other than the gas chromatography instrument 500.

[0053] In the above-described embodiment, whether or not abnormal combustion is occurring is determined based on information input from the in-cylinder pressure sensor 400, but the present disclosure is not limited to this. For example, by providing a vibration sensor in the combustion chamber R1, it may be determined whether or not abnormal combustion is occurring based on information input from the vibration sensor.

[0054] Further, in the above embodiment, in the case where the compression-end pressure is increased, the adjustment by the exhaust valve-adjusting unit 304 is performed, but the present invention is not limited to this. In the case of increasing the compression-end pressure, for example, the hydraulic pressure-adjusting unit 306 may adjust the compression-end pressure.

[Industrial Applicability]

[0055] According to the present disclosure, in the case where a compression-end pressure is higher than a reference range determined in advance, a compression-end pressure is decreased by lowering a compression ratio of the combustion chamber. Therefore, a discharge amount of gas in the combustion chamber does not change, and thus it is possible to decrease a compression-end pressure without reducing the amount of air charged into the combustion chamber. Therefore, it is possible to prevent abnormal combustion without increasing the concentration of gaseous fuel in the combustion chamber.

[Reference Signs List]

[0056] 

1 Engine

2 Frame

3 Cylinder unit

3a Cylinder liner

3b Cylinder head

3c Cylinder jacket

4 Piston

5 Exhaust valve unit

5a Exhaust valve

5b Exhaust valve housing

5c Exhaust valve driving unit

6 Piston rod

7 Crosshead

7a Crosshead pin

7b Guide shoe

7c Lid member

8 Hydraulic unit

8a Supply pump

8b Oscillating pipe

8c Plunger pump

8c1 Plunger

8c2 Cylinder

8c3 Plunger driving unit

8d First check valve

8e Second check valve

8f Relief valve

8f1 Main body portion

8f2 Relief valve driving unit

9 Connecting rod

10 Crank angle sensor

11 Crank shaft

12 Scavenging reservoir

13 Exhaust reservoir

14 Air cooler

100 Engine system

200 Supercharger

300 Control unit (compression-end pressure control device)

301 Compression-end pressure-determining unit

302 Self-ignition timing calculating unit

303 Abnormal combustion-estimating unit (abnormal combustion-estimating device)

304 Exhaust valve-adjusting unit (exhaust valve-adjusting device)

305 Compression ratio-setting unit (compression ratio-setting device)

306 Hydraulic pressure-adjusting unit (variable compression device adjusting device)

400 In-cylinder pressure sensor

500 Gas chromatography instrument

H Exhaust port

O Outlet hole

R1 Combustion chamber

R2 Scavenging chamber

R3 Hydraulic chamber (fluid chamber)

R4 Supply flow path

R5 Relief flow path

S Scavenging port

Claims

1. A compression-end pressure control device for controlling a supply amount of a pressurized working fluid for a variable compression device, the variable compression device that increases a compression ratio of a combustion chamber by supplying the working fluid to a fluid chamber, the compression-end pressure control device comprising:

a compression ratio-setting device that sets a compression ratio so as to decrease a compression ratio of the combustion chamber by controlling the variable compression device in the case where a compression end pressure acquired in the combustion chamber is higher than a reference range determined in advance; and

a variable compression device adjusting device that controls a supply amount of the working fluid based on the compression ratio determined by the compression ratio-setting device.

2. The compression-end pressure control device according to claim 1, further comprising:
an exhaust valve-adjusting device that makes a valve-closing timing of an exhaust valve device that opens and closes an exhaust port in the combustion chamber earlier than a current valve-closing timing, in the case where the compression-end pressure is lower than the reference range.

3. The compression-end pressure control device according to claim 1, further comprising:

an abnormal combustion-estimating device that estimates whether or not abnormal combustion is occurring under the compression-end pressure, based on a composition of fuel to be supplied to the combustion chamber, in the case where the compression-end pressure in the combustion chamber is higher than the reference range,

wherein the compression ratio-setting device determines the compression ratio based on an estimation result of the abnormal combustion-estimating device.

4. The compression-end pressure control device according to claim 2, further comprising:

an abnormal combustion-estimating device that estimates whether or not abnormal combustion is occurring under the compression-end pressure, based on a composition of fuel to be supplied to the combustion chamber, in the case where the compression-end pressure in the combustion chamber is higher than the reference range,

wherein the compression ratio-setting device determines the compression ratio based on an estimation result of the abnormal combustion-estimating device.

5. An engine system, comprising:

a plurality of cylinders each one of which includes a combustion chamber;

a variable compression device including a fluid chamber in which a piston rod is moved in a direction to increase a compression ratio of the combustion chamber by supplying a pressurized working fluid; and

the compression-end pressure control device according to any one of claims 1 to 4.

Drawing