CN112302810B

CN112302810B - Diesel engine for ship

Info

Publication number: CN112302810B
Application number: CN201910681676.4A
Authority: CN
Inventors: 柳润; 松田力; 沟口顺之
Original assignee: Japan Engine Corp
Current assignee: Japan Engine Corp
Priority date: 2019-07-26
Filing date: 2019-07-26
Publication date: 2023-06-16
Anticipated expiration: 2039-07-26
Also published as: CN112302810A

Abstract

The invention provides a marine diesel engine capable of suppressing the increase of heat loss and improving fuel consumption. In a marine diesel engine, the stroke cylinder diameter ratio S/D is 4.4 or more. The nominal value of the marine diesel engine is selected from the range of the maximum net average effective pressure of the engine design to the minimum net average effective pressure of the engine design. When the rated value is selected so that the derating rate Rd of the marine diesel engine becomes 1.00, the stroke volume compression ratio is 19 to 21, and when the rated value is selected so that the derating rate Rd of the marine diesel engine becomes 0.75, the stroke volume compression ratio is 22.5 to 25. The aspect ratio H/D of the combustion chamber of the engine meets H/D not less than 0.31 (Rd not less than 0.736), and H/D not less than 0.15xRd+0.20 (0.736 < Rd not more than 1.00).

Description

Diesel engine for ship

Technical Field

The present invention relates to a marine diesel engine mounted on a ship.

Background

Conventionally, in the field of ships, a marine diesel engine having a combustion chamber formed by a cylinder, a piston, and the like is known (for example, refer to patent document 1). In general, a cylinder of a marine diesel engine is formed by fixing a cylinder head to an upper portion of a cylindrical cylinder liner. The piston is provided in the cylinder so as to be capable of reciprocating along an inner wall surface of the cylinder liner between a top dead center and a bottom dead center. The marine diesel engine combusts fuel supplied to a combustion chamber in a cylinder together with combustion gas (compressed gas) to reciprocate a piston, thereby rotationally moving an output shaft such as a crankshaft to output propulsive force of a marine vessel.

In order to improve the fuel consumption rate (hereinafter, appropriately abbreviated as fuel consumption) of such a marine diesel engine, it is effective to improve the thermal efficiency (hereinafter, appropriately abbreviated as thermal efficiency) of the marine diesel engine. As a general method for improving the thermal efficiency, for example, it is known to improve the stroke volume compression ratio at the time of a stroke of one stroke of the piston movement from the bottom dead center to the top dead center.

The stroke volume compression ratio is represented by the ratio of the volume of the cylinder when the piston is at the bottom dead center (the volume obtained by adding the stroke volume of the cylinder to the gap volume) to the volume of the gap (gap volume) existing at the top of the cylinder when the piston is at the top dead center. The stroke volume of the cylinder is a volume of a stroke in which the piston moves one stroke between the top dead center and the bottom dead center in the cylinder. As a method for increasing the stroke volume compression ratio, conventionally, the position of the top dead center of the piston is relatively increased with respect to the cylinder.

Prior art literature

Patent literature

Patent document 1, japanese patent application laid-open No. 2014-20275

However, in the above-described conventional technique, in order to increase the stroke volume compression ratio, the clearance volume of the cylinder (i.e., the volume of the combustion chamber) is often reduced. In this case, since the ratio of the surface area of the combustion chamber to the volume (=surface area of the combustion chamber/volume of the combustion chamber) increases, there is a possibility that the heat energy lost from the combustion chamber (hereinafter referred to as heat loss) among the heat energy generated by the combustion of the fuel in the combustion chamber increases. This increase in heat loss causes deterioration of the thermal efficiency of the marine diesel engine, and further causes deterioration (increase) of fuel consumption.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a marine diesel engine capable of suppressing an increase in heat loss and improving fuel consumption.

In order to solve the above problems and achieve the object, a marine diesel engine according to the present invention includes: a cylinder having a combustion chamber for combusting a fuel; a piston that reciprocates in the cylinder by combustion of fuel in the combustion chamber; and an output shaft that converts the reciprocating motion of the piston into a rotational motion to output a propulsive force of the ship, wherein a stroke cylinder diameter ratio, which is a ratio of a stroke of the piston to an inner diameter of the cylinder, is 4.4 or more, a ratio of a volume of the cylinder when the piston is positioned at a bottom dead center to a volume of the cylinder when the piston is positioned at a top dead center is a stroke volume compression ratio, and a ratio of a net average effective pressure at 100% load of the diesel engine for the ship to a designed maximum net average effective pressure of the diesel engine for the ship is a derate (japanese: a step of selecting a combination of a rated value (japanese: a ratio of a height to an inner diameter of the combustion chamber when the piston is positioned at a top dead center is a combustion chamber aspect ratio) of an engine speed and an engine output at 100% load required for the marine diesel engine, the rated value being selected from a combination of the engine speed and the engine output in a range from a maximum net average effective pressure on design to a minimum net average effective pressure on design of the marine diesel engine, the stroke volume compression ratio being 19 or more and 21 or less when the rated value is selected such that the derating ratio becomes 1.00, the stroke volume compression ratio being 22.5 or more and 25 or less when the rated value is selected such that the derating ratio becomes 0.75, the combustion chamber aspect ratio being H/D when the derating ratio is defined as Rd, the combustion chamber aspect ratio satisfying the following formulas (1) and (2):

H/D≥0.31(Rd≤0.736)…(1)

H/D≥0.15×Rd+0.20(0.736＜Rd≤1.00)…(2)。

in addition, the marine diesel engine according to the present invention is characterized by comprising: a fuel injection valve provided in the cylinder; and a fuel injection pump that pressure-feeds the fuel to the fuel injection valve, the fuel injection valve injecting the pressure-fed fuel into the combustion chamber.

In the marine diesel engine according to the present invention, the marine diesel engine further includes a water injection pump that injects water into the fuel flow path, and the fuel injection valve injects the pressurized fuel and the injected water into the combustion chamber.

The marine diesel engine according to the present invention is characterized by comprising NO _x A reducing device, NO _x The reducing means reduces nitrogen oxides generated in the cylinder or nitrogen oxides in the exhaust gas discharged from the cylinder.

In the marine diesel engine according to the present invention, the engine further includes a control device that controls the fuel injection pump to delay an injection timing of the fuel into the combustion chamber, thereby generating NO that reduces the generation of nitrogen oxides in the cylinder by itself _x Reducing the adjustment.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, the effect is achieved that the fuel consumption can be improved while suppressing an increase in heat loss of the marine diesel engine.

Drawings

Fig. 1 is a schematic view showing an example of a configuration of a marine diesel engine according to an embodiment of the present invention.

Fig. 2 is an enlarged view showing an example of the structure of a piston portion of a marine diesel engine according to an embodiment of the present invention.

Fig. 3 is an enlarged view showing an example of the structure of a combustion chamber portion of a marine diesel engine according to an embodiment of the present invention.

Fig. 4 is a diagram showing an example of a rating map of a marine diesel engine according to an embodiment of the present invention.

Fig. 5 is a diagram showing an example of the stroke volume compression ratio of the marine diesel engine according to the embodiment of the present invention.

Fig. 6 is a view showing an example of the aspect ratio of the combustion chamber of the marine diesel engine according to the embodiment of the present invention.

Symbol description

1. Base seat

2. Crankshaft

3. Bearing

4. Crank arm

5. Framework

6. Connecting rod

7. Guide plate

8. Crosshead

9. Cross pin

10. Diesel engine for ship

11. Cylinder seat

12. Cylinder

13. Cylinder sleeve

14. Cylinder head

15. Piston

15a recess

16. Piston rod

17. Combustion chamber

18. Exhaust valve

19. Valve device

20. Exhaust manifold

20a supercharger

21. Exhaust pipe

21a vent

22. Fuel injection valve

23. Fuel injection pump

24. Water injection pump

25 NO _x Lowering device

26 pinch bolt

27. Nut

100. Nominal value diagram

110. First compression ratio region

111. Second compression ratio region

C _t Top dead center

C _b Bottom dead center

Rated value points P1 to P4 and Pa

PL1 upper limit pressure line

PL2 lower limit pressure line

PLa net average effective pressure line

R1-R4, R11-R14 correlation line

Rs lower limit line

Detailed Description

Hereinafter, preferred embodiments of the marine diesel engine according to the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the present embodiment. Note that the drawings are schematic, and dimensional relationships of elements, ratios of elements, and the like may be different from actual ones. The drawings may include portions having different dimensional relationships and ratios from each other. In the drawings, the same components are denoted by the same reference numerals.

(Structure of Diesel engine for Ship)

First, a configuration of a marine diesel engine according to an embodiment of the present invention will be described. Fig. 1 is a schematic view showing an example of a configuration of a marine diesel engine according to an embodiment of the present invention. The marine diesel engine 10 is a propulsion engine (main engine) that rotates a propulsion propeller (neither of which is shown) of a marine vessel via a propeller shaft. For example, the marine diesel engine 10 is a two-stroke diesel engine such as a single-flow exhaust type crosshead diesel engine.

In the present embodiment, as shown in fig. 1, a marine diesel engine 10 includes: a base 1 located below, a frame 5 provided on the base 1, and a cylinder block 11 provided on the frame 5. These base 1, frame 5 and cylinder block 11 are fastened and fixed integrally by a plurality of tie bolts (coupling members) 26 and nuts 27 extending in the up-down direction. The marine diesel engine 10 further includes: a cylinder 12 provided in the cylinder block 11, a piston 15 provided in the cylinder 12, and an output shaft (e.g., a crankshaft 2) that rotates in conjunction with the reciprocation of the piston 15.

The base 1 and the frame 5 constitute a crankcase of the marine diesel engine 10. As shown in fig. 1, a crankshaft 2 having a crank 4 and a bearing 3 are provided in a base 1. The crankshaft 2 is an example of an output shaft that outputs propulsion of a ship, and is rotatably supported by a bearing 3. The lower end portion of the connecting rod 6 is rotatably coupled to the crankshaft 2 via a crank 4.

As shown in fig. 1, the frame 5 is provided with a link 6, a guide plate 7, and a cross head 8. In the present embodiment, the frame 5 is arranged such that a pair of guide plates 7 provided along the piston axial direction are formed at intervals in the width direction. The connecting rod 6 is disposed between a pair of guide plates 7 with its lower end portion connected to the crankshaft 2. The cross pin 9 connected to the lower end portion of the piston rod 16 and a cross bearing (not shown) connected to the upper end portion of the connecting rod 6 are rotatably connected to the cross head 8 at the lower half portion of the cross pin 9, respectively. As shown in fig. 1, the crosshead 8 is disposed between a pair of guide plates 7 and is supported so as to be movable along the pair of guide plates 7.

As shown in fig. 1, a cylinder block 11 is provided at an upper portion of the frame 5, and supports a cylinder 12. In the present embodiment, the cylinder 12 is a tubular structure (cylinder) formed of a cylinder liner 13 and a cylinder head 14, and has a combustion chamber 17 for combusting fuel. The cylinder liner 13 is a cylindrical structure, for example, and is disposed in the cylinder block 11. A cylinder head 14 is fixed to an upper portion of the cylinder liner 13, and thereby a space portion (a combustion chamber 17, etc.) in the cylinder liner 13 is partitioned. In the space portion of the cylinder liner 13, a piston 15 is provided so as to be reciprocable in the piston axial direction (up-down direction in fig. 1). As shown in fig. 1, an upper end portion of a piston rod 16 is connected to a lower end portion of the piston 15.

As shown in fig. 1, the cylinder head 14 is provided with an exhaust valve 18 and a valve device 19. The exhaust valve 18 is a valve that openably closes an exhaust port (exhaust hole) of the exhaust pipe 21, and the exhaust pipe 21 is communicated with the combustion chamber 17 in the cylinder 12. The valve device 19 is a device that opens and closes the exhaust valve 18. The combustion chamber 17 is a space surrounded by the exhaust valve 18, the cylinder liner 13, the cylinder head 14, and the piston 15. The marine diesel engine 10 further includes an exhaust manifold 20 in the vicinity of the cylinders 12. The exhaust manifold 20 receives exhaust gas from the combustion chamber 17 of the cylinder 12 through the exhaust pipe 21, temporarily stores the received exhaust gas, and changes the dynamic pressure of the exhaust gas into a static pressure. The marine diesel engine 10 further includes a supercharger 20a that supercharges combustion gas such as air. The supercharger 20a compresses the combustion gas by rotating a compressor together with a turbine (neither of which is shown) by the energy of the exhaust gas. The combustion gas compressed by the supercharger 20a is supplied to the combustion chamber 17 in the cylinder 12 via a pipe or the like.

As shown in fig. 1, the marine diesel engine 10 includes a fuel injection valve 22, a fuel injection pump 23, and a water injection pump 24. The fuel injection valve 22 is provided to the cylinder 12 (e.g., the cylinder head 14) in such a manner as to direct the injection port into the combustion chamber 17. As shown in fig. 1, a fuel injection pump 23 and a water injection pump 24 are provided in the vicinity of the cylinder 12. Although not particularly shown, the fuel injection pump 23 and the water injection pump 24 are communicably connected to the fuel injection valve 22 via a pipe, a valve, and the like. The fuel injection pump 23 appropriately pressure-feeds fuel to the fuel injection valve 22 through a flow path formed by piping or the like. The water injection pump 24 appropriately injects water such as distilled water into a flow path of the fuel from the discharge port of the fuel injection pump 23 to the injection port of the fuel injection valve 22. The fuel injection valve 22 alternately injects (i.e., stratified injection) the fuel pumped by the fuel injection pump 23 and the water injected by the water injection pump 24 into the combustion chamber 17 by the pumping action of the fuel injection pump 23.

In the present embodiment, as shown in fig. 1, the marine diesel engine 10 includes NO _x A lowering means 25, the NO _x The reducing device 25 reduces nitrogen oxides (NOx) generated in the cylinder 12 or reduces NO in the exhaust gas discharged from the cylinder 12 _x . As the NO _x The reduction device 25 may be, for example, an exhaust gas recirculation (EGR: expst Gas Recirculation) system, a selective catalytic reduction (SCR: selective Catalytic Reduction) system, or the like. NO (NO) _x In the case of the EGR system, the reduction device 25 mixes a part of the exhaust gas discharged from the cylinder 12 with air and recirculates the mixed gas to the cylinder 12, thereby suppressing NO caused by combustion of the fuel in the combustion chamber 17 _x Is capable of reducing NO in exhaust gas _x Is used (amount of discharged). On the other hand, NO _x In the case of the SCR system, the reducing device 25 injects a reducing agent into the exhaust gas discharged from the cylinder 12, thereby reducing the amount of NOx discharged.

In the marine diesel engine 10 having the above-described configuration, fuel, or fuel and water are supplied from the fuel injection valve 22 to the combustion chamber 17 in the cylinder 12, and the combustion gas compressed by the supercharger 20a is supplied. Thus, in the combustion chamber 17, the supplied fuel is burned by the combustion gas, and when water is supplied thereto, the combustion temperature of the fuel is lowered by the water, and NO is lowered _x Is used for the discharge amount of the fuel. Although not particularly shown, the marine diesel engine 10 includes a control device that controls the driving timing of the fuel injection pump 23. In the direction from the fuel injection valve 22When the combustion chamber 17 is supplied with fuel without supplying water, the control device may control the fuel injection pump 23 to delay the injection timing of the fuel into the combustion chamber 17, thereby performing NO injection _x Generating self-reduced NO within cylinder 12 _x Reducing the adjustment. By such NO _x The reduction adjustment can also reduce the amount of NOx emissions.

The piston 15 reciprocates in the piston axial direction within the cylinder 12 using energy generated by combustion of fuel in the combustion chamber 17. At this time, when the exhaust valve 18 is operated by the valve device 19 to open the cylinder 12, the exhaust gas generated by the combustion of the fuel is pushed out to the exhaust pipe 21. On the other hand, the combustion gas is reintroduced into the cylinder 12 from a scavenging port (not shown).

In addition, when the piston 15 reciprocates in the piston axial direction as described above, the piston rod 16 reciprocates in the piston axial direction together with the piston 15. With this, the crosshead 8 reciprocates in the piston axial direction along the guide plate 7. Thereby, the crosshead pin 9 of the crosshead 8 applies a rotational driving force to the link 6 via the crosshead bearing. By this rotational driving force, the crank 4 connected to the lower end portion of the connecting rod 6 performs a crank motion, and as a result, the crankshaft 2 rotates. The crankshaft 2 converts the reciprocating motion of the piston 15 into a rotational motion in this way, and rotates the propulsion propeller of the ship together with the propeller shaft, thereby outputting the propulsion force of the ship.

Fig. 2 is an enlarged view showing an example of the structure of a piston portion of a marine diesel engine according to an embodiment of the present invention. In the marine diesel engine 10 shown in fig. 1, as described above, the piston 15 reciprocates in the piston axial direction within the cylinder 12. In detail, as shown in fig. 2, the piston 15 reciprocates in the piston axial direction (direction indicated by a bold double arrow in fig. 2) along the inner wall surface of the cylinder liner 13 constituting the cylinder 12.

The stroke S of the piston 15 during the reciprocating motion is the top dead center C of the piston 15 _t With bottom dead center C _b The distance between them, e.g. as shown in FIG. 2, is at the top dead center C _t Upper end face of piston 15 and is positioned at bottom dead center C _b Upper end face of piston 15 of (2)Distance between them. In addition, the inner diameter D of the cylinder 12 is the inner diameter of the cylinder liner 13, and is the same value as the inner diameter of the combustion chamber 17. The stroke bore ratio (also referred to as a bore stroke ratio) of the marine diesel engine 10 is a ratio (=s/D) of the stroke S of the piston 15 to the inner diameter D of the cylinder 12 shown in fig. 2. In this embodiment, the stroke inside diameter ratio S/D is 4.4 or more.

As shown in fig. 2, the stroke volume V for the volume of the internal space of the cylinder 12 _st And gap volume V _c And (3) representing. Stroke volume V _st Is that the piston 15 is at the top dead center C in the cylinder 12 _t With bottom dead center C _b A volume of travel that is displaced by one stroke (the amount of stroke S). Gap volume V _c Is that the piston 15 is positioned at the upper dead point C _t And a volume of the gap that exists at the top of the cylinder 12. Specifically, the gap volume V _c Is positioned at the top dead center C _t The volume of the space surrounded by the upper end surface of the piston 15, the inner wall surfaces of the cylinder liner 13 and the cylinder head 14, and the lower end surface of the exhaust valve 18. The gap volume V _c Is that the piston 15 is positioned at the upper dead point C _t The volume of the combustion chamber 17.

The interior of the cylinder 12 is here from the bottom dead center C by the piston 15 _b Move to the upper dead point C _t And compressed. The compression ratio of the internal space of the cylinder 12 is referred to as stroke volume compression ratio ε, and is set at bottom dead center C by the piston 15 _b The volume of the cylinder 12 (hereinafter, appropriately referred to as the bottom dead center volume) and the piston 15 are positioned at the top dead center C _t The ratio (=bottom dead center volume/top dead center volume) of the volume of the cylinder 12 (hereinafter, appropriately referred to as top dead center volume) is expressed. As shown in fig. 2, the bottom dead center volume of the cylinder 12 is defined by the stroke volume V _st And gap volume V _c Sum (=v) _st +V _c ) And (3) representing. The top dead center volume of the cylinder 12 is the clearance volume V _c . Therefore, the stroke volume compression ratio ε uses these stroke volumes V _st And gap volume V _c And is represented by the following formula (3):

stroke volume compression ratio epsilon= (V) _st +V _c )/V _c …(3)

In the present embodiment, the stroke volume compression ratio epsilon is set in a predetermined range by selecting specifications such as the rotational speed (hereinafter, appropriately referred to as engine rotational speed) and the output (hereinafter, appropriately referred to as engine output) of the marine diesel engine 10.

Fig. 3 is an enlarged view showing an example of the structure of a combustion chamber portion of a marine diesel engine according to an embodiment of the present invention. In the marine diesel engine 10 shown in fig. 1, the cylinder 12 has a combustion chamber 17 surrounded by a cylinder liner 13, a cylinder head 14, a piston 15, and an exhaust valve 18. Specifically, as shown in fig. 3, a recess 15a is formed in an upper end surface (piston crown) of the piston 15. Further, the cylinder head 14 is formed with an exhaust hole 21a communicating with the exhaust pipe 21 (see fig. 1 and 2). The exhaust valve 18 closes the exhaust hole 21a so as to be openable and closable. The combustion chamber 17 is a space surrounded by an upper end surface of the piston 15, inner wall surfaces of the cylinder liner 13 and the cylinder head 14, and a lower end surface of the exhaust valve 18.

Such a combustion chamber 17 is located at the top dead center C while the piston 15 is in reciprocating motion _t (see FIG. 2) is the flattest shape. The combustion chamber 17 being flattened by the piston 15 at top dead centre C _t The ratio of the height to the inner diameter of the combustion chamber 17. As shown in FIG. 3, the combustion chamber 17 has a height H at the top dead center C _t A distance (separation distance) between an upper end surface of the piston 15 in a state (in this embodiment, a bottom portion of the recess 15 a) and a lower end surface of the exhaust valve 18 in a state where the exhaust hole 21a is closed. The inner diameter of the combustion chamber 17 is the same value as the inner diameter D of the cylinder 12 (specifically, the inner diameter of the cylinder liner 13). In the present embodiment, as an index indicating the degree of flatness of the combustion chamber 17, a combustion chamber aspect ratio H/D, which is a ratio (=h/D) of the height H to the inner diameter (=d) of the combustion chamber 17, is defined. The combustion chamber aspect ratio H/D varies with the internal surface area A and volume of the combustion chamber 17 (i.e., the gap volume V _c ) Ratio A/V _c And decreases as it decreases.

(specification selection of marine diesel engine)

Next, specification selection of the marine diesel engine 10 according to the embodiment of the present invention will be described. The specifications of the marine diesel engine 10 are selected so that the propulsion force and the propeller rotational speed required for the marine vessel can be obtained. The specifications of the selected marine diesel engine 10 include: such as pattern, cylinder number, engine rotation speed Ne, engine output Le, and the like. The engine rotation speed Ne is the engine rotation speed at 100% load required for the marine diesel engine 10. The engine output Le is an engine output at 100% load required for the marine diesel engine 10.

The term "100% load" refers to a state in which the marine diesel engine 10 is operated at 100% load. That is, the "engine speed at 100% load" is the maximum engine speed obtained according to the specification selected for the marine diesel engine 10. The "engine output at 100% load" is the maximum engine output per cylinder obtained according to the specification selected for the marine diesel engine 10.

The rated value of the combination of the engine rotational speed Ne and the engine output Le required for the marine diesel engine 10 is selected based on a rated value map corresponding to the type of the marine diesel engine 10. Fig. 4 is a diagram showing an example of a rating map of a marine diesel engine according to an embodiment of the present invention. The rating map 100 shown in fig. 4 is set corresponding to the marine diesel engine 10 of a type having a stroke inside diameter ratio S/D of 4.4 or more.

Specifically, as shown in fig. 4, the rating map 100 is a map showing ratings selected for the marine diesel engine 10 in a region from the upper limit pressure line PL1 to the lower limit pressure line PL2 (a region indicated by oblique lines in fig. 4).

The upper limit pressure line PL1 is limited in terms of the engine speed Ne and the engine output Le, and is the net average effective pressure Pme that is the maximum in terms of the engine design of the marine diesel engine 10 _MAX A corresponding line. The upper limit pressure line PL1 represents the net average effective pressure Pme that is the maximum in designing the engine _MAX Net average effective pressure Pme at 100% load of marine diesel engine 10 _MCR A nominal value is selected. For example, the engine speed Ne and the engine output indicated by the rated value point P1 on the upper limit pressure line PL1The combination (N2, L4) of Le is selected when the engine speed at which the engine design maximum engine speed is set as the engine speed at 100% load and the engine output at which the engine design maximum engine output is set as the engine output at 100% load in the marine diesel engine 10. In addition, in the combination (N1, L3) of the engine rotation speed Ne and the engine output Le indicated by the other rated value point P3 on the upper limit pressure line PL1, the net average effective pressure Pme of the marine diesel engine 10 is calculated _MCR Net average effective pressure Pme as maximum in engine design _MAX Then, the engine speed at 100% load and the engine output are selected to be the minimum.

The lower limit pressure line PL2 is limited for the engine speed Ne and the engine output Le, and is equal to the lower limit of the net average effective pressure Pme set in the marine diesel engine 10 (i.e., the net average effective pressure Pme that is the smallest in engine design) _MIN ) A corresponding line. The lower limit pressure line PL2 represents the net average effective pressure Pme that is the smallest in designing the engine _MIN Net average effective pressure Pme at 100% load of marine diesel engine 10 _MCR A nominal value is selected. For example, in the marine diesel engine 10, the combination (N2, L2) of the engine speed Ne and the engine output Le indicated by the rated value point P2 on the lower limit pressure line PL2 is the engine speed at which the engine design maximum engine speed is 100% load and the net average effective pressure Pme is the net average effective pressure Pme of the lower limit _MIN Is selected as the engine output at 100% load. In addition, in the combination (N1, L1) of the engine rotation speed Ne and the engine output Le indicated by the other rated value point P4 on the lower limit pressure line PL2, the net average effective pressure Pme of the marine diesel engine 10 is calculated _MCR Net average effective pressure Pme as lower limit _MIN Then, the engine speed at 100% load and the engine output are selected to be the minimum.

In the present embodiment, the nominal value of the marine diesel engine 10 is the maximum net average effective pressure Pme from the engine design _MAX Minimum net mean effective pressure Pme to engine design _MIN The combination of the engine speed Ne and the engine output Le in the range of (a) is selected from the nominal value map 100. For example, as the rated value of the marine diesel engine 10, a combination of the engine rotation speed Ne and the engine output Le indicated by the rated value point Pa on the net average effective pressure line PLa in the rated value map 100 is selected. The net mean effective pressure line PLa is the net mean effective pressure Pme from the upper limit within the nominal value diagram 100 _MAX Net mean effective pressure Pme to a lower limit _MIN A line corresponding to the desired net average effective pressure selected for the marine diesel engine 10 among the net average effective pressures Pme. In the present embodiment, the desired net average effective pressure is the net average effective pressure Pme at 100% load of the marine diesel engine 10 _MCR . The rated value point Pa is a point on the net average effective pressure line PLa, and represents a value obtained by setting the net average effective pressure Pme of the marine diesel engine 10 to a desired net average effective pressure Pme _MCR The combination of the engine rotational speed Ne and the engine output Le selected in the manner of (a).

Here, in the selection of the rated value of the marine diesel engine 10, a rated value point (for example, a rated value point Pa shown in fig. 4) at which the net average effective pressure Pme is lower than a rated value point P1 indicating a combination of the engine rotational speed at the maximum in the engine design and the engine output may be selected from the rated value map 100 as a point indicating the rated value at the time of 100% load. In this case, by decreasing at least one of the engine speed and the engine output, which are the maximum engine design values indicated by the rated value point P1, the net average effective pressure Pme at 100% load of the marine diesel engine 10 is reduced _MCR Set to be greater than the maximum net average effective pressure Pme in the engine design _MAX Low. In such a way that the net average effective pressure Pme at 100% load _MCR Compared to the maximum net average effective pressure Pme on the engine design _MAX The rated value at the rated value point P1 is adjusted so as to be lower than the rated value at 100% load of the marine diesel engine 10, and is referred to as derating in the present embodiment.

For example, as shown in fig. 4, derating is performed as follows: at the position ofIn the rating of the rating point P1, the engine speed Ne is maintained at the engine speed (=n2) that is the maximum in the engine design, and the engine output Le becomes the net average effective pressure Pme of the upper limit _MAX Net mean effective pressure Pme reduced to a lower limit _MIN And the resulting engine output (=l2). Thus, the rated value at the rated value point P2 can be set (selected) as the rated value at 100% load of the marine diesel engine 10.

In the present embodiment, the net average effective pressure Pme at 100% load of the marine diesel engine 10 is set _MCR The net average effective pressure Pme that is maximum in engine design with respect to the marine diesel engine 10 _MAX Ratio of (=pme) _MCR /Pme _MAX ) Defined as derate Rd. The derating rate Rd takes a constant value between the same nominal values of the net average effective pressure Pme in the nominal value map 100 (e.g., between nominal value points on the net average effective pressure line PLa shown in fig. 4). In addition, the net average effective pressure Pme of derating rate Rd at 100% load _MCR Maximum net average effective pressure Pme for engine design _MAX Takes the maximum value (=1.00) of the net average effective pressure Pme at 100% load _MCR Minimum net average effective pressure Pme for engine design _MIN Takes the minimum value (=pme) _MIN /Pme _MAX )。

As described above, the rating map 100 used for selecting the rating of the marine diesel engine 10 can be set by improving the stroke volume compression ratio epsilon by taking into consideration the flatness of the combustion chamber 17 (i.e., the combustion chamber aspect ratio H/D) of the marine diesel engine 10.

Fig. 5 is a diagram showing an example of the stroke volume compression ratio of the marine diesel engine according to the embodiment of the present invention. In fig. 5, a first compression ratio region 110 indicated by a broken line is a region indicating the stroke volume compression ratio epsilon corresponding to the derate Rd of the marine diesel engine before the stroke volume compression ratio epsilon is improved (hereinafter referred to as a marine diesel engine of conventional specification). The correlation lines R1 and R2 indicated by broken lines are lines illustrating the correlation between the derating rate Rd and the stroke volume compression ratio epsilon of the conventional marine diesel engine. The second compression ratio region 111 indicated by a solid line is a region indicating the stroke volume compression ratio epsilon corresponding to the derate Rd of the marine diesel engine of the present invention (hereinafter, the marine diesel engine 10 according to the present embodiment is exemplified) in which the stroke volume compression ratio epsilon is improved. The correlation lines R11 and R12 indicated by solid lines are lines illustrating the correlation between the derating rate Rd and the stroke volume compression ratio epsilon of the marine diesel engine 10.

Fig. 6 is a view showing an example of the aspect ratio of the combustion chamber of the marine diesel engine according to the embodiment of the present invention. In fig. 6, a lower limit line Rs is a line indicating a lower limit of the combustion chamber aspect ratio H/D (specifically, the combustion chamber aspect ratio H/D corresponding to the derating rate Rd) at the time of improving the stroke volume compression ratio epsilon. The correlation lines R3 and R4 indicated by broken lines are lines illustrating the correlation between the derating rate Rd and the combustion chamber aspect ratio H/D of the conventional marine diesel engine. The correlation lines R13 and R14 indicated by solid lines are lines illustrating the correlation between the derating rate Rd and the combustion chamber aspect ratio H/D of the marine diesel engine 10.

In the conventional marine diesel engine, there is a tendency that the stroke S of the piston is increased by lengthening the cylinder or the like in order to increase the engine output Le per cylinder. With the increase of the stroke S, the stroke volume V is different according to the stroke inner diameter ratio S/D _st And (3) increasing. This tendency of engine design specifications is particularly remarkable when the stroke inner diameter ratio S/D is 4.4 or more. In the stroke volume V _st In the case of an increase, in the conventional marine diesel engine, the stroke volume compression ratio ε (= (V) _st +V _c )/V _c ) The accompanying stroke volume V is usually set without changing from the original required value to a constant value _st To increase the gap volume V _c Increased engine design. The present inventors have found, based on the engine design as described above: if in clearance volume V _c The combustion chamber of the conventional diesel engine for a ship is compressed to a limited extent, so that the heat loss from the combustion chamber can be prevented from being excessively large compared with the conventional diesel engine for a shipThe stroke volume compression ratio epsilon is improved, and the present invention has been completed.

Specifically, as shown in fig. 5, the stroke volume compression ratio epsilon of the marine diesel engine of the conventional specification is improved to the stroke volume compression ratio epsilon of the marine diesel engine 10 according to the present embodiment by increasing the stroke volume compression ratio epsilon in the first compression ratio region 110 to the stroke volume compression ratio epsilon in the second compression ratio region 111. In the present embodiment, the first compression ratio region 110 of the conventional marine diesel engine represents the stroke volume compression ratio epsilon of 18 to 19 when the derating rate Rd is 1.00, and represents the stroke volume compression ratio epsilon of 20 to 22 when the derating rate Rd is 0.75. By increasing the stroke volume compression ratio epsilon of the stroke volume compression ratio epsilon in the first compression ratio region 110, for example, the stroke volume compression ratio S/d=4.6 indicated by the correlation line R1, to the stroke volume compression ratio epsilon in the second compression ratio region 111 indicated by the correlation line R11, the stroke volume compression ratio epsilon of the stroke volume compression ratio S/d=4.6 indicated by the correlation line R1 is improved to the stroke volume compression ratio epsilon of the marine diesel engine 10 with the stroke volume compression ratio S/d=4.6. The stroke volume compression ratio epsilon of the marine diesel engine 10 in which the stroke internal diameter ratio S/d=4.43 indicated by the correlation line R2 is improved to the stroke volume compression ratio epsilon of the marine diesel engine 10 in which the stroke internal diameter ratio S/d=4.43 indicated by the correlation line R2 by increasing the stroke volume compression ratio epsilon of the stroke internal diameter ratio S/d=4.43 indicated by the correlation line R12 to the stroke volume compression ratio epsilon in the second compression ratio region 111.

When the rated value of the marine diesel engine 10 is selected so that the derating rate Rd becomes 1.00, the stroke volume compression ratio epsilon of the marine diesel engine 10 after the improvement is 19 to 21 as shown in the second compression ratio region 111 in fig. 5. When the rated value of the marine diesel engine 10 is selected so that the derating rate Rd becomes 0.75, the stroke volume compression ratio epsilon of the marine diesel engine 10 is 22.5 or more and 25 or less as shown in the second compression ratio region 111 of fig. 5.

In the present embodiment, the stroke volume is set as described aboveExamples of the method for increasing the product compression ratio ε include: the piston 15 is set to be at the top dead center C under the condition that the stroke S of the piston is set to be constant _t A method of approaching the distance between the piston 15 and the cylinder head 14 in the state (hereinafter referred to as a first method), a method of changing the shape of the constituent members of the combustion chamber 17 (hereinafter referred to as a second method), and the like. Examples of the first method include: a method of increasing the thickness of a gasket (not shown) provided between the piston rod 16 and the cross pin 9, a method of extending the length of the piston rod 16, a method of extending the length of the connecting rod 6 by adjusting the thickness of the gasket by providing the connecting rod 6 as a "two-split structure with the gasket interposed therebetween", a method of relatively lowering the position of the cylinder head 14 with respect to the piston 15, and the like. Examples of the second method include: a method of making the recess depth of the recess 15a in the upper end surface of the piston 15 shallow, a method of changing the shape of the cylinder head 14, a method of changing the shape of the exhaust valve 18, and the like.

The above-described improvement of the stroke volume compression ratio epsilon is performed in consideration of the lower limit of the combustion chamber aspect ratio H/D of the marine diesel engine 10. In the present embodiment, the lower limit of the combustion chamber aspect ratio H/D at the time of improving the stroke volume compression ratio epsilon is represented by, for example, the lower limit line Rs in fig. 6. Here, the lower limit of the combustor aspect ratio H/D corresponds to a limit value at which heat loss from the combustor 17 during combustion of the fuel in the combustor 17 can be suppressed to a degree of flatness of the combustor 17 that is not excessively large compared to a conventional specification marine diesel engine. The lower limit line Rs represents the lower limit of such a combustor aspect ratio H/D in terms of the derate Rd. In the present embodiment, the lower limit line Rs is set as follows.

In detail, as shown in fig. 6, the lower limit of the combustor aspect ratio H/D can be a variable or constant value according to the derating rate Rd. The lower limit of the aspect ratio H/D of the combustion chamber is set to a minimum value of 0.31 in accordance with the actual performance of the past marine diesel engine (hereinafter referred to as the past performance of the marine diesel engine) in which the stroke inner diameter ratio S/D is 4.4 or more.

Further, scavenging of the marine diesel engine 10The pressure Ps is set to be equal to the derating rate Rd (=pme _MCR /Pme _MAX ) Proportional to the ratio. Then, the product value of the scavenging pressure Ps and the stroke volume compression ratio epsilon becomes equal to the piston 15 at the top dead center C _t The pressure Pc of the combustion gas (compressed gas) in the combustion chamber 17 is substantially the same constant value. Thus, the stroke volume compression ratio ε is inversely proportional to the derate Rd (see FIG. 5). Here, as described above, the stroke volume compression ratio epsilon is the bottom dead center volume (=v) of the cylinder 12 _st +V _c ) And gap volume V _c Ratio ((V) _st +V _c )/V _c ＝V _st /V _c +1), thus stroke volume compression ratio ε and clearance volume V _c In inverse proportion. In addition to this, the gap volume V _c In a proportional relationship with the combustion chamber aspect ratio H/D, and therefore, the combustion chamber aspect ratio H/D is proportional to the derate Rd. At this time, the inclination of the combustion chamber aspect ratio H/D to the derate Rd becomes 0.15 according to the past results of the marine diesel engine. In addition, a typical combination (Rd, H/D) of the derating rate Rd and the combustor aspect ratio H/D is (Rd, H/D) = (0.736,0.31) according to the past performance of the marine diesel engine.

From the above, the lower limit line Rs indicating the lower limit of the combustor aspect ratio H/D is represented by the following formulas (4) and (5):

H/D＝0.31(Rd≤0.736)…(4)

H/D＝0.15×Rd+0.20(0.736＜Rd≤1.00)…(5)

that is, in the present embodiment, when the stroke volume compression ratio ε is improved in consideration of the lower limit of the combustion chamber aspect ratio H/D of the marine diesel engine 10, the combustion chamber aspect ratio H/D satisfies the following expressions (1) and (2):

H/D≥0.31(Rd≤0.736)…(1)

H/D≥0.15×Rd+0.20(0.736＜Rd≤1.00)…(2)

for example, as shown in fig. 6, the lower limit of the combustion chamber aspect ratio H/D obtained based on the above-described formulas (1) and (2) is set to a limit, and for example, the combustion chamber aspect ratio H/D having the stroke inner diameter ratio S/d=4.6 indicated by the correlation line R3 is reduced to the combustion chamber aspect ratio H/D indicated by the correlation line R13. The combustion chamber aspect ratio H/D, represented by the correlation line R4, with the stroke inner diameter ratio S/d=4.43, is reduced to the combustion chamber aspect ratio H/D, represented by the correlation line R14.

As described above, in the marine diesel engine 10 according to the embodiment of the present invention, the stroke inside diameter ratio S/D is 4.4 or more, and the nominal value of the marine diesel engine 10 is the maximum net average effective pressure Pme from the engine design point of view _MAX Up to a minimum net average effective pressure Pme in the engine design _MIN The combination of the engine output Le and the engine speed Ne (i.e., the nominal value map 100) in the range up to this point is selected as the net average effective pressure Pme _MCR Relative to net average effective pressure Pme _MAX When the rated value is selected so that the derating rate Rd of the ratio is 1.00, the stroke volume compression ratio epsilon of the marine diesel engine 10 is 19 to 21, and when the rated value is selected so that the derating rate Rd is 0.75, the stroke volume compression ratio epsilon of the marine diesel engine 10 is 22.5 to 25, and the combustion chamber aspect ratio H/D of the marine diesel engine 10 satisfies H/D of 0.31 (when Rd of 0.736) or H/D of 0.15xrd+0.20 (when 0.736 < Rd of 1.00).

Therefore, the stroke volume compression ratio epsilon can be increased from that of the conventional marine diesel engine without excessively compressing the combustion chamber 17 of the marine diesel engine 10 to be flat. As a result, the heat loss from the combustion chamber 17 can be suppressed from becoming excessive as compared with the conventional diesel engine for a ship, and the thermal efficiency of the diesel engine 10 for a ship can be improved as compared with the conventional diesel engine for a ship, and as a result, the fuel consumption of the diesel engine 10 for a ship can be improved.

The marine diesel engine 10 according to the embodiment of the present invention is configured such that fuel is pumped from the fuel injection pump 23 to the fuel injection valve 22 provided in the cylinder 12, water is injected into the fuel flow path from the water injection pump 24, and the pumped fuel and the injected water are injected from the fuel injection valve 22 to the combustion chamber 17. Therefore, the marine firewood can be suppressedNO caused by combustion of fuel in combustion chamber 17, which may occur due to an increase in stroke volume compression ratio epsilon of oil engine 10 _x And, compared with the conventional NO exemplified as a delay of the fuel injection timing (delay of the injection timing) _x The reduction in thermal efficiency of the marine diesel engine 10 can be suppressed as compared with the reduction technique. This allows efficient consideration of NO in the marine diesel engine 10 _x Emission reduction and fuel efficiency improvement.

The marine diesel engine 10 according to the embodiment of the present invention is configured such that NO _x The reducing device 25 reduces NO generated in the cylinder 12 _x Or NO in the exhaust gas discharged from the cylinder 12 _x . Therefore, the fuel efficiency can be improved by the increase in the thermal efficiency of the marine diesel engine 10, and NO can be realized _x Further reduction of emissions.

In the marine diesel engine 10 according to the embodiment of the present invention, even when the compression pressure of the combustion gas in the cylinder 12 (in-cylinder compression gas pressure) increases with an increase in the stroke volume compression ratio epsilon, the scavenging pressure of the combustion gas fed from the supercharger 20a into the cylinder 12 is reduced in advance, so that it is possible to easily avoid a situation in which the in-cylinder compression gas pressure exceeds the maximum pressure in the cylinder 12 in terms of design.

In the above embodiment, the number of cylinders of the marine diesel engine 10 is not particularly limited, and may be one or a plurality (two or more). That is, in the present invention, the number of cylinders is not particularly limited.

In the above-described embodiment, fuel and water are injected in layers to the combustion chamber 17 in the cylinder 12, but the present invention is not limited to this. For example, water may be injected separately from the fuel into the combustion chamber 17, or a liquid (aqueous emulsion fuel) obtained by mixing the fuel and water and emulsifying the mixture may be injected, or a combustion gas in a humidified state by a method such as injecting water into the combustion gas compressed by the supercharger 20a may be supplied to the cylinder 12 (supply air humidification). In addition, canAccording to the NO required by the marine diesel engine 10 _x The water injection means such as the water injection pump 24 for injecting water into the fuel flow path may be provided for reducing the amount of discharge, and the marine diesel engine 10 may not necessarily be provided with the water injection means such as the water injection pump 24. This is true for NO _x The same applies to the lowering device 25.

The present invention is not limited to the above-described embodiments, and a configuration in which the above-described components are appropriately combined is also included in the present invention. Other embodiments, examples, and operating techniques, etc., which are made by those skilled in the art based on the above embodiments, are all included in the scope of the present invention.

Claims

1. A marine diesel engine is provided with: a cylinder having a combustion chamber for combusting a fuel; a piston that reciprocates in the cylinder by combustion of fuel in the combustion chamber; and an output shaft that converts the reciprocating motion of the piston into a rotational motion to output propulsion of a ship, wherein the marine diesel engine is characterized in that,

the ratio of the stroke diameter of the piston to the inner diameter of the cylinder is 4.4 or more,

when the ratio of the volume of the cylinder when the piston is at the bottom dead center to the volume of the cylinder when the piston is at the top dead center is set as a stroke volume compression ratio, the ratio of the net average effective pressure at 100% load of the marine diesel engine to the designed maximum net average effective pressure of the marine diesel engine is set as a derating rate, the combination of the engine speed and the engine output at 100% load required by the marine diesel engine is set as a rated value, and the ratio of the height of the combustion chamber to the inner diameter at the top dead center of the piston is set as a combustion chamber aspect ratio,

the nominal value is selected from a combination of engine speed and engine output in a range from a design maximum net average effective pressure to a design minimum net average effective pressure of the marine diesel engine,

the stroke volume compression ratio is inversely proportional to the derate,

the derate is maximized where the net average effective pressure at 100% load is the maximum net average effective pressure on the design, the derate is minimized where the net average effective pressure at 100% load is the minimum net average effective pressure on the design,

in the association between the derate and the stroke volume compression ratio, the stroke volume compression ratio is 19 or more and 21 or less when the rated value is selected so that the derate becomes 1.00, the stroke volume compression ratio is 22.5 or more and 25 or less when the rated value is selected so that the derate becomes 0.75,

when the derating ratio is Rd and the combustor aspect ratio is H/D, the combustor aspect ratio satisfies the following formulas (1) and (2):

H/D≥0.31(Rd≤0.736)…(1)

H/D≥0.15×Rd+0.20(0.736＜Rd≤1.00)…(2)。

2. the marine diesel engine according to claim 1, comprising:

a fuel injection valve provided in the cylinder; and

a fuel injection pump that pressure-feeds the fuel to the fuel injection valve,

the fuel injection valve injects the fuel that is pressurized into the combustion chamber.

3. The marine diesel engine according to claim 2, wherein,

the fuel injection device further comprises a water injection pump for injecting water into the fuel flow path,

the fuel injection valve injects the fuel that is pressurized and the water that is injected into the combustion chamber.

4. A marine diesel engine as claimed in any one of claims 1 to 3, characterized in that,

is provided with NO _x A reducing device, NO _x The reducing means reduces nitrogen oxides generated in the cylinder or nitrogen oxides in the exhaust gas discharged from the cylinder.

5. The marine diesel engine according to claim 2, wherein,

the engine is provided with a control device which controls the fuel injection pump so as to delay the injection timing of the fuel into the combustion chamber, thereby reducing the generation of NO in the cylinder by itself of nitrogen oxides _x Reducing the adjustment.