reciprocating internal combustion engine

Abstract

To suppress generation of nitrogen oxide and improve thermal efficiency by distribution of water supplied to the inside of a combustion chamber.SOLUTION: A reciprocating internal combustion engine 10 comprises a fuel injection nozzle 18 that is disposed at the center of the top of a cylinder 12 for radially injecting fuel into a combustion chamber 16, and a water supply device 22 having a water injection nozzle 20 for injecting water into the combustion chamber 16. The water supply device 22 injects water from the water injection nozzle 20, and before the fuel injection nozzle 18 performs a main injection, stratificationally forms a flat column-shaped water-containing region 26 including water droplets and water vapor at a central part of the combustion chamber 16. A jet flow of fuel, when passing through the water-containing region 26, takes in surrounding gas and water that are cooled by evaporation heat, thereby lowering combustion temperature.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a reciprocating internal combustion engine, and more particularly to a reciprocating internal combustion engine that injects fuel and water into a combustion chamber defined by a cylinder and a piston. [Background technology]

[0002] In a reciprocating internal combustion engine in which fuel is injected into a combustion chamber defined by a cylinder and a piston, a technique for injecting water into the combustion chamber is known. Patent Document 1 listed below discloses a technique for injecting water radially from the center of the combustion chamber toward the outer periphery in a diesel engine so that water vapor exists on the trajectory of the fuel jet. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-77391 Summary of the Invention [Problem to be solved by the invention]

[0004] There is room for improvement in the arrangement within the combustion chamber of the water-containing region that contains the water droplets injected into the combustion chamber and the water vapor that evaporates from these water droplets. [Means for solving the problem]

[0005] The reciprocating internal combustion engine according to the present invention comprises: a fuel injection nozzle disposed at the top center of the cylinder and configured to inject fuel into a combustion chamber defined by the cylinder and the piston; From multiple nozzle holes arranged offset from the center of the cylinder and arranged in the same plane toward the center of the cylinder in the combustion chamber and a water supply device having a water injection nozzle for injecting water, the water supply device injecting water from the water injection nozzle into the center of the combustion chamber before the fuel injection nozzle performs main injection. ,water Droplets and water vapor Including nothing Flat cylindrical shape The water-containing region is stratified. In this reciprocating internal combustion engine, the shape of the water spray formed by the water injection nozzle when it injects water is fan-shaped, and the central angle of the fan-shaped water spray formed by the water injection nozzle is 50° × (0.5Dbore / Xoff) or more and 75° × (0.5Dbore / Xoff) or less, where Dbore is the cylinder diameter and Xoff is the offset of the water injection nozzle from the center of the cylinder.This results in the formation of a flattened cylindrical water-containing region containing water droplets and water vapor in the center of the combustion chamber, where the water concentration is higher than the surrounding area.

[0006] By stratifying the water-containing region in the center of the combustion chamber, the fuel jet injected from the top center of the cylinder can efficiently pick up water.

[0007] Also, Flat cylindrical shape The reciprocating internal combustion engine may have a diameter of the water-containing region that is 0.3 to 0.6 times the diameter of the cylinder.

[0010] Furthermore, the invention may be a reciprocating internal combustion engine in which the water injection nozzle injects the water toward a position shifted from the center of the cylinder so that the jet along the center line of the fan-shaped water spray formed by the water injection nozzle has a velocity component opposite to the swirl formed to swirl inside the combustion chamber.

[0011] Furthermore, the water supply device may be a reciprocating internal combustion engine in which water is injected from the water injection nozzle in two separate injections.

[0012] Furthermore, the water supply device may be a reciprocating internal combustion engine in which the water injection nozzle performs main water injection and, after the main water injection, additional water injection with an injection amount smaller than the main water injection at an interval from the main water injection.

[0013] Furthermore, the water supply device for performing main injection and additional water injection may be a reciprocating internal combustion engine in which the additional water injection ends immediately before the start of the main injection of fuel.

[0014] Furthermore, the reciprocating internal combustion engine may be configured such that the water supply device that performs main injection and additional water injection injects 25 percent of the total amount of water injected by the additional water injection.

[0015] Furthermore, the reciprocating internal combustion engine may have a compression ratio of 18 or more and 21 or less, more preferably 20 or more and 21 or less.

[0016] Furthermore, the reciprocating internal combustion engine may have, in place of the water supply device, a high latent heat liquid supply device that supplies a liquid having a higher latent heat of vaporization than the fuel. [Effects of the Invention]

[0017] By locating the water-containing region in the center of the combustion chamber, the jet of fuel injected from the center of the top of the cylinder can efficiently take in water, thereby making it possible to enjoy the benefits of water injection more effectively. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram schematically illustrating a configuration of a main part of an internal combustion engine according to an embodiment of the present invention; [Figure 2] FIG. [Figure 3] FIG. 10 is a diagram showing an example of specifications used in numerical calculations. [Figure 4] FIG. 2 shows water-containing regions within a combustion chamber. [Figure 5] FIG. 4 is a diagram showing an example of water distribution in a combustion chamber. [Figure 6] FIG. 10 is a diagram showing the amount of nitrogen oxides generated for each water distribution. [Figure 7] FIG. 10 is a diagram showing the indicated thermal efficiency for each water distribution. [Figure 8] FIG. 10 illustrates how a jet of fuel entrains water. [Figure 9] FIG. 10 is a graph showing the relationship between the diameter of the water-containing region and the amount of nitrogen oxides generated. [Figure 10] FIG. 10 is a graph showing the relationship between the water spray central angle and the amount of nitrogen oxides generated. [Figure 11] FIG. 10 is a diagram showing the manner in which water is sprayed when a water injection nozzle is disposed on a cylinder wall. [Figure 12] FIG. 10 is a diagram showing the relationship between the position of the water injection nozzle and the spray of water. [Figure 13] FIG. 10 is a graph showing the amount of nitrogen oxides generated for each water spray deflection angle. [Figure 14] FIG. 10 is a diagram showing the distribution of water in a combustion chamber for each water spray deflection angle. [Figure 15] FIG. 4 is a diagram showing the timing of water injection. [Figure 16] FIG. 10 is a graph showing the amount of nitrogen oxides generated for each number of water injections. [Figure 17]FIG. 10 is a diagram showing the water concentration distribution in the combustion chamber for each number of water injections. [Figure 18] FIG. 10 is a diagram showing a comparison of the relationship between compression ratio and indicated thermal efficiency with and without water injection. [Figure 19] FIG. 10 is a diagram showing a comparison of the relationship between the compression ratio and the amount of nitrogen oxides generated with and without water injection. [Figure 20] FIG. 10 is a diagram showing a comparison of the relationship between compression ratio and soot with and without water injection. [Figure 21] FIG. 1 is a diagram showing a schematic diagram of a water-containing region formed by a single water injection. [Figure 22] FIG. 10 is a diagram showing a schematic diagram of a water-containing region due to divided water jets. [Figure 23] FIG. 10 is a diagram showing another example of parameters used in the numerical calculations. [Figure 24] FIG. 4 is a diagram showing conditions for water injection timing. [Figure 25] FIG. 4 is a diagram showing conditions for water injection timing. [Figure 26] FIG. 10 is a diagram showing the reduction rate of nitrogen oxides for each condition of water injection timing. [Figure 27] FIG. 10 shows the water distribution in the combustion chamber for single and split water injection. DETAILED DESCRIPTION OF THE INVENTION

[0019] An embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a schematic diagram showing the main components of a reciprocating internal combustion engine 10, particularly a diesel engine, according to this embodiment. The reciprocating internal combustion engine 10 includes a cylindrical cylinder 12 and a piston 14 that reciprocates within the cylinder 12 along the axial direction of the cylinder 12. The space defined by the cylinder 12 and the piston 14, particularly when the piston 14 is near top dead center, is called a combustion chamber 16. A fuel injection nozzle 18 is disposed at the center of the top surface 12a of the cylinder 12. The reciprocating internal combustion engine 10 also includes a water supply device 22 that supplies water as droplets into the combustion chamber 16. The water supply device 22 includes a water injection nozzle 20 disposed away from the center of the top of the cylinder 12. A recess 21 having a diameter Dre is formed in the top surface of the piston 14, defining the combustion chamber 16. The center line of the cylinder 12 is defined as the z-axis, the axis perpendicular to the z-axis and passing through the position where the water injection nozzle 20 is arranged is defined as the x-axis, and the axis perpendicular to the x-axis and z-axis is defined as the y-axis. The x-axis, y-axis, and z-axis intersect at the center O of the top surface 12a.

[0020] In the reciprocating internal combustion engine 10, intake and exhaust valves are disposed on the top surface 12a of the cylinder 12, but for the sake of simplicity, these are omitted from Figure 1. Also, a connecting rod is connected to the piston 14 for connection to a crankshaft (not shown), but this is also omitted.

[0021] The fuel injection nozzle 18 injects fuel radially from the center O toward the periphery, for example, in eight directions. The water injection nozzle 20 is offset by Xoff from the center O in the x-axis direction. This Xoff is referred to as the placement offset amount.

[0022] FIG. 2 shows the spraying behavior of the water spray nozzle 20 of the water supply device 22. (a) is a view of the water supply device 22 as seen along the z-axis, (b) is a view as seen along the y-axis, and (c) is a bird's-eye view. The water spray nozzle 20 has multiple nozzle holes arranged in the same plane. A thin conical jet is formed from each nozzle hole, and overall, a flat, fan-shaped water spray 24 is formed. The central angle of this fan is defined as the water spray central angle θsc. The water spray nozzle 20 sprays water toward the center O. The angle between the center line 24a of the water spray 24 and the x-axis in the xy plane is defined as the water spray deflection angle θxy (see FIG. 1). When viewing the cylinder 12 from above, the positive direction of the water spray deflection angle θxy is counterclockwise. Furthermore, water spray 24 is sprayed downward from the xy plane, and the angle between the plane defined by the sector of water spray 24 and the z axis is defined as water spray downward angle θxz (see Figure 1). Water spray 24 has a shape that is symmetrical with respect to a plane that includes center line 24a of the sector and is parallel to the z axis.

[0023] FIG. 3 shows the basic specifications of the reciprocating internal combustion engine 10 used in the numerical calculations. In the following numerical calculations comparing the effects of each specification, the values ​​shown in FIG. 3 are used for specifications not being compared. The water rate is the mass ratio of the water injection amount to the fuel injection amount. The water injection timing indicates the water injection start time, and water is injected between 21° and 13° before top dead center. The water injection period indicates the period during which water is injected at 20 MPa. The water injection amount per unit time (water injection rate) within the water injection period is constant. (Note that, in the numerical calculations in which water injection is divided into main injection and additional injection, which will be described in relation to FIGS. 21 to 27, some specifications different from the basic specifications in FIG. 3 are used.)

[0024] FIG. 4 is a diagram showing the water-containing region 26 containing water supplied by the water supply device 22. In FIG. 4, the dotted region is the water-containing region 26. The water-containing region 26 is a region containing water droplets of the water spray 24 injected from the water injection nozzle 20 and water vapor resulting from evaporation of these droplets. In the following description, unless otherwise specified, "water" includes liquid water in the form of droplets and water vapor. Water injected toward the center O of the cylinder 12 from the water injection nozzle 20 offset from the center O is distributed in a flat, cylindrical region in the center of the combustion chamber 16 in the xy plane. This region is the water-containing region 26. This reciprocating internal combustion engine 10 forms a stratified water-containing region 26 in the center of the combustion chamber 16. In other words, a region with a high water concentration is formed in the center of the cylinder 12, and a region with a low water concentration is formed around it in a layered manner. The diameter (bore) of the cylinder 12 is indicated by Dbore, and the diameter of the water-containing region 26 is indicated by Dwa.

[0025] FIG. 5 shows an example of water distribution in the combustion chamber 16, and FIG. 6 is a graph showing the amount of nitrogen oxides (NOx) generated for each water distribution shown in FIG. 5. FIG. 5(a) shows a case where water is distributed in the center of the combustion chamber 16, forming a flattened cylindrical water-containing region 26. The distribution shown in FIG. 5(a) is referred to as a central stratified distribution. The diameter Dwa of the water-containing region 26 is half the bore Dbore (Dwa = 0.5 × Dbore). FIG. 5(b) shows a case where water is uniformly distributed throughout the combustion chamber 16, with water distributed in the dotted region. The distribution shown in FIG. 5(b) is referred to as a globally uniform distribution. FIG. 5(c) shows a case where water is distributed near the periphery of the combustion chamber 16, with water distributed in the dotted region 29. The distribution shown in FIG. 5(c) is referred to as a peripheral stratified distribution. The water ratio is 60% in all of FIG. 5(a) to (c).

[0026] FIG. 6 shows the amount of nitrogen oxides generated for the water distributions (a) to (c) in FIG. 5, and the amount of nitrogen oxides generated is shown as a relative amount to the amount when no water is supplied into the combustion chamber 16, i.e., when no water is injected. It is shown that the case (a), in which water is distributed in the central portion, is the most effective. The amount of nitrogen oxides generated for each water distribution in FIG. 6 was calculated under the condition that the amount of soot generated was equal. FIG. 7 also shows the indicated thermal efficiency when no water is supplied and when water is distributed in the above-mentioned cases (a) to (c). It is shown that the thermal efficiency is higher in the case (a), in which water is distributed in the central portion. The indicated thermal efficiency for each water distribution in FIG. 7 was calculated under the condition that the amount of nitrogen oxides generated was equal.

[0027] Figure 8 shows the distribution of water injected into the combustion chamber 16 after fuel injection, as determined by numerical calculation. (a) shows a central stratified distribution, (b) shows a uniform distribution throughout the combustion chamber, and (c) shows a peripheral stratified distribution. The darker areas indicate areas with a higher water concentration. In the case of the central stratified distribution in (a), the fuel jet 28 from the fuel injection nozzle 18 absorbs surrounding water as it passes through the water-containing region 26 in the center of the combustion chamber 16, resulting in a large amount of water being incorporated into the fuel jet 28. In the case of the uniform distribution throughout the combustion chamber in (b), it can be seen that less water is incorporated into the fuel jet 28 than in the case of the central stratified distribution. In the case of the peripheral stratified distribution in (c), it can be seen that the water is blown away by the fuel jet 28, resulting in almost no water being incorporated into the fuel jet 28.

[0028] As shown in FIG. 8( a), when the water-containing region 26 is located in the center of the combustion chamber 16, the fuel jet 28 takes in gas containing water droplets and water vapor from the water-containing region 26. The water-containing region 26 is cooled by the evaporation of the injected water droplets. The fuel jet 28 takes in this cooled gas, and the evaporated water droplets lower the temperature of the flame ignited by the fuel jet 28. This reduces the generation of nitrogen oxides and the amount of nitrogen oxides generated. Furthermore, the lower temperature of the fuel jet 28 shifts the ignition position downstream of the fuel jet 28. Meanwhile, the downstream side of the fuel jet 28 takes in more ambient gas than the upstream side, resulting in a lower temperature and leaner fuel. This reduces combustion in the high-temperature rich region and suppresses soot generation. Furthermore, the lower temperature of the spray flame reduces the temperature of the flame in contact with the combustion chamber wall, narrowing the temperature difference between the wall and the flame, thereby reducing heat loss. This improves thermal efficiency.

[0029] FIG. 9 is a diagram showing the relationship between the diameter of the water containing region 26 and the amount of nitrogen oxides generated. The horizontal axis represents the diameter Dwa of the water containing region 26 relative to the diameter Dbore of the cylinder 12, and the vertical axis represents the amount of nitrogen oxides generated, particularly as a relative value to the case where water is not supplied to the combustion chamber 16 (no water injection). It can be seen that the amount of nitrogen oxides generated is reduced in the case of the central stratified charge distribution compared to the case of a uniform distribution throughout the entire region (Dwa / Dbore = 1). In particular, the amount of nitrogen oxides generated can be significantly reduced when the diameter Dwa of the water containing region 26 is 0.3 to 0.6 times the cylinder diameter.

[0030] Figure 10 is a diagram showing the relationship between the water spray central angle θsc and the amount of nitrogen oxides generated. As shown in Figure 11, Figure 10 shows the relationship between the water spray central angle θsc0 and the amount of nitrogen oxides generated when the arrangement offset amount Xoff is set to 0.5Dbore and the water spray deflection angle θxy is set to 0. The horizontal axis shows the water spray central angle θsc0, and the vertical axis shows the amount of nitrogen oxides generated, particularly as a relative value to the case where water is not supplied to the combustion chamber 16. It can be seen that the effect of reducing nitrogen oxides is greater when the water spray central angle θsc0 is 50° or more and 75° or less.

[0031] As mentioned above, Fig. 10 shows the results when the water injection nozzle 20 is provided on the wall surface of the cylinder 12, that is, when the placement offset amount Xoff is set to the cylinder radius 0.5D bore. From this result, it is possible to estimate a preferable value for the water spray central angle θsc when the water injection nozzle 20 is moved closer to the center O of the cylinder 12.

[0032] Figure 12(a) shows a case where the water injection nozzle 20 is provided on the wall surface of the cylinder 12, as in Figure 11. In this case, the water spray 24 with a central angle θsc0 is injected toward a circular region 30 whose center is concentric with the cylinder center O, as shown by the dashed line in the figure. This region 30 is a circle with a radius R0 and a center at the cylinder center O, with both edges of the fan-shaped water spray being tangents. Figure 12(b) shows a state where the water injection nozzle 20 is closer to the center O than to the wall surface of the cylinder 12 (Xoff<0.5Dbore). To obtain a water distribution similar to that shown in (a), it is considered necessary to spray water toward the entire region 30, and the central angle θsc of the water spray 24 for this purpose is θsc=(0.5Dbore / Xoff)×θsc0 (1) However, θ=sinθ is approximated. As shown in Fig. 10, when the water injection nozzle 20 is provided on the wall surface of the cylinder 12, the effect of suppressing nitrogen oxides is recognized when the water spray central angle θsc0 is in the range of 50 to 75°, and in order to obtain the same effect, water should be injected so that it is supplied to the region 30. To achieve this, from equation (1), the range of the water spray central angle θsc should be set to 50° × (0.5D bore / X off) or more and 75° × (0.5D bore / X off) or less.

[0033] 1 is generated in the combustion chamber 16, the amount of nitrogen oxides is shown when the water injection deflection angle θxy is set to 15°, 0°, and -5°. The amount of nitrogen oxides is shown as a relative amount to the amount when water is not supplied to the combustion chamber 16. FIG. 14 is a diagram showing the distribution of water in the combustion chamber 16 when the water injection deflection angle θxy is set to 15°, 0°, and -5°. The water injected from the water injection nozzle 20 is distributed in the shaded area. When the water injection deflection angle θxy is 0°, the jet flow along the center line 24a of the water spray is perpendicular to the circulating swirl 32, and when it is 15°, the jet flow along the center line 24a has a component that faces the swirl 32.

[0034] It can be seen from Figure 13 that nitrogen oxides are reduced further when the water injection deflection angle θxy is 15°. This is thought to be because, as shown in Figure 14, when the water injection deflection angle θxy is 15°, the water is not unevenly distributed but is distributed closer to the center O, reducing the unevenness in the amount of water taken in by each jet of radially injected fuel and lowering the temperature of each jet.

[0035] Figure 15 shows the timing of water injection, with (a) showing the injection timing for a single injection and (b) showing the injection timing for a double injection. The solid line indicates water injection, and the dashed line indicates the main fuel injection. For a single water injection, injection begins 21° before top dead center and the injection period is 8°. For a double water injection, injection begins 23° and 10° before top dead center, with each injection period being 4°. The first and second injections have the same amount of injection. Figure 16 shows the amount of nitrogen oxides generated for different injection counts, with (a) showing the case of a single injection and (b) showing the case of a double injection, corresponding to the injection timing shown in Figure 15. The amount of nitrogen oxides generated is also shown as a relative value to the case without water injection. As shown, the amount of nitrogen oxides generated is lower when water is injected twice. Figure 17 shows an example of the water concentration distribution calculated by numerical calculation, with (a) showing the case of a single injection and (b) showing the case of a double injection, corresponding to the injection timing shown in Figure 15. The darker areas are areas with a higher concentration of water. The reason why the double injection produces less nitrogen oxides is thought to be because the water is distributed more symmetrically around the central axis of the combustion chamber 16, and the amount of water taken in by each jet of radially injected fuel is not biased.

[0036] 18 to 20 are graphs comparing the indicated thermal efficiency, the amount of nitrogen oxides generated, and the amount of soot generated when the compression ratio is changed, with and without water being supplied into the combustion chamber 16. The compression ratio was changed by changing the diameter Dre of the recess 21. The smaller the diameter Dre, the higher the compression ratio. The compression ratio was changed in 1 increments from 15.1 to 21.1 when water was not supplied, and from 15.1 to 22.1 when water was supplied. As shown in FIGS. 19 and 20, it can be seen that the amount of nitrogen oxides and soot generated is suppressed by supplying water over the entire range of compression ratios. Furthermore, as shown in FIG. 18, it can be seen that the thermal efficiency improves at compression ratios of 18 or higher, and even higher thermal efficiency is shown in the compression ratio range of 21 to 22.

[0037] Instead of water, the liquid supplied into the combustion chamber 16 can be a liquid with a higher latent heat of vaporization than the fuel. For example, if the fuel is diesel, methanol water or ethanol water can be used instead of water. In addition to diesel engines, the present invention can also be applied to gasoline engines in which fuel is directly injected into the cylinder and water is injected to supply water to the combustion chamber.

[0038] When water is injected once from the water injection nozzle 20, it may not be possible to obtain a water distribution that is symmetrical about the central axis of the combustion chamber 16. Below, we will explain a method for suppressing bias in water distribution by performing water injections in separate injections.

[0039] FIG. 21 is a diagram schematically illustrating a water inclusion region 26A formed by a single water injection (hereinafter referred to as a single water injection). In the case of a single water injection, the injected water has a large momentum and passes over the cylinder center O, and the center of gravity of the water distribution tends to move to the opposite side of the water injection nozzle 20 with respect to the cylinder center O. In addition, the leading edge of the water spray is likely to experience resistance from the surrounding gas and therefore its velocity is likely to decrease. On the other hand, the trailing portion of the water spray follows the leading portion, so it experiences less resistance from the surrounding gas and its velocity does not decrease as much. For this reason, the trailing portion catches up with the leading portion, and the water inclusion region 26A roughly takes on the shape of a sector or horseshoe with a central angle of more than 180°, as shown in FIG. 21.

[0040] Figure 22 is a diagram showing a schematic diagram of a water inclusion region 26B formed when additional water injection is performed at intervals after the main water injection. Hereinafter, the main water injection will be referred to as the main water injection, the additional water injection will be referred to as the additional water injection, and the water injection performed by dividing the main water injection and the additional water injection into separate water injections will be referred to as the divided water injection. In Figure 22, (a) shows the water inclusion region 26C formed by the main water injection, and (b) shows the water inclusion region 26B after the additional water injection. The water inclusion region 26C formed by the main water injection is a sector with a central angle of more than 180°, as in the case of a single water injection, and the water inclusion region 26B is formed by filling in the missing part of this sector with water from the additional water injection.

[0041] Figure 23 shows the basic specifications of the reciprocating internal combustion engine 10 used in the numerical calculations when split water injection is performed, as described below. The water ratio (mass ratio of the water injection amount to the fuel injection amount) is 50 percent. Figures 24 and 25 show the timing of water injection. The timing of the main fuel injection is common to all conditions, and is from 4° before top dead center to 6° after top dead center, as shown by the dashed line. The timing of water injection is shown by the solid line. Condition 1 is a condition in which water injection 40 is performed from 39 to 27° before top dead center at a water injection rate of 21.0 g / s, and is used for comparison with split water injection. Conditions 2 to 6 show conditions for split water injection, divided into main water injection 42 and additional water injection 44. In conditions 2 to 6, the water injection rate of the main water injection 42 and additional water injection 44 is 15.8 g / s. The timing of the main water injection 42 is the same as condition 1, from 39 to 27° before top dead center. The timing of additional water injection 44 differs for each condition: Condition 2 is from 18 to 14 degrees before top dead center, Condition 3 is from 14 to 10 degrees before top dead center, Condition 4 is from 10 to 6 degrees before top dead center, Condition 5 is from 6 to 2 degrees before top dead center, and Condition 6 is from 2 degrees before top dead center to 2 degrees after top dead center. The total amount of water injected is the same for Conditions 1 to 6, and the amount of water injected by additional water injection 44 in Conditions 2 to 6 is 25 percent of the total amount of water. Condition 7 injects the same amount of water in the main water injection and additional water injection, and like Conditions 2 to 6, the injection rate is 15.8 g / s. The timing of main water injection 42 and additional water injection 44 is from 39 to 31 degrees before top dead center and from 14 to 6 degrees before top dead center, respectively. In Condition 7, the timing of the end of additional water injection 44 is the same as in Condition 4.

[0042] Figure 26 shows the reduction rate of nitrogen oxides (NOx) in exhaust gas under conditions 1 to 7 shown in Figures 24 and 25, compared to when water injection is not performed. The greater the reduction rate, the less nitrogen oxides there are in exhaust gas. Figure 26 shows that the closer the additional water injection is to the main fuel injection, the greater the reduction in nitrogen oxides (conditions 2 to 4), and that the reduction rate worsens when the additional water injection and the main fuel injection overlap (conditions 5 and 6). Separating the water injection reduces the momentum of the water per injection, preventing the water injected by the main water injection 42 from excessively passing through the fuel injection nozzle 18 at the center O of the combustion chamber 16, making it easier to form a water-containing region 26 in the center of the combustion chamber 16. As with the main water injection 42, the momentum of the water injected by the additional water injection 44 also decreases, making it more likely to be present in the center of the combustion chamber 16. Furthermore, when the timing of additional water injection 44 is brought closer to top dead center, the density of gas inside the combustion chamber 16 is high near top dead center, so the injected water encounters greater resistance and decelerates, preventing it from catching up with and entering the preceding water containing region 26C formed by the main water injection 42. As a result, the water from the additional water injection 44 fills in the missing part of the water containing region 26C, making it possible to form a water containing region 26B that is approximately symmetrical to the axis in the center of the combustion chamber 16.

[0043] If part or all of the additional water injection 44 overlaps with the main fuel injection, as in conditions 5 and 6, the water spray is pushed back by the fuel spray, and the water spray cannot be filled in for the missing portion of the preceding water-containing region C. This makes it impossible to form an axisymmetric water-containing region 26B in the center of the combustion chamber 16. Therefore, it is clear that it is desirable to start the additional water injection 44 near top dead center and end it just before the main fuel injection starts.

[0044] Comparing Condition 4 and Condition 7, it is clear that it is desirable to reduce the amount of water injected by the additional water injection 44 compared to the main water injection 42. When the proportion of additional water injection increases, the residence time of the water until near top dead center where combustion starts becomes relatively shorter. As a result, the amount of water evaporation decreases overall, and the amount of decrease in the temperature of the gas in the combustion chamber 16 becomes smaller, which is thought to result in a smaller NOx reduction effect.

[0045] 27 shows water distributions calculated by numerical calculations, with (a) showing an example of a water distribution 34 formed by single water injection and (b) showing an example of a water distribution 36 formed by divided water injection. The shaded area in the figure is an area containing water vapor formed by evaporation of injected water, and the area surrounded by thin lines is an area where many water droplets exist. In divided water injection, an axisymmetric water distribution 36 is formed in the center of the combustion chamber 16 as a whole by a water distribution 36a formed by main water injection and a water distribution 36b formed by additional water injection.

[0046] As described above, by injecting water into the center of the combustion chamber, the main water injection is performed and the additional water injection is performed at an interval from the main water injection, with the injection amount being smaller than the main water injection. Flat cylindrical shape water containing area of This allows stratification of the charge and suppresses the emission of nitrogen oxides. It is also preferable that the additional water injection is performed immediately before the main fuel injection. It is preferable that: <Additional Notes> [Configuration 1] a fuel injection nozzle disposed at the top center of the cylinder for injecting fuel into a combustion chamber defined by the cylinder and the piston; a water supply device having a water injection nozzle that injects water into the combustion chamber; and the water supply device injects water from the water injection nozzle to form a stratified flattened cylindrical water-containing region containing water droplets and water vapor in a central portion of the combustion chamber before the fuel injection nozzle performs a main injection. Reciprocating internal combustion engine. [Configuration 2] In the reciprocating internal combustion engine according to [Configuration 1], the diameter of the water-containing region is 0.3 to 0.6 times the diameter of the cylinder. [Configuration 3] In the reciprocating internal combustion engine according to [Configuration 1] or [Configuration 2], the shape of the spray formed by the water injection nozzle when it injects water is fan-shaped, and the water injection nozzle is positioned offset from the center of the cylinder and injects water toward the center of the cylinder. [Configuration 4] [Configuration 3] A reciprocating internal combustion engine according to the present invention, wherein the central angle of the fan-shaped spray formed by the water injection nozzle is 50° × (0.5Dbore / Xoff) or more and 75° × (0.5Dbore / Xoff) or less, where Dbore is the cylinder diameter and Xoff is the offset amount of the water injection nozzle from the center of the cylinder. [Configuration 5] In the reciprocating internal combustion engine described in [Configuration 3], the spray is injected toward a position shifted from the center of the cylinder so that a jet along the center line of the fan-shaped spray has a velocity component opposite to a swirl formed to swirl inside the combustion chamber. [Configuration 6] The reciprocating internal combustion engine according to any one of [Configuration 1] to [Configuration 5], wherein the water supply device injects water from the water injection nozzle in two separate injecting operations. [Configuration 7] In the reciprocating internal combustion engine according to any one of [Configuration 1] to [Configuration 4], the water supply device performs main water injection from the water injection nozzle, and, after the main water injection, additional water injection with an injection amount smaller than the main water injection at an interval from the main water injection. [Configuration 8] In the reciprocating internal combustion engine according to [Configuration 7], the water supply device terminates the additional water injection immediately before the start of the main injection of fuel. [Configuration 9] The reciprocating internal combustion engine according to [Configuration 7] or [Configuration 8], wherein the amount of water injected by the additional water injection is 25 percent of the total amount of water injection. [Configuration 10] A reciprocating internal combustion engine according to any one of [Configuration 1] to [Configuration 9], wherein the compression ratio is 18 or more and 21 or less. [Configuration 11] [Configuration 10] The reciprocating internal combustion engine according to the present invention, wherein the compression ratio is 20 or more and 21 or less. [Configuration 12] The reciprocating internal combustion engine according to any one of [Configuration 1] to [Configuration 11], further comprising, instead of the water supply device, a high latent heat liquid supply device that supplies a liquid having a higher latent heat of vaporization than the fuel. [Explanation of symbols]

[0047] 10 reciprocating internal combustion engine, 12 cylinder, 14 piston, 16 combustion chamber, 18 fuel injection nozzle, 20 water injection nozzle, 21 recess, 22 water supply device, 24 water spray, 26, 26A, 26B, 26C water containing area, 28 fuel jet, 30 area, 32 swirl, 34 water distribution by single injection, 36 water distribution by split injection, 40 timing of single water injection, 42 timing of main water injection, 44 timing of additional water injection, Xoff placement offset amount, θsc water spray central angle, θxy water spray deflection angle, θxz water spray downward angle.

Claims

1. a fuel injection nozzle disposed at the top center of the cylinder for injecting fuel into a combustion chamber defined by the cylinder and the piston; a water supply device having a water injection nozzle arranged offset from the center of the cylinder and injecting water from a plurality of nozzle holes arranged in the same plane toward the center of the cylinder in the combustion chamber; and the water supply device injects water from the water injection nozzle to form a stratified flattened cylindrical water-containing region containing water droplets and water vapor in a central portion of the combustion chamber before the fuel injection nozzle performs a main injection; A reciprocating internal combustion engine, The water supply device is The shape of the spray formed by the water injection nozzle when it injects water is fan-shaped, and the central angle of the fan-shaped spray is 50° × (0.5Dbore / Xoff) or more and 75° × (0.5Dbore / Xoff) or less, where Dbore is the cylinder diameter and Xoff is the offset amount of the water injection nozzle from the center of the cylinder. This causes the water-containing region having a flattened cylindrical shape containing water droplets and water vapor to be stratified in the center of the combustion chamber as a region where the water concentration is higher than that of the surrounding area. Reciprocating internal combustion engine.

2. 2. The reciprocating internal combustion engine according to claim 1, wherein the diameter of said water-containing region is not less than 0.3 times and not more than 0.6 times the diameter of said cylinder.

3. 3. The reciprocating internal combustion engine according to claim 1, wherein the water supply device injects water from the water injection nozzle in two separate injecting operations.

4. 3. The reciprocating internal combustion engine according to claim 1, wherein the water supply device performs a main water injection from the water injection nozzle, and an additional water injection, the additional water injection having an injection amount smaller than that of the main water injection, at an interval after the main water injection.

5. 5. The reciprocating internal combustion engine according to claim 4, wherein the water supply device terminates the additional water injection immediately before the start of the main injection of fuel.

6. 6. A reciprocating internal combustion engine according to claim 4, wherein the amount of injection by the additional water injection is 25 percent of the total amount of water injection.

7. 7. The reciprocating internal combustion engine according to claim 1, wherein the compression ratio is 18 or more and 21 or less.

8. 8. The reciprocating internal combustion engine according to claim 7, wherein the compression ratio is 20 or more and 21 or less.

9. 9. A reciprocating internal combustion engine according to claim 1, further comprising, in place of the water supply device, a high latent heat liquid supply device for supplying a liquid having a higher latent heat of vaporization than the fuel.

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