JP4924702B2 - Direct injection compression ignition engine - Google Patents

Description

  The present invention relates to a combustion chamber of a direct injection compression ignition engine mainly used in an automobile.

  As a combustion chamber of a direct injection type compression ignition engine (diesel engine), in order to promote mixing of spray fuel and intake air, the crest at the center of the bottom of the cavity is raised to narrow the central area where the swirl is weak, It has been proposed to reduce the proportion of the swirl's weak central area in the total area of the cavity.

  For example, in the reentrant combustion chamber described in Patent Document 1, the diameter of the cylinder bore 100 shown in FIG. 12 is set to 100, and the dimensions of each part are set as follows. The opening diameter B in the piston top surface 102 of the cavity 101 is set to 45 to 62, the outer edge diameter C of the cavity 101 is set to about 65, and the maximum depth D is set to about 18.

  By adopting such a combustion chamber shape, it is possible to avoid an increase in NOx by using the minimum necessary air present in the center of the cavity during light load operation for combustion, and around the cavity during high load operation. The generation of smoke can be reduced by using a large amount of air present in the section for combustion.

Japanese Patent Laid-Open No. 11-210467 Japanese Patent Laid-Open No. 1-200014 JP 2000-352316 A JP 60-119323 A JP 2002-364366 A

  However, in the reentrant combustion chamber proposed in Patent Document 1, the relationship between the opening diameter B of the cavity 101 and the outer edge diameter C or the relationship between the outer edge diameter C of the cavity 101 and the maximum depth D is specifically described. Not mentioned. According to the research of the present inventor, it has been found that it is not possible to suppress the occurrence of smoke during light load operation depending on these relationships.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a technique capable of reducing the generation of smoke in the entire operation region.

  In order to achieve the above object, in the reentrant combustion chamber of the direct injection compression ignition engine according to the present invention, the maximum diameter of the cavity formed in the piston is D1, the lip diameter is D2, and the maximum depth is H. In this case, the value of (D1-D2) / D1 which is a reentrant ratio is approximately 0.1, and the value of D1 / H which is an aspect ratio is approximately 4.

According to the research of the present inventor, when the aspect ratio is approximately 4, when the internal combustion engine that is a direct injection compression ignition engine is in the low speed operation region, the reentrant rate is less than 0.1. It has been found that when the ratio is larger than 1, the squish flow is directed toward the center of the combustion chamber, so that the fuel and air are not mixed well and more smoke is generated. On the other hand, when the internal combustion engine is in the high speed operation region, the tumble flow generated in the combustion chamber is large, and therefore the injected fuel is smaller than 0.1 when the reentrant rate is 0.1 or more. It has been found that more smoke is generated because it easily enters between the piston top surface and the cylinder head. Therefore, in order to reduce the generation of smoke in the entire operation region, it is preferable that the reentrant rate is approximately 0.1.

  Further, in the reentrant combustion chamber, the spray from the fuel injection valve provided in the internal combustion engine is configured to collide with the wall surface of the enlarged diameter portion from the lip portion to the maximum diameter portion formed below the lip portion. Yes. Therefore, as the maximum diameter D1 of the cavity decreases, that is, when the maximum depth H is the same, the aspect ratio decreases from the nozzle hole of the fuel injection valve to the spray combustion chamber wall surface. The distance to the collision position becomes shorter.

  According to the inventor's research, when the reentrant rate is approximately 0.1, when the internal combustion engine is in the high speed operation region, the fuel combustion chamber is larger than 4 when the aspect ratio is 4 or less. Since the collision distance to the wall surface is long and the tumble flow generated in the combustion chamber is strong in such an operating region, it becomes difficult for the spray to reach the wall surface of the combustion chamber, so the fuel and air are not mixed well and there is more smoke. It was found to occur.

  Further, when the internal combustion engine is in the medium speed operation region, the distance between the fuel injection valve nozzle hole and the combustion chamber wall surface is shorter when the aspect ratio is less than 4 than when the aspect ratio is 4 or more, and high speed operation is performed. It is easier for the spray to reach the combustion chamber wall than in the region, but the tumble flow generated in the combustion chamber is also relatively weak, so the injected fuel adheres more to the combustion chamber wall and the fuel and air are mixed well. It turned out that more smoke was generated.

  Further, when the internal combustion engine is in the low speed operation region, it becomes difficult to form a tumble flow in the cylinder, and as the aspect ratio becomes larger than 4, it becomes difficult to form a tumble flow in the combustion chamber. It was found that more smoke was generated when the air and the air were not mixed well. From the above, it is preferable that the aspect ratio is approximately 4 in order to reduce the occurrence of smoke in the entire operation region.

  In the reentrant combustion chamber of the direct injection compression ignition engine according to the present invention, since the reentrant rate is approximately 0.1 and the aspect ratio is approximately 4, the occurrence of smoke can be minimized. .

  Further, when the outer diameter of the piston is D0, it is preferable that a value obtained by dividing the lip diameter D2 by the piston outer diameter D0 is 0.5 or more and 0.7 or less.

In the internal combustion engine, swirl energy from the intake port is preserved and momentum is preserved in the combustion chamber in the compression stroke in which the piston rises from bottom dead center to top dead center, so that the angular velocity of the swirl flow is (D2 / D0 ² ) Proportional to swirl ratio.

  Therefore, the smaller the value of the outer diameter D0 of the piston, the faster the angular velocity, and the adjacent sprays tend to overlap with each other, so that smoke is likely to occur. On the other hand, as the outer diameter D0 of the piston increases, the angular velocity becomes slower and it becomes difficult for adjacent sprays to overlap each other. However, in this case, the swirl flow becomes weak and the fuel and air are difficult to mix well, so smoke is generated. It becomes easy.

According to the research of the present inventor, when the reentrant ratio is fixed to 0.1 and the aspect ratio is fixed to 4, D2 / D0 which is a value obtained by dividing the lip diameter D2 by the piston outer diameter D0 is smaller than 0.5, and 0 It became clear that the smoke generation amount increased as the value became larger than .7. Therefore, when the value of D2 / D0 is 0.5 or more and 0.7 or less, the occurrence of smoke can be minimized.

  In the direct injection compression ignition engine having a reentrant combustion chamber according to the present invention, a fuel injection valve having a plurality of injection holes is provided so as to face the injection holes in the combustion chamber, and the fuel The cylinder axial distance L from the intersection P of the fuel spray axis injected by the injection valve and the combustion chamber wall surface when the piston is located at the top dead center to the top surface of the piston is defined as the cavity formed in the piston. A value divided by the maximum depth H is 0.3 or more and 0.5 or less, and on a plane passing through the spray axis and the intersection point P, a tangent line that contacts the wall surface of the combustion chamber at the intersection point P The angle formed by the spray axis is 30 ° or more and 45 ° or less.

  When the cylinder axial distance L from the intersection P of the spray axis of the fuel injected by the fuel injection valve and the wall surface of the combustion chamber when the piston is located at the top dead center to the top surface of the piston is short, the squish area Since it becomes easy for the spray to enter, smoke is likely to be generated. On the other hand, when the distance L is long, the spray after the collision on the wall surface of the combustion chamber easily flows backward with respect to the tumble flow formed in the combustion chamber, so that it is difficult to mix the fuel and air well and smoke is likely to be generated. The inventor's research has revealed that the generation of smoke is reduced when L / H, which is a value obtained by dividing the distance L by the maximum cavity depth H, is 0.3 or more and 0.5 or less.

  Further, if the angle α between the tangent line that contacts the combustion chamber wall surface at the intersection point P and the spray axis line on the plane that passes through the fuel spray axis and the intersection point P of the fuel injected by the fuel injection valve is small, the spray energy is fine. Most of the fuel is not used for conversion to the combustion chamber wall surface or exists in the vicinity of the wall surface, and smoke is generated. On the other hand, if the angle α is large, the spray tends to roll up in the opposite direction to the tumble flow formed in the combustion chamber, so that it is difficult to mix the fuel and air well and smoke is likely to be generated. The inventor's research has revealed that the occurrence of smoke is reduced when the angle α is not less than 30 ° and not more than 45 °.

  In the direct injection compression ignition engine according to the present invention, since L / H is 0.3 or more and 0.5 or less and the angle α is 30 ° or more and 45 ° or less, the generation of smoke is minimized. Can be suppressed.

  Also in this direct injection compression ignition engine, when the maximum diameter of the cavity is D1 and the lip diameter is D2, the reentrant rate (D1-D2) / D1 is approximately 0.1. In addition, as described above, it is preferable that the value of the aspect ratio D1 / H is approximately 4. Furthermore, when the outer diameter of the piston is D0, the value obtained by dividing the lip diameter D2 by the piston outer diameter D0 is preferably 0.5 or more and 0.7 or less, as described above. is there.

Further, a relationship of (D0 / D2) ² × S × N = approximately 56 is established among the piston outer diameter D0, the lip diameter D2, the swirl ratio S, and the number N of the injection holes of the fuel injection valve. Preferably it is formed.

As described above, the angular velocity of the swirl flow is proportional to (D2 / D0) ² × swirl ratio, and when this angular velocity is divided by the number of nozzle holes of the fuel injection valve, the arrival time to the adjacent spray is obtained. Therefore, if D0 and D2 are constant, the arrival time becomes shorter as the number of injection holes of the fuel injection valve increases, and smoke tends to be generated because adjacent sprays tend to overlap. On the other hand, the smaller the number of nozzle holes, the longer the arrival time and the more difficult the adjacent sprays overlap. However, when the total fuel injection amount is the same, the amount of fuel injected from one nozzle hole increases and the fuel atomizes.・ Since it is difficult to vaporize, it becomes difficult to mix fuel and air well, and smoke is likely to be generated.

According to the research of the present inventor, the relationship between the piston outer diameter D0, the lip diameter D2, the swirl ratio S, and the number of injection holes N of the fuel injection valve is (D0 / D2) ² × S × N = approximately 56 It has been found that the generation of smoke can be minimized when it is formed so as to hold. Therefore, the configuration of the direct injection compression ignition engine according to the present invention can minimize the generation of smoke.

  As described above, according to the present invention, it is possible to reduce the occurrence of smoke in the entire operation region.

1 is a partial sectional view of a direct injection compression ignition engine having a reentrant combustion chamber according to Embodiment 1. FIG. It is a figure which shows the relationship between a reentrant rate and a smoke generation rate. It is a figure which shows the mode of generation | occurrence | production of the squish flow in a reentrant type | mold combustion chamber in case a reentrant rate is large. It is a figure which shows the mode of the flow of the fuel in a reentrant type | mold combustion chamber in case a reentrant rate is small. It is a figure which shows the relationship between an aspect-ratio and a smoke incidence. It is a figure which shows the relationship between D2 / D0 and the amount of smoke generation. It is a figure which shows the relationship between D2 / D0 and HC generation amount. It is a figure which shows the relationship between A and the amount of smoke generation. It is a figure which shows the spray axis of the fuel injection valve which has ten injection holes. It is a figure which shows the relationship between L / H and the amount of smoke generation. It is a figure which shows the relationship between (alpha) and the amount of smoke generation. It is a fragmentary sectional view of the direct injection type compression ignition engine which has the conventional reentrant type combustion chamber.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the best mode are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

  A combustion chamber of a direct injection compression ignition engine according to the first embodiment will be described with reference to FIG. The combustion chamber is configured by fitting a piston 2 having a piston outer diameter D0 to a cylinder 1 of a cylinder block and closing a piston top surface 2a side opening in the cylinder 1 with a cylinder head 3 fixed to the cylinder block. . A fuel injection valve 4 is provided so that the injection hole faces the combustion chamber.

  As shown in FIG. 1, the piston 2 has a cavity 5 formed on the top surface thereof in a concentric rotating body shape. As shown in FIG. 1, the cavity 5 is a so-called reentrant combustion chamber where lip diameter D2 <maximum diameter D1, where D1 is the maximum diameter, D2 is the lip diameter, and H is the maximum depth. On the other hand, it is also a shallow dish type combustion chamber having a small maximum depth H.

In general, the swirl flow and the tumble flow generated in the combustion chamber differ depending on the operation region such as the low speed operation region and the high speed operation region of the internal combustion engine. Further, according to the research of the present inventor, in such a reentrant combustion chamber, the mixture of air and fuel is also determined by the values of the reentrant rate (= (D1-D2) / D1) and the aspect ratio (= D1 / H). It was also found that the degree of smoke was different and the amount of smoke generated was different accordingly.

  FIG. 2 shows experimental data of smoke generation rates in the low-speed operation region and the high-speed operation region when the aspect ratio is fixed at 4 and the reentrant rate is changed. As shown in the figure, when the internal combustion engine is in the low speed operation region, the smoke generation rate is zero when the reentrant rate is 0.1 or less, whereas the reentrant rate is less than 0.1. The larger it becomes, the larger it becomes than zero. If the reentrant rate is large, the squish flow is directed toward the center of the combustion chamber as shown in FIG. 3, so that it is considered that the fuel and air are not mixed well and smoke is increased.

  On the other hand, when the internal combustion engine is in a high speed operation region, the smoke generation rate is 4% when the reentrant rate is 0.1 or more, whereas when the reentrant rate is less than 0.1, As the value decreases, the smoke generation rate increases. This is because in this operating region, the tumble flow generated in the combustion chamber is also large. Therefore, when the reentrant rate is small, the injected fuel tends to enter between the piston top surface 2a and the cylinder head 3 as shown in FIG. Therefore, it is thought that smoke will increase.

  Further, FIG. 5 shows experimental data of smoke generation rates in the low speed, medium speed, and high speed operation regions when the aspect ratio is changed with the reentrant rate fixed at 0.1. As shown in the figure, when the internal combustion engine is in the low speed operation region, the smoke generation rate is zero when the aspect ratio is 4 or less, but increases as the aspect ratio becomes larger than 4. . This is because, in such an operating region, a tumble flow is less likely to be formed in the cylinder, and a tumble flow is less likely to be formed in the combustion chamber when the aspect ratio is large. It is thought that it will occur.

  Further, when the internal combustion engine is in the medium speed operation region, the smoke generation rate is zero when the aspect ratio is 4 or more, but increases as the aspect ratio becomes smaller than 4. This is because if the aspect ratio is small, the distance between the injection hole of the fuel injection valve and the wall surface of the combustion chamber is short, and the tumble flow generated in the combustion chamber is weak in such an operating region. It is considered that smoke adheres to the wall surface and the fuel and air are not mixed well and smoke is generated.

  Further, when the internal combustion engine is in the high-speed operation region, the smoke generation rate is 3% when the aspect ratio is 4 or less, but increases as the aspect ratio becomes larger than 4. This is because, when the aspect ratio is large, the piston speed is high, whereas the injected fuel has a long collision distance with the wall of the combustion chamber, and the tumble flow generated in the combustion chamber is strong in such an operating region. It is difficult to reach the wall of the combustion chamber, and it is thought that smoke is generated because the fuel and air are not mixed well.

  In addition, if the aspect ratio is small, the distance between the injection hole of the fuel injection valve and the wall surface of the combustion chamber is short, so that the injected fuel adheres to the wall surface of the combustion chamber, and is less likely to be insulated and the fuel consumption deteriorates. .

  From the above, in such a reentrant combustion chamber, it is preferable that the reentrant rate is approximately 0.1 and the aspect ratio is approximately 4.

In an internal combustion engine having such a combustion system, swirl energy from the intake port is stored in the compression stroke in which the piston 2 rises from bottom dead center to top dead center, and momentum is stored in the combustion chamber. The angular velocity of the swirl flow is proportional to (D2 / D0) ² × swirl ratio. Then, when this angular velocity is divided by the number of injection holes of the fuel injection valve 4, the arrival time to the adjacent spray is obtained.

  Therefore, assuming that the number of injection holes of the fuel injection valve 4 is the same, the smaller the value of the outer diameter D0 of the piston 2, the faster the angular velocity, and the adjacent sprays tend to overlap with each other, so that smoke is likely to occur. On the other hand, as the value of the outer diameter D0 is increased, the arrival time is delayed, and adjacent sprays are less likely to overlap each other. It becomes easy.

  According to the inventor's research, the amount of smoke and HC generated when D2 / D0 is changed with the reentrant rate fixed at 0.1 and the aspect ratio fixed at 4 is shown in FIGS. did. As shown in FIG. 6, it can be seen that the amount of smoke generated increases as D2 / D0 becomes smaller than 0.5 and larger than 0.7. This means that it is necessary to delay the fuel injection timing in order to drive the engine so as not to generate smoke, resulting in deterioration of fuel consumption. Further, as shown in FIG. 7, it can be seen that the amount of HC generation increases as D2 / D0 becomes larger than 0.5. From the above, the value of D2 / D0 is preferably 0.5 or more and 0.7 or less.

  When the reentrant ratio is fixed to 0.1 and the aspect ratio is fixed to 4, the compression ratio varies according to the value of D2 / D0. That is, the compression ratio decreases as the value of D2 / D0 increases. Therefore, the value of D2 / D0 being 0.5 or more and 0.7 or less means that the compression ratio is lower than that in the case where the value of D2 / D0 is smaller than 0.5.

As described above, the angular velocity of the swirl flow is proportional to (D2 / D0) ² × swirl ratio, and when this angular velocity is divided by the number of nozzle holes of the fuel injection valve, the arrival time to the adjacent spray is obtained. Therefore, when D0 and D2 are constant, when the number of injection holes of the fuel injection valve is large, the arrival time is shortened and adjacent sprays are likely to overlap with each other, so that smoke is likely to be generated. On the other hand, when the number of nozzle holes is small, the arrival time becomes long and adjacent sprays hardly overlap each other. However, since the total fuel injection amount is the same, the amount of fuel injected from one nozzle hole increases, resulting in atomization / vaporization. Therefore, it becomes difficult to mix fuel and air well, and smoke is likely to be generated.

The present inventor studied how the amount of smoke generated fluctuates according to A as A = (D0 / D2) ² × swirl ratio × number of nozzle holes, and found that the result is as shown in FIG. . That is, when A is approximately 56, the smoke discharge amount becomes the minimum. Therefore, when D0 = 86 (mm), D2 = 52.7 (mm), and swirl ratio = 2.1, 56 / ((86 / 52.7) ² × 2.1) = 10. It can be seen that the number of injection holes of the fuel injection valve 4 is preferably 10. In other words, in such a case, as shown in FIG. 9, it is preferable to form ten injection holes in the fuel injection valve 4 so as to inject fuel in the direction of equal intervals of 36 ° in the circumferential direction. is there.

  Further, according to the research by the present inventor, as shown in FIG. 1, the piston is determined from the intersection P between the spray axis of the fuel injected by the fuel injection valve 4 and the wall surface of the combustion chamber when the piston is located at the top dead center. Assuming that the cylinder axial distance to the top surface 2a is L, when L / H is smaller than 0.3, spraying easily enters the squish area and smoke is also likely to occur. On the other hand, when L / H is larger than 0.5, the spray after the collision with the combustion chamber wall surface tends to flow backward with respect to the tumble flow formed in the combustion chamber, so that it is difficult to mix fuel and air well and smoke is generated. It becomes easy to do. That is, the smoke generation level when L / H is changed is as shown in FIG. Therefore, L / H is preferably 0.3 or more and 0.5 or less.

  Further, according to the inventor's research, on the plane passing through the spray axis and the intersection point P as shown in FIG. 1, the angle α formed by the spray axis and the tangent line contacting the wall of the combustion chamber at the intersection point P is 30 °. The smaller the fuel, the more the fuel is deposited on the combustion chamber wall surface or near the wall surface without using the spray energy for atomization, and the amount of smoke generated increases. In such a case, heat insulation becomes difficult and fuel consumption deteriorates. On the other hand, as the angle α is larger than 50 °, the spray is more likely to roll up in the opposite direction to the tumble flow formed in the combustion chamber, so that it is difficult to mix the fuel and air well and smoke is likely to be generated. That is, the amount of smoke generated when the angle α is changed is as shown in FIG. Accordingly, the angle α is preferably 30 ° or greater and 45 ° or less.

  As described above, the shape of the cavity 5, that is, the shape of the reentrant combustion chamber, is such that the reentrant rate is approximately 0.1, the aspect ratio is approximately 4, and D2 / D0 is 0.5 or more and 0.7 or less. The formation of smoke can be reduced by forming.

  In a direct injection compression ignition engine having a reentrant combustion chamber, the reentrant rate is approximately 0.1, the aspect ratio is approximately 4, and D2 / D0 is 0.5 or more and 0.7 or less. The occurrence of smoke is reduced by determining the position of the fuel injection valve 4 and the shape of the reentrant combustion chamber so that L / H is 0.3 to 0.5 and α is 30 ° to 45 °. be able to.

Further, when the swirl ratio of the engine is S and the number of injection holes of the fuel injection valve is N, the smoke is smoked by forming the relationship of (D0 / D2) ² × S × N = approximately 56. Can be reduced.

1 Cylinder 2 Piston 3 Cylinder Head 4 Fuel Injection Valve 5 Cavity

Claims (4)

In a direct injection compression ignition engine having a reentrant combustion chamber,
A fuel injection valve having a plurality of injection holes is provided to face the injection holes in the combustion chamber,
The relationship of (D0 / D2) ² × S × N = approximately 56 is established among the outer diameter D0 of the piston, the lip diameter D2 of the cavity formed in the piston, the swirl ratio S, and the number of injection holes N of the fuel injection valve. A direct injection type compression ignition engine characterized by being formed to When the maximum diameter of the cavity is D1, the lip diameter is D2, and the maximum depth is H, the value of (D1-D2) / D1, which is the reentrant ratio, is approximately 0.1, and the aspect ratio. 2. The direct injection compression ignition engine according to claim 1, wherein a value of D1 / H is approximately 4. The direct injection according to claim 2 , wherein when the outer diameter of the piston is D0, a value obtained by dividing the lip diameter D2 by the piston outer diameter D0 is 0.5 or more and 0.7 or less. Type compression ignition engine. The cylinder axial distance L from the intersection P of the fuel spray axis injected by the fuel injection valve and the combustion chamber wall surface when the piston is located at the top dead center to the piston top surface is defined as the maximum of the cavity. The value divided by the depth H is not less than 0.3 and not more than 0.5, and on the plane passing through the spray axis and the intersection point P, the tangent line that contacts the wall surface of the combustion chamber at the intersection point P and the spray The direct injection compression ignition engine according to any one of claims 1 to 3, wherein an angle formed by the axis is not less than 30 ° and not more than 45 °.

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