JP4992772B2 - Fuel injection system for diesel engine - Google Patents

Description

  The present invention relates to a fuel injection device for a diesel engine that directly injects fuel into a combustion chamber in a cylinder, and in particular, a fuel injection for a diesel engine having a fuel injection nozzle having a plurality of injection hole groups each consisting of two injection holes. Relates to the device.

The fuel injection nozzle of the diesel engine has a plurality of injection hole groups composed of a plurality of injection holes, and the fuel injected from the plurality of injection holes of each injection hole group each forms one fuel spray. A so-called group nozzle hole nozzle (group hole nozzle, abbreviated as GHN) is used to reduce the diameter of the injection hole and atomize the fuel, while increasing the number of injection holes to ensure the entire flow area of the injection holes. In this way, by devising the angle between the injection holes (angle between the central axes of the injection holes) constituting each injection hole group, soot (black smoke) can be reduced by promoting atomization of fuel. In the past, it has been proposed to enhance the spray penetration (penetration) (for example, see Patent Document 1).
JP 2007-51624 A

  In order to reduce soot (black smoke) discharged from a diesel engine, it is effective to promote fuel atomization by using a group nozzle nozzle (GHN). In particular, the ignition delay is increased, When setting to ignite after the fuel hits the combustion chamber wall, in order to further reduce soot, and to sufficiently reduce nitrogen oxide (NOx) along with soot, in addition to promoting fuel atomization, It is important to enhance the vertical vortex in the combustion chamber and promote recombustion by mixing the combustion gas with surplus air. In order to strengthen the vertical vortex in the combustion chamber, in addition to strengthening the penetration force (penetration) of the spray before reaching the wall surface of the combustion chamber, the penetration force (penetration) after the fuel spray wall collision is increased. Therefore, it is necessary to strengthen the fuel spray downstream of the combustion region and the wraparound of the already burned gas.

  The fuel spray injected into the combustion chamber of the diesel engine collides with the cavity wall surface during the ignition delay period and spreads along the wall surface by setting the appropriate spray penetration. The fuel spray burns best near the wall surface, and the combustion gas (burned gas) rides on the flow of the vertical vortex by the combustion expansion flow together with the fuel spray, and goes around the cavity wall surface in the vertical direction. When the entrained fuel spray and burned gas quickly reach the center of the cavity, there is low temperature surplus air that contains a large amount of oxygen that is not used for combustion. The burning gas is rapidly cooled by being mixed with low-temperature surplus air, so that the production of NOx is reduced, and soot contained in the burning gas comes into contact with oxygen and reburns, soot (black smoke) ) Is reduced. Therefore, by increasing the penetration force (penetration) after the wall surface collision of the fuel spray and strengthening the vertical wrapping of the fuel spray and the burnt gas, the burnt gas is quickly mixed with the surplus air, While being able to reduce NOx, it is possible to re-burn soot to reduce soot.

  However, the above conventional technique maintains the penetration force of the spray by collision between atomized sprays and uses the air in the combustion chamber space from the nozzle hole to the combustion chamber wall surface without waste. Is not intended to enhance the penetration force after the fuel spray wall collision, but to enhance the penetration force after the fuel spray wall collision. Further, generation of nitrogen oxides (NOx) and soot (black smoke) cannot be sufficiently reduced.

  The present invention relates to a diesel engine equipped with a fuel injection nozzle that can sufficiently reduce the generation of NOx and soot by enhancing the penetration force after a wall collision of spray formed by fuel injected into a combustion chamber in a cylinder. An object of the present invention is to provide a fuel injection device.

In the fuel injection device for a diesel engine according to the present invention, the piston is provided with a concave section at the center of the top surface of the piston, and a cavity that forms a combustion chamber and a position that faces the substantially center of the combustion chamber. A fuel injection nozzle that injects fuel toward the side wall surface of the combustion chamber, and the combustion chamber has an annular lip portion whose opening edge portion close to the top surface of the piston projects inward in the piston radial direction The bottom central portion located in the center of the piston radial direction has a shape that rises toward the opening end side, and the fuel spray injected into the combustion chamber collides with the cavity wall surface during the ignition delay period. The fuel spray spreads along the wall surface of the cavity along with the air-fuel mixture, and the fuel spray burns in the vicinity of the colliding wall surface, and the fuel spray and burned gas after the wall surface collision are converted into a vertical vortex flow by the combustion expansion flow. Thus, the fuel injection device of the diesel engine is configured to wrap around in the vertical direction along the wall surface and the lower bottom surface of the cavity, and the injection holes of the fuel injection nozzle each include a plurality of injection holes each having two injection holes. The two injection holes of each nozzle hole group are jet nozzles in the nozzle longitudinal section, which constitute a hole group, and the lip radius r / bore radius of the combustion chamber is 24/43 <(r / bore radius) <35/43. The inter-hole angle α is −5 deg <α <+5 deg, the inter-hole angle β in the nozzle cross section is 7.5 deg <β <12.5 deg, and the fuel spray injected from the two injection holes is the combustion chamber. One fuel spray is formed for each nozzle hole group after colliding with the wall surface, and the distance X between the collision points when the fuel spray injected from the two injection holes collides with the combustion chamber wall surface is 4. 5 to 7.5 mm As a result, the spray penetration force in the vertical direction of the combustion chamber obtained after the collision of the combustion chamber wall surface is enhanced by the characteristic that the spread of the spray after the collision is amplified in a direction perpendicular to the line connecting the two injection holes and spreads in an elliptical shape. Thus, the spray penetration force in the vertical direction of the combustion chamber is within a predetermined range that maintains the vicinity of the maximum value, thereby enhancing the vertical wrapping of the fuel spray and the burned gas after the wall collision. Is.

  In the form in which fuel is injected from the upper part of the combustion chamber toward the side wall surface of the combustion chamber, the fuel spray downstream of the combustion region is near the center of the combustion chamber located below the fuel injection nozzle as compared with the vicinity of the side wall surface of the combustion chamber. Combustion is not promoted and excess air tends to remain. Therefore, the fuel injection nozzle is configured as described above. By doing so, fuel atomization can be promoted and spray penetration (penetration) in the vertical direction of the combustion chamber after wall collision can be strengthened, whereby the vertical direction of fuel spray and burned gas downstream of the combustion region Therefore, the fuel spray and the burned gas reach the vicinity of the center of the combustion chamber below the fuel injection nozzle along the wall surface of the combustion chamber. As a result, the burned gas can be quickly mixed with the surplus air, the burned gas can be rapidly cooled to suppress the generation of NOx, and the soot reburning in the burned gas can be promoted. Generation of NOx and soot can be reduced.

  The spray particle diameter after the wall collision of the fuel spray injected from the two injection holes is the distance between the collision points when the fuel spray injected from the two injection holes collides with the combustion chamber wall. As the “wall collision point distance” increases, the atomization proceeds monotonously. On the other hand, the spray penetration force (penetration) in the vertical direction of the combustion chamber after the wall collision is in the middle of the range of the wall collision point distance where the penetration force increases, and the penetration force decreases monotonously before and after that. The characteristics of the atomization of the fuel spray and the spray penetration force in the longitudinal direction of the combustion chamber after the wall collision are uniquely determined by the wall collision point distance regardless of the size of the combustion chamber. Therefore, the wall surface collision point distance is set within a predetermined range in which the spray penetration force in the vertical direction of the combustion chamber after the wall surface collision is maintained in the vicinity of the maximum value, thereby enhancing the penetration force after the wall surface collision. It can be maintained within a range where atomization can be promoted. The wall collision point distance is basically determined by setting the distance between the injection holes of the two injection holes, the angle between the injection holes, and the shape of the combustion chamber (distance from the nozzle center to the spray collision point on the combustion chamber wall surface). .

  Here, within the predetermined range in which the spray penetration force in the vertical direction of the combustion chamber is maintained in the vicinity of the maximum value, the spray penetration force in the vertical direction of the combustion chamber is at least 20% or more larger than the spray penetration force in the horizontal direction of the combustion chamber. Within range.

  The two injection holes of each injection hole group have two injection holes such that the distance between the two collision points (wall surface collision point distance) is in the range of 4.5 to 7.5 mm. The distance between them and the angle between the injection holes should be set. By doing so, fuel atomization can be promoted while strengthening the spray penetration force after the wall surface collision.

  As is apparent from the above, according to the present invention, the penetration force (penetration) after the collision of the spray wall formed by the fuel injected into the combustion chamber in the cylinder is strengthened, and the generation of NOx and soot is reduced. Can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 5 show an embodiment of the present invention. FIG. 1 is a cross-sectional view of the vicinity of a combustion chamber of a diesel engine according to the embodiment, FIG. 2 is an explanatory diagram showing a wall spray collision distance X of fuel spray, and FIG. 3 is a diagram for explaining parameters of the nozzle hole layout of the fuel spray nozzle. (A) is explanatory drawing of inter-hole distance Y and nozzle hole angle (alpha) in a nozzle vertical cross section, (b) is explanatory drawing of inter-hole distance Z and nozzle hole angle (beta) in a nozzle cross section, (c). 4 is an explanatory view of the combustion chamber lip radius r, FIG. 4 is an explanatory view for explaining the penetration force (penetration) after the fuel spray wall collision, FIG. 5 is the fuel spray wall collision point distance X, and the spray after the wall collision. It is a graph which shows the relationship between penetration force (penetration), the average particle diameter of fuel spray, and smoke performance.

  The diesel engine of this embodiment is an in-line multi-cylinder engine. As shown in FIG. 1, a cylinder head 2 is disposed on the upper part of the cylinder block 1, and the cylinder bore 3 of each cylinder formed in the cylinder block 1 is vertically moved. A piston 4 is operably disposed, and a combustion chamber 5 is defined by the cylinder head 2, the cylinder bore 3, and the piston 4. The cylinder head 2 is provided with a swirl-type intake port (helical port) 6 and an exhaust boat 7 for each cylinder, and an intake valve 8 and an exhaust valve are respectively opened and closed to open and close the intake port 6 and the exhaust port 7. 9 is disposed. In addition, a fuel injection valve 10 of a fuel injection device is attached to the cylinder head 2 at a position facing substantially the center of the combustion chamber 5 of each cylinder. The cylinder head 2 is a flat type, and the intake valve 8 and the exhaust valve 9 are upright.

  At the top of the piston 4 is formed a reentrant cavity 11 which is recessed with the piston operating direction (vertical direction in FIG. 1) as the axial direction and having a smaller diameter on the opening end side.

  The cavity 11 constitutes the combustion chamber 5 and forms an annular lip portion 12 whose opening edge near the top surface of the piston 4 protrudes inward in the piston radial direction. An annular recess 13 that is recessed outward in the direction is formed, and a bottom central portion of the cavity 11 located at the center in the piston radial direction has a raised portion 14 that protrudes toward the opening end side of the cavity 11. Forming.

  The tip of the fuel injection valve 10 constitutes a fuel injection nozzle 15, and the fuel injection nozzle 15 slightly protrudes into the combustion chamber 5 so as to inject fuel directly into the cavity 11 at the top of the piston 4.

  The fuel injection nozzle 15 is provided with a plurality of nozzle hole groups 20 (see FIG. 2) each having two injection holes 21 and 22 arranged in the circumferential direction at substantially equal intervals. The number of the nozzle hole groups 20 is 5 to 12, for example.

  From the injection holes 21 and 22 of each injection hole group 20, fuel is injected obliquely downward from above in the cavity axis direction (piston axis direction) toward the wall surface of the lip 12 of the cavity 11 at the top of the piston 4. Each nozzle hole group 20 has one (a lump) fuel spray 31 for each nozzle hole group 20 after the fuel spray injected from the two injection holes 21 and 22 collides with the combustion chamber wall surface (wall surface of the cavity 11). Form.

Each of the two injection holes 21 and 22 of each injection hole group 20 has an injection direction of fuel injected from the two injection holes 21 and 22 (direction of the injection hole central axis) as shown in FIG. The distance between the two adjacent points (collision point A and collision point B) is substantially perpendicular to the wall surface of the lip portion 12 of the cavity 11 at two points adjacent to each other (collision point A and collision point B ). That is, the wall surface collision point distance X is configured to be in the range of 4.5 to 7.5 mm.

  The wall collision point distance X is basically determined by setting the distance between the injection holes of the two injection holes 21 and 22 and the angle between the injection holes (angle between the central axes of the injection holes) and from the center of the nozzle to the wall surface of the combustion chamber. It is determined by the distance to the upper spray collision point. Here, the distance between the injection holes is determined by the distance Y between the nozzle holes in the nozzle longitudinal section shown in FIG. 3A and the distance Z between the nozzle holes in the nozzle cross section shown in FIG. The angle between the injection holes is determined by the injection hole angle α in the nozzle longitudinal section shown in FIG. 3A and the injection hole angle β in the nozzle cross section shown in FIG. Further, the distance from the nozzle center to the spray collision point on the combustion chamber wall surface is a combustion chamber lip radius r shown in FIG.

The equation for obtaining the wall surface collision point distance X is as follows.

The setting ranges of the parameters of the nozzle specifications shown in FIGS. 3A to 3C are, for example, 0.25 <Y <0.5 mm, 0.25 <Z <0.5 mm, −5 <α <+5 deg, 7.5 <β <12.5 deg, 145 <θ <160 deg, 24/43 <(r / bore radius) <35/43. θ is the nozzle cone angle.

  As shown in FIG. 4, the fuel spray (fuel spray 31) injected into the combustion chamber 5 collides with the wall surface of the cavity 11 during the ignition delay period, and spreads along the wall surface of the cavity 11 together with the air-fuel mixture 32. The fuel spray 31 burns in the vicinity of the colliding wall surface, and the fuel spray 31A and the burned gas (combustion gas) 33 after the wall collision collide with the flow of the vertical vortex caused by the combustion expansion flow, And it goes around in the vertical direction along the bottom of the bottom (arrow T). When the wraparound is strong in the vertical direction, the fuel spray 31 </ b> A and the burned gas 33 quickly reach the center of the cavity 11.

  Near the center of the cavity 11, there is low-temperature surplus air 34 containing a large amount of oxygen that is not used for combustion. When the penetration force (penetration) in the vertical direction of the fuel spray 31A and the burned gas 33 after the wall collision is large, the fuel spray 31A and the burned gas 33 downstream of the combustion region 35 wrap around in the vertical direction, and the burned gas 33 Can be quickly mixed with the surplus air 34, the burned gas 33 can be rapidly cooled to suppress the generation of NOx, and the reburning of soot in the burned gas 33 can be promoted. The exhausted NOx and smoke can be reduced.

  As described above, the fuel injection nozzle 15 of this embodiment is configured such that the nozzle specifications of the two injection holes 21 and 22 of each injection hole group 20 have a wall surface collision point distance X of 4.5 to 7.5 mm. ing. In this case, the vertical spray penetration after the fuel spray wall collision is strong, and fuel atomization is also promoted. As a result, atomization of the fuel can be promoted and the penetration force (penetration) of the fuel spray after the collision with the wall surface can be strengthened, thereby enhancing the fuel spray downstream of the combustion region and the wraparound of the burned gas in the vertical direction. The burned gas 33 can be quickly mixed with the surplus air 34, the burned gas 33 can be rapidly cooled to suppress the generation of NOx, and the soot in the burned gas 33 can be reduced. Reburning can be promoted, and the generation of NOx and soot can be sufficiently reduced.

  As shown in FIG. 5, the spray particle size after the wall collision of the fuel spray injected from the two injection holes is expressed as follows: Wall collision point distance X (the fuel spray injected from the two injection holes is applied to the combustion chamber wall surface) As the distance between the collision points at the time of collision increases, the atomization proceeds monotonously. On the other hand, the spray penetration force (penetration) in the vertical direction of the combustion chamber after the wall collision is in the middle of the range of the wall collision point distance where the penetration force increases, and the penetration force decreases monotonously before and after that. Therefore, by setting the wall surface collision point distance X to be within the predetermined range in which the spray penetration force in the vertical direction of the combustion chamber after the wall surface collision is maintained in the vicinity of the maximum value, While strengthening the penetration force, it can be maintained in a range where fuel atomization can be promoted.

  As shown in FIG. 5, the wall collision point distance X is 4.5 to 7.5 mm within the predetermined range (optimum range) in which the spray penetration force in the vertical direction of the combustion chamber after the wall collision maintains the vicinity of the maximum value. Is within the range. Within this optimum range, the spray penetration force in the vertical direction of the combustion chamber is at least 20% greater than the spray penetration force in the horizontal direction of the combustion chamber, and the lower limit of 4.5 mm burns the spray penetration force in the vertical direction of the combustion chamber. The wall collision point distance X is 25% larger than the spray penetration force in the horizontal direction of the chamber, and the upper limit of 7.5 mm is such that the spray penetration force in the vertical direction of the combustion chamber is relative to the spray penetration force in the horizontal direction of the combustion chamber. The wall surface collision point distance X is increased by 20%. Since the average particle size is smaller on the upper limit side than on the lower limit side, it is advantageous to deal with emissions. Therefore, the spray penetration force in the vertical direction of the combustion chamber is 20% larger than the spray penetration force in the horizontal direction of the combustion chamber. The wall surface collision point distance X becomes a threshold value. Even in the actual machine test data (actual machine smoke performance) illustrated, the soot (smoke) discharge is sufficiently low when the distance X between the collision points is in the range of 4.5 to 7.5 mm.

  FIG. 6 shows the wall surface when fuel is injected to the wall surface in the case of one and two injection holes in relation to the spray penetration force (penetration) after the fuel spray wall collision in the diesel engine of the above embodiment. The results of measurement of the spray shape after the collision are shown. (A) and (b) are explanatory diagrams of measurement results when there is one injection hole, and (c) and (d) are measurements when there are two injection holes. It is result explanatory drawing. From the measurement result shown in FIG. 6, when the fuel spray 31 normally injected from one injection hole 23 collides with the wall surface, the spray 31A after the collision spreads concentrically. The injection holes 21 and 22 are arranged adjacent to each other with an appropriate distance, and the fuel spray 31 injected from the two injection holes 21 and 22 becomes one spray 31 and collides with the wall surface of the cavity 11. It can be seen that the spread of the spray 31A after the collision is amplified in a direction orthogonal to the line connecting the two injection holes 21 and 22, and spreads in an elliptical shape. By utilizing this characteristic, the penetration force (penetration) after the wall collision can be strengthened, and thereby the wraparound in the vertical direction of the fuel spray 31A and the burned gas 33 after the wall collision can be strengthened. .

It is sectional drawing of the combustion chamber vicinity of the diesel engine which concerns on embodiment of this invention. It is explanatory drawing which shows the wall surface collision point distance X of the fuel spray in the diesel engine of embodiment of this invention. The parameter of the nozzle hole layout of the fuel spray nozzle in the diesel engine of embodiment of this invention is demonstrated, (a) is explanatory drawing of the distance Y between nozzle holes and the angle α between nozzle holes in a nozzle vertical cross section, (b). Is an explanatory view of the inter-hole distance Z and the inter-hole angle β in the nozzle cross section, and FIG. It is explanatory drawing explaining the spray penetration force (penetration) after the wall surface collision of the fuel spray injected from the fuel injection nozzle in the diesel engine of embodiment of this invention. The relationship between the wall collision point distance X of the fuel spray injected from the fuel injection nozzle in the diesel engine of the embodiment of the present invention, the spray penetration (penetration) after the wall collision, the average particle diameter of the fuel spray, and the smoke performance It is a graph to show. In relation to the spray penetration force (penetration) after the wall collision of the fuel spray injected from the fuel injection nozzle in the diesel engine of the embodiment of the present invention, the fuel is supplied to the wall surface in the case of one injection hole and in the case of two injection holes. FIG. 4 shows the result of measuring the spray shape after a wall collision when being injected into the nozzle. FIGS. (A) and (b) are explanatory diagrams of measurement results when there is one injection hole, and (c) and (d) are the injection holes. It is measurement result explanatory drawing in the case of two.

Explanation of symbols

5 Combustion chamber 10 Fuel injection valve 15 Injection nozzle 20 Injection hole group 21, 22 Injection hole 31, 31A Fuel spray 32 Mixture 33 Burned gas (combustion gas)
34 Excess air 35 Combustion areas A, B Collision point X Wall collision point distance Y Distance between nozzle holes in nozzle vertical section α Angle between nozzle holes in nozzle vertical section Z Distance between nozzle holes in nozzle cross section β Hole in nozzle cross section Angle r Combustion chamber lip radius

Claims (2)

The piston is provided with a concave cross section in the center of the top surface of the piston, in a cavity that forms a combustion chamber, and at a position facing the approximate center of the combustion chamber, toward the side wall surface of the combustion chamber A fuel injection nozzle for injecting fuel, and the combustion chamber forms an annular lip portion with an opening edge near the top surface of the piston protruding inward in the piston radial direction, and at the center in the piston radial direction. The center portion of the bottom portion is shaped to protrude toward the opening end side, and the spray of fuel injected into the combustion chamber collides with the cavity wall surface during the ignition delay period, along with the air-fuel mixture along the wall surface of the cavity. The fuel spray burns in the vicinity of the colliding wall surface, and the fuel spray and burned gas after the wall collision ride along the vertical vortex flow caused by the combustion expansion flow along the cavity wall surface and bottom bottom surface. A fuel injection system for a diesel engine that is configured to wrap around the longitudinal direction,
The injection holes of the fuel injection nozzle constitute a plurality of injection hole groups each consisting of two injection holes, and the lip radius r / bore radius of the combustion chamber is 24/43 <(r / bore radius) <35 / 43 , the nozzle hole angle α in the nozzle longitudinal section is −5 deg <α <+5 deg, and the nozzle hole angle β in the nozzle cross section is 7.5 deg <β <12. After the fuel spray injected from these two injection holes collides with the combustion chamber wall surface, one fuel spray is formed for each injection hole group, and the fuel spray injected from these two injection holes When the distance X between the collision points when it collides with the combustion chamber wall surface becomes 4.5 to 7.5 mm, the spread of the spray after the collision is amplified in the direction orthogonal to the line connecting the two injection holes And the combustion chamber wall surface The combustion penetration in the longitudinal direction of the combustion chamber obtained later is strengthened, and the spray penetration in the longitudinal direction of the combustion chamber is within a predetermined range to maintain the vicinity of the maximum value, so that fuel spray and burned gas after wall collision A fuel injection device for a diesel engine, characterized in that the wraparound in the vertical direction is enhanced. The predetermined range in which the spray penetration force in the vertical direction of the combustion chamber is maintained in the vicinity of the maximum value is a range in which the spray penetration force in the vertical direction of the combustion chamber is at least 20% larger than the spray penetration force in the horizontal direction of the combustion chamber. The fuel injection device for a diesel engine according to claim 1, wherein

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