JP5006905B2 - In-cylinder injection spark ignition internal combustion engine - Google Patents

Description

  The present invention relates to a direct injection spark ignition internal combustion engine.

In an in-cylinder spark-ignition internal combustion engine, fuel is directly injected into the cylinder during the intake stroke to form a homogeneous mixture in the cylinder to perform homogeneous combustion, or directly into the cylinder during the compression stroke. By injecting fuel, there is a type in which a flammable mixture with good ignitability is formed only near the spark plug at the time of ignition, and stratified combustion is performed that enables combustion of a lean mixture as a whole in the cylinder .
In order to perform stratified combustion well, the fuel spray injected in the compression stroke is sufficiently vaporized in a short period until the ignition timing, and the fuel spray and the air-fuel mixture are collected only in the vicinity of the spark plug and diffused widely in the combustion chamber. It is important not to let them.

  On the other hand, in a conventional in-cylinder spark-ignition internal combustion engine, during stratified combustion, fuel injected from the fuel injection valve in the in-cylinder vertical swirl main flow direction formed in the combustion chamber in the intake stroke By setting the spray to collide directly, the relative speed of fuel spray and flow is maximized, the fuel is atomized and the fluid friction can be utilized to the maximum, thereby vaporizing the fuel spray and forming a combustible mixture In addition, the diffusion of fuel spray is suppressed by a pair of standing walls that suppress the diffusion in the lateral direction with respect to the fuel injection axis provided on the crown surface of the piston, thereby forming a local combustible mixture. In some cases, good stratified combustion is possible (see, for example, Patent Document 1).

JP 2000-104550 A (pages 4-5, FIG. 1)

However, in the conventional in-cylinder injection spark ignition internal combustion engine, as described above, the in-cylinder longitudinal swirl main flow and the fuel spray injected from the fuel injection valve are set to collide with each other, The increase in relative speed promotes vaporization of the fuel spray, while the fuel spray is subjected to the opposite direction force due to the in-cylinder vertical swirling main stream, its movement direction is easily changed, and the fuel spray after the collision is in various directions. Easy to scatter.
At this time, a pair of standing walls that suppress the diffusion of the fuel spray are provided near the left and right of the position where the in-cylinder vertical swirling main flow collides with the fuel spray. Colliding with the wall surface to form a liquid film.

The liquid film formed on the cylinder wall surface and piston crown surface, including the above-mentioned standing wall surface, causes smoke and unburned hydrocarbons during combustion, and the deposited fuel accumulates as deposits on the cylinder inner wall surface. , Combustion efficiency decreases, fuel consumption rate deteriorates.
Therefore, in order to comply with exhaust gas regulations that will become stricter in the future during stratified combustion, in addition to improving combustion by forming a good combustible air-fuel mixture near the spark plug, fuel adheres to the cylinder wall and piston crown. It is necessary to suppress.

  The present invention has been made to solve the above-described problems, and improves the exhaust gas properties by suppressing fuel adhesion to the cylinder wall surface and the piston crown surface during fuel injection, and stratifies at the time of ignition. The aim is to form a good mixture for carrying out the combustion.

The in-cylinder injection spark ignition internal combustion engine according to the present invention includes a multi-hole injector that directly injects fuel into a cylinder from a plurality of nozzles, and the multi-hole injector uses kinetic energy of fuel spray during stratified combustion. The fuel is injected so that the spray reach distance is an internal region of the vertical swirl main flow formed in the cylinder, the mounting angle θ _I of the multi-hole injector, the inclination angle θ _{N of} the injection hole, the injection hole shape characteristics By setting the L / D, the fuel pressure, and the nozzle arrangement angle θ _P , the spray reach distance becomes an internal region of the vertical swirl mainstream formed in the cylinder, and the fuel spray movement direction of the multi-hole injector and the The direction of motion of the vertical swirling mainstream is almost orthogonal, and the center position in the cylinder at the fuel injection end crank angle is the center of the multi-hole injector. Be those determined the mounting angle theta _I multi-hole injector as a line passes through the piston a distance of the piston crown surface and the cylinder head top portion in the top dead center of the reference h, and the piston crown surface located at the top dead center Assuming that the crown surface displacement is z, assuming a circle of radius (h + z) / 4 centered on the center position in the cylinder at the fuel injection end crank angle, the central axis of the fuel spray injected from the plurality of nozzles is The fuel spray inclination angle θ _α is determined so as to contact each of the circles.

  In the in-cylinder injection spark-ignition internal combustion engine according to the present invention, the fuel spray injected from the multi-hole injector in the compression stroke collides with the vertical swirl main flow formed in the cylinder immediately after the injection, but the movement of the fuel spray immediately after the injection The energy is relatively large compared to the flow, and the direction of motion of the fuel spray and the direction of motion of the vertical swirl main flow are almost orthogonal, and only momentary influences occur. Unlike the case where the direction is directly opposite, the movement direction of the fuel spray is not greatly changed. As a result, the fuel spray does not scatter in the cylinder due to the collision with the longitudinally swirling mainstream, so that fuel adhesion to the cylinder wall surface or the piston crown surface can be suppressed.

  Further, the fuel spray injected from the multi-hole injector enters the mainstream of the vertical rotation without largely changing the direction of movement as described above, and loses kinetic energy in the internal region. At this time, since the same swirl flow having the same center as that of the swirl main stream and having a small swirl radius is generated inside the swirl main flow, the fuel spray that has lost its kinetic energy moves along the swirl flow and moves vertically. The swirl floats inside the swirl mainstream. Therefore, since the fuel spray injected from the multi-hole injector is held in the longitudinal swirl mainstream inner area and does not scatter to the outer area, the fuel spray can be prevented from colliding with and adhering to the cylinder wall surface, improving the exhaust gas properties during stratified combustion can do.

Furthermore, the fuel spray held in the longitudinal swirl main flow inner area is atomized by the flow turbulence caused by the swirl flow, and the evaporation is promoted, and the swirl flow agitates the fuel spray and the air-fuel mixture in the longitudinal swirl main flow inner area. The air density unevenness is reduced, and a stable air-fuel mixture with a high degree of stratification can be formed.
The stable air-fuel mixture having a high degree of stratification formed in this way is pushed up to the upper part of the cylinder as the piston rises in the in-cylinder compression, and at the ignition timing, the air-fuel mixture is arranged near the spark plug. Thus, stable stratified combustion can be performed.
When the distance between the piston crown surface at the top dead center and the top of the cylinder head is h, and the piston crown displacement based on the piston crown surface position at the top dead center is z, the cylinder center position at the fuel injection end crank angle by assuming a circle having a radius (h + z) / 4 around the central axis of the fuel spray injected from a plurality of injection ports was to determine the inclination angle theta _alpha of the fuel spray so as to contact each said circle The fuel spray can be surely introduced into the internal region of the longitudinal swirl mainstream.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows embodiment of the cylinder injection type spark ignition internal combustion engine by this invention. The expanded sectional view which shows the front-end | tip part of a multi-hole injector. The schematic longitudinal cross-sectional view of the fuel spray injected from the multi-hole injector in embodiment of this invention. The nozzle hole arrangement | positioning figure of the multi-hole injector nozzle plate in embodiment of this invention. The figure which shows the schematic shape of the piston crown surface position in the fuel injection start at the time of fuel injection in a compression stroke, the fuel injection end crank angle, and a vertical swirl mainstream. The figure which shows the setting method of attachment angle (theta) _I of a multi-hole injector. The figure which shows the fuel spray inclination angle (theta) ( _{alpha) of} a multi-hole injector, and the setting method of the penetration of fuel spray. The figure which shows the relationship between the penetration of fuel spray, and the nozzle characteristic L / D. The figure which shows the relationship between the penetration of fuel spray, and a fuel pressure. The figure which shows the setting method of the nozzle arrangement angle (theta) _P.

FIG. 1 is a schematic view showing an embodiment of a direct injection spark ignition internal combustion engine according to the present invention. In FIG. 1, 1 is a cylinder wall surface, 2 is a piston, 3 is a crankshaft for changing the reciprocating motion of the piston into a rotational motion, 4 is a connecting rod connecting the crankshaft and the piston, and 5 is a cylinder head.
A multi-hole injector 6 that directly injects fuel into a cylinder from a plurality of nozzle holes is attached to the cylinder head 5 at an attachment angle θ _I , and a fuel spray 7 is formed in the cylinder by the fuel injection from the multi-hole injector 6. Is done. 8 is a fuel pressure control means for adjusting the pressure of the fuel supplied to the multi-hole injector 6, and an ignition plug 9 for igniting an air-fuel mixture formed in the cylinder is provided near the center of the cylinder head 5.

  The cylinder head 5 is provided with two intake ports 10 and two exhaust ports 11. The intake port 10 leads to the inside of the cylinder via the intake valve 12, and the exhaust port 11 passes through the exhaust valve 13. Yes. The intake port 10 has a forward tumble direction in which intake fresh air supplied into the cylinder through the intake port 10 during the intake stroke descends on the exhaust valve 13 side in the cylinder and rises on the intake valve 12 side in the cylinder. Are installed so as to form a vertical swirling main flow 14.

The intake port 10 is provided with a vertical separation plate 15 for dividing the intake port vertically, and a flow control valve 16 for controlling an opening area under the intake port 10 divided by the vertical separation plate 15. By controlling the opening area of the valve 16 by the valve control means 17, the flow rate ratio of the fresh intake air passing through the upper and lower parts of the upper and lower separation plates 15 is changed, and the swirling of the vertical swirling main flow 14 formed in the cylinder is changed. You can adjust the power.
For example, when the flow rate of fresh intake air is slow and the swirl force of the main swirl formed in the cylinder is weak, such as at a low engine speed, the flow control valve 16 is closed and sucked only into the upper part of the upper / lower separation plate 15. By passing the fresh air, the fresh intake air is drifted to the upper side of the intake port 10 and flows mainly into the cylinder from the upper part of the intake valve 10, so that the turning force of the vertical swirl main flow 14 formed in the cylinder is strengthened. be able to.
Note that a swirl flow 14 a having the same center as that of the vertical swirl main flow 14 and a small swirl radius is formed inside the vertical swirl main flow 14.

  FIG. 2 is an enlarged vertical sectional view of the tip portion of the multi-hole injector 6. Here, since the tip portion of the multi-hole injector 6 is symmetric, FIG. 2 shows only the left portion from the central axis 18 of the multi-hole injector 6. In FIG. 2, reference numeral 19 denotes a needle. The needle 19 can shield and open the fuel passage 21 by being seated on and away from the valve seat 20 by moving in the vertical direction. During fuel injection, when the needle 19 moves upward and the fuel passage 21 is opened, high-pressure fuel is supplied to the fuel cavity 23 provided between the valve seat 20 and the nozzle plate 22, and the nozzle plate 22. Is injected into the cylinder through a plurality of nozzle holes 24 provided in the cylinder.

FIG. 3 is a schematic longitudinal sectional view of the fuel spray 7 injected from the multi-hole injector 6 in the present embodiment. The inclination θ _α of the fuel spray 7 injected from each nozzle hole with respect to the central axis 18 of the multi-hole injector substantially coincides with the inclination angle θ _{N of the} nozzle hole 24 shown in FIG. 2, and therefore θ _α is determined by setting θ _N. Further, the spray reach distance (hereinafter referred to as penetration) P by the fuel spray's own kinetic energy is the nozzle shape characteristic L / D represented by the ratio of the nozzle length L and the nozzle effective diameter D shown in FIG. 2, and a multi-hole injector. It can be adjusted by the pressure (fuel pressure) of the fuel supplied to 6.

FIG. 4 shows the arrangement of the plurality of nozzle holes 24 provided in the nozzle plate 22 in the multi-hole injector 6 in the present embodiment. Here, the section indicated by AA in FIG. 4 corresponds to the longitudinal section of FIG. As shown in FIG. 4, the nozzle hole 24 is provided on a concentric circle within a range in which the longitudinal section AA is rotated by ± θ _P with respect to the center O of the nozzle hole 24, and the fuel spray is radially centered around O. Therefore, the spread of fuel spray in the in-cylinder horizontal direction can be adjusted by the nozzle arrangement angle θ _P.

The in-cylinder injection spark ignition internal combustion engine according to the embodiment of the present invention is configured as described above, and the mounting angle θ _I of the multi-hole injector 6 described above, the inclination angle θ _{N of} the injection hole, the injection hole shape characteristic L / D, By setting the fuel pressure and the nozzle opening angle θ _P , the fuel is injected so that the penetration of the fuel spray 7 injected from the multi-hole injector 6 becomes an internal region of the vertical swirl main flow 14 formed in the cylinder. It is possible.
According to this embodiment, as shown in FIG. 1, the fuel spray 7 injected from the multi-hole injector 6 in the compression stroke loses kinetic energy in the internal region of the longitudinal swirl main flow 14 formed in the cylinder. At this time, a similar swirl flow 14a having the same center as that of the vertical swirl main flow 14 and a small swirl radius is generated inside the vertical swirl main flow 14, so that the fuel spray that has lost its kinetic energy rides on this swirl flow 14a. It moves and swirls and floats inside the vertical swirl main flow 14. Accordingly, since the fuel spray 7 injected from the multi-hole injector 6 is held in the inner region of the vertical swirl main flow 14 and does not scatter to the outer region, the fuel spray 7 can be prevented from colliding and adhering to the cylinder wall surface 1, and during stratified combustion The exhaust gas properties can be improved.

Further, the fuel spray 7 held in the inner region of the vertical swirl main flow 14 is atomized by the flow disturbance generated by the swirl flow 14a, and evaporation is promoted. Since stirring is performed in the region, the concentration unevenness of the air-fuel mixture is reduced, and a stable air-fuel mixture having a high stratification degree can be formed. As a result, stable stratified combustion can be performed.
As shown in FIG. 1, the fuel spray 7 injected from the multi-hole injector 6 interferes with the longitudinal swirl main flow 14 formed in the cylinder immediately after the injection, but the fuel spray 7 immediately after the injection The kinetic energy is relatively large compared to the flow, and the direction of movement of the fuel spray 7 and the direction of movement of the longitudinal swirl main flow 14 are almost orthogonal and are only affected instantaneously, so the direction of movement of the fuel spray 7 is large. The fuel spray 7 can be injected into the inner region of the vertical swirl main flow 14 without change.

Next, a method for setting the mounting angle θ _I , the nozzle tilt angle θ _N , the nozzle shape characteristic L / D, the fuel pressure, and the nozzle arrangement angle θ _P of the multi-hole injector 6 in this embodiment will be described with reference to FIGS. Will be described in detail.
FIG. 5 shows the schematic shape of the fuel injection start crank angle when fuel is injected in the compression stroke, the piston crown surface position at the fuel injection end crank angle, and the vertical swirl main flow. In FIG. 5, 2S and 14S indicated by broken lines indicate the piston crown surface position at the fuel injection start crank angle and the schematic shape of the longitudinal main flow, respectively, and 2F and 14F indicated by solid lines indicate the piston crown surface at the fuel injection end crank angle, respectively. The position and the general shape of the vertical turning mainstream are shown.

As shown in FIG. 5, from the start of fuel injection to the end of injection, the longitudinal main flow formed in the cylinder becomes smaller as the piston rises. Therefore, in order to put all the injected fuel into the internal region of the vertical swirl main flow formed in the cylinder, the fuel is injected toward the internal region of the vertical swirl main flow 14F formed in the cylinder at the fuel injection end crank angle. There is a need to. Accordingly, the setting values of the mounting angle θ _I of the multi-hole injector 6, the nozzle tilt angle θ _N , the nozzle shape characteristic L / D, the fuel pressure, and the nozzle arrangement angle θ _P are based on the longitudinally swirling main flow 14 F at the fuel injection end crank angle. Determine.

Figure 6 is a diagram showing a method of setting the mounting angle theta _I of multi-hole injector 6 shows a cylinder longitudinal sectional view of a fuel injection termination crank angle. In the compression stroke, a vertical swirling main flow is generally formed around the center position in the cylinder. Therefore, in order to put fuel spray into the internal region of the vertical swirling main flow, the cylinder at the fuel injection end crank angle The attachment angle θ _I of the multi-hole injector 6 may be determined so that the central axis 18 of the multi-hole injector 6 passes through the center position C. b is the cylinder diameter, d is the connecting rod length, e is the crank diameter, h is the distance between the piston crown surface at the top dead center and the top of the cylinder head 5, and z is the piston crown based on the piston crown surface position at the top dead center. Assuming that the surface is displaced, the in-cylinder center position C is determined as shown in FIG. Here, assuming that θ _R is the fuel injection end crank angle [deg] (defined as shown in FIG. 6), z is expressed by Expression (1).

When the injector is mounted at a position where the tip position of the multi-hole injector 6 is x in the cylinder horizontal direction and y in the cylinder vertical direction with respect to the cylinder center position C, the mounting angle θ _I of the multi-hole injector 6 Is represented by equation (2).

Next, the inclination angle θ _N of the injection hole 24, the injection hole shape characteristic L / D, and the fuel pressure are determined.
FIG. 7 is a diagram showing a method of setting the inclination angle θ _α of the fuel spray 7 injected from the multi-hole injector 6 and the penetration of the fuel spray, and shows a schematic diagram of a longitudinal section in the cylinder at the fuel injection end crank angle. Yes. Since the vertical swirl main flow formed in the cylinder is generally not less than 1/2 of the distance between the piston crown surface and the top of the cylinder head 5, in order to put the fuel spray into the internal region of the vertical swirl main flow, Assuming a circle S having a radius (h + z) / 4 centered on the in-cylinder center position C at the fuel injection end crank angle, θ _α is set so that the central axis of the fuel spray 7 injected from the nozzle 24 contacts the circle S. It is good to decide.

Here, as described above, the inclination θ _α of the fuel spray 7 with respect to the central axis 18 of the multi-hole injector 6 is substantially equal to the inclination angle θ _N of the injection hole 24. Accordingly, as shown in FIG. 7, if the distance between the tip of the multi-hole injector 6 attached at an angle θ _I and the in-cylinder center position C is m, the inclination angle θ _{N of the} injection hole is expressed by the following equation (3). .

  Further, the penetration P of the fuel spray at this time can be expressed by equation (4) from FIG.

FIG. 8 shows the relationship between the fuel spray penetration P and the nozzle characteristics L / D, and shows that the fuel spray penetration P can be reduced by reducing the nozzle characteristics L / D. Similarly, FIG. 9 shows the relationship between the fuel spray penetration P and the fuel pressure, and shows that the fuel spray penetration can be adjusted by adjusting the fuel pressure.
Therefore, the nozzle characteristics L / D and the fuel pressure are set to be the fuel spray penetration P obtained from the equation (4) based on FIGS. Here, for example, if L / D is set to 2 and the fuel pressure is set to 15 MPa, the penetration of fuel spray can be about 50 mm.

FIG. 10 is a diagram showing a method for setting the nozzle opening angle θ _P and is a schematic top view inside the cylinder. Here, 25 and 26 are longitudinal sections passing through the central axis of the intake valve 12, respectively. The vertical swirl main flow in the compression stroke is generally formed in the central part of the cylinder where the vertical swirl flow is easily maintained. Therefore, assuming that the region where the vertical swirl flow is easily maintained is a region sandwiched between the intake valve center longitudinal sections 25 and 26, the in-cylinder horizontal spread of the fuel spray is set so that the fuel spray enters the region.

As shown in FIG. 10, assuming that the distance between the axes of the intake valves is v, the nozzle opening angle θ _P is expressed by equation (5) from FIG.

As described above, according to the in-cylinder injection spark ignition internal combustion engine of the present invention, the mounting angle θ _I of the multi-hole injector, the inclination angle θ _{N of} the injection hole, the injection hole shape characteristic L / D, the fuel pressure, and the injection hole arrangement angle θ By setting _P , it is possible to inject the fuel so that the penetration of fuel spray injected from the multi-hole injector becomes the internal region of the vertical swirling mainstream formed in the cylinder, and to the cylinder wall surface and piston crown surface The fuel adhesion can be suppressed, and the exhaust gas properties can be improved.

1 Cylinder wall surface, 2 piston, 3 crankshaft, 4 connecting rod, 5 cylinder head, 6 multi-hole injector, 7 fuel spray, 8 fuel pressure control means, 9 spark plug, 10 intake port, 11 exhaust port, 12 intake valve, 13 Exhaust valve, 14 Longitudinal swirling main flow, 14a Swirling flow, 15 Vertical separation plate, 16 Flow control valve, 17 Valve control means, 18 Multi-hole injector central axis, 24 nozzle, θ _I multi-hole injector mounting angle.

Claims (1)

A multi-hole injector that directly injects fuel into a cylinder from a plurality of nozzles, and in stratified combustion, the multi-hole injector has a vertical swirl in which the spray reach distance due to the kinetic energy of the fuel spray is formed in the cylinder The fuel is injected so as to be an internal region of the mainstream. By setting the mounting angle θ _I of the multi-hole injector, the inclination angle θ _{N of} the injection hole, the injection hole shape characteristic L / D, the fuel pressure, and the injection hole arrangement angle θ _P The spray reach distance is an internal region of the vertical swirl main flow formed in the cylinder, and the fuel spray movement direction of the multi-hole injector and the vertical swirl main flow movement direction are substantially orthogonal to each other. Mounting angle θ of the multi-hole injector so that the central axis of the multi-hole injector passes through the center position in the cylinder at the injection end crank angle Fuel injection ends when _I is defined and the distance between the piston crown surface at the top dead center and the top of the cylinder head is h, and the piston crown displacement at the top dead center is z Assuming a circle with a radius (h + z) / 4 centered on the center position in the cylinder at the crank angle, the inclination angle θ of the fuel spray is such that the central axis of the fuel spray injected from the plurality of nozzles is in contact with the circle, respectively. An in-cylinder spark ignition internal combustion engine in which _α is defined.

Images