JP2003083120A - Fuel combustion device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To strengthen longitudinal vortex generated within a reentrant type cavity 8 formed on an upper part of a piston 1 and to stably strengthen the longitudinal vortex, even if an engine is in a comparatively high rotation state. SOLUTION: This device is provided with a fuel injection valve 9 for injecting fuel toward a lip part 11 to be an opening edge of the cavity 8 of the piston 1. A region of fuel vapor 16 is formed in the vicinity of the lip part 11 by making fuel spray injected by the fuel injection valve 9 arrive in the lip part 11 for an ignition delay period. Expansion flow is generated by igniting fuel vapor 16 in the front of a fuel injection direction. Fuel vapor in front of an ignition position is allowed to abut on a peripheral wall surface 12 of the cavity 8 and is guided to the bottom of the cavity 8. The device is provided with a penetration control means for controlling penetration Sp of fuel spray injected from the fuel injection valve 9 to be increased as compared with that when engine speed Ne is less than a prescribed value Ne0 , when the engine speed Ne becomes more than the prescribed Ne0 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technical field of a diesel engine fuel combustion apparatus for combusting a fuel directly injected into a reentrant type cavity formed in a piston.

[0002]

2. Description of the Related Art A direct injection diesel engine having a reentrant cavity at the top of a piston is generally known. For example, JP-A-9-41
In the 975 publication, the fuel spray and the air are sprayed by defining the cavity shape so that the fuel injected toward the lip portion of the piston is separated from the side wall of the cavity when it goes from the lip portion to the bottom portion of the cavity. It is described that the mixing with and to suppress the generation of soot.

Also, Vol.31, No.3, Ju
ly 2000, pp. 51-56, if the bottom center of the reentrant cavity of the piston is raised, a vertical vortex is formed to flow downward along the side wall below the lip during the compression stroke. , The fuel spray is drawn into the vertical vortex to form a flow that rotates downward along the side wall below the lip, and increasing the lip diameter weakens the reverse squish flow and suppresses the outflow of the air-fuel mixture to the squish area. The vertical vortex becomes a spiral vortex due to the influence of swirl, and the spiral vortex promotes mixture formation and combustion in the cavity.
It is described that the air-fuel mixture is discharged to the squish area and oxidizes the unburned soot.

[0004]

However, it is not only the soot that is generated by the driving operation of the direct injection type diesel engine. That is, there is a problem that NOx is also produced at the same time by oxidizing the nitrogen in the air taken into the combustion chamber. However, in each of the above-mentioned conventional ones, although soot discharge is suppressed, not only soot but N
It is difficult to suppress the generation of Ox at the same time.

Therefore, a fuel spray is injected with a predetermined penetration (spray penetration force) to form a region of fuel vapor near the lip portion during the ignition delay period in a relatively gathered state, and a part of this fuel vapor is formed. It is conceivable to reduce the generation of both NOx and soot by inducing the vertical vortices by inducing to the cavity bottom by the fuel gas expansion flow after ignition.

On the other hand, as the engine speed increases, the speed of intake air supplied into the cavity increases, so that the swirl speed in the cavity increases.
The increased swirl speed increases the penetration of the fuel spray injected from the fuel injection valve toward the lip, weakening the area of the fuel vapor near the lip. difficult.

Therefore, when the engine is in a relatively high rotation state, it is difficult to induce the fuel vapor in the vicinity of the lip portion to the cavity bottom portion by the expansion flow generated by ignition to generate a strong vertical vortex. Therefore, there is a problem that the generation of NOx and soot cannot be effectively reduced by strengthening the vertical vortex.

The present invention has been made in view of the above points, and its main purpose is to strengthen the longitudinal vortices generated in the cavity and, particularly, when the engine is in a relatively high rotation state. However, it is also intended to reduce the production amount of both NOx and soot as much as possible by enabling the vertical vortex to be stably strengthened.

[0009]

In order to achieve the above object, in the present invention, a part of the fuel vapor is guided to the bottom of the cavity by the expansion flow generated by ignition to strengthen the longitudinal vortex, and The fuel spray penetration is increased when the engine speed exceeds a predetermined value.

Specifically, according to the first aspect of the present invention, a piston having a reentrant type cavity formed in the top thereof, the diameter of which becomes smaller toward the opening end, and a lip portion forming a cavity opening edge of the piston are provided. A fuel injection valve for injecting fuel, the fuel spray injected from the fuel injection valve reaches the lip portion during an ignition delay period to form a region of fuel vapor near the lip portion, and the fuel injection valve The fuel is ignited in the front of the fuel injection direction, and the expansion flow of the combustion gas due to this ignition causes the fuel vapor in front of the ignition position to impinge on the peripheral wall surface of the cavity toward the bottom of the cavity, and the flame A diesel engine fuel combustor configured to propagate to the bottom of the cavity is of interest. And, when the engine speed becomes equal to or higher than a predetermined value, the penetration of the fuel spray injected from the fuel injection valve is increased as compared with the penetration of the fuel spray when the engine speed is lower than the predetermined value. It is equipped with a penetration control means for controlling.

According to the above invention, the fuel spray is injected from the fuel injection valve and reaches the lip portion during the ignition delay period, whereby a region of fuel vapor is formed near the lip portion. Since the ignition position (ignition point) of the fuel spray is the upstream position in the fuel injection direction in the region of the fuel vapor, a strong expansion flow explosively spreading from the ignition position to the downstream side is generated by the combustion due to this ignition. To be done.

The fuel vapor in the vicinity of the lip portion on the downstream side of the fuel vapor region is caused by the expansion flow to form an inner peripheral wall surface of the cavity (in particular, a lip portion and a portion recessed outward of the lip portion in the radial direction of the piston). Around the boundary), the strong vertical vortex is generated by being guided to the bottom side of the cavity along the inner wall surface of the cavity. Further, as the flame propagates following the fuel guided to the bottom of the cavity, vertical vortices grow further.

With the flow of this vertical vortex, the flame also wraps around from the lip to the bottom of the cavity. As a result, the heat spot (local high temperature region) spreads from the vicinity of the lip portion to the bottom of the cavity, while the fuel vapor decreases near the lip portion, so the heat spot near the lip portion disappears promptly. That is, by the end of fuel injection, the highest temperature portion in the cavity moves from the lip portion to the cavity bottom side and is dispersed.

Therefore, the heat spot is prevented from existing at a specific position in the cavity for a long time, or the heat spot is quickly extinguished, so that the production amount of NOx can be effectively reduced. Further, since the vertical vortices are strengthened, the mixing of the fuel and the air in the cavity and the mixing of the combustion gas and the air in the latter half of the combustion are respectively promoted, so that the soot generation amount is effectively reduced. be able to.

By the way, generally, the speed of the swirl generated in the cavity (swirl speed) increases as the engine speed increases. Thus, as the swirl becomes stronger, the penetration of the fuel spray decreases. On the other hand, in the present invention, when the engine speed becomes equal to or higher than the predetermined value, the penetration of fuel spray against the swirl is performed by the penetration control means when the engine speed is lower than the predetermined value. Increased compared to spray penetration.

Therefore, even when the engine speed is higher than a predetermined value and at a relatively high speed, a fuel vapor region is stably formed in the vicinity of the lip portion and vertical vortices generated in the cavity are generated. Can be fully strengthened. That is,
Even if the engine is in a high rotation state, the enhanced vertical vortex can stably reduce the generation of NOx and soot.

In a second aspect based on the first aspect, the penetration control means sets the fuel injection pressure of the fuel injection valve when the engine speed exceeds a predetermined value.
It is assumed that the engine speed is controlled to be higher than the fuel injection pressure when the engine speed is less than the predetermined value.

According to the above invention, the fuel injection pressure of the fuel injection valve when the engine speed becomes equal to or higher than the predetermined value by the penetration control means is the fuel injection pressure when the engine speed is lower than the predetermined value. The fuel spray is able to sufficiently counter the swirl which becomes stronger as compared with the above. Therefore, as in the first aspect of the invention, even when the engine is in a relatively high rotation state, the vertical vortices can be sufficiently strengthened and the generation of NOx and soot can be effectively reduced.

According to a third aspect of the invention, in the first or second aspect of the invention, the penetration control means determines the swirl ratio in the cavity when the engine speed exceeds a predetermined value and the engine speed reaches the predetermined value. The swirl ratio should be controlled so as to decrease when the value is less than.

According to the above invention, when the engine speed becomes higher than the predetermined value by the penetration control means, the swirl ratio in the cavity is higher than the swirl ratio when the engine speed is the predetermined value. Since it is reduced, the swirl speed corresponding to the engine speed can be reduced. That is, even when the engine speed is relatively high, suppressing the swirl reinforcement,
It is possible to effectively suppress the reduction of the fuel spray penetration due to the strengthening of the swirl, and it is possible to sufficiently strengthen the vertical vortex generated in the cavity.

In a fourth aspect of the invention, in any one of the first to third aspects of the invention, the penetration Sp is defined as the arrival distance of the fuel spray at the time point 0.42 ms has elapsed from the start of fuel injection by the fuel injection valve. , The cone angle Θ of the fuel spray of the fuel injection valve and the minimum diameter Dlip at the lip portion of the cavity are expressed by the following equation: Dlip = k × Sp × sin (Θ / 2) (1) (where k = 1. 4 to 1.8) is satisfied.

That is, according to the present invention, the fuel is injected from the fuel injection valve toward the lip portion, and the fuel spray reaches the lip portion during the ignition delay period of the fuel so that the fuel vapor is formed near the lip portion. Is what you are trying to do. Therefore, the minimum diameter Dlip of the cavity is 0.4, which is a typical ignition delay period during medium load operation from the start of fuel injection.
It is determined based on the fuel spray arrival distance Sp (spray penetration) when 2 ms has elapsed. Si on this Sp
The reason for multiplying by n (Θ / 2) is that the fuel spray is carried out with the cone angle Θ, and therefore the reaching distance of the fuel spray in the horizontal direction is obtained.

By the way, when the above-mentioned k value is less than 1.4 and the minimum diameter Dlip of the cavity becomes relatively small, the fuel injected from the fuel injection valve as a liquid jet flows until it reaches the lip portion. As it does not split sufficiently, it becomes an incomplete spray state. Therefore, the formation of fuel vapor becomes insufficient, and the expansion flow of the combustion gas does not work effectively. Furthermore, the core of the fuel spray (the liquid column portion existing in the fuel spray injected from the fuel injection valve or the portion having a very high fuel concentration) collides with the lip portion to deteriorate the combustion and reduce the output. However, even if the NOx generation amount decreases, the soot generation amount increases.

On the other hand, when the above k value exceeds 1.8, the above D
If the lip becomes too large, the distance from the ignition point to the lip becomes longer, so even if the expansion flow of the combustion gas due to ignition acts on the fuel vapor in front of it, that fuel vapor will not reach the lip. Disperse around. Therefore, since the fuel vapor cannot be guided toward the bottom of the cavity by the expansion flow, the NOx generation amount increases.

Therefore, from the above, it is desirable that the above k value is k = 1.4 to 1.8. Further, from such a viewpoint, as the above k value, k = 1.5
It is more preferable that it is set to be 1.7.

[0026]

(First Embodiment) FIG. 1 shows the vicinity of a combustion chamber of a direct injection diesel engine equipped with a fuel combustion device according to an embodiment of the present invention. In the figure, 2
Is a cylinder block, 2a is a cylinder formed in the cylinder block 2, and 1 is a piston provided in the cylinder 2a. Further, 3 is a flat type cylinder head mounted on the upper portion of the cylinder block 2.

At the top of the piston 1, there is formed a concave reentrant type cavity 8 whose diameter becomes smaller as it approaches the opening end. As shown enlarged in FIG.
Reference numeral 11 denotes an annular lip portion that protrudes inward at the piston top surface portion so as to form the opening edge of the cavity 8, and reference numeral 12 denotes an annular recess portion that follows the lip portion 11 and is recessed radially outward of the piston. In addition, the piston 1 has a cavity 8
At the center of the bottom of the cavity, a protrusion 13 is formed which is raised toward the opening of the cavity 8.

A fuel injection valve 9 is attached and fixed to the lower portion of the cylinder head 3 with an injection nozzle 10 at the tip thereof facing the inside of the cylinder 2a. As also shown in FIG. 4, the fuel injection valve 9 transfers the fuel from the injection nozzle 10 to the lip portion 1.
This is for directly injecting the fuel into the cavity 8 by uniformly injecting radially toward 1, for example, 6 directions. The fuel injection valve 9 outputs signals from an electromagnetic crank angle sensor 22 that detects a rotation angle of a crankshaft (not shown), an accelerator opening sensor 23 that detects an accelerator pedal opening (accelerator operation amount), and the like. Based on the above, the operation is controlled by a control unit (hereinafter referred to as ECU) 40.

In the fuel combustion apparatus according to this embodiment, the fuel spray injected from the fuel injection valve 9 reaches the lip portion 11 during the ignition delay period, and the region of the fuel vapor 16 is provided near the lip portion 11. Configured to form. Further, the fuel is ignited at a predetermined position in front of the fuel injection valve 9 in the fuel injection direction, and the expansion flow of the combustion gas caused by the ignition causes the fuel vapor in front of the ignition position to hit the inner peripheral wall surface of the cavity 8 and the cavity. 8 is directed towards the bottom of the cavity 8 and the flame is propagated to the bottom of the cavity 8.

Reference numeral 4 is an intake port (helical port) formed in the lower portion of the cylinder head 3 for supplying air into the cavity 8, and 5 is similarly formed in the lower portion of the cylinder head 3 from the inside of the cavity 8. An exhaust port for exhausting exhaust gas. As shown in FIG. 2, for example, two intake ports 4 and two exhaust ports 5 are provided, respectively. Upright intake valve 6 in intake port 4
However, similar exhaust valves 7 are provided in the exhaust ports 5, respectively.

The intake passage 2 is provided in the intake ports 4 and 4.
4, 24 are connected to each other, while exhaust passages 25, 25 are connected to the exhaust port 5, respectively. One of the two intake passages 24, 24 is provided with a swirl control valve 30 for changing the flow rate of intake air in the one intake passage 24. The swirl control valve 30 is, for example, a butterfly valve, and is opened and closed by being driven by an actuator. Then, as shown in FIG. 2, the swirl control valve 30 is completely closed, so that the intake air flows from only the other intake passage 24 to the cavity 8
To generate a relatively strong swirl in the cavity 8 as shown by the arrow in FIG.

Then, as the swirl control valve 30 gradually opens from the completely closed state, the two intake passages 2
The intake air flows in from both 4, 4 and 24, and the tumble component of the intake air is strengthened and the swirl component is weakened. The swirl control valve 30 is configured to be controlled by the ECU 40 based on the engine speed Ne calculated from the crankshaft rotation angle detected by the crank angle sensor 22.

Further, the fuel combustion apparatus according to this embodiment
Is the engine speed Ne is a predetermined value Ne ₀When it is over
First, the penetration of the fuel spray injected from the fuel injection valve 9
The engine speed Ne is equal to the above predetermined value Ne.
₀Compared with the fuel spray penetration Sp below
Penetration control means to control
I have it.

Here, the penetration Sp is the penetration degree (also called penetration force) of the fuel spray, and the ignition delay period from the start of fuel injection (typically 0.4
2 ms), the length in the injection direction of the fuel spray, that is, the arrival distance from the injection nozzle 10 to the tip of the fuel spray.

Then, the penetration control means, when the engine speed Ne exceeds a predetermined value Ne ₀ ,
The fuel injection pressure Pr of the fuel injection valve 9 is set to the engine speed Ne.
Is for controlling to increase as compared with the fuel injection pressure Pr when is less than the predetermined value Ne ₀ . That is,
The penetration control unit increases the fuel injection pressure Pr to increase the fuel spray penetration Sp.

Further, the penetration control means, when the engine speed Ne exceeds a predetermined value Ne ₀ ,
The swirl ratio Sw of the swirl in the cavity 8 is controlled so as to be smaller than the swirl ratio Sw when the engine speed Ne is less than the predetermined value Ne ₀ . That is, the penetration control means is the ECU 40,
The crank angle sensor 22, the fuel injection valve 9, the swirl control valve 30 and the like are included. Also, the swirl ratio S
w is a ratio of the swirl speed (swirl speed) V in the cavity 8 to the engine speed Ne, that is, Sw = V / Ne.

In this way, when the engine speed Ne is less than the predetermined value Ne ₀ , the swirl ratio Sw is increased by decreasing the opening degree of the swirl control valve 30 (for example, in the fully closed state). Is trying to strengthen. On the other hand, when the engine speed Ne becomes equal to or higher than the predetermined value Ne ₀ , the opening degree of the swirl control valve 30 is increased (for example, the fully open state) to reduce the swirl ratio Sw to weaken the swirl and reduce the fuel injection valve. By increasing the fuel injection pressure Pr from No. 9, the penetration Sp of the fuel spray is strengthened.

The fuel combustion device for the diesel engine is constructed as follows. That is, the arrival distance Sp (penetration) of the fuel spray when 0.42 ms has elapsed from the start of fuel injection of the fuel injection valve 9 and the fuel injection valve 9
The cone angle Θ of the fuel spray and the minimum diameter (hereinafter, referred to as lip diameter) Dlip in the lip portion 11 of the cavity 8 have a relationship satisfying the following equation.

Dlip = k × Sp × sin (Θ / 2) (1) where k = 1.4 to 1.8 and k = 1.5 to 1.7.
Is more preferable. Also, the cone angle Θ =
It is preferably 153 to 157 degrees, and Θ = 154 to
More preferably, it is 156 degrees. The time 0.42 ms from the start of fuel injection is a typical ignition delay period in the emission operation mode (during medium load operation).

In the present invention, the fuel injection valve 9 to the lip portion 11 are used.
The fuel is injected toward and the fuel spray reaches the lip portion 11 during the ignition delay of the fuel so that the fuel vapor 16 is formed in the vicinity of the lip portion 11.
Therefore, the minimum diameter Dlip of the cavity 8 is determined based on the arrival distance Sp (penetration) of the fuel spray when the ignition delay period 0.42 ms elapses from the start of fuel injection. This Sp is multiplied by sin (Θ / 2) because the fuel is injected with the cone angle Θ, so that the reaching distance of the fuel spray in the horizontal direction is obtained.

The reach distance Sp is a constant vessel experiment (fuel injection pressure 80 MPa, atmospheric pressure 2.5 MPa, temperature 20 ° C.)
Required by. If there is no constant container experimental data, it can be estimated from Hiroan's formula. Hiro's formula is an empirical formula that relates the reaching distance Sp and the nozzle diameter of the fuel injection valve 9, and is as follows.

Sp = Spb + 2.95 × (ΔP × 10 ⁶ / ρf) ^0.25 ×
(Dn × (t-tb)) ^0.5 Spb = 0.39 × (2 × ΔP × 10 ⁶ / ρf) ^0.5 × tb tb = 28.65 × (ρf × Dn × 10 ^-3 ) / (ρA × ΔP × 10 ⁶ ) ^0.5 / 10 ^-3 However, ΔP: differential pressure (MPa) between container pressure and injection pressure, ρ
f: light oil density (kg / m ³ ), Dn: nozzle diameter (mm), t: time after injection start (0.42 ms), ρA: container air density.

The cylinder bore diameter B has a relationship satisfying the following equation.

B = K × Dlip (2) However, it is preferable that K = 1.8 to 2.5, and K =
More preferably, it is 2.0 to 2.3.

For example, when the reaching distance Sp = 27 mm and the cone angle Θ = 154 degrees, the lip diameter Dlip = 38.94-
44.20 mm, bore diameter B = 77.87-100.
It will be 33 mm. The height of the convex portion 13 may be about 0.2 to 0.25 times the lip diameter Dlip.

The spray angle of the fuel spray is preferably 15 to 24 degrees, more preferably 18 to 23 degrees. The fuel injection pressure P of the fuel injection valve 9 is preferably P = 50 MPa or more, and more preferably P = 80 MPa or more. The upper limit of injection pressure is, for example, 150MP
a, and further 200 MPa.

When the fuel spray injected from the fuel injection valve 9 first reaches the lip portion 11 of the cavity 8 of the piston, the ratio of the swirl momentum to the fuel spray momentum in the lip portion 11 is 0.9. The ratio of momentum is preferably 1.5 to 1.5, and more preferably 1.1 to 1.3. This momentum ratio can be calculated by the following equation.

Momentum ratio = ((ρa / ρao) × Va) / ((ρs / ρso) × Vs) (3) where ρa: filled air density, ρao: air density in standard state, Va: compression Swirl velocity at the lip portion 11 at the top dead center of the stroke, ρs: Density of fuel spray in constant container experiment, ρs
o: Density of fuel spray in the standard state, Vs: Spray speed when the lip reaches in the constant container experiment. Standard condition is 20 ℃,
It is 1 atm (0.1013 MPa).

Where ρa / ρao = (Pin / 101.3) / (Tin / 2
93.3), Va = ρa × SRi × (Dlip / B / 2)) ² × (N × 2π / 6
0) × Dlip. It is possible to set ρs / ρso = 1.

Where Pin: pressure in the intake manifold (k
Pa), Tin: temperature in intake manifold, SRi: swirl ratio in rig test, N: engine speed (rpm).

Next, the effect of the k value on the amount of NOx produced will be described. That is, as is clear from the above equation (1), the magnitude of the k value is reflected as the magnitude of the lip diameter Dlip, and if the reaching distance Sp is constant, the strength of the vertical vortex is affected. Therefore, the amount of NO produced when the k value was changed was examined. The result is shown in FIG.

In the figure, the data of k = 1.9 shows the reentrant rate R = 1 and the convex portion 1 at the center of the cavity 8.
It is a PAN type that does not have 3. The reentrant rate R is a Dlip / Dmax value when the maximum inner diameter of the cavity 8 is Dmax. The data of k = 1.73 is a reentrant type having a reentrant rate R = 1.73 / 1.9 and a convex portion 13 at the center of the cavity 8. The respective data of k = 1.65 and k = 1.54 are the amount of recess Re from the lip 11 of the recess 12 (FIG. 3 (B)).
(Ref.) Is the same as that of k = 1.73.

According to FIG. 5, the NO generation amount decreases as the k value decreases. This is because the expansion flow of the combustion gas at the initial stage of combustion strongly acts on the inner peripheral wall surface of the cavity 8 due to the smaller lip diameter, and the vertical vortex is promoted.
Furthermore, the distance between the recessed portion 12 and the protruding portion 13 becomes short, and vertical vortices are easily generated.

However, when the k value is less than 1.4 and the minimum diameter Dlip of the cavity 8 becomes relatively small, the fuel injected from the fuel injection valve 9 as a liquid jet flows to the lip portion 11. It does not split sufficiently before reaching, resulting in incomplete atomization. Therefore, the formation of the fuel vapor 16 is also insufficient, and the expansion flow does not work effectively. Further, the core of the fuel spray (the liquid column portion existing in the fuel spray injected from the fuel injection valve 9 or the portion having a very high fuel concentration) collides with the lip portion 11 to deteriorate the combustion and reduce the output. Therefore, even if the NOx generation amount decreases, the soot generation amount increases.

On the other hand, when the k value exceeds 1.8, the minimum diameter D
If the lip becomes relatively large, the distance from the ignition point to the lip portion 11 becomes large, so even if the expansion flow acts on the fuel vapor 16 in front of it, the fuel vapor 16
Disperse around the periphery before hitting the lip 11. Therefore, since the fuel vapor 16 cannot be guided toward the bottom of the cavity by the expansion flow, the NOx generation amount increases.

From this, as the above k value, k = 1.
It is desirable that it is 4 to 1.8. Further, from such a viewpoint, it is more preferable that the above k value is k = 1.5 to 1.7.

Next, the combustion concept of the diesel engine of the present invention will be described with reference to FIGS. 3 (A) to 3 (C). As shown in the figure (A) of the ignition delay period, a vertical vortex (the lip portion 11 of the cavity 8 is formed in the cavity 8).
From the fuel injection valve 9 to the lip portion 11 of the piston 1 when the flow from the fuel injection valve 9 to the lip portion 13 through the concave portion 12, the deepest portion, and the convex portion 13 to the lip portion 13 is not substantially generated. . Fuel spray 1 during the ignition delay period of this fuel
5 reaches the lip portion 11 to form a region of the fuel vapor 16 near the lip portion 11. Then, the fuel vapor 16 is ignited at a position on the upstream side in the fuel injection direction in this fuel vapor pool region. The ignition point is indicated by a star in the figure (A). The reason why the ignition point is located on the upstream side of the fuel vapor 16 region is that a strong vertical vortex is not formed in the compression stroke.
While the fuel becomes excessively rich in the vicinity of the lip portion 11,
It is considered that the concentration is suitable for ignition at a place slightly away from the lip portion 11.

In this case, by increasing the spray penetration Sp, the fuel vapor 1
Six regions can be formed. This is advantageous for inducing a large amount of the fuel vapor 16 toward the recess 12 by the expansion flow described below. In addition, it is preferable to increase the cone angle Θ (θ = 153 to 157 degrees) to the lip portion 1.
1 is advantageous in forming the region of the fuel vapor 16 in the vicinity of 1.

As shown in the initial combustion state in FIG.
The ignition causes a strong expansive flow that explosively expands toward the downstream side. The fuel vapor 16 in the vicinity of the lip portion on the downstream side (in front of the ignition position) in the fuel vapor region is formed by the expansion flow of the combustion gas 17 on the inner wall surface of the cavity 8 (especially the lip portion 11 and the piston 1 more than the lip portion 11). It contacts the vicinity of the boundary with the recessed portion 12 that is recessed radially outward. Then, the fuel vapor 16 is guided to the bottom side of the cavity 8 along the inner peripheral wall surface of the cavity 8 to generate a strong vertical vortex. Further, as the flame propagates following the fuel guided to the bottom of the cavity 8, the vertical vortex grows further.

In this case, the above-mentioned spray penetration Sp
When is increased, the expansion flow forward in the injection direction is increased, which is advantageous in promoting vertical vortices. Further, the smaller the lip diameter Dlip, the more advantageous it is for the expanded flow to be strongly applied to the inner peripheral wall surface of the cavity 8 to guide the fuel vapor toward the bottom of the cavity. However, if the lip diameter Dlip becomes too small, the maximum output of the engine becomes low. Therefore, the lip diameter Dlip is preferably larger than 1/2 of the bore diameter B.

As shown in the state of the latter stage of combustion in FIG. 6C, the convex portion 13 in the central portion of the cavity 8 extends along the rising surface of the convex portion 13 of the combustion gas 17 from the deepest portion of the cavity bottom. Promote winding.

As described above, the highest temperature portion in the cavity 8 is moved to the bottom side of the cavity 8 rather than the lip portion 11 by the end of fuel injection. Therefore, the heat spot does not become large at a specific portion in the cavity 8, the heat spot disappears quickly, and NOx can be reduced. Further, since the combustion gas 17 and oxygen remaining above the central portion of the cavity 8 are mixed by the above-mentioned winding in the latter stage of combustion, and further the combustion gas 17 flows into the squish area, the air utilization rate is increased, and the combustion gas 17
Reburning of the soot inside is promoted, and soot emissions are reduced.

Next, with reference to the flow chart shown in FIG. 6, a specific processing procedure of the fuel combustion control of the diesel engine according to the embodiment of the present invention will be described. First,
In step S1 after the start, output signals from various sensors such as the crank angle sensor 22 and the accelerator opening sensor 23 are input to the ECU 40.

Subsequently, in step S2, the ECU 4
With 0, the engine speed Ne is calculated based on the output from the crank angle sensor 22, and the accelerator opening is calculated based on the output from the accelerator opening sensor 23. Then, the basic injection timing Ib is calculated by the ECU 40 based on the engine speed Ne, the accelerator opening degree, and the like.

Further, in step S2, the basic injection pressure Pb of the fuel spray injected from the fuel injection valve 9 is calculated by the ECU 40 based on the engine speed Ne. That is, as also shown in FIG. 7A, the basic injection pressure Pb is a function f (Ne) = a ₀ · a of the engine speed Ne.
Determined by Ne. However, a ₀ is an increase rate of the basic injection pressure Pb with respect to the engine speed Ne, that is, a ₀ =
(ΔPb) / (ΔNe).

Then, in step S3, it is determined whether or not the engine speed Ne calculated in step S2 is equal to or higher than the speed Ne ₀ which is a predetermined threshold value.
When the engine speed Ne is equal to or higher than the predetermined speed Ne ₀ and the engine is in a relatively high speed state and YES is determined, the process proceeds to step S4.

In step S4, the ECU 40 calculates the corrected injection pressure Pa based on the engine speed Ne. That is, as shown in FIG. 7A, the corrected injection pressure Pa is a function g (Ne) = a ₁ · a of the engine speed Ne.
Determined by Ne. However, a ₁ is a constant larger than a ₀ (a ₁ > a ₀ ), and the rate of increase of the corrected injection pressure Pa with respect to the engine speed Ne, that is, a ₁ = (ΔPa)
/ (ΔNe). After that, proceed to step S5,
The fuel injection pressure Pr actually injected from the fuel injection valve 9 into the cavity 8 is set to the corrected injection pressure Pa. That is,
Since the fuel injection pressure Pr from the fuel injection valve 9 is corrected to be large, the penetration Sp of the fuel spray is strengthened. Then, it moves to step S6.

In step S6, the swirl control valve 30
The valve opening degree is increased and the valve is fully opened. As a result, air is taken in from both of the two intake ports 4 and 4, so the swirl in the cavity 8 is weakened. After that, the routine proceeds to step S7, where the fuel injection pressure Pr is strengthened and the swirl is weakened, the ECU 40 executes fuel injection based on the basic injection timing Ib and the corrected injection pressure Pa.

On the other hand, in step S3, when the engine speed Ne is less than the predetermined speed Ne ₀ , the engine is in a relatively low speed state and it is judged NO, the process proceeds to step S8. In step S8, the fuel injection pressure Pr actually injected from the fuel injection valve 9 into the cavity 8 is set to the basic injection pressure Pb, and the process proceeds to step S9.

In step S9, the swirl control valve 30
Is made fully closed by reducing its valve opening. As a result, only one of the two intake ports 4 and 4 is inhaled, so that the swirl in the cavity 8 is strengthened. After that, the routine proceeds to step S7, where the ECU 40 performs the fuel injection based on the basic injection timing Ib and the basic injection pressure Pb while the swirl is relatively strong.

Thus, the basic injection pressure P of the fuel injection valve 9 is
b is set to increase at a predetermined increase rate a _{0 as} the engine speed Ne increases. Then, when the engine speed Ne becomes equal to or higher than the predetermined value Ne ₀ , the basic injection pressure Pb is corrected to the corrected injection pressure Pa having the increase rate a ₁ larger than the increase rate a ₀ of the basic injection pressure Pb. It

As shown in FIG. 8, when the engine speed Ne is less than the predetermined value Ne ₀ , the swirl control valve 30 is fully closed, so that the swirl ratio Sw is made relatively large. , The swirl in the cavity 8 is strengthened. Then, when the engine speed Ne is increased to reach the predetermined value Ne ₀ or more, the valve opening degree of the swirl control valve 30 increases while the swirl ratio Sw decreases as the engine speed Ne increases. Then, once the swirl control valve 30 is fully opened with the increase of the engine speed Ne, the swirl control valve 30 is maintained in the fully open state even if the engine speed Ne further increases.

As described above, according to the present embodiment, the fuel vapor 16 near the lip portion 11 in the fuel vapor region formed during the ignition delay period is expanded by the ignition, and the inner peripheral wall surface of the cavity 8 is caused. Along the cavity 8
Since it is guided to the bottom side, a strong vertical vortex can be generated. Furthermore, since the flame propagates following the fuel guided to the bottom of the cavity 8, vertical vortices can be further grown. The vertical vortex causes the flame to propagate toward the bottom of the cavity 8 and the heat spot to move to the lip portion 1.
1 spreads from the vicinity of 1 to the bottom of the cavity 8 while the lip 1
Since the fuel vapor 16 decreases in the vicinity of 1, the lip portion 1
The heat spot near 1 disappears promptly. Therefore, by the end of the fuel injection, the highest temperature portion in the cavity 8 can move from the vicinity of the lip portion 11 to the bottom side of the cavity 8 and be dispersed.

That is, the heat spot is the cavity 8.
Since it is possible to prevent the heat spot from existing at a specific position for a long time and to extinguish the heat spot quickly, the amount of NOx produced can be effectively reduced. In addition, since the vertical vortices are strengthened, the mixing of the fuel and the air in the cavity 8 and the mixing of the combustion gas and the air in the latter half of the combustion are promoted, respectively, so that the soot generation amount is made effective. Can be reduced.

When the engine load becomes less than the predetermined value and the amount of NOx produced by combustion becomes relatively small, the swirl in the cavity 8 is strengthened by the swirl control means in preference to the vertical vortex. As a result, the enhanced swirl further promotes the mixing of the fuel and air in the cavity 8 and the mixing of the combustion gas and air in the latter half of combustion, so that the soot generation is effectively performed. Can be suppressed.

In addition to this, the fuel injection pressure of the fuel injection valve 9 is set such that when the engine speed Ne becomes a predetermined value Ne ₀ or more, the penetration control means causes the engine speed Ne to be the predetermined value Ne _0. It is controlled to increase as compared with when it is less than. In other words, in the fuel spray penetration Sp, the engine speed Ne is the predetermined value N.
When e ₀ or more, the engine speed Ne is increased compared to when the engine speed Ne is less than the predetermined value Ne ₀ . Therefore, the fuel spray can sufficiently oppose the swirl even when the engine speed Ne is at or above the predetermined value Ne ₀ and is in a relatively high speed state. Therefore, the fuel spray becomes stronger as the engine speed Ne increases. The swirl can prevent the penetration Sp of the fuel spray from decreasing.
Therefore, the region of the fuel vapor 16 can be stably formed near the lip portion 11, and the vertical vortex generated in the cavity 8 can be sufficiently strengthened. That is, even when the engine is in a high rotation state, the enhanced vertical vortex can stably reduce the generation of NOx and soot.

Further, when the engine speed Ne becomes greater than the predetermined value Ne ₀ by the penetration control means, the swirl ratio Sw in the cavity 8 is determined by the swirl when the engine speed Ne is the predetermined value Ne _0. Since it is reduced compared to the ratio Sw, the swirl speed corresponding to the engine speed Ne can be reduced. That is, even when the engine speed is relatively high, it is possible to suppress the reinforcement of the swirl and effectively suppress the reduction of the fuel spray penetration Sp due to the swirl.
The vertical vortex generated in the cavity 8 can be sufficiently strengthened.

In the above embodiment, the penetration control means increases the fuel injection pressure Pr by increasing the increase rate a ₀ of the basic injection pressure Pb when the engine speed Ne is equal to or higher than the predetermined value Ne _0. In addition, the swirl ratio Sw is reduced to weaken the swirl, but the present invention is not limited to this. That is, when the engine speed Ne is equal to or greater than the predetermined value Ne ₀ , the fuel injection pressure Pr
May be increased, and the swirl ratio S
Only w may be reduced. Even in this case, the penetration Sp of the fuel spray can be appropriately maintained and the vertical vortex can be sufficiently strengthened.

(Second Embodiment) FIG. 7B shows a second embodiment of the present invention (note that in each of the following embodiments, FIG.
The same parts as those in FIGS. 6, 7A and 8 are designated by the same reference numerals and detailed description thereof will be omitted), and the correction contents of the basic injection amount Pb in the above-described first embodiment are changed. .

As shown in FIG. 7B, this second embodiment
Then, as in the first embodiment, the basic injection pressure Pb of the fuel injection valve 9 is set to increase at a predetermined increase rate a _{0 as} the engine speed Ne increases. Then, when the engine speed Ne becomes equal to or higher than the predetermined value Ne ₀ , the basic injection pressure Pb holds the increase rate a ₀ of the basic injection pressure Pb and increases the injection pressure by the predetermined pressure ΔP. It is corrected to the set correction injection pressure Pa.

That is, in step S4 in the flowchart of FIG. 6, the corrected injection pressure Pa is determined by the function g (Ne) = a ₀ · Ne + ΔP of the engine speed Ne (where ΔP is a positive constant).

[0082] Thus, corrected injection pressure by setting the Pa, when the engine speed Ne is the predetermined value Ne ₀ or more, effective than when the engine rotational speed Ne is smaller than the predetermined value Ne ₀ Since the fuel injection pressure Pr can be increased, the same effect as that of the first embodiment can be obtained.

(Third Embodiment) FIG. 7C shows a third embodiment of the present invention, in which the basic injection amount P in the first embodiment is set.
The correction contents of b are changed.

As shown in the figure, in the third embodiment,
Similar to the first embodiment, the basic injection pressure P of the fuel injection valve 9
b is a predetermined increase rate as the engine speed Ne increases.
A ₀It is set to increase with. And EN
Jin rotation speed Ne is a predetermined value Ne₀When the above
For the main injection pressure Pb, the engine speed Ne is equal to the predetermined value Ne.
₀Is less than a predetermined constant value that is greater than the injection pressure when
Injection pressure Pr₀Is corrected to the corrected injection pressure Pa set to
It

That is, in step S4 in the flowchart of FIG. 6, the corrected injection pressure Pa is determined by the function g (Ne) = Pr ₀ of the engine speed Ne (where Pr ₀ is a positive constant). Thus, by setting the corrected injection pressure Pa, when the engine speed Ne is the predetermined value Ne ₀ or more, effectively fuel injection as compared to when the engine speed Ne is smaller than the predetermined value Ne ₀ Since the pressure Pr can be increased, the same effect as that of each of the above-described embodiments can be obtained.

[0086]

As described above, according to the first aspect of the present invention, a piston having a reentrant type cavity formed on the top thereof, the diameter of which decreases as it approaches the opening end, and a lip portion forming the cavity opening edge of the piston. A fuel injection valve for injecting fuel toward the fuel injection valve, and makes the fuel spray injected from the fuel injection valve reach the lip portion during the ignition delay period to form a region of fuel vapor near the lip portion. Diesel engine configured to ignite fuel in the front of the fuel injection direction and to cause the fuel vapor in front of the ignition position to impinge on the peripheral wall surface of the cavity toward the bottom of the cavity by the expansion flow of combustion gas resulting from this ignition For the fuel combustion device, the penetration of the fuel spray injected from the fuel injection valve is changed when the engine speed exceeds a predetermined value. By down speed comprises penetration control means for controlling so as to increase as compared to the penetration of the fuel spray when less than the predetermined value,
It prevents the heat spot from existing at a specific position in the cavity for a long time, effectively reduces the amount of NOx produced, and promotes the mixing of fuel or combustion gas with air in the cavity, soot. It is possible to effectively reduce the production amount of. In addition to that, the vertical vortices in the cavity are sufficiently strengthened to stably reduce the generation of NOx and soot even when the engine speed is at a predetermined value or higher and relatively high speed. You can

According to the second aspect of the present invention, the penetration control means controls the fuel injection pressure of the fuel injection valve when the engine speed becomes equal to or higher than a predetermined value, and the fuel injection pressure when the engine speed is lower than the predetermined value. By controlling so as to increase in comparison with the pressure, the fuel spray sufficiently opposes the swirl, so that the penetration of the fuel spray can be effectively increased.

According to the third aspect of the invention, the penetration control means compares the swirl ratio in the cavity with the swirl ratio when the engine speed is less than the predetermined value when the engine speed becomes equal to or higher than the predetermined value. By controlling so as to decrease, the swirl strengthening is weakened even when the engine is in a relatively high rotation state, so that reduction in fuel spray penetration can be effectively suppressed.

According to the fourth aspect of the invention, the penetration Sp, which is the reaching distance of the fuel spray when 0.42 ms has elapsed from the fuel injection start of the fuel injection valve, the cone angle Θ of the fuel spray of the fuel injection valve, and the lip of the cavity. The minimum diameter Dlip in the section is such that Dlip = k × Sp × sin (Θ / 2) (where k = 1.4 to 1.8) is satisfied, so that from the fuel injection valve to the lip section. To inject fuel toward
During the fuel ignition delay period, the fuel spray can reach the lip portion and the fuel vapor can be appropriately formed near the lip portion.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a fuel combustion device for a diesel engine according to an embodiment of the present invention.

FIG. 2 is an enlarged plan view showing a main part of the fuel combustion device.

FIG. 3 is an explanatory diagram showing a combustion concept of the present invention.

FIG. 4 is a plan view showing a combustion chamber in which fuel spray is injected.

FIG. 5 is a graph showing the relationship between k value and NO production amount.

FIG. 6 is a flowchart showing fuel combustion control in the fuel combustion device.

FIG. 7 is a graph showing the relationship between engine speed Ne and fuel injection pressure Pr.

FIG. 8 is a graph showing a relationship between an engine speed Ne, a swirl valve opening degree, and a swirl ratio.

[Explanation of symbols] Sp penetration (penetration force, fuel spray reach distance) Θ Fuel spray cone angle Dlip Minimum diameter of lip Ne Engine speed Ne ₀ Predetermined value of engine speed Sw Swirl ratio 1 Piston 8 Cavity 9 Fuel Injection valve (penetration control means) 11 Lip portion 12 Recessed portion (circumferential wall surface of cavity) 16 Fuel vapor 22 Crank angle sensor (penetration control means) 24 Intake passage (penetration control means) 30 Swirl control valve (penetration control means stage) 40 ECU (penetration control means)

Front page continuation (51) Int.Cl. ⁷ Identification symbol FI theme code (reference) F02D 41/02 380 F02D 41/02 380G F02F 3/26 F02F 3/26 C (72) Inventor Yasuyuki Terazawa Aki-gun, Hiroshima Prefecture 3-1, Fuchu-cho Shinchi Mazda Co., Ltd. (72) Inventor Hiroshi Hayashibara 3-1-1, Shinchi Fuchu-cho, Aki-gun, Hiroshima Prefecture F-Term (reference) 3G023 AA04 AA05 AA18 AB05 AC05 AD02 AD07 AD09 AD14 AG01 3G301 HA02 HA17 JA24 JA25 LA05 MA18 MA28 MA29 NA08 PA07Z PE01Z PF03Z

Claims (4)

[Claims] 1. A piston having a reentrant type cavity formed on the top thereof, the diameter of which decreases as it approaches the opening end, and a fuel injection valve for injecting fuel toward a lip portion forming the cavity opening edge of the piston. The fuel spray injected from the fuel injection valve reaches the lip portion during an ignition delay period to form a fuel vapor region near the lip portion, and the fuel is ignited in front of the fuel injection direction of the fuel injection valve. Let
Due to the expansion flow of the combustion gas due to this ignition, the fuel vapor in front of the ignition position is applied to the peripheral wall surface of the cavity to guide it toward the bottom of the cavity, and the flame is propagated to the bottom of the cavity. In a fuel combustion device for a diesel engine, the penetration of fuel spray injected from the fuel injection valve when the engine speed exceeds a predetermined value,
A fuel combustion device for a diesel engine, comprising: a penetration control means for controlling so as to increase compared to the penetration of fuel spray when the engine speed is less than the predetermined value. 2. The fuel combustion device for a diesel engine according to claim 1, wherein the penetration control means determines the fuel injection pressure of the fuel injection valve when the engine speed becomes a predetermined value or more, and the engine speed is the predetermined value. A fuel combustion device for a diesel engine, which is controlled so as to increase compared to a fuel injection pressure when the value is less than a value. 3. The fuel combustion device for a diesel engine according to claim 1 or 2, wherein the penetration control means determines the swirl ratio in the cavity when the engine speed becomes a predetermined value or more, and the engine speed is the predetermined value. A fuel combustion device for a diesel engine, which is controlled so as to decrease compared to a swirl ratio when the value is less than a value. 4. The fuel combustion apparatus for a diesel engine according to any one of claims 1 to 3, wherein the penetration Sp is defined as a reaching distance of fuel spray when 0.42 ms has elapsed from the start of fuel injection of the fuel injection valve. And the cone angle Θ of the fuel spray of the fuel injection valve,
Diesel engine characterized in that the minimum diameter Dlip at the lip portion of the cavity satisfies the following expression Dlip = k x Sp x sin (Θ / 2) (where k = 1.4 to 1.8) Fuel combustion equipment.