JPH10148128A - Direct injection type diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve air utilization factor by forming an inlet part which is cylindrically opened to a part of a piston crown, in a main combustion chamber, and injecting fuel spray from a fuel injection valve toward the inlet part of the main combustion chamber. SOLUTION: When fuel pressure which is pressure-fed from a fuel pump to a combustion chamber 46 through a passage is low and a lift rate of a needle 45 is small, fuel is injected and supplied from only first injection port. When fuel pressure which is pressure fed to the combustion chamber 46 is high and the lift quantity of the needle 45 is large, fuel is injected and supplied from the first injection port 43 and a second injection port 42. In a large injection angle region 1, fuel which collides with an inlet part 12 is dispersed inward and outward of the main combustion chamber 5, fuel is dispersed to all regions of the combustion chamber 5, and pre-mixture combustion is sufficiently carried out. On the other hand, in a small injection angle region 2, almost of fuel spray reaches a recessed part 13 where the turbulence of intake flow is large, and thereby, dispersion combustion is promoted in the main combustion chamber 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a direct injection diesel engine.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for lower pollution and higher output of diesel engines, and various proposals have been made regarding the shape of a combustion chamber.

[0003] As a combustion chamber of a conventional direct-injection diesel engine, for example, there is one shown in FIG. 15 (see Japanese Patent Application Laid-Open No. 63-162925).

[0004] To explain this, the main combustion chamber 5 which is concavely recessed in the crown 15 of the piston 4 has an inlet 12 which opens cylindrically with respect to the piston crown 15, and a recess with respect to the inlet 12. It is defined by a depression 13 that is depressed and a projection 14 that protrudes from the center of the bottom.

The fuel injection valve 7 is arranged on the center line of the cylinder and faces the center of the main combustion chamber 5. The fuel injection valve 7 has a plurality of nozzles for injecting fuel, and the fuel spray is radially injected from each nozzle toward the recess 13 of the main combustion chamber 5.

When most of the fuel spray reaches the depression 13 where the intake air flow is largely turbulent, diffusion combustion in the main combustion chamber 5 is promoted.

[0007]

SUMMARY OF THE INVENTION Incidentally, Japanese Patent Application Laid-Open No.
Japanese Patent Application Laid-Open No. 004287 proposes a method in which the ignition delay period is greatly lengthened according to the operating conditions, most of the fuel is burned in a premixed gas, and the generation of particulates is suppressed.

However, in the conventional device shown in FIG.
When most of the fuel is to be burned in a premixed gas mixture, since the region where the fuel spray injected from the fuel injection valve 7 reaches is set in the recessed portion 13 of the main combustion chamber 5, it is generated in the main combustion chamber 5. The fuel spray is collected in the main combustion chamber 5 by the flowing gas, and the fuel cannot be dispersed in the entire area of the combustion chamber 5, so that the premixed gas combustion is not sufficiently performed. As a result, there is a problem that the amount of particulate emissions cannot be sufficiently suppressed.

The present invention has been made in view of the above problems, and has as its object to control the fuel injection direction in a combustion chamber of a direct injection diesel engine to improve the air utilization rate.

[0010]

According to a first aspect of the present invention, there is provided a direct-injection diesel engine, wherein a combustion chamber ceiling wall defining a combustion chamber between the main combustion chamber recessed in the crown of the piston and the piston. And a fuel injection valve mounted on the ceiling wall of the combustion chamber to inject fuel toward the main combustion chamber, and a direct injection diesel engine that sets a premixed gas combustion mode region that lengthens the ignition delay period according to operating conditions. In the engine, the main combustion chamber is formed with an inlet that opens cylindrically with respect to the crown of the piston,
Fuel spray is injected from the fuel injection valve toward the inlet of the main combustion chamber.

According to a second aspect of the present invention, in the direct injection diesel engine according to the first aspect of the present invention, the main combustion chamber is formed with a concave portion that is concave with respect to a cylindrical inlet portion, and a premixed gas is formed. The fuel spray is injected from the fuel injection valve toward the depression of the main combustion chamber outside the combustion mode range.

According to a third aspect of the present invention, there is provided a direct injection diesel engine according to the first aspect, wherein a side wall of the main combustion chamber is formed in a cylindrical shape continuous with an inlet portion, and fuel is supplied outside a premixed gas combustion mode region. The fuel spray is injected from the injection valve toward the side wall below a position 7 mm below the opening edge with respect to the crown of the piston.

According to a fourth aspect of the present invention, in the direct injection diesel engine according to any one of the first to third aspects, the fuel injection timing is delayed until after the compression top dead center in the premixed gas combustion mode region.

[0014]

In the direct injection diesel engine according to the first aspect of the present invention, the fuel spray injected from the fuel injection valve collides with the inlet of the main combustion chamber, and the fuel that collides with the inlet is in the main combustion chamber. Spread inside and out. Thus, if the ignition delay period is greatly increased in a state where the fuel is dispersed throughout the combustion chamber, most of the fuel is burned in a premixed gas state, and the generation of particulates can be effectively suppressed.

[0015] In the direct injection diesel engine according to the second aspect, most of the fuel is injected into the premixed gas combustion mode region by injecting fuel spray from the fuel injection valve toward the inlet of the main combustion chamber. Combustion and generation of particulates can be effectively suppressed.

By injecting the fuel spray from the fuel injection valve toward the depression where the turbulence of the intake air flow is large outside the premixed gas combustion mode range, the diffusion combustion in the main combustion chamber is promoted and the outside of the main combustion chamber is accelerated. The amount of fuel scattered on the surface is reduced. As a result, the unburned H generated near the cylinder wall
While reducing the amount of C and particulates generated,
It is possible to prevent the generated torque from dropping at a high speed or the like.

In the direct injection diesel engine according to the third aspect, most of the fuel is supplied to the premixed gas combustion mode by injecting fuel spray from the fuel injection valve toward the inlet of the main combustion chamber. Combustion and generation of particulates can be effectively suppressed.

Outside the premixed gas combustion mode region, fuel spray is injected toward the inner part of the main combustion chamber located below a position 7 mm below the edge of the opening with respect to the crown of the piston. Diffusion combustion is promoted by the generated gas flow, and the amount of fuel scattered outside the main combustion chamber is reduced. As a result, the amount of unburned HC and particulates generated near the cylinder wall can be suppressed, and the generated torque can be prevented from dropping at the time of high speed or the like.

In the direct-injection diesel engine according to the fourth aspect, as a means for extending the ignition delay period in the premixed-gas combustion mode, the ignition delay period is greatly controlled by controlling the fuel injection timing after the top dead center. It is possible to lengthen the combustion, and most of the combustion is premixed gas combustion, so that the generation of particulates can be effectively suppressed.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 3, reference numeral 21 denotes a diesel engine main body, reference numeral 23 denotes an intake passage, reference numeral 25 denotes an exhaust passage, reference numeral 26 denotes an EGR passage connecting the exhaust passage 25 and the intake passage 23, and reference numeral 27 denotes a diaphragm type which responds to a control negative pressure. It is an EGR valve.

Reference numeral 28 denotes a negative pressure control valve which adjusts a constant negative pressure from a negative pressure source in three stages according to a duty signal from the control unit 31. For example, when the OFF duty (OFF time ratio of a constant cycle) to the negative pressure adjusting valve 28 is the maximum value and a constant negative pressure is directly introduced into the EGR valve 27, 50% of the exhaust gas is recirculated. This corresponds to an EGR rate of 100%. When the OFF duty decreases stepwise, the control negative pressure to the EGR valve 27 decreases and E
The degree of opening of the GR valve decreases, and the EGR flow rate decreases. That is, each time the OFF duty is reduced, the EGR rate decreases to 60% and 30%. The three stages of EGR rates thus obtained are set as shown in FIG.

In order to control the EGR rate according to the operating conditions of the engine 21, a control unit 31 including a microcomputer is provided. In the control unit 31,
EGR is performed based on a signal from a sensor 32 that detects an accelerator opening (accelerator pedal opening) and an air flow meter 33, and a reference pulse and a scale pulse described later.
The flow rate is controlled stepwise.

When the EGR rate is increased, NOx
Although the concentration can be reduced, on the other hand, the particulate concentration tends to increase sharply.

To cope with this, the control unit 31 sets a premixed gas combustion mode region in which the fuel injection timing is delayed until after the top dead center, corresponding to an operation region in which the particulate concentration may increase. I do. By delaying the injection timing of the fuel until after the top dead center, the intake timing is lowered due to a significant delay of the injection timing, the ratio of premixed gas combustion is increased, and the generation of particulates is suppressed.

FIG. 5 shows the characteristics of the fuel injection timing in comparison with the characteristics of the EGR rate (FIG. 4). The injection timing in the premixed gas combustion mode range from a medium load to a high load in a low rotation speed region is shown. Is set after top dead center (+4 ATDC and +2 ATDC). In FIG. 5, when the engine speed becomes a middle to high load range from a middle rotation to a high rotation, the injection timing is advanced as the engine speed increases. This is because even if the ignition delay time is constant, the ignition delay crank angle (the value obtained by converting the ignition delay time into a crank angle) increases in proportion to the increase in the engine speed. Is to be kept almost constant.

On the other hand, in FIG. 5, the injection timing is advanced from the high load region in order to eliminate the need to suppress the generation of particulates in the low load region where no particulates are generated and to suppress the rapid increase of hydrocarbon HC. this is,
If the same injection timing is used in the low load region where the combustion chamber wall temperature is low and in the high load region, the ignition timing is delayed due to the longer ignition delay period, and the combustion temperature is lowered. is there.

In FIG. 2, 1 is a cylinder block, 2
Is a cylinder, 4 is a piston, 5 is a crown 15 of the piston 4
The main combustion chamber is concavely concave.

6 is a cylinder head, 8 is an intake port formed on the cylinder head 6, 9 is an intake valve for opening and closing the intake port 8, 10 is an exhaust port formed on the cylinder head 6, and 11 is an exhaust port. It is an exhaust valve.

The cylinder head 1 has a combustion chamber ceiling wall defining a combustion chamber with the piston 4. A fuel injection valve 7 for radially injecting fuel into the main combustion chamber 5 is installed on the ceiling wall of the combustion chamber. The fuel injection valve 7 is arranged on the cylinder center line and faces the center of the main combustion chamber 5.

On the ceiling wall of the combustion chamber, two intake valves 9 and two exhaust valves 11 are provided so as to surround the fuel injection valve 7. As each intake valve 9 is opened in the intake stroke in which the piston 4 descends, air is sucked into the cylinder 2 from each intake port 8 and compressed by the piston 4, and the piston 4 is moved to the vicinity of the top dead center. When it reaches, the fuel injected from the fuel injection valve 7 is ignited and burned. The burned gas is exhausted by each exhaust valve 11 in the stroke in which the piston 4 rises.
Are discharged to the respective exhaust ports 10 as the nozzles are opened.
Each of these steps is repeated continuously. The reciprocating motion of the piston 4 is converted into a rotational motion of the crankshaft via the connecting rod 3.

As shown in FIG. 1, the crown 1 of the piston 4
5 is formed in a plane shape orthogonal to the cylinder center line. The piston crown 15 extends annularly around the main combustion chamber 5 and compresses air in the cylinder 2 between the combustion chamber ceiling walls of the cylinder head 6 when the piston 4 reaches the vicinity of the top dead center. A squish area for generating a squish flow flowing into the combustion chamber 5 is formed.

The main combustion chamber 5 has an inlet portion 12 which is open in a cylindrical shape with respect to the piston crown portion 15, a concave portion 13 which is concavely concave with respect to the inlet portion 12, and a raised portion 14 which is raised from the center of the bottom. Is defined by

The inlet 12 constitutes the upper part of the side wall of the main combustion chamber 5 which opens into the piston crown 15. The inlet 12 is formed in a right cylindrical surface concentric with the piston 4. Therefore, the cross section of the inlet 12 is orthogonal to the crown 15 of the piston 4. Piston crown 1 by inlet 12
Since the edge formed by the inner wall surface of the main combustion chamber 5 and the inner combustion wall 5 is eliminated, it is possible to prevent the thermal load of the piston 4 from becoming excessive.

The recess 13 forms the lower part of the side wall of the main combustion chamber 5 and the outer peripheral part of the bottom wall. The depression 13 has a cross section curved in an elliptical arc shape. The depression 13 is the piston 4
And extend in a concentric ring.

The protruding portion 14 forms the center of the bottom surface of the main combustion chamber 5. The protruding portion 14 is formed to protrude in a conical shape concentric with the piston 4.

The fuel injection valve 7 has a plurality of injection ports for injecting fuel, and the fuel injection is radially injected from each injection port toward the main combustion chamber 5.

As the gist of the present invention, when the piston 4 reaches the vicinity of the top dead center, each of the injection ports of the fuel injection valve 7 or the inlet 12 of the main combustion chamber 5 is formed so as to be directed. The fuel spray injected from the injection port is configured to collide with the inlet 12 of the main combustion chamber 5.

The width of the entrance 12 in the height direction is set to about 7 mm. The fuel spray injected from the fuel injection valve reaches an area above a position 7 mm below the edge of the opening of the piston 4 with respect to the crown 15.

The operation will be described below.

The combustion of the diesel engine 21 includes premixed gas combustion in which the premixed gas formed during the ignition delay period burns at a stretch, and diffusion combustion in which the combustion speed following the combustion is limited by the diffusion speed of air and fuel. Consists of By controlling the fuel injection timing after the top dead center in the predetermined premixed gas combustion mode range, the ignition delay period can be greatly lengthened, and most of the fuel burns in the premixed gas and particulates are generated. Can be effectively suppressed.

However, in the premixed gas combustion mode region in which the fuel injection timing is set after the compression top dead center, the region where the fuel spray injected from the fuel injection valve 7 reaches is set in the depression 13 of the main combustion chamber 5. In such a case, the fuel spray is collected in the main combustion chamber 5 due to the gas flow generated in the main combustion chamber 5, and the fuel cannot be dispersed throughout the combustion chamber, so that the premixed gas combustion is not sufficiently performed. As a result, as shown in FIG. 6 as a characteristic of the conventional example, the amount of generated particulates increases in the premixed gas combustion mode region.

According to the present invention, the fuel spray injected from each of the nozzles is caused to collide with the inlet 12 of the main combustion chamber 5 so that the fuel colliding with the inlet 12 flows into and out of the main combustion chamber 5. It diffuses and disperses the fuel throughout the combustion chamber, so that the premixed gas combustion is sufficiently performed. As a result, as shown in the characteristics of the present invention in FIG. 6, the amount of generated particulates can be suppressed in the premixed gas combustion mode region as compared with the conventional example.

FIG. 7 shows the relationship between the engine speed and the generated torque. In the low-speed and high-load region, the same generated torque can be obtained as compared with the conventional example in which fuel is injected toward the depression 13. However, there is a problem that the generated torque is lower in the high-speed and high-load region than in the conventional example. It is considered that this is because the fuel injection period becomes longer in the high-speed high-load region, the amount of fuel scattered outside the main combustion chamber 5 becomes excessive, and the output performance deteriorates.

As another embodiment for dealing with this, FIG.
The fuel spray is injected from the fuel injection valve 7 toward the inlet 12 of the main combustion chamber 5 in the large injection angle range 1 set as shown in FIG. It is good also as composition which injects toward hollow part 13 of combustion chamber 5.

As shown in FIG. 8, the fuel injection valve 7 has a needle 45 housed inside a hollow cylindrical nozzle body 41, and the needle 45 according to the fuel pressure fed from a fuel pump through a passage. Are lifted in stages to perform fuel injection.

A through hole 44 is formed inside the needle 45 to guide the fuel pressure-fed from the fuel injection pump to the tip of the needle 45 as shown by the arrow in the figure. The upper end of the through hole 44 communicates with the fuel chamber 46, and the lower end of the through hole 44 opens at the tip end surface of the needle 45.

The distal end of the needle 45 is formed in a right cylindrical shape, and a cylindrical portion 54 is formed in the nozzle body 41 so as to slidably fit the distal end.

A plurality of first injection ports 43 for injecting fuel are formed radially in the middle of the cylindrical portion 54, and a plurality of second injection ports 42 are formed above the first injection ports 43 in a radial manner. .

The angle of inclination of each first injection port 43 with respect to the cylinder center line is set to be larger than that of each second injection port 42. The fuel spray injected from each first injection port 43 reaches the inlet 12 of the main combustion chamber 5, while the fuel spray injected from each second injection port 42 reaches the depression 13 of the main combustion chamber 5.

When the pressure of the fuel pumped from the fuel pump to the fuel chamber 46 through the passage is low and the lift amount of the needle 45 is small, the fuel is injected and supplied only from the first injection port 43. On the other hand, if the pressure of the fuel fed into the fuel chamber 46 is high and the lift amount of the needle 45 is large, the fuel
From the second injection port 42.

In the large injection angle range 1, the fuel is injected into the first injection port 43.
Only the fuel is injected from only the fuel, and the fuel spray reaches the inlet 12 of the main combustion chamber 5. On the other hand, the fuel is injected from the first injection port 43 and the second injection port 42 in the small injection angle range 2, and most of the fuel spray reaches the depression 13 of the main combustion chamber 5.

The configuration is as described above. Next, the operation will be described.

In the large injection angle range 1, the fuel is injected into the first injection port 43.
Only when fuel is injected from the fuel chamber and the fuel spray reaches the inlet 12 of the main combustion chamber 5, the fuel colliding with the inlet 12 diffuses into and out of the main combustion chamber 5, and the fuel is dispersed throughout the combustion chamber. As a result, the premixed gas combustion is sufficiently performed. As a result,
As shown in the characteristics of the present invention in FIG. 10, the amount of generated particulates can be sufficiently suppressed in the premixed gas combustion mode region in which the fuel injection timing is delayed as compared with the conventional example.

In the small injection angle range 2, the fuel is injected into the first injection port 43.
Is injected from the second injection port 42, and most of the fuel spray reaches the depression 13 where the intake air flow is largely turbulent, so that diffusion combustion in the main combustion chamber 5 is promoted and The amount of scattered fuel is reduced. As a result, the amount of unburned HC and particulates generated in the vicinity of the cylinder wall can be suppressed, and as shown in FIG. 11, at the high speed, the same generated torque as in the conventional example can be obtained.

Next, the embodiment shown in FIG. 12 will be described. The parts corresponding to those in FIG. 1 are denoted by the same reference numerals.

The main combustion chamber 5 has an inlet portion 12 which opens cylindrically with respect to the piston crown portion 15, a cylindrical side wall 17 continuous with the inlet portion 12, and a protruding portion which protrudes from the center of the bottom. 14.

The inlet 12 constitutes the upper part of the side wall 17 of the main combustion chamber 5 which opens into the piston crown 15. Entrance part 1
2 and the side wall 17 are formed in a right cylindrical surface concentric with the piston 4. Accordingly, the cross section of the inlet 12 and the side wall 17 is orthogonal to the crown 15 of the piston 4.

Large injection angle range 1 set as shown in FIG.
The fuel spray is injected from the fuel injection valve 7 toward the inlet portion 12 of the main combustion chamber 5 at the time, and the fuel spray from the fuel injection valve 7 in the small injection angle range 2 with respect to the opening edge with respect to the piston crown 15 is X. Injection is made toward the side wall 17 below the 7 mm position.

The operation will be described below.

In the large injection angle range 1, when the fuel spray reaches the inlet 12 of the main combustion chamber 5, the fuel colliding with the inlet 12 is diffused into and out of the main combustion chamber 5, and the fuel is discharged from the combustion chamber. Dispersed in the entire area, and the premixed gas combustion is sufficiently performed.
As a result, as shown in the characteristics of the present invention in FIG. 13, in the large injection angle range 1, the amount of particulate generation can be sufficiently suppressed in the premixed gas combustion mode range in which the fuel injection timing is delayed.

In the small injection angle range 2, the main combustion is performed by injecting the fuel spray toward the back of the main combustion chamber 5 located below the position 7 mm below the opening edge of the crown 4 with respect to the crown 15 of the piston 4. Diffusion combustion is promoted by the gas flow generated in the chamber 5 and the amount of fuel scattered outside the main combustion chamber 5 is reduced. As a result, the amount of unburned HC and particulates generated near the cylinder wall can be suppressed, and the torque generated at high speed can be increased as shown in FIG.

[Brief description of the drawings]

FIG. 1 is a sectional view of a piston showing an embodiment of the present invention.

FIG. 2 is a sectional view of the engine.

FIG. 3 is a system diagram of the same.

FIG. 4 is a characteristic diagram in which an EGR rate is set according to operating conditions.

FIG. 5 is a characteristic diagram in which a fuel injection timing is set according to the operating conditions.

FIG. 6 is a characteristic diagram showing the relationship between the fuel injection timing and the amount of discharged particulate.

FIG. 7 is a characteristic diagram showing the relationship between the engine speed and the generated torque.

FIG. 8 is a cross-sectional view of a fuel injection valve showing another embodiment.

FIG. 9 is a characteristic diagram in which a fuel injection angle is set according to the operating conditions.

FIG. 10 is a characteristic diagram showing the relationship between the fuel injection timing and the amount of discharged particulate.

FIG. 11 is a characteristic diagram showing the relationship between the engine speed and the generated torque.

FIG. 12 is a sectional view of a piston showing still another embodiment.

FIG. 13 is a characteristic diagram showing the relationship between the fuel injection timing and the amount of discharged particulate.

FIG. 14 is a characteristic diagram showing the relationship between the engine speed and the generated torque.

FIG. 15 is a sectional view of a piston showing a conventional example.

[Explanation of symbols]

 Reference Signs List 4 piston 5 main combustion chamber 7 fuel injection valve 12 inlet 13 dent 15 piston crown 17 side wall

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02M 61/14 310 F02M 61/14 310D

Claims (4)

[Claims] 1. A main combustion chamber concavely recessed in a crown of a piston; a combustion chamber ceiling wall defining a combustion chamber between the piston; and a fuel chamber attached to the combustion chamber ceiling wall to transfer fuel to the main combustion chamber. A direct injection diesel engine that has a fuel injection valve that injects fuel toward the engine and sets a premixed-gas combustion mode region that extends the ignition delay period according to operating conditions. A direct-injection diesel engine, wherein an inlet opening is formed in the fuel injection valve, and fuel spray is injected from a fuel injection valve toward an inlet of a main combustion chamber. 2. A recess formed in the main combustion chamber so as to be concave with respect to a cylindrical inlet, and a fuel spray is directed from a fuel injection valve to a recess in the main combustion chamber outside a premixed gas combustion mode region. The direct-injection diesel engine according to claim 1, wherein the direct injection is performed. 3. A side wall of the main combustion chamber is formed in a cylindrical shape continuous with an inlet portion, and a position where fuel spray from a fuel injection valve falls 7 mm from an opening edge with respect to a crown of a piston outside a premixed gas combustion mode region. The direct-injection diesel engine according to claim 1, wherein the injection is performed toward a lower side wall. 4. The direct-injection diesel engine according to claim 1, wherein a fuel injection timing is delayed until after a compression top dead center in a premixed gas combustion mode region.