JPH0431650A - Direct injection type internal combustion engine - Google Patents

Abstract

PURPOSE:To decrease generation amount of NOx by devising the internal combustion engine so that a part of fuel spray is caught on a central projection part while injection pressure and injection rate are restrained low at an injection initial stage and to that a combustion field is kept at a very low temperature. CONSTITUTION:A central projection part 10 projected upward from a bottom wall 5a part is formed in the central part of a combustion chamber 5 of an upper end open type formed on the upper wall of a piston 1. Additionally, a high pressure injection rate control injection system is set to start injecting fuel slightly before a top dead center and to restrain injection rate and injection pressure low during an injection initial stage near the top dead center together. Furthermore, an intercooler 27 connected to a compressor unit 26 of a supercharger 24 is connected to a supply air manifold 21, and supercharged air is cooled down by an aftercooler 35 after it is recompressed by a compressor unit 31, and it is lowered down to 0 - 5 deg.C simultaneously while supply air pressure is lower by expanding it at an air turbine unit 32.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a direct injection system that includes an exhaust turbine supercharger and an intercooler, and injects fuel directly from a fuel injection valve into a combustion chamber formed on an upper wall of a piston. Regarding internal combustion engines.

(Prior Art) FIG. 20 shows the general overall structure of this type of internal combustion engine, which includes an intake manifold 21 and an exhaust manifold 22 on both sides of the engine, and an exhaust turbine supercharger 24 connected to the exhaust manifold 22. The turbine section 25 is connected to the compressor section 2.
6 is connected to the air supply manifold 21 via an intercooler 27.

If the temperature of the intake air is, for example, approximately 20°C, the supercharger 2
By being compressed by the compressor section 26 of 4, approximately ゛1
00℃ and 40℃~50℃ at intercooler 27
The air is cooled down and supplied to the air supply manifold 21.

Conventional combustion chambers include a toroidal type as shown in Figure 17, a shallow dish type as shown in Figure 18, and a squish lip type with a tapered inner surface as shown in Figure 19. No measures were taken to suppress fuel spray.

In addition, in conventional fuel control injection systems, when the injection pressure is increased by changing the injection cam shape as shown in Figure 21, the fuel injection rate increases rapidly from the initial stage of injection, so the injection is performed all at once as soon as the fuel valve opens. The amount increases. When the fuel is combusted in such a state, a large amount of fuel is atomized by increasing the pressure during the ignition delay period after the start of fuel injection, and at the time of ignition, the fuel mixed with a large amount of air is combusted all at once. During this combustion,
The pressure and temperature of compressed air are high, and the oxygen concentration is the same as standard air, so the flame temperature is extremely high and NOx
is emitted in large quantities. That is, a problem arises in that the amount of NOx emitted during the initial stage of fueling increases.

(Objective of the Invention) The object of the present invention is to improve the effect of reducing NOx generated in the early stage of combustion by reducing the intake air temperature, controlling the fuel injection rate and injection pressure, and devising the shape of the combustion chamber. The goal is to improve the mixture formation by increasing the fuel injection pressure and creating a back squish vortex to improve output performance and reduce the generation of black smoke.

(Technical Means for Achieving the Object) In order to achieve the above object, the present invention suppresses the fuel injection rate and fuel injection pressure at the early stage of combustion near top dead center, and increases at the middle and late stages of combustion, resulting in high pressure. The inner peripheral surface of the combustion chamber is formed into an annular tapered surface that narrows at the upper end, and a central protrusion that protrudes upward is formed in the center of the combustion chamber, and the protrusion The upper end surface of is formed into a generally conical shape,
The relationship between the fuel injection angle of the fuel injector located above the protrusion and the upper end surface of the protrusion is as follows: At the beginning of injection, part of the spray area comes into contact with the upper end surface of the protrusion, and after the middle stage of combustion, the piston descends. A combustion chamber that is set so that the entire spray area is injected away from the protrusion toward the tapered inner circumferential surface, a compressor section that recompresses the air supplied from the intercooler, and a compressor section that recompresses the air supplied from the compressor. The present invention is characterized by comprising an aftercooler for cooling, and an air supply cooling system that expands the air supply from the aftercooler and supplies it to the air supply manifold, and also includes an air turbine section that drives the compressor section.

In order to further improve output performance, a low-pressure stage supercharger and pre-intercooler are connected to the exhaust turbine supercharger to provide two-stage supercharging.

Additionally, in order to further improve the NOx reduction effect, an EGR device is added that recirculates a portion of the exhaust gas to the supply air.

(Operation) The supply air temperature is kept as low as possible to 0 to 5 degrees Celsius by the supply air cooling system using an air turbine, etc., and low injection rate and low injection are applied at the beginning of combustion when the pressure and temperature near top dead center are high. By performing a small amount of pressure injection and suppressing a portion of the injected spray by catching it on the central protrusion of the combustion chamber, the local high temperature flame temperature and amount around the initial spray are suppressed.

That is, the initial combustion is suppressed, thereby suppressing the generation of NOx.

During the subsequent middle stage of combustion, the piston descends (pressure drop)
The injection rate and injection pressure are gradually increased in synchronization with the combustion chamber, and the spray is grown while matching the shape of the combustion chamber. That is, as the injection rate increases, the spray region moves away from the central protrusion, and the distance from the fuel injection valve to the inner peripheral surface of the combustion chamber becomes longer, so that the spray combustion region expands.

High-pressure injection is applied to the injection path, and the characteristics of the spray due to high-pressure injection (extended spray reach, atomization, etc.) are fully demonstrated, and combustion is controlled in proportion to the injection (maintaining super NOx combustion).
In the later stages of combustion, when the field pressure has further decreased,
Combustion is rapidly completed due to the back squish disturbance caused by almost all of the high-pressure spray hitting the inner peripheral surface of the taper.

In other words, the mixture is better formed and the generation of black smoke is suppressed.

Incidentally, the fuel accumulated on the upper end surface of the protrusion at the early stage of the combustion described above gradually evaporates and burns.

(Example) First, to explain the shape of the combustion chamber, FIG. 1 shows a sectional view of a squish lip type combustion chamber of a direct injection diesel engine to which the present invention is applied. is fixed in a slightly inclined state, and the lower end nozzle portion of the fuel injection valve 3 is located at a position slightly shifted from the center line 01 of the cylinder 4 and faces into the cylinder 4 from above.

A disk-shaped combustion chamber 5 is formed in the upper wall of the piston 1 and has an open upper end, the combustion chamber 5 being centered on a center line 02 at the same position as the nozzle portion of the fuel injection valve 3 . The annular inner circumferential surface 7 of the combustion chamber 5 is tapered so that the upper end side becomes narrower, and the lower end portion of the tapered inner circumferential surface 7 is an arcuate portion 7a.
It is connected to the combustion chamber bottom wall 5a via.

A cylindrical central projection 10 is formed in the center of the combustion chamber 5 and projects upward from the bottom wall 5a.
The upper end surface 10a of the combustion chamber 0 is formed into a gentle conical shape centered on the combustion chamber centerline 02. The upper end surface 10a of the central protrusion 10 is formed at a position slightly lower than the upper end surface of the piston 1.

The periphery of the lower end of the central protrusion 10 is connected to the combustion chamber bottom wall 5a via an arcuate portion 10c.

A plurality of nozzles are formed in the tip nozzle portion of the fuel injection valve 3 , and the injection angle α between the virtual centerline A of the spray P injected from each nozzle and the combustion chamber centerline 02 is equal to the angle α between the central projection 10 and the combustion chamber centerline 02 . The settings are as follows.

At the initial stage of injection shown in FIG. 1, approximately 50% of the spray P contacts the upper end surface 10a of the central protrusion 10, and at the middle stage of injection, as shown in FIG.
It is set so that the spray P deviates substantially completely from 0a and comes into contact with the tapered inner circumferential surface 7. Incidentally, in FIG. 1, the virtual center line A passes through the outer peripheral edge of the upper end surface 10a of the central protrusion 10.

In FIG. 6, on the upper end surface 10a of the central protrusion 10,
A plurality of concentric annular grooves 12 of different diameters are formed to control the amount of fuel deposited.

The cross-sectional shape of the annular groove 12 is formed into a wedge shape that gradually becomes deeper as it goes radially outward from the center line 02.

Next, the high-pressure injection rate control injection system will be explained. The injection rate and injection pressure are set as shown in FIG. 8 by changing the height and shape of the cam surface of the injection cam. That is, fuel injection is started slightly before top dead center (TDC), and both the injection rate and injection pressure are kept low during the initial injection period near top dead center.

The injection rate and injection pressure increase in the middle stage of injection, and in the late stage of injection, the injection pressure reaches a high level and the injection rate reaches its maximum, and then rapidly decreases. Note that ■ to ■ in FIG. 8 correspond to the states in FIGS. 1 to 5, respectively.

FIG. 7 shows an overall schematic diagram of a diesel engine, with an intake manifold 21 and an exhaust manifold 22 on both sides of the engine 20.
A turbine section 25 of a high pressure ratio exhaust turbine supercharger 24 is connected to the exhaust manifold 22 .

An EGR (exhaust gas recirculation) device 42 is provided between the turbine section 25 and the compressor section 26 via a control valve 41, and controls a small amount (for example, about 5 to 10%) of exhaust gas to recirculate the air supply. It is now possible to do so.

A small intercooler 27 is connected to the compressor section 26 of the supercharger 24, and the intercooler 27 is connected to the air supply manifold 2 through a turbine type air supply cooling system 30.
Connected to 1.

In the air path in the supply air cooling system 30, in order from the upstream side, there is a compressor section 31 for recompressing the supply air, an aftercooler 35 for cooling the supply air again, and a compressor section 35 for cooling the supply air again, and lowering the supply air to an extremely low temperature by expansion. an air turbine section 32 for
An auxiliary air supply port 37 is connected to which air can be replenished from the outside. The compressor section 31 and the air turbine section 32 are interlocked and connected via a turbine shaft 33.
The compressor section 31 is driven by this. The auxiliary air supply port 37 is provided with a check valve 38 that only allows atmospheric air to be introduced from the outside, and is replenished with atmospheric air from the outside when the pressure becomes negative due to the expansion of the air supply by the turbine section 32.

Explain the operation. In FIG. 7, the flow of supply air and its temperature change will be explained first.
For example, approximately 20
℃ intake air is sucked in, and a small amount of exhaust gas is sucked in from the exhaust manifold 22 side via the EGR device 42 and compressed. Due to this compression, the supply air temperature is approximately 100℃
rise to Furthermore, within the EGR device 42, carbon components in the exhaust gas are removed.

The air supply compressed by the compressor section 26 is
After being cooled to 40-50°C, the supply air cooling system 30
to go into. In the supply air cooling system 30, the air is first recompressed in the compressor section 31 and its temperature rises to approximately 100.degree. C., but is cooled to approximately 40.degree. C. in the aftercooler 35 and expanded in the air turbine section 32. As a result, the supply air pressure decreases, and at the same time, the supply air temperature decreases to an extremely low temperature (0 to 5° C.) and is supplied to the supply air manifold 21.

Next, changes in the combustion chamber will be explained. At the start of injection, the injection rate and pressure are suppressed to low values,
Further, as shown in FIG. 1, approximately 50% of the spray P is directly injected into the combustion chamber 5, but the remaining 50% comes into contact with the upper end surface 10a of the protrusion 10 and is suppressed.

A part of it slides into the combustion chamber 5, but the rest accumulates in the annular structure 12 on the upper end surface 10a.

Therefore, the injection amount and air inflow amount are kept low, and as mentioned above, the pressure and temperature of the field are reduced as much as possible by the charge air cooling system 30, so rapid combustion in the early stage of combustion is suppressed, and NOx is generated. can be suppressed.

As the piston 1 descends, the projection 10 moves away from the fuel injection valve 3 as shown in FIG.
The proportion of the spray P that comes into contact with the projection 0a decreases, and almost all of the spray P comes off the upper end surface 10a of the protrusion 10 in the middle of the injection period as shown in FIG. In synchrony with this, the injection rate and injection pressure are increased by the control injection system, so that the spray area expands and the spray length also increases, causing the spray area to grow and hit the tapered inner circumferential surface 7 of the combustion chamber 5. come into contact with

In the latter half of the injection, with the maximum high-pressure injection, a back squish flow S is formed as shown in FIG. 4, the amount of air inflow increases, the flame spreads, and combustion is promoted. On the other hand, the protrusion 10
The fuel accumulated in the groove 12 evaporates and burns together with the flame of the back squish flow S.

Furthermore, in the later stages of combustion when the pressure has further decreased, a portion of the spray P is also directly supplied between the piston 1 and the cylinder head 2, as shown in FIG.

FIG. 9 is a graph showing changes in exhaust color and NOx generation amount. Graph AI shown by a solid line is the conventional example, graph A3 shown by a dashed-dotted line is the combustion chamber of FIG. It shows changes in the case where the high-pressure injection rate control injection system and the supply air cooling system and EGR device of FIG. 7 are provided. Further, graph A2 indicated by a broken line shows a change when the EGR device is removed from the above conditions of graph A3.

(Another Embodiment) (1) As shown by the imaginary line in FIG. 7, the EGR device 42 may be directly placed between the air supply manifold 21 and the exhaust manifold 22.

(2) FIG. 10 is an example in which the two-stage supercharging method according to claim 2 is applied, in which a low-pressure stage supercharger 50 is added to the high-pressure stage exhaust turbine supercharger 24. Turbine sections 51.25 of both superchargers 24.50 are connected via an exhaust pipe 55,
Compressor section 52.26 comrade is pre-intercooler 5
It is connected via 3.

According to this, increasing the boost pressure increases the pressure ratio of the supply air,
The expansion ratio of the air turbine section 32 of the charge air cooling system 30 can be increased to increase the flow rate of cryogenic charge air and further improve output performance.

Further, by attaching a scroll switching valve 60 to the inlet of the turbine section 51 of the low-pressure stage supercharger 50, the flow cross-sectional area of the exhaust gas entering the turbine section 51 can be made variable. That is, by detecting with a sensor etc. when the supply pressure of the supply air manifold 21 is low or when the supply air temperature is high, etc., the exhaust pipe 55 is half-filled with the scroll valve 60 as shown in the figure.
Increases the flow rate of the exhaust gas and increases the rotation of the turbine to compensate for the lack of air supply.

(3) Figure 11 shows the adoption of the two-stage supercharging system and the EG
This is an example in which an R device 42 is also attached. The EGR device 42 includes a turbine section 51 and a compressor section 52 of a low-pressure supercharger 50.
Although it is installed between the air supply manifold 21 and the exhaust manifold 22 as shown in phantom, it is also possible to install it directly between the air supply manifold 21 and the exhaust manifold 22.

(4) FIG. 12 shows a modification of the combustion chamber, which has a structure in which an annular constriction 15 is formed in the central protrusion 10. The peripheral wall of the central protrusion 10 is constricted in a curved manner so that the outer diameter is the minimum near the upper part.

According to this structure, by efficiently heating the upper end surface 10a of the protrusion 10 by the flame of the back squish flow S, the evaporation of the accumulated fuel is promoted, carbon deposition is prevented, and the evaporated spray Q is converted into the back squish flow. Since it can be placed well and combusted, combustion is promoted.

(5) FIG. 13 shows a structure in which an annular constriction 15 is formed on the peripheral wall of the central protrusion 10 as in FIG. There is.

(6) FIG. 14 shows a circumferential groove 1 on the upper end surface 10a of the protrusion 10.
2 and radial grooves 13 are formed.

(7) FIG. 15 shows an example in which a large number of depressions 17 are formed in the upper end surface 10a of the protrusion 10.

(8) FIG. 16 shows an example in which a large number of wart-like protrusions 18 are formed on the upper end surface 10a of the protrusion 10.

(Effects of the Invention) As explained above, according to the present invention: (1) In the early stage of injection, the injection pressure and injection rate are kept low by the high-pressure injection rate control injection system, and a part of the spray P is Since it is caught on the central protrusion 1°, and the combustion field is kept at an extremely low temperature by the air supply cooling system 30, initial combustion is suppressed along with reliable stone fire, thereby producing nitrogen.

The amount of X produced can be reduced.

(2) As the piston 1 descends, the spray P is transferred to the central protrusion 1.
0, and as the injection pressure and injection rate increase, the distance from the fuel injector 3 to the combustion chamber circumferential surface 7 becomes longer, and after the middle of combustion, almost all of the high-pressure spray hits the tapered inner circumferential surface 7. As a result, a back squish vortex is formed, which improves air-fuel mixture formation, leading to rapid combustion and completion of combustion. Therefore, the output is improved and at the same time, the generation of black smoke is suppressed.

(3) By adding the low-pressure stage supercharger 50 to the exhaust turbine supercharger 24 to achieve two-stage supercharging, the pressure ratio of the charge air is increased by increasing the supercharging pressure, and the air in the charge air cooling system 30 is The expansion ratio of the turbine section 32 can be increased. Therefore, the flow rate of the cryogenic supply air can be increased, and the output performance can be further improved.

(4) By adding an EGR device, the oxygen concentration can be lowered and combustion can be slowed down, so the amount of NOx generated can be further reduced.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of the combustion chamber of a diesel engine to which the present invention is applied, showing the state at the start of combustion, and FIGS.
The figure is a vertical cross-sectional view showing sequential changes in the injection state from the start of fuel to the late stage of combustion in Figure 1 above, Figure 6 is a perspective view of the central protrusion in Figure 1, and Figure 7 is the entire diesel engine. Schematic diagram,
Figure 8 is a graph showing changes in cylinder pressure, injection pressure, injection rate, average gas temperature, and heat release rate. Figure 9 is a graph showing changes in NOx and exhaust color. Figure 10 is a graph showing two-stage supercharging. Figure 11 is an overall schematic diagram of a diesel engine that employs a two-stage supercharging system and an EGR system, and Figures 12 and 13 are cross-sectional views showing modified examples of the central protrusion, respectively. , FIGS. 14 to 16 are perspective views showing modified examples of the upper end surface of the central protrusion, FIGS. 17 to 19 are schematic vertical cross-sectional views of the conventional example, and FIG. 20 is an overall schematic diagram of the conventional diesel engine. , FIG. 21 is a graph of injection pressure and injection rate by a conventional fuel control injection system. 1... Piston,
2... Cylinder head, 3... Fuel injection valve, 4...
・Cylinder, 5... Combustion chamber, 7... Tapered inner peripheral surface, 10... Center protrusion, 10a... Upper end surface, 24...
...Exhaust turbine supercharger, 27...Intercooler,
30... Supply air cooling system, 31... Aftercooler, 32... Expansion air turbine, 42... EGR
Device, 50...Low pressure stage supercharger, 53...Pre-intercooler patent applicant Yanmar Diesel Co., Ltd. No. 4
Figure 6: Joji on side yA (no change in content) EGR device Jυ Utsukurei! p cis rotation TDC → 7 rank M cliff top pressure Tanlong Fig. 7 Fuel consumption Fig. 12 Fig. 13 Fig. 1-+ Fig. 17 Fig. 1'? Figure 18■nσcho2＼gu〉Evening 7

Claims (3)

[Claims] (1) Equipped with an exhaust turbine supercharger and an intercooler,
In a direct injection internal combustion engine, in which fuel is injected directly from a fuel injection valve into a combustion chamber formed on the upper wall of the piston, the fuel injection rate and fuel injection pressure are suppressed at the early stage of combustion near top dead center, and at the middle and late stages of combustion. A high-pressure injection rate control injection system that increases pressure and increases the pressure, an annular tapered inner surface of the combustion chamber that narrows at the upper end, and a central protrusion that protrudes upward in the center of the combustion chamber. forming the upper end surface of the protrusion into a generally conical shape;
The relationship between the fuel injection angle of the fuel injector located above the protrusion and the upper end surface of the protrusion is as follows: At the early stage of combustion, part of the spray area comes into contact with the upper end surface of the protrusion, and after the middle stage of combustion, the piston descends. A combustion chamber configured so that the entire spray area is injected away from the protrusion toward the tapered inner peripheral surface, a compressor section that recompresses the air supplied from the intercooler, and a compressor section that compresses the air supplied from the compressor again. A direct cooling system characterized by comprising an aftercooler for re-cooling, and an air supply cooling system comprising an air turbine section that expands and supplies the supply air from the aftercooler to the supply air manifold and drives the compressor section. Injection internal combustion engine. (2) The direct injection internal combustion engine according to claim 1, characterized in that the exhaust turbine supercharger is connected to a low pressure stage supercharger and a pre-intercooler to provide two-stage supercharging. institution. (3) The direct injection internal combustion engine according to claim 1, further comprising an EGR device that recirculates part of the exhaust gas to air supply.