JPH0431651A - 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 the conical part of fuel spray injected from a fuel injection valve 3 flows along a conical surface while injection pressure and injection rate are restrained low at an injection initial stage and so that a combustion field is kept at a very low temperature, too. CONSTITUTION:A conical part 10 of a gently inclined angle is formed on the bottom part of a combustion chamber 5 of an upper edge open type formed on the upper wall of a piston 1. Additionally, a high pressure injection rate control injection system is set to start fuel injection a little before a top dead center and to restrain injection rate and injection pressure low during an injection initial period near the top dead center. Furthermore, an intercooler 27 connected to a compressor unit 26 of a supercharger 24 is connected to a supply air manifold 21 through a supply air cooling system 30, and after recompressing supercharged air in a compressor unit 31, supply air is lowered down to 0 - 5 deg.C simultaneously when the supply air pressure is lowered by expanding it by an air turbine unit 32.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is equipped with an exhaust turbine supercharger and an intercooler, and injects fuel directly from a fuel injection valve into a shallow combustion chamber formed on the upper wall of a piston. Relating to direct injection internal combustion engines.

(Prior Art) Fig. 12 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 a turbine of an exhaust turbine supercharger 24 in the exhaust manifold 22. section 25 and 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 10
The temperature rises to 0° C., is cooled to 40° C. to 50° C. by the intercooler 27, and is supplied to the air supply manifold 21.

In conventional fuel control injection systems, when the injection pressure is increased by changing the shape of the injection cam as shown in Figure 13, the fuel injection rate increases rapidly from the initial stage of injection, so the amount of injection increases at once as soon as the fuel valve opens. increases.

9 to 11 show a conventional shallow-bottomed combustion chamber, which has a gentle conical portion 10 at the bottom of the combustion chamber 5, facing the fuel injection valve 3 above. Assuming that the top dead center is at a crank angle of 0°, Figure 9 shows the early stage of injection at a crank angle of 2'', Figure 10 shows the early stage of combustion at a crank angle of 6°, and Figure 11 shows the late stage of injection (middle stage of combustion) at a crank angle of 23''. ing.

In the conventional combustion chamber 5, the apex angle θC of the conical portion 10 and the fuel injection angle θN are set to be approximately the same, and the reach distance L2 of the spray center line A from the initial stage of injection in FIG. It is a space jet that cannot be touched. The reach distance of the spray center line A hardly changes regardless of the displacement of the piston 1, as shown by L7 in FIG. 10 and L23 in FIG. 11.

As shown in FIG. 10, when combustion is in a so-called space injection state and the injection pressure is high at the beginning of combustion, a large amount of air flows into the spray P, and at the time of ignition, a large amount of fuel mixed with air is combusted at once. In the combustion field at this time, the pressure and temperature of the compressed air are high and the oxygen concentration is the same as standard air, so the flame temperature is very high and a large amount of NOx is emitted. That is, a problem arises in that a large amount of NOx is emitted at the initial stage of combustion.

(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. Then, improve the mixture formation by increasing the fuel injection pressure, etc.
The objective is 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. A fuel control injection system that forms a conical part at the bottom of the combustion chamber with a gently sloped surface that gradually becomes lower as it goes radially outward from the center of the combustion chamber, and a fuel injection system that is located above the conical part. By making the fuel injection angle of the valve smaller than the apex angle of the conical part, the entire spray area comes into contact with the conical surface and flows along the conical surface at the beginning of injection, and as the piston descends, the spray reach distance gradually increases. , from the middle stage onward, the spray area moves away from the conical surface and high-pressure injection is performed.A shallow-bottomed combustion chamber, a compressor section that recompresses the air supplied from the intercooler, and a re-cooling of the air supplied from the compressor. The present invention is characterized by comprising an aftercooler that expands and supplies air from the aftercooler to an air supply manifold, and an air supply cooling system that includes an air turbine section that drives the compressor section.

In addition, in order to further improve output performance, a low pressure stage supercharger and brain cooler are connected to the exhaust turbine supercharger.
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. In addition to performing a small amount of injection using pressure, the spray injected from the fuel injection valve comes into contact with the conical part and partially adheres to the conical surface.
Others flow along the conical surface. This reduces the amount of air flowing into the spray, suppressing the local high temperature flame temperature and volume around the initial spray. In other words, it suppresses initial combustion, thereby reducing NOx
suppresses the generation of

After that, the injection rate and injection pressure gradually increase in synchronization with the downward displacement (pressure drop) of the piston, and at the same time, the reach distance of the spray becomes longer, the spray moves away from the cone, the adhering spray decreases, and the high pressure causes This increases the amount of incoming air and promotes combustion.

Further, at this time, the fuel attached during the initial stage of combustion evaporates and flows into the spray at the latter stage along with air. This improves air-fuel mixture formation and suppresses the generation of black smoke.

(Example) First, to explain the shape of the combustion chamber, Figs. 1 to 3 show cross-sectional views of the shallow-bottomed combustion chamber of a direct injection diesel engine to which the present invention is applied, and the top dead center is As the angle O'', Fig. 1 shows the initial state of injection at a crank angle of about 2°, Fig. 2 shows the initial stage of combustion at a crank angle of about 6°, and Fig. 3 shows the middle stage of combustion (late injection) at a crank angle of about 23°. It shows.

In FIG. 1, a fuel injection valve 3 is fixed to the cylinder head 2 in a slightly inclined state, and the lower end nozzle portion of the fuel injection valve 3 is located at a position slightly offset from the center line 01 of the cylinder 4. It faces into the cylinder 4 from above.

The earth wall of the piston 1 has a center line 02 at a position slightly shifted toward the cylinder center 01 from the nozzle portion of the fuel injection valve 3.
A shallow disk-shaped combustion chamber 5 with a center at the bottom is formed with an open top end. The inner circumferential surface 7 of the combustion chamber 5 is formed into a gentle arc shape.

A conical part 10 is formed at the bottom of the combustion chamber 5 and has a gentle slope that gradually decreases as it goes radially outward from the combustion chamber center line 02, and the apex of the conical part 10 is higher than the piston top wall surface. It is located low.

A plurality of nozzles are formed in the tip nozzle portion of the fuel injection valve 3, and the injection angle θN between the virtual center lines A of the spray P injected from each nozzle is determined based on the relationship with the electric point angle θC of the conical portion 10. It is set as follows.

At the initial stage of injection as shown in FIG. Reach distance L2 (e.g. 5-30+om < lei)
The fuel injection angle θN and the angle θC of the conical portion 10 are set so that
is related to.

Next, the high-pressure injection rate control injection system will be explained. The injection rate and injection pressure are set as shown in FIG. 5 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 pressure is set so that it increases from the middle of injection, reaches the maximum injection pressure in the latter half of injection (2), and then decreases rapidly. ■ to ■ in FIG. 5 correspond to the states shown in FIGS. 1 to 3. FIG. 4 shows an overall schematic diagram of a diesel engine.
A turbine section 24 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 24 and the compressor section 26 via a regulating valve 41 to regulate a small amount (for example, about 5 to 10%) of exhaust gas and 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 when the air supply becomes negative or positive due to the expansion of the air supply by the turbine section 32, atmospheric air is replenished from the outside.

Explain the operation. In Fig. 4, the flow of supply air and its temperature change will be explained first.
For example, about 2 compressor parts 26 are connected to the compressor part 26 from the outside.
While the intake air at 0°C is sucked in, the exhaust manifold 22
A small amount of exhaust gas is sucked in from the side via the EGR device 42 and compressed. Due to this compression, the supply air temperature is approximately 100
rises to ℃. Furthermore, within the EGR device 42, carbon components in the exhaust gas are removed.

The supply air 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 the temperature rises to approximately 100.degree. C., or is cooled to approximately 40.degree. C. in the aftercooler 35, and then expanded in the air turbine section 32. As a result, the supply air pressure is lowered, and at the same time, the supply air temperature is lowered to an extremely low temperature (0 to 5° C.), and the supply air is supplied to the intake manifold 21.

Next, changes in the combustion chamber will be explained. At the initial stage of injection, all of the spray P hits the conical part 10 as shown in FIG.
A portion attaches to the cone 10 and the rest flows outward along the cone 10. At this time, air flows into the spray only from the upper side of the spray, and the amount of air flowing in is suppressed.

In the early stage of combustion in Fig. 2, the spray reach L7 is longer than the reach #ItL2 in Fig. 1, and the amount of air inflow increases slightly, but the injection rate and injection pressure are suppressed to low values, and the spray P is still in contact with the conical part 10 in its entirety, and as in FIG. 1 only flows into the spray from the upper side, so the amount of incoming air is suppressed, and as mentioned above, the supply air cooling system 30, the supply air temperature in the field is reduced as much as possible, so that rapid combustion at the initial stage of combustion is suppressed, and the amount of NOx emitted is reduced.

As the piston moves further down, the latter stage of injection (middle stage of combustion) shown in Figure 3.
, the reach distance L23 of the spray P becomes longer and the spray P
[conical part] 0, the adhering spray decreases, becomes an aerial jet due to high pressure, the amount of incoming air increases, and it is blown out into the gap 11 between the piston 1 and the cylinder head 2 along the arcuate inner circumferential surface 7. , combustion is promoted.

Further, at this time, the fuel attached during the initial stage of combustion evaporates and flows into the spray at the latter stage along with air. These improve air-fuel mixture formation and suppress the generation of black smoke.

FIG. 6 is a graph showing changes in exhaust color and NOx generation amount. Graph Al shown by a solid line is the conventional example, graph A3 shown by a dashed-dotted line is the combustion chamber of FIG. 1 according to the present invention, and 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. 4 are provided. Graph A2 indicated by a broken line shows the change when the EGR device is removed from the above conditions of graph A3.

(Another Embodiment) (1) A structure may be adopted in which the EGR device 42 is directly passed between the air supply manifold 21 and the exhaust manifold 22 as shown by the imaginary line in FIG.

(2) FIG. 7 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 exhaust pipes 55, compressor sections 52.26 and pre-intercooler 53
are connected via.

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-closed 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 8 shows that a two-stage supercharging system is adopted and at the same time EGR
This is an example in which a device 42 is also attached. The EGR device 42 is installed between the turbine section 51 and the compressor section 52 of the low-pressure supercharger 50.
A structure in which the device 42 is directly placed between the air supply manifold 21 and the exhaust manifold 22 may be used.

(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 the spray injected from the fuel injection valve 3 P comes into contact with the conical part 10, with some of it adhering to the conical surface and the other flowing along the conical surface, and the combustion field is kept at a cryogenic temperature by the air supply cooling system 30. Therefore, the amount of air flowing into the spray is reduced, and the initial combustion is suppressed, thereby reducing the amount of NOx produced.

(2) As the piston 1 descends, the reach of the spray P becomes longer, the spray P separates from the conical part 10, and the adhering spray decreases, and then becomes aerial injection due to high pressure, and the amount of incoming air increases, resulting in combustion. is promoted.

These improve air-fuel mixture formation and suppress the generation of black smoke.

(3) By adding a low-pressure stage supercharger 50 to the exhaust turbine supercharger 24 to achieve two-stage supercharging, the compression 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 cross-sectional view of the combustion chamber of a day cell engine to which the present invention is applied, showing the initial state of injection, FIG. 2 is a longitudinal cross-sectional view of the combustion chamber showing the initial combustion state, and FIG. is late injection (
Fig. 4 is a schematic diagram of the entire diesel engine; Fig. 5 is a graph showing changes in cylinder pressure, injection pressure, injection rate, average gas temperature, and heat release rate; Fig. 6 is a graph showing changes in NOx and exhaust color, and Figure 7 is an overall schematic diagram of a diesel engine that uses a two-stage supercharging system.
Fig. 8 is an overall schematic diagram of a diesel engine that employs a two-stage supercharging system and an EGR device, and Figs. FIG. 12 is an overall schematic diagram of a conventional diesel engine, and FIG. 13 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, 10
... Conical part, 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, 5
3... Pre-intercooler patent applicant Yanmar Diesel Co., Ltd. Display of the case 1990 Patent Application No. 1347542, Name of the invention Direct injection internal combustion engine3, Person making the amendment Relationship to the case Patent applicant address 1-32 Chayamachi, Kita-ku, Osaka Name ( 678) Yanmar Diesel Co., Ltd. Representative Representative Director Atsushi Yamaoka 4, Agent address 7th floor, East Building, Chiyoda Building, 2-9-4 Higashitenma, Kita-ku, Osaka (Koma 530) (1) First attached to the application form Print the drawing as shown on the attached sheet (no changes to the content). 8. Inventory drawings of attached documents (all drawings) At least 1 copy each 5. Date of amendment order (dispatch) August 28, 1990 6. Subject of amendment Drawings

Claims (3)

[Claims] (1) Equipped with an exhaust turbine supercharger and an intercooler,
In a direct injection internal combustion engine that injects fuel directly from a fuel injection valve into a shallow-bottomed 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 during the middle stage of combustion. , a high-pressure injection rate control injection system that increases pressure in the later stage, and a conical part with a gently sloped surface that gradually becomes lower as it goes radially outward from the center of the combustion chamber at the bottom of the combustion chamber. By making the fuel injection angle of the fuel injection valve located above the conical part smaller than the apex angle of the conical part, at the beginning of injection, the entire spray area comes into contact with the conical surface and flows along the conical surface, causing the piston to A shallow combustion chamber in which the spray reach distance gradually increases as it descends, and the spray region moves away from the conical surface in the middle and later stages for high-pressure injection; a compressor section that recompresses the air supplied from the intercooler; A supply air cooling system comprising an aftercooler that cools the supply air from the compressor section again, and an air turbine section that expands the supply air from the aftercooler and supplies it to the supply manifold, and also drives the compressor section. A direct 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.