JP2759375B2 - Direct injection internal combustion engine - Google Patents

Description

The present invention relates to a direct injection that includes an exhaust turbine supercharger and an intercooler, and directly injects fuel from a fuel injection valve into a combustion chamber formed on an upper wall of a piston. The present invention relates to an internal combustion engine.

(Prior Art) FIG. 11 shows a general overall structure of an internal combustion engine of this kind. The engine has an intake manifold 21 and an exhaust manifold 22 on both sides of the engine, and the exhaust manifold 22 has an exhaust turbine supercharger 24.
And a compressor unit 26 is connected to the air supply manifold 21 via an intercooler 27. Assuming that the temperature of the intake air is, for example, approximately 20 ° C., the air temperature rises to approximately 100 ° C. by being compressed by the compressor unit 26 of the supercharger 24, and is cooled to 40 ° C. to 50 ° C. by the intercooler 27, and Supplied to 21.

Conventional combustion chambers include a toroidal type as shown in FIG. 9 and a squish lip type having an inner peripheral tapered surface as shown in FIG. 10. In these combustion chambers, means for suppressing fuel spray is provided. Not been.

Also, in the conventional fuel control injection system, when the injection pressure is increased as shown in Fig. 12 by changing the injection cam shape, the fuel injection rate rises rapidly from the initial stage of injection, so that the fuel valve is opened and the injection is performed at once. The amount increases. When the fuel is burned in such a state, a large amount of fuel is atomized by the high 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 burns at once. The combustion field at this time is
Since the pressure and temperature of the compressed air are high and the oxygen concentration is the same as the standard air, the flame temperature is very high and a large amount of NOx is emitted. That is, there is a problem that the amount of NOx emission in the early stage of combustion increases.

(Object of the Invention) An object of the present invention is to improve the effect of reducing NOx generated in the early stage of combustion by reducing the supply air temperature, controlling the fuel injection rate and the injection pressure, and devising the shape of the combustion chamber. The purpose of the present invention is to improve the air-fuel mixture by increasing the fuel injection pressure and the back squish vortex, thereby improving the output performance and reducing the generation of black smoke.

(Technical Means for Achieving the Object) In order to achieve the above object, the present invention is to suppress the fuel injection rate and the fuel injection pressure in the early stage of combustion near the top dead center, increase in the middle and late stages of combustion, and increase the pressure. The fuel control injection system to be converted to an inner peripheral surface of the combustion chamber is formed into an annular tapered surface having a narrow upper end, and a rounded surface is formed at the lower end. Form an upward projection,
A rounded surface is formed on the peripheral side surface of the projecting portion to be recessed toward the center of the projecting portion, and a lower end of the rounded surface and a lower end rounded surface of the inner peripheral taper surface are connected via a planar annular bottom portion to form a bottom space for flame expansion. And a combustion chamber in which fuel is caused to collide with the inner peripheral surface of the taper at the beginning of the injection, and the injection pressure rises along with the lowering of the piston to generate a vortex in the lower space, and the air supply from the intercooler. A compressor that recompresses the air, an aftercooler that recools the air supplied from the compressor, and an air turbine that expands the air supplied from the aftercooler and supplies the expanded air to the air supply manifold and drives the compressor. And a supply air cooling system.

In order to further improve the output performance, a two-stage supercharger is provided by connecting a low-pressure stage supercharger and a pre-intercooler to the exhaust turbine supercharger.

To further improve the NOx reduction effect, an EGR device that recirculates part of the exhaust gas to the air supply is added.

(Operation) The supply air temperature is reduced as much as possible to 0 to 5 ° C. by an air supply cooling system such as an air turbine, and the injection rate and the injection rate are low in the early stage of combustion when the pressure and temperature near the top dead center are high. A small amount of spray by pressure is applied, and a part of the spray to be sprayed is applied to the inner peripheral tapered surface to suppress the temperature and amount of the local high-temperature flame around the initial spray. That is, the initial combustion is suppressed, thereby suppressing the generation of NOx.

The fuel injection pressure rises as the piston descends, and the flame flows toward the central projection while drawing a radius from the inner peripheral surface of the taper to the bottom of the plane, and expands in the space between the bottom of the plane and the radius of the projection. . At this time, the flow of the air flowing into the combustion chamber is directed in the forward direction and the forward direction after the collision of the spray by the action of the inner peripheral tapered surface and the conical surface of the central projection.

After the middle stage of combustion, high pressure injection scatters fuel on the tapered inner peripheral surface at the beginning of injection, and the flame expands rapidly due to the narrowing between the upper end of the tapered inner peripheral surface and the upper end of the central projection. And then blows out of the combustion chamber, thereby improving the exhaust color.

(Embodiment) First, the shape of a combustion chamber will be described. FIG. 1 is a cross-sectional view of a squish lip type combustion chamber of a direct injection type diesel engine to which the present invention is applied. In FIG. , The fuel injection valve 3 is fixed in a slightly inclined state, the lower end nozzle portion of the fuel injection valve 3 is located at a position slightly shifted from the center line O1 of the cylinder 4,
It faces the cylinder 4 from above.

On the upper wall of the piston 1, a disk-shaped combustion chamber 5 having a center line O2 slightly deviated from the nozzle portion of the fuel injection valve 3 toward the cylinder center is formed in an upper end opening shape. An annular inner peripheral surface 7 of the combustion chamber 5 is formed in a tapered shape so that an upper end portion side is narrowed, and a lower end portion of the tapered inner peripheral surface 7 is connected to a combustion chamber bottom wall 9 via a round surface 8. I have.

The bottom wall 9 of the combustion chamber 5 is formed in a planar shape, and a mushroom-shaped central projection 10 projecting upward from the bottom wall 9 is formed at the center of the combustion chamber 5. Top edge of
10a is formed in a gentle conical shape centered on the combustion chamber center line O2. The upper end surface 10a of the central projection 10 is the piston 1
Is formed at a position slightly lower than the upper end surface of. An annular round surface 11 is formed on the peripheral side surface of the central projection 10 so as to be recessed toward the center of the combustion chamber. The lower end of the round surface 11 is smoothly connected to the flat bottom 9, and both round surfaces 8, 11 are formed. The flat bottom 9 secures a large flame expansion bottom space S.

A plurality of nozzles are formed in the tip nozzle portion of the fuel injection valve 3, and the direction of the virtual center line A of the spray P injected from each nozzle is set so as to be substantially parallel to the upper end surface of the protrusion. Initially, the low pressure spray P is applied to the inner peripheral surface 7 of the taper.
Are to collide.

Next, the high-pressure injection rate control injection system will be described. 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, during the initial stage of injection near the top dead center, the injection rate and the injection pressure are both kept low.

In the middle stage of injection, the injection rate and the injection pressure increase, and in the latter half of the injection, the injection rate becomes high and the injection rate becomes maximum.

FIG. 7 shows an overall schematic view of a diesel engine. An intake manifold 21 and an exhaust manifold 22 are provided on both sides of an engine 20. Is connected. Turbine section
EG via a control valve 41 between 25 and the compressor section 26
An R (exhaust gas recirculation) device 42 is provided so that a small amount (for example, about 5 to 10%) of exhaust gas can be adjusted and recirculated to the supply air.

A small-sized intercooler 27 is connected to the compressor section 26 of the supercharger 24, and the intercooler 27 is connected to the air supply manifold 21 via a turbine-type air supply cooling system 30.

In the air path in the supply air cooling system 30, in order from the upstream side, a compressor unit 31 for compressing the supply air again,
An actor cooler 35 for re-cooling, an air turbine section 32 for lowering the supply air to an extremely low temperature by expansion, and an auxiliary air supply port 37 for replenishing the atmosphere from the outside are connected. The compressor section 31 and the air turbine section 32 are linked to each other via a turbine shaft 33, and the compressor section 31 is driven by the turbine section 32. The auxiliary air supply port 37 is provided with a check valve 38 that allows only the introduction of air from the outside,
When a negative pressure is caused by expansion of the supply air by the turbine section 32, the atmosphere is externally replenished.

The operation will be described. First, the flow of the supply air and its temperature change will be described with reference to FIG.
Into the compressor part 26 of the compressor 24, for example, intake air at approximately 20 ° C. is sucked from the outside, and the EG is supplied from the exhaust manifold 22 side.
A small amount of exhaust gas is sucked through the R device 42 and compressed. This compression raises the supply air temperature to approximately 100 ° C.
In the EGR device 42, carbon components in the exhaust gas are removed.

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

Next, changes in the combustion chamber will be described. In the initial stage of injection near the top dead center as shown in FIG. 1, the fuel spray P injected at a low injection pressure collides with the tapered inner peripheral surface 7,
A part of the gas adheres to the tapered inner peripheral surface 7 and the other flows along the tapered inner peripheral surface. Further, since the supply air temperature is extremely low as described above, rapid combustion is suppressed and NO
The generation amount of x decreases.

As shown in FIG. 2, when the piston descends to a crank angle of about 10 °, the fuel injection pressure rises, and the flame spreads on the tapered inner peripheral surface 7.
Draw a radius from the radius surface 8 to the flat bottom 9 from
While expanding in the bottom space (expansion chamber) S, it flows to the round surface 11 of the projection 10. A spiral flame flow is formed in the bottom space (expansion chamber) S together with the spray continuously sprayed.

As shown in FIG. 3 (around the crank angle of 20 °), after the middle stage of combustion, the fuel on the tapered inner peripheral surface attached at the initial stage of injection is scattered by high-pressure injection, and the upper end of the tapered inner peripheral surface 7 and the central projection 10 The flame expands rapidly due to the squeezed portion between the upper ends of the fuel cells and blows out of the combustion chamber 5 as a strong squish flow, so that the exhaust color is improved.

FIG. 6 is a graph showing changes in the exhaust color and the amount of generated NOx. A graph A1 shown by a solid line is a conventional example, a graph A3 shown by a dashed line is a combustion chamber of FIG. 1 according to the present invention, and a high pressure of FIG. 9 shows changes when the injection rate control injection system, the air supply cooling system and the EGR device shown in FIG. 7 are provided. A graph A2 indicated by a broken line shows a change when the EGR device is removed from the above condition of the graph A3.

(Another embodiment) (1) As shown by the phantom line in FIG. 4, the EGR device 42 may be directly bridged between the air supply manifold 21 and the exhaust manifold 22.

(2) FIG. 7 shows 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 section 5 of both turbochargers 24, 50
1 and 25 are connected via exhaust pipe 55, and compressor section 5
2, 26 comrades are connected via the pre-intercooler 53.

According to this, the pressure ratio of the air supply is increased by increasing the supercharging pressure, the expansion ratio of the air turbine unit 32 of the air supply cooling system 30 is increased, the flow rate of the cryogenic air supply is increased, and the output performance is further improved. Can be improved.

Further, a scroll switching valve 60 may be attached to the inlet of the turbine unit 51 of the low-pressure stage turbocharger 50 so that the cross-sectional area of exhaust gas flowing into the turbine unit 51 can be made variable. That is, a sensor or the like detects when the supply pressure of the supply manifold 21 is low or when the supply temperature is high, etc., and closes the exhaust pipe 55 halfway with the scroll valve 60 as shown to increase the flow rate of exhaust gas. To increase the turbine rotation to compensate for the shortage of air supply.

(3) FIG. 8 shows an example in which the two-stage supercharging method is adopted and the EGR device 42 is also attached. The EGR device 42 is a low-pressure stage turbocharger 5
Although it is attached between the turbine section 51 and the compressor section 52, it can also be provided directly between the supply manifold 21 and the exhaust manifold 22 as shown by a virtual line.

(Effects of the Invention) As described above, according to the present invention: (1) In the initial stage of injection, the injection pressure and the injection rate are suppressed low by the high-pressure injection rate control injection system, and the spray P is formed into the tapered inner peripheral surface in the combustion chamber. 7 and the combustion field is cryogenically cooled by the charge air cooling system 30, so that the initial combustion is suppressed together with the reliable ignition, thereby reducing the NOx generation.

(2) As the piston 1 descends, the fuel injection pressure increases,
The flame is rounded 8 from the tapered inner peripheral surface 7 to the flat bottom 9.
, And flows to the round surface 11 of the projection 10 while expanding in the bottom space (expansion chamber) S. A spiral flame flow is formed in the bottom space (expansion chamber) S together with the spray continuously sprayed.

After the middle stage of combustion, the fuel on the tapered inner peripheral surface 7 attached at the initial stage of the injection is scattered by the high pressure injection, and the flame is formed by the narrowed portion between the upper end of the tapered inner peripheral surface 7 and the upper end of the central projection 10. It expands rapidly and blows out of the combustion chamber 5 as a strong squish flow, so that the exhaust color is improved.

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

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

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a combustion chamber of a diesel engine to which the present invention is applied, showing an initial injection state, and FIGS. 2 and 3 sequentially show changes in the injection state with an increase in crank angle. FIG. 4 is a vertical sectional view, FIG. 4 is a general schematic view of a diesel engine, FIG. 5 is a graph showing changes in in-cylinder pressure, injection pressure, injection rate, average gas temperature and heat generation rate, and FIG. 6 is a change in NOx and exhaust color. FIG. 7 is a general schematic view of a diesel engine employing a two-stage supercharging system, and FIG.
9 and 10 are vertical cross-sectional schematic views of a conventional combustion chamber, FIG. 11 is a general schematic view of a conventional diesel engine, and FIG. 12 is a conventional fuel control system. It is a graph of injection pressure and injection rate by an injection system. 1
...... Piston, 2 ... Cylinder head, 3 ... Fuel injection valve, 4 ... Cylinder, 5 ... Combustion chamber, 7 ... Taper inner peripheral surface, 8 ... R surface, 9 ... Planar bottom portion, 10 …… Central protrusion, 11 …… Round surface, 24 …… Exhaust turbine supercharger,
27 ... Intercooler, 30 ... Air supply cooling system, 31 ...
… Aftercooler, 32 …… Inflation air turbine, 42 ……
EGR device, 50 …… Low pressure supercharger, 53 …… Pre-intercooler

──────────────────────────────────────────────────の Continuation of front page (51) Int.Cl. ⁶ Identification code FI F02D 43/00 301 F02D 43/00 301G F02M 25/07 570 F02M 25/07 570D 570P (72) Inventor Shigeru Yoshikawa Osaka-shi, Osaka 1-32 Chayama-cho, Kita-ku Inside Yanmar Diesel Co., Ltd. (56) References JP-A-57-108424 (JP, A) JP-A-49-93717 (JP, A) JP-A-3-87928 (JP, A) U) Japanese Utility Model Showa 61-155636 (JP, U)

Claims (3)

(57) [Claims] A direct injection type internal combustion engine having an exhaust turbine supercharger and an intercooler, wherein fuel is directly injected from a fuel injection valve into a combustion chamber formed on an upper wall of a piston. A high-pressure injection rate control injection system that suppresses at the early stage of combustion near the top dead center and increases and increases the pressure in the middle and late stages of combustion, and the inner peripheral surface of the combustion chamber is formed as an annular tapered surface with a narrow upper end. A rounded surface is formed at a lower end, an upper end surface forms a conical upward protruding portion at a central portion of the combustion chamber, and a rounded surface is formed on a peripheral side surface of the protruding portion so as to be recessed toward the center of the protruding portion. By connecting the lower end of the inner peripheral taper surface and the lower end round surface of the inner peripheral taper surface through a planar annular bottom portion, a flame expansion bottom space portion is secured, and fuel is caused to collide with the taper inner peripheral surface at the beginning of injection. Injection pressure rises with piston down A combustion chamber for generating a vortex in the lower end space, a compressor section for compressing the air supply from the intercooler again, an aftercooler for cooling the air supply from the compressor section again, and a supply from the aftercooler. A direct-injection type internal combustion engine, comprising: a supply air cooling system including an air turbine unit that expands air and supplies the air to an intake manifold and drives the compressor unit. 2. A direct injection type internal combustion engine according to claim 1, wherein a low pressure stage supercharger and a pre-intercooler are connected to the exhaust turbine supercharger to perform two-stage supercharging. Type internal combustion engine. 3. The direct injection type internal combustion engine according to claim 1, further comprising an EGR device for recirculating a part of exhaust gas to supply air.