JP2001280140A - Direct injection-type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce both of NOx and soot. SOLUTION: In this direct injection-type internal combustion engine where the fuel is injected to a combustion chamber 1 from a central part of a ceiling face opposite to a top face of a piston toward a circumferential part of a cavity 9 of a central part of the piston top face, the combustion chamber 1 is provided with the intake free from the circulated exhaust or the intake 11 of low concentration of the circulated exhaust, and the intake containing the circulated exhaust or the intake 12 of high concentration of circulated exhaust in an inner region and an outer region of an approximately hemispherical face or an approximately flat hemispherical face 13 around a fuel injecting position in starting of the fuel combustion near a final period of the compressing stroke. The intake containing the circulated exhaust or the intake of high concentration of the circulated exhaust is located in the inner region and the intake free from the circulated exhaust or the intake of low concentration of circulated exhaust is located in the outer region in a high load or high rotation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection type internal combustion engine in which fuel is injected into a combustion chamber, and NOx (nitrogen oxide) or soot (soot) in the exhaust gas by mixing recirculated exhaust gas into intake air of the combustion chamber. It relates to technologies for reducing harmful substances such as.

[0002]

2. Description of the Related Art In a direct injection type internal combustion engine provided with an exhaust gas recirculation device, a part of exhaust gas passing through an exhaust port is mixed into intake air passing through an intake port, and the recirculated exhaust gas is introduced into a combustion chamber. The mixed intake air is caused to flow in, the recirculated exhaust gas is evenly distributed in the intake air of the combustion chamber, and the oxygen concentration and the combustion temperature of the combustion chamber are reduced to reduce the generation of NOx.

A second prior art (Japanese Patent Laid-Open No. 11-148429)
In a direct injection compression ignition internal combustion engine equipped with an exhaust gas recirculation device, a technique for stratifying intake air in a combustion chamber has been proposed in order to reduce NOx and PM (particulate matter) in exhaust gas.

The combustion chamber is provided with two intake ports for concentrically forming a swirl flow in the same direction. In the intake port on the upstream side of the swirl flow, a small-diameter swirl flow is provided at the center of the combustion chamber, A large-diameter swirl flow is formed at the periphery of the combustion chamber at the intake port.

[0005] The recirculated exhaust gas is mixed into the intake air passing through the upstream intake port, and the recirculated exhaust gas is not mixed into the intake air passing through the downstream intake port. The intake air mixed with the exhaust gas is disposed in the annular region around the combustion chamber, and the intake air is not mixed with the recirculated exhaust gas.

[0006]

In the first prior art, when the recirculation rate of the exhaust gas is increased during the medium-load or high-load operation of the internal combustion engine, as in the low-load operation, the effect of reducing NOx increases. However, at the time of medium-load or high-load operation, since there is an oxygen-deficient region locally in the combustion chamber, if a large amount of recirculated exhaust gas is evenly distributed by increasing the exhaust gas recirculation rate,
The oxygen deficient region becomes more and more deficient in oxygen, and PM increases due to increased soot generation and inhibition of soot oxidation. NOx
And soot cannot be reduced at the same time.

In the second prior art, a small-diameter swirl flow and a large-diameter swirl flow of intake air are formed inside and outside of the combustion chamber. However, the swirl flow has a centrifugal force that enlarges the diameter. The swirl flow expands outward due to the centrifugal force, and collides with and mixes with the large-diameter swirl flow whose diameter does not increase due to the peripheral wall of the combustion chamber.

Further, even if swirl flows of small diameter and large diameter are formed inside and outside the combustion chamber in the intake stroke, in the next compression stroke, the intake air on the periphery of the top surface of the piston becomes the center of the piston top surface. A large swirl flow around the combustion chamber is transported to the center of the combustion chamber by the squish flow, and collides with the small swirl flow at the center of the combustion chamber because a squish flow flows into the cavity of the combustion chamber. Will do.

Therefore, at a point near the end of the compression stroke in which fuel is sprayed into the combustion chamber to start combustion, it is recognized that the intake air mixed with the recirculated exhaust gas and the intake air not mixed are stratified in and out. Absent. It is unknown whether NOx and PM in the exhaust gas decrease.

[0010]

1) According to the research of the present inventors, in a direct injection compression ignition internal combustion engine, the combustion chamber is as shown in FIGS. 9 (a) and 10 (a). ,
In the squish area and the periphery of the cavity, there is a high temperature region where the fuel flow injected from the fuel injection valve burns.

In the high-temperature combustion region, FIG.
As illustrated in (c) and FIGS. 10 (b) and (c), NOx is generated in the lean region near the stoichiometric air-fuel ratio. Therefore, if the recirculated exhaust gas is distributed in the squish area of the combustion chamber and the periphery of the cavity during the combustion period, the oxygen concentration and the combustion temperature in the high-temperature combustion area decrease, and the generation of NOx decreases.

Further, in the high temperature combustion region, FIG.
As illustrated in (d) and FIGS. 10 (b) and 10 (d), in the oxygen-deficient combustion region richer than the stoichiometric air-fuel ratio, that is, at the tip of the fuel flow injected from the fuel injector or the valley of the cavity. A soot occurs. To control the occurrence of soot,
Supplying oxygen to the fuel flow front that burns in an oxygen-deficient state,
It is effective to eliminate the lack of oxygen at the fuel flow front end.

2) On the other hand, the fuel flow injected from the fuel injection valve during the intake of the combustion chamber entrains the surrounding air into the fuel flow at the root side portion, and transfers the surrounding air to the outer periphery of the fuel flow. It entrains and induces an air flow associated with the fuel flow. In addition, the fuel flow flies at a high speed, splits and atomizes, turns into steam, and burns at a leading end portion where the steam is turned into a flame. It should be noted that there is a case where a flame is generated by burning on the base side from the front end portion, but a portion where the high-temperature flame is generated on a large scale is a front end portion of the fuel flow.

In the combustion chamber, a fuel / air mixture region is formed at the base of the fuel flow to mix the fuel and air to form a fuel / air mixture during fuel injection and combustion. At the front end side, a flame generation region where the air-fuel mixture burns violently and a high-temperature flame is generated on a large scale is formed, and is roughly divided into an air-fuel mixture formation region and a flame generation region. The air-fuel mixture formed in the air-fuel mixture formation region of the combustion chamber is carried to the flame generation region of the combustion chamber by the fuel flow or the air-fuel mixture flow.

Therefore, in a direct injection compression ignition internal combustion engine provided with an exhaust gas recirculation device, fresh air is distributed around the root side portion of the fuel flow injected from the fuel injection valve without distributing the recirculated exhaust gas. The fresh air is transported to the tip by the fuel flow or the mixture flow, and oxygen is supplied to the fuel flow tip or the cavity valley that burns in an oxygen-deficient state, so that the oxygen concentration increases to the soot generation suppression value or more. ,
The occurrence of soot is reduced. However, at this time, control is performed so that the oxygen concentration does not increase to the NOx generation value. Also,
When the intake air containing the recirculated exhaust gas is distributed around the squish area of the combustion chamber and around the cavity where NOx is generated by high-temperature combustion in the lean side region near the stoichiometric air-fuel ratio, the oxygen concentration and combustion temperature decrease, and NOx Occurrence is reduced.

In the combustion chamber, at the start of combustion, the intake air, which does not mix the recirculated exhaust gas, into the air-fuel mixture formation region including the root portion of the fuel flow injected from the fuel injection valve, is introduced into the flame generation region outside the mixture. When the intake air mixed with the recirculated exhaust gas is arranged,
Both NOx and soot can be reduced.

3) The flame generation start position at which the generation of a large-scale high-temperature flame at the front end portion of the fuel flow starts is defined by the distance from the injection port of the fuel injection valve to the start position of the fuel flow division. The position is about 1 to 1.5 times as long as the spray split distance from the injection valve orifice position. Note that the spray split distance = 15.8 (fuel density / air density) ^1/2 · (fuel injection nozzle diameter).

In the fuel injection valve, a number of injection ports are arranged at the center of the ceiling surface of the combustion chamber facing the top surface of the piston, and the injection direction thereof is a radial direction. It inclines toward the surface and heads toward the periphery of the cavity at the center of the piston top surface near the end of the compression stroke.

Therefore, the above-mentioned flame generating region of the combustion chamber is:
In each fuel injection direction, the fuel injection valve is located in a region which is at least about 1 to 1.5 times the spray split distance from the position of the injection port of the fuel injection valve in the combustion chamber, and is substantially symmetric with respect to the central axis of the combustion chamber. The mixture formation region is a region within about 1 to 1.5 times the spray split distance from the fuel injection valve orifice position of the combustion chamber in each fuel injection direction, and is substantially symmetric with respect to the central axis of the combustion chamber. .

From these facts, the intake air of the combustion chamber is substantially semispherical or substantially flat hemispherical around the center of the ceiling surface of the combustion chamber where fuel is injected near the end of the compression stroke where fuel starts to burn. If the intake air in which the recirculation exhaust gas is not mixed and the mixed intake air can be stratified in the inner region and the outer region of the surface, both NOx and soot can be reduced.

4) A plurality of intake swirl flows in the same direction are formed in the combustion chamber by the plurality of intake ports, and the fuel is directed from the center of the ceiling surface of the combustion chamber toward the peripheral portion of the cavity at the center of the piston top surface. In a direct-injection compression ignition internal combustion engine that performs injection, if the shapes of the combustion chamber and the intake port, and thus the flow characteristics of the intake squish flow and swirl flow, are selected, the intake air can be stratified as follows.

In the intake stroke, as illustrated in FIG. 2, at the intake port 3 downstream of the swirl flow, the combustion chamber 1
The swirl flow of the first intake 11 along the peripheral wall at the top of
In the intake port 4 on the upstream side, a swirl flow of the second intake 12 along the peripheral wall is formed below the combustion chamber 1. As illustrated in FIGS. 4 and 5, the state in which the swirl flow of the first intake 11 and the swirl flow of the second intake 12 having different compositions are vertically arranged in the combustion chamber 1 is continued until the middle of the compression stroke. You.

In the latter half of the compression stroke in which the squish flow is generated, the swirl flow on the periphery of the piston top surface is carried by the squish flow into the cavity at the center of the piston top surface, and the swirl velocity due to the diameter reduction is generated. Due to the centrifugal force caused by the increase in the flow rate, the fluid flows along the peripheral wall of the cavity without going to the center of the cavity and toward the bottom surface of the cavity. In the cavity, before the squish flow occurs, the second intake air exists in the entire region. However, when the squish flow occurs, as illustrated in FIGS. 6A, 6B, and 6C in the order of lapse of time,
The first intake air 11 flows into the central region, and the second intake air 12 exists only in the peripheral region and the bottom region.

In the vicinity of the end of the compression stroke in which fuel starts to burn, as shown in FIG. 1, the combustion chamber 1 has a substantially flat semi-spherical surface 13 centered on the center position of the ceiling surface where fuel is injected. The first intake air 11 mainly exists in the region, and the second intake air 12 mainly exists in the region outside the region.

When the recirculated exhaust gas is not mixed into the first intake air 11 but the recirculated exhaust gas is mixed into the second intake air 12, the combustion chamber at the start of fuel combustion has a substantially hemispherical surface or a substantially flat hemispherical shape centered on the fuel injection position. In the area inside and outside the surface, the intake air in which the recirculation exhaust gas is not mixed or the intake air with a low recirculation exhaust gas concentration and the intake air in which the recirculation exhaust gas is mixed or the intake air with a high recirculation exhaust gas concentration are stratified. Become.

5) When the load of the direct injection type internal combustion engine is high,
The end timing of the fuel is delayed, and the ratio of the fuel distributed to the peripheral portion of the combustion chamber 1 and the squish area is increased. Therefore, it is better to suppress the soot by increasing the amount of fresh air present in the peripheral portion of the combustion chamber 1 and the squish area than to suppress the soot by increasing the amount of fresh air entrained in the base portion of the fuel flow. It is effective.

That is, when the load is high, the stratification pattern of the combustion chamber 1 is changed from that at the time of low load. In the combustion chamber 1, the intake air mixed with the recirculated exhaust gas is present in a region within the substantially flat hemisphere 13. It is desired to form a reverse stratified pattern in which a fresh air intake which does not mix the recirculated exhaust gas exists in a region outside the recirculated exhaust gas.

6) In the case where intake air containing recirculated exhaust gas or intake air having a high recirculated exhaust gas concentration is arranged in a region outside the substantially hemispherical surface or the approximately flat hemispherical surface around the fuel injection position of the combustion chamber, Assuming that the amount of exhaust is constant, the radius of the substantially hemispherical surface or the approximately flat hemispherical surface increases as the recirculation exhaust gas concentration outside the approximately hemispherical surface or the approximately flat hemispherical surface increases.

When the NOx generation region is wide and extends inside the approximately hemispherical surface or the approximately flat hemispherical surface, the recirculation exhaust gas concentration outside the approximately hemispherical surface or the approximately flattened hemispherical surface is reduced to reduce the approximate hemispherical surface or the approximately flat hemispherical surface. Reduce the radius and reduce NOx over a wide area. Conversely, when the NOx generation region is narrow, the recirculation exhaust gas concentration outside the substantially hemispherical surface or the approximately flat hemispherical surface is increased to increase the radius of the approximately hemispherical surface or the approximately flat hemispherical surface. Reduce.

As described above, when the recirculation exhaust gas concentration in the region inside or outside the substantially hemispherical surface or the approximately flat hemispherical surface is changed according to the size of the NOx generation region, the soot and the N
Ox can be further reduced.

[0031]

SUMMARY OF THE INVENTION 1) In a direct injection internal combustion engine in which fuel is injected into a combustion chamber, the combustion chamber has a substantially hemispherical surface or a center around the fuel injection position at the start of fuel combustion near the end of the compression stroke. A configuration in which intake air with no recirculation exhaust gas or intake air with low recirculation exhaust gas concentration and intake air with recirculation exhaust gas enrichment or intake air with a high recirculation exhaust gas concentration are arranged in an inner region and an outer region of the roughly flat hemisphere. A direct injection type internal combustion engine, characterized in that:

2) A plurality of intake swirl flows in the same direction are formed in the combustion chamber by the plurality of intake ports, and the fuel is supplied to the combustion chamber from the center of the ceiling facing the piston top surface to the center of the piston top surface. In the direct injection type internal combustion engine that injects fuel toward the peripheral portion of the engine, in the intake stroke, the first intake air into which the recirculated exhaust gas is not mixed is turned into a swirl flow along the peripheral wall above the combustion chamber, and the second intake air into which the recirculated exhaust gas is mixed. The intake air is swirled along the peripheral wall at the lower part of the combustion chamber, and in the latter half of the compression stroke in which squish flow occurs, the first intake air flows into the central region in the cavity at the center of the piston top surface, and flows into the peripheral region and the bottom region. 2 In the vicinity of the end of the compression stroke in which the intake air is left and the fuel starts burning, the combustion chamber is provided with a recirculated exhaust gas in a region inside the substantially hemispherical surface or the approximately flat hemispherical surface around the fuel injection position. Direct-injection type internal combustion, characterized in that intake air with a low concentration of recirculated exhaust gas or intake air with a low recirculation exhaust gas concentration is arranged in the outer region, and intake air with a high concentration of recirculated exhaust gas or intake air with a high recirculation exhaust gas concentration is arranged in the outer region. organ.

3) In the above direct injection type internal combustion engine,
At the time of high load or high rotation, the combustion chamber arranges, at the start of fuel combustion in the vicinity of the end of the compression stroke, intake air in which recirculation exhaust gas is mixed or intake air with high recirculation exhaust gas concentration in the inner region, In the outside region, intake air in which recirculation exhaust gas is not mixed or intake air with low recirculation exhaust gas concentration is arranged.

4) In the above direct injection type internal combustion engine,
The ratio of the concentration of the recirculated exhaust gas in the outer region to the concentration of the recirculated exhaust gas in the inner region is changed according to operating conditions.

5) In the above direct injection type internal combustion engine,
A substantially hemispherical surface or a substantially flat hemispherical surface centered on the fuel injection position of the combustion chamber is characterized in that the fuel injection direction is apart from the fuel injection position by about 1 to 1.5 times the spray split distance.

[0036]

As described above, at the start of fuel combustion near the end of the compression stroke,
In the combustion chamber, intake air containing recirculated exhaust gas or intake air having a high recirculated exhaust gas concentration is arranged in a region outside a substantially hemispherical surface or a substantially flat hemispherical surface with a fuel injection position as a center. In the combustion chamber, intake air containing recirculated exhaust gas or intake air having a high recirculated exhaust gas concentration is arranged in a squish area where a high-temperature combustion region is generated and around the cavity.
Ox generation is reduced.

At the same time, in the combustion chamber, intake air containing no recirculated exhaust gas or intake air having a low recirculated exhaust gas concentration is arranged in a region inside a substantially hemispherical surface or a substantially flat hemispherical surface centered on the fuel injection position. You. In the combustion chamber, intake air in which recirculation exhaust gas is not mixed or intake air with low recirculation exhaust gas concentration is arranged in a region around the base side portion of the fuel flow injected from the fuel injection valve. Or oxygen is supplied to the fuel flow tip or cavity that is carried to the fuel flow tip by the air-fuel mixture and burns in an oxygen-deficient state,
The occurrence of soot is reduced.

As a result, both NOx and soot are reduced.

At the time of high load or high rotation, intake air containing recirculated exhaust gas or intake air having a high recirculated exhaust gas concentration is arranged in the above inner region, and recirculated exhaust gas is mixed in the above outer region. No intake air or intake air having a low recirculation exhaust gas concentration is arranged. NOx and soot are further reduced.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Example (see FIGS. 1 to 10)]
As shown in FIG. 1, the direct injection compression ignition internal combustion engine of this embodiment has a large number of injection ports of fuel injection valves 2 arranged at the center of the ceiling surface of a combustion chamber 1 and one side of the ceiling surface of the combustion chamber 1. Two intake ports 3 and 4 and intake valves 5 and 6 are provided on the side, two exhaust ports 7 and an exhaust valve 8 are provided on the other side, and a central axis symmetric cavity 9 is provided at the center of the piston top surface. It is formed concentrically.

The cavity 9 is provided with a peak 10 in the center of the bottom surface, and the periphery of the peak 10 is a valley. Fuel injection valve 2
Near the end of the compression stroke, fuel is injected from a number of nozzles in a radial direction toward the periphery of the cavity 9.

As shown in FIG. 2, the two intake ports 3 and 4 form swirl flows 11 and 12 of intake air in the same direction in the combustion chamber 1 during the intake stroke. The intake port 3 on the downstream side of the swirl flow has a helical port shape as shown in FIGS. 2 and 3, and the intake air flows out substantially along the ceiling surface of the combustion chamber 1. A strong first intake swirl flow 11 is formed along the peripheral wall at the upper part. The upstream intake port 4 has a tangential port shape, and the intake air flows obliquely downward to avoid collision with the swirl flow 11 of the first intake air. A swirl flow 12 of the second intake air is formed along the peripheral wall.

The internal combustion engine of this embodiment has an exhaust gas recirculation device,
Part of the exhaust gas passing through the exhaust port 7 is mixed into the second intake air 12 passing through the upstream intake port 4. The recirculated exhaust gas is not mixed into the first intake air 11 passing through the downstream intake port 3.

In the internal combustion engine of this embodiment, during the intake stroke,
As shown in FIG. 2, when a swirl flow 11 of the first intake air and a swirl flow 12 of the second intake air are formed along the peripheral wall of the upper and lower portions of the combustion chamber 1, respectively, at the end of the intake stroke,
As shown in FIG. 4, the swirl flow 1 of the first intake air flows into the combustion chamber 1.
The swirl flows 12 of the first and second intake air are stratified up and down.
At the end of the intake stroke, the rearmost portion of the second intake air 12 that has flowed last from the upstream intake port 4 exists above the combustion chamber 1, so that the boundary surface 1 between the first intake air 11 and the second intake air 12.
3 is not a plane parallel to the top surface of the piston, but an inclined concave and convex curved surface.

The first intake 11 and the second intake 12 of the combustion chamber 1
Is mixed with the passage of time, the recirculated exhaust gas contained only in the second intake air 12 becomes contained in the first intake air 11 and the concentration of the recirculated exhaust gas changes continuously. A surface at which the concentration of exhaust gas has a substantially intermediate value is defined as a boundary surface 13 between the first intake 11 and the second intake 12.

In the compression stroke, the last part of the second intake air 12 moves to the lower part of the combustion chamber 1, and the mixing of the first intake air 11 and the second intake air 12 progresses. As shown in FIG. 5, an interface 13 between the first intake 11 and the second intake 12
Approaches a plane parallel to the piston top surface. The state in which the first intake swirl flow 11 and the second intake swirl flow 12 are vertically stratified in the combustion chamber 1 continues to the middle of the compression stroke.

In the latter half of the compression stroke in which a squish flow is generated, the swirl flow on the periphery of the piston top surface is carried by the squish flow into the cavity 9 at the center of the piston top surface, and the swirl is caused by the diameter reduction. Due to the centrifugal force caused by the increase in the directional speed, the fluid flows along the peripheral wall of the cavity 9 without going to the center of the cavity 9 and goes to the bottom surface of the cavity 9. As shown in FIG. 6A, FIG. 6B, and FIG. 6C, the inside of the cavity 9 is filled with the second intake 12 at the lower part of the combustion chamber 1 and then the first intake at the upper part of the combustion chamber 1 is placed in the central region. 11 and the second intake 12 only in the peripheral area and the bottom area.
Remains.

In the vicinity of the end of the compression stroke in which fuel is injected from the fuel injection valve 2 to start combustion, as shown in FIG.
In the combustion chamber 1, the first intake air 11 mainly exists in a region inside the substantially flat hemispherical surface 13 centered on the center of the ceiling surface into which fuel is injected, and the second intake air 12 exists in a region outside the same. Mainly exists. At the start of combustion of the fuel, the combustion chamber 1 contains the intake air 11 having a low recirculated exhaust gas concentration in a region inside the roughly flat hemisphere 13.
However, the intake air 12 having a high recirculation exhaust gas concentration is arranged in the outer region.

When the radius in the fuel injection direction is set to about 1 to 1.5 times the spray split distance, the above roughly flat hemispherical surface 13 draws the intake air 11, 1, 1 into the mixture formation region and the flame generation region of the combustion chamber 1.
2 is stratified. At the start of fuel combustion, in the flame generation region including the squish area of the combustion chamber 1 and the periphery of the cavity, the intake air 12 having a high recirculation exhaust gas concentration is arranged, so that the combustion temperature is reduced and the generation of NOx is reduced. At the same time, in the air-fuel mixture forming region of the combustion chamber 1, the intake air 11 having a low recirculation exhaust gas concentration is arranged.
1 is supplied to the fuel flow front by the fuel flow, the shortage of oxygen in the burning fuel flow front or the cavity 9 is reduced, and soot generation is reduced.

In the vicinity of the end of the compression stroke, the first intake air 1
If the swirl flow 1 is too strong, as shown in FIG. 7A, when the first intake air 11 is carried to the bottom surface of the cavity 9 by the squish flow, it becomes an inverse toroidal flow down the peripheral wall of the cavity 9, and The second intake air 12 flowing into the bottom surface of the cavity 9 and present on the peripheral wall and the bottom surface of the cavity 9 is pushed away to the center of the cavity 9.

In the internal combustion engine of this embodiment, the intake air 11, 1
Since the swirl flow and the squish flow of No. 2 are appropriate, FIG.
As shown in (b), the first intake air 11 becomes a toroidal flow that goes down between the crest portion 10 of the cavity 9 and the intermediate portion of the peripheral wall, and the second intake air 12 existing in the intermediate portion is converted into the peripheral region of the cavity 9 and the bottom portion. The intake air 11 and 12 are pushed into and out of the roughly flat hemispherical surface 13 centered on the fuel injection position of the combustion chamber 1.
Is stratified.

In the internal combustion engine of this embodiment, the combustion chamber 1 and the intake ports 3 and 4 which determine the flow characteristics of the squish flow and the swirl flow of the intake air 11 and 12 so that the intake air 11 and 12 are stratified in this way. Is selected. The degree of stratification of the intake air 11 and 12 and the shape and size of the boundary surface 13 can be controlled by these shapes.

The above-mentioned shape has the cavity 9 of the combustion chamber 1.
The shape, the distance between the periphery of the piston top surface and the periphery of the ceiling surface, and the amount of depression of the lower surface of the intake valves 5 and 6 from the ceiling surface are exemplified.

Simulated Experimental Example 1 The first intake air flowing into the combustion chamber from the intake port on the downstream side is:
The distribution of the recirculated exhaust gas concentration (EGR rate) of the combustion chamber at the end of the compression stroke when the fresh air is 100% and the second intake air flowing from the upstream intake port is 50% fresh air and 50% recirculated exhaust gas. Was obtained by numerical calculation.

FIG. 8B shows the distribution in the central longitudinal section of the combustion chamber passing between the downstream and upstream intake ports, and FIG. 8A shows the distribution in the central longitudinal section perpendicular to the central longitudinal section.

As is clear from these figures, at the end of the compression stroke, the contour surface of the recirculated exhaust gas concentration distribution of the combustion chamber appears in a substantially flat hemispherical shape centered on the fuel injection position, and approaches the fuel injection position. Accordingly, the recirculation exhaust gas concentration becomes thinner, and the distribution of the recirculation exhaust gas concentration becomes substantially axially symmetric. This indicates that the intake air of the combustion chamber is stratified into the intake air having a low recirculation exhaust gas concentration and the intake air having a high concentration, inside and outside a substantially flat hemisphere centered on the fuel injection position.

Simulated Experimental Example 2 In an internal combustion engine that does not recirculate exhaust gas, the engine speed was 18
00 rpm, the number of nozzles of the fuel injection valve is 5, and the diameter of the nozzle is 0.
18mm, injection amount 35mm ³ , injection pressure 55MP
a, When the injection period is set to 0 ° to 12.5 ° ATDC, the temperature of the combustion chamber, fuel vapor, NO (nitrogen monoxide)
And soot distribution were obtained by numerical calculation.

FIG. 9 is at 10 ° ATDC, and FIG.
The distribution at the time of ATDC is shown, in which (a) is the temperature distribution, (b) is the fuel vapor distribution, (c) is the NO distribution, and (d)
Indicates a soot distribution.

As shown in FIGS. 9 (a) and 10 (a), the combustion chamber has a high temperature region in the squish area and around the cavity where the fuel flow injected from the fuel injector burns.

In the high-temperature combustion region, FIG.
As shown in (c) and FIGS. 10 (b) and 10 (c), NO is generated in a lean region near the stoichiometric air-fuel ratio. The flame generation area including the squish area of the combustion chamber and the periphery of the cavity,
It can be seen that if intake air with a high recirculation exhaust gas concentration is distributed during the combustion period, the combustion temperature decreases and the generation of NO decreases.

In the high temperature combustion region, FIG.
As shown in FIGS. 10 (d) and 10 (b) and 10 (d), the soot is formed in the oxygen-deficient combustion region richer than the stoichiometric air-fuel ratio, that is, at the tip of the fuel flow injected from the fuel injector or the valley of the cavity. Occurs. At the start of combustion, when intake air having a low concentration of recirculated exhaust gas is distributed in the air-fuel mixture formation region including the base portion of the fuel flow, the intake air is carried to the front end of the fuel flow by the fuel flow or the air-fuel mixture, and the front end of the fuel flow or It can be seen that the lack of oxygen in the cavity valleys is reduced and soot generation is reduced.

[Second example (see FIG. 11)] The internal combustion engine of the present example differs from that of the first example in that the stratification degree of the intake air mixed with the recirculated exhaust gas is increased so that the downstream and upstream intake ports 3,
At 4, the opening periods of the intake valves 5 and 6 are shifted.

In the downstream intake port 3 through which the first intake air 11 flows into the upper part of the combustion chamber 1, as shown in FIG. 11, the intake valve 5 is opened at a later time and closed at a later time. Combustion chamber 1
In the intake port 4 on the upstream side through which the second intake air 12 flows into the lower part of the intake port, the intake valve 6 is opened early and closed early.

In the first half of the intake stroke, only the intake valve 6 of the intake port 4 on the upstream side is opened, and only the second intake 12 disposed below the combustion chamber 1 flows into the combustion chamber 1. In the middle stage of the intake stroke, the intake valves 5, 6 of both intake ports 3, 4 are opened, and the first intake 11 and the second intake 12 flow into the combustion chamber 1. In the latter half of the intake stroke, only the intake valve 5 of the downstream intake port 3 opens, and only the first intake 11 arranged above the combustion chamber 1 flows into the combustion chamber 1.

At the end of the intake stroke, the first intake port 11 and the second intake port 12 are at the end of the intake stroke, as compared with the first example in which the opening periods of the intake valves 5 and 6 at the downstream and upstream intake ports 3 and 4 match. Is more or less stratified up and down, and at the end of the compression stroke, the recirculation exhaust gas concentration difference between the intake air located inside the approximately flat hemispherical surface 13 centered on the fuel injection position and the intake air located outside. Becomes larger. The effect of reducing both NOx and soot increases.

The other points are the same as in the first example.

[Third example (see FIG. 12)] The internal combustion engine of the present example differs from that of the first example in that the stratification of the intake air mixed with the recirculated exhaust gas is increased from only one side of the intake port 4 on the upstream side. The second intake air 12 flows into the combustion chamber 1.

At the upstream intake port 4, the intake air flows obliquely downward and collides obliquely with the peripheral wall of the combustion chamber 1.
The swirl flows along the peripheral wall at the lower part of the combustion chamber 1. The intake air flowing out of the tangential port-shaped intake port 4 on the peripheral wall side of the combustion chamber 1 has a shorter distance before colliding with the peripheral wall of the combustion chamber 1 than the intake air flowing out of the central part on the combustion chamber 1, It easily flows into the lower part of the combustion chamber 1.

Therefore, the intake port 4 on the upstream side is
As shown in the figure, the peripheral wall side portion and the central side portion of the combustion chamber 1
A partition wall 21 for dividing is provided, and the combustion chamber 1 of the intake port 4 is provided.
The second intake air 12 containing the recirculated exhaust gas flows into the peripheral wall side portion, and the second intake air 1 flows from the peripheral wall side portion of the combustion chamber 1 of the intake port 4.
2 flows into the lower part of the combustion chamber 1. Like the upstream intake port 3, the first intake air 11, which does not mix recirculated exhaust gas, flows into the central portion of the combustion chamber 1 of the intake port 4.
The first intake air 11 flows into the combustion chamber 1 from the central portion of the combustion chamber 1.

The second intake air 12 flowing into the combustion chamber 1 from the portion of the intake port 4 on the peripheral wall side of the combustion chamber 1 has a narrow air flow.
Mixing with the first intake air 11 becomes difficult.

As compared with the first example in which the second intake air 12 flows into the combustion chamber 1 from the entire intake port 4 on the upstream side,
At the end of the intake stroke, the degree of stratification of the first intake air 11 and the second intake air 12 in the vertical direction increases, and at the end of the compression stroke, the intake air arranged inside the substantially flat hemispherical surface 13 centered on the fuel injection position. Then, the difference between the recirculated exhaust gas concentration and the intake air arranged outside is increased. The effect of reducing both NOx and soot increases.

The other points are the same as in the first example.

[Fourth Example (See FIGS. 13 and 14)] The internal combustion engine of the present example differs from that of the first example in that the stratification pattern and the degree of stratification of the intake air in the combustion chamber 1 are changed according to the operating conditions. .

In the internal combustion engine of the first example, the first intake passage 23 connected to the intake port 3 on the downstream side of the swirl flow
As shown in FIG. 13, the first flow control valve 24
A second flow control valve 27 is connected to a second intake passage 26 connected to the exhaust gas recirculation passage 25 and to the intake port 4 on the upstream side.
Is connected to the second exhaust gas recirculation passage 28 via the second exhaust gas recirculation passage. A device 29 is provided for controlling the opening of the first flow control valve 24 and the opening of the second flow control valve 27 in accordance with operating conditions.

When the opening degree of the first flow control valve 24 and the opening degree of the second flow control valve 27 are controlled in accordance with the operating conditions of the internal combustion engine, the opening degree of the first flow control valve 24 is mixed with the first intake air passing through the downstream intake port 3. The amount of recirculated exhaust gas and the amount of recirculated exhaust gas mixed into the second intake air passing through the upstream intake port 4 increase and decrease, respectively, and the stratification pattern of the combustion chamber 1 is changed. A positive stratified pattern in which the concentration of the recirculated exhaust gas is lower in a region inside the substantially flat semi-spherical surface 13 of the combustion chamber 1 than in a region outside the flat hemisphere 13 is obtained. In addition, a reverse stratified pattern in which the concentration of the recirculated exhaust gas is higher in the region inside the substantially flat hemispherical surface 13 of the combustion chamber 1 than in the region outside the same. Furthermore, a homogeneous pattern is obtained in which the recirculation exhaust gas has the same concentration in the region inside the substantially flat hemispherical surface 13 of the combustion chamber 1 and in the region outside thereof.

The normal stratification pattern, reverse stratification pattern and homogeneous pattern are switched as shown on the operation map of FIG.

When the load on the internal combustion engine is small and the rotational speed of the internal combustion engine is low, the stratification pattern of the combustion chamber 1 is a positive stratification pattern. When the load increases or the number of rotations increases, a uniform pattern is formed. When the load is further increased or the rotation speed is further increased, the reverse stratified pattern is formed.

Further, depending on the operating conditions of the internal combustion engine, the first
When the opening of the flow control valve 24 and the opening of the second flow control valve 27 are controlled, the stratification of the combustion chamber 1 is changed. The ratio of the recirculation exhaust gas concentration outside the roughly flat hemisphere 13 to the recirculation exhaust gas concentration in the roughly flat hemisphere 13, specifically, the roughly flat hemisphere with respect to the recirculation exhaust gas concentration at the fuel injection position inside the roughly flat hemisphere 13. The ratio of the recirculated exhaust gas concentration and the degree of stratification in the peripheral region around the bottom of the cavity 13 increase or decrease.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of a direct injection compression ignition internal combustion engine according to a first example of an embodiment of the present invention.

FIG. 2 is a schematic perspective view of a combustion chamber in the middle of an intake stroke in the internal combustion engine.

FIG. 3 is a schematic plan view of a combustion chamber in the internal combustion engine.

FIG. 4 is a schematic perspective view of a combustion chamber at the end of an intake stroke in the internal combustion engine.

FIG. 5 is a schematic perspective view of a combustion chamber in the middle of a compression stroke in the internal combustion engine.

FIG. 6 is a schematic longitudinal sectional view of a combustion chamber near the end of a compression stroke in the internal combustion engine, showing a flow state of intake air.

FIG. 7 is a schematic vertical sectional view of a combustion chamber at the end of a compression stroke in an internal combustion engine, showing a flow state of intake air.

FIG. 8 is a diagram showing a stratified state of intake air at the end of a compression stroke in a simulation test example 1.

FIG. 9 is a diagram showing the distribution of the temperature, fuel vapor, NO and soot at 10 ° ATDC in the simulated experimental example 2.

FIG. 10 is a view similar to FIG. 9, showing a state at 20 ° ATDC.

FIG. 11 is an intake valve lift diagram of a direct injection compression ignition internal combustion engine according to a second example of the embodiment.

FIG. 12 is a schematic plan view of a combustion chamber of a direct injection compression ignition internal combustion engine in a third example.

FIG. 13 is a schematic view of an intake passage portion of a direct injection compression ignition internal combustion engine in a fourth example.

FIG. 14 is a diagram of an operation map in the internal combustion engine.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 combustion chamber 2 fuel injection valve 3 intake port on the downstream side of swirl flow 4 intake port on the upstream side of swirl flow 5 intake valve on the downstream side of swirl flow 6 intake valve on the upstream side of swirl flow 9 cavity 11 mixed with recirculated exhaust gas 1st intake not used 12 2nd intake mixed with recirculated exhaust 13 Boundary surface between 1st intake and 2nd intake, roughly flat hemisphere

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) F02B 31/02 F02B 31/02 L F02D 21/08 301 F02D 21/08 301A 41/02 355 41/02 355 F02M 25/07 570 F02M 25/07 570A 570D (72) Inventor Kiyomi Nakakita 41-Yukumichi Yokomichi, Oji-cho, Nagakute-cho, Aichi-gun, Aichi Pref. (1) Inside the Toyota Central R & D Laboratories Co., Ltd. (72) Inventor Sanjiro Inayoshi 41-42, Nagakute-cho Ochi-Chamu Yokomichi, Aichi-gun, Aichi Pref. Inventor Ichiro Sakata 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation

Claims (7)

[Claims] In a direct injection type internal combustion engine that injects fuel into a combustion chamber, the combustion chamber is located inside a substantially hemispherical surface or a substantially flat hemispherical surface around a fuel injection position at the start of fuel combustion near the end of a compression stroke. And the outside region, the intake air containing no recirculated exhaust gas or the intake air having a low recirculated exhaust gas concentration and the intake air containing recirculated exhaust gas or the intake air having a high recirculated exhaust gas concentration are arranged. Direct injection internal combustion engine. 2. A plurality of intake ports forming a plurality of intake swirl flows in the combustion chamber in the same direction in the combustion chamber, and supplying fuel to the combustion chamber from a center portion of a ceiling surface facing the piston top surface to a central portion of the piston top surface. In the direct injection type internal combustion engine that injects fuel toward the peripheral portion of the engine, in the intake stroke, the first intake air into which the recirculated exhaust gas is not mixed is turned into a swirl flow along the peripheral wall above the combustion chamber, and the second intake gas is mixed with the recirculated exhaust gas. In the second half of the compression stroke in which the squish flow occurs, the first intake air flows into the central region of the piston at the center of the piston top surface, and the first intake air flows into the peripheral region and the bottom region. (2) In the vicinity of the end of the compression stroke in which the intake air is left and the fuel starts burning, the combustion chamber is provided with a recirculated exhaust gas in a region inside the approximate semi-spherical surface or the approximately flat semi-spherical surface centered on the fuel injection position. , Or the intake air with a low recirculation exhaust gas concentration
A direct injection type internal combustion engine, wherein intake air containing recirculated exhaust gas or intake air having a high recirculated exhaust gas concentration is arranged. 3. At high load or high revolution, the combustion chamber is
At the start of fuel combustion near the end of the compression stroke, intake air containing recirculated exhaust gas or intake air having a high recirculated exhaust gas concentration is arranged in the above inner region, and no recirculated exhaust gas is mixed in the above outer region. 3. The direct injection type internal combustion engine according to claim 1, wherein intake air having a low intake or recirculation exhaust gas concentration is arranged. 4. The apparatus according to claim 1, wherein a ratio of a concentration of the recirculated exhaust gas in the outer region to a concentration of the recirculated exhaust gas in the inner region is changed according to an operating condition. 4. The direct injection internal combustion engine according to 2 or 3. 5. An intake port for forming a swirl flow of a first intake air in an upper part of a combustion chamber and a suction port for forming a swirl flow of a second intake air in a lower part of a combustion chamber, in which an opening period of an intake valve is shifted. At the front of the stroke, only the intake valve of the latter intake port is opened and only the second intake air flows into the combustion chamber. At the rear of the intake stroke, only the intake valve of the former intake port is opened and the second intake valve is opened. The direct injection type internal combustion engine according to any one of claims 1 to 4, wherein only one intake air flows into the combustion chamber. 6. A substantially hemispherical surface or a substantially flat hemispherical surface centered on a fuel injection position of a combustion chamber is separated from the fuel injection position by about 1 to 1.5 times the spray split distance in the fuel injection direction. The direct injection type internal combustion engine according to any one of claims 1 to 5, characterized in that: 7. The direct injection type internal combustion engine according to claim 1, wherein the direct injection type internal combustion engine is a compression ignition internal combustion engine.