JP2000145461A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent most of unburnt HC and a malodor from being released even when injection fuel is made to collide against a cavity internal wall of a piston during low-load operation. SOLUTION: In this internal combustion engine, either the first combustion wherein quantity of EGR gas in a combustion chamber 5 is more than that of EGR gas which produces maximum soot and thereby very little soot is generated, or the second combustion wherein quantity of EGR gas in the combustion chamber 5s is less than that of EGR gas which produces maximum soot is selected. Fuel is injected from a fuel injection valve 6 toward the inside of a cavity formed in a piston 4. When either the first or the second combustion is done, the fuel injected from the fuel injection valve 6 is made to collide against a cavity internal wall.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an internal combustion engine.

[0002]

Conventionally than internal combustion engines, for example exhaust gas recirculation and engine exhaust passage and the engine intake passage in order to suppress the generation of the NO _x in the diesel engine (hereinafter, referred to as EGR) connected by passages, the Exhaust gas, that is, EGR gas, is recirculated through the EGR passage into the engine intake passage. In this case, the EGR gas has a relatively high specific heat, and therefore can absorb a large amount of heat.
The combustion temperature in the combustion chamber decreases as the GR gas amount increases, that is, as the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) increases. When the combustion temperature is lowered to decrease the generated amount of NO _x, thus the generation amount of the more NO _x to be increased EGR rate is lowered.

[0003] It has been found that can reduce the generation amount of the NO _x Thus conventionally increasing the EGR rate. However, when the EGR rate is increased, the soot generation amount, that is, smoke, starts to increase rapidly when the EGR rate exceeds a certain limit. In this regard, it has conventionally been considered that if the EGR rate is further increased, the smoke will increase indefinitely. Therefore, the smoke starts to increase rapidly.
The GR rate is considered to be the maximum allowable limit of the EGR rate.

Therefore, conventionally, the EGR rate is set within a range not exceeding the maximum allowable limit. The maximum allowable EGR rate varies considerably depending on the type of engine and fuel, but is approximately 30 to 50%.
Therefore, in a conventional diesel engine, the EGR rate is at most 3
It is reduced from 0% to about 50%.

As described above, conventionally, it has been considered that the maximum allowable limit exists for the EGR rate.
If the R rate is within the range not exceeding this maximum allowable limit, NO
_It was set so that the amount of _x and smoke generated was as small as possible. However, in this way EGR
Rate that there is a limit to the reduction of the NO _x and the amount of generated NO _x and the amount of smoke produced also defined to be as small as possible of smoke, in fact still a significant amount of N
At present, O _x and smoke are generated.

However, if the EGR rate is made larger than the maximum allowable limit in the course of research on the combustion of a diesel engine, the smoke rapidly increases as described above. However, the amount of generated smoke has a peak, and the peak exceeds this peak. EGR
When the rate is further increased, the smoke starts to decrease rapidly, and when the EGR rate is increased to 70% or more during idling operation, and when the EGR gas is cooled strongly, the smoke is reduced to about 55% or more. It was found that it was almost zero, that is, almost no soot was generated. In this case, N
Generation amount of O _x is also found that a very small amount.
After that, the reason why no soot was generated was examined based on this finding, and as a result, unprecedented soot and NO
_This has led to the construction of a new combustion system capable of simultaneously reducing _x . This new combustion system will be described in detail later, but in short, it is basically based on stopping the growth of hydrocarbons in the middle stage until the hydrocarbons grow into soot.

That is, as a result of repeated experimental studies, it has been found that when the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is lower than a certain temperature, the growth of hydrocarbons is stopped at a halfway stage before reaching soot. However, when the temperature of the fuel and the gas around it rises above a certain temperature, the hydrocarbons grow into soot at a stretch. In this case, the temperature of the fuel and the surrounding gas is greatly affected by the heat absorbing action of the gas around the fuel when the fuel is burned, and the amount of heat absorbed by the gas around the fuel is adjusted according to the calorific value at the time of burning the fuel. As a result, the temperature of the fuel and the surrounding gas can be controlled.

Accordingly, if the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, soot will not be generated, and the fuel during combustion in the combustion chamber and its surroundings will not be generated. Can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, by adjusting the amount of heat absorbed by the gas around the fuel. On the other hand, hydrocarbons whose growth has stopped halfway before reaching soot can be easily purified by post-treatment using an oxidation catalyst or the like. This is the basic idea of a new combustion system. An internal combustion engine employing this new combustion system has already been filed by the present applicant (Japanese Patent Application No. 9-305850).

[0009]

Conventionally, a compression ignition type in which a cavity is formed on the top surface of a piston, fuel is injected into the cavity from a fuel injection valve, and the injected fuel collides with the inner wall surface of the cavity. Internal combustion engines are known. In a typical example of such a compression ignition type internal combustion engine, a fuel thin film is formed on an inner wall surface of a piston by tangentially colliding fuel injected from a fuel injector on an inner wall surface of a cavity. The fuel is sequentially evaporated.

[0010] Thus sequentially the less the amount of smoke produced and NO _x with the combustion noise and the fuel evaporation is lowered from the fuel film and thus a method of burning fuel by such method are excellent combustion method It can be said.
However, when fuel is burned by such a method, a large amount of unburned HC and white smoke is generated, particularly during partial load operation, and a large amount of liquid HC and aldehyde emitting a bad smell are generated. Therefore, when burning fuel by such a method, it is necessary to provide a catalyst for oxidizing HC and aldehyde in the engine exhaust passage.

In this case, in the engine operating region where the exhaust gas temperature is high enough to activate the catalyst, HC and aldehyde are relatively well oxidized by the catalyst. However, during low engine load operation, the catalyst is not activated due to the low exhaust gas temperature.
C and aldehydes cannot be satisfactorily purified. Therefore, although this combustion method is an excellent combustion method, it has not been put to practical use at present.

However, when new combustion is performed, the exhaust gas temperature increases even during low load operation, as described later. Therefore, when an oxidation catalyst is disposed in the engine exhaust passage, the oxidation catalyst must be maintained in an active state. Can be. Therefore, under a new combustion, it is possible to use a combustion method in which the fuel is sequentially evaporated from the fuel thin film.

[0013]

Therefore, in the first invention, when the amount of inert gas in the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and the amount of inert gas in the combustion chamber is reduced. As the temperature increases further, the temperature of the fuel during combustion in the combustion chamber and the temperature of the surrounding gas become lower than the temperature at which the soot is generated, and soot is hardly generated. A first combustion in which the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of generated soot is at a peak, and soot is hardly generated;
Switching means for selectively switching between the second combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot becomes a peak, forming a cavity on the piston top surface, An internal combustion engine in which fuel is injected from a fuel injection valve into a cavity, and at least during the first combustion, the fuel injected from the fuel injection valve collides against an inner wall surface of the cavity.

In the second invention, in the first invention,
The fuel injected from the fuel injection valve tangentially collides with the inner wall surface of the cavity to form a thin fuel film on the inner wall surface of the piston, and the fuel is evaporated from the thin fuel film sequentially. According to a third aspect, in the first aspect, the fuel injected from the fuel injection valve is caused to collide almost vertically with the inner wall surface of the cavity.

In a fourth aspect, in the first aspect,
A raised portion is formed at the center of the cavity, and a collision surface is formed at the top of the raised portion, so that the fuel injected from the fuel injector collides with the collision surface so that the colliding fuel is scattered in the radial direction of the cavity. ing. In the fifth invention, 1
In the second invention, the operating range of the engine is set to the first load on the low load side.
Is divided into a first operating region and a second operating region on the high load side.
The first combustion is performed in the operation region, and the second combustion is performed in the second operation region.

In the sixth invention, in the fifth invention,
On the low load side of the second operation region, the fuel injected from the fuel injector tangentially collides with the inner wall surface of the cavity to form a thin fuel film on the inner wall surface of the piston, and the fuel is sequentially evaporated from the thin fuel film. On the high load side of the second operating region, the fuel injected from the fuel injector collides with the inner wall surface of the cavity almost vertically.

In the seventh invention, in the fifth invention,
A ridge is formed at the center of the cavity, and a collision surface is formed at the top of the ridge. At the low load side of the second operation area, fuel injected from the fuel injector collides almost perpendicularly to the inner wall surface of the cavity. On the high load side of the second operating region, the fuel injected from the fuel injection valve collides with the collision surface, and the colliding fuel is scattered in the radial direction of the cavity.

In the eighth invention, in the fifth invention,
A ridge is formed at the center of the cavity and a collision surface is formed at the top of the ridge, and the fuel injected from the fuel injection valve tangentially collides with the inner wall surface of the cavity on the low load side of the second operation region. As a result, a fuel thin film is formed on the inner wall surface of the piston, and the fuel is sequentially evaporated from the fuel thin film. On the high load side of the second operation region, the fuel injected from the fuel injector collides with the collision surface. The collision fuel is scattered in the radial direction of the cavity.

In the ninth invention, in the fifth invention,
In the second operation region, pilot injection is performed prior to the main injection, and fuel injected from the fuel injection valve tangentially collides with the inner wall surface of the cavity during the pilot injection to form a fuel thin film on the inner wall surface of the piston. Then, the fuel is sequentially evaporated from the fuel thin film, and the fuel injected from the fuel injection valve at the time of the main injection is caused to collide almost vertically with the inner wall surface of the cavity.

According to a tenth aspect, in the fifth aspect, a raised portion is formed at the center of the cavity and a collision surface is formed at the top of the raised portion. In the second operation region, the pilot injection is performed prior to the main injection. The fuel injected from the fuel injection valve at the time of the pilot injection is caused to collide with the inner wall surface of the cavity almost vertically, and the fuel injected from the fuel injection valve at the time of the main injection collides with the collision surface to remove the colliding fuel. It is made to scatter in the radial direction of the cavity.

According to an eleventh aspect, in the fifth aspect, a ridge is formed at the center of the cavity and a collision surface is formed at the top of the ridge. In the second operation region, pilot injection is performed prior to main injection. The fuel is injected from the fuel injection valve at the time of pilot injection to tangentially collide with the inner wall surface of the cavity to form a fuel thin film on the inner wall surface of the piston so that the fuel is sequentially evaporated from the fuel thin film, The fuel injected from the fuel injection valve at the time of the main injection is caused to collide with the collision surface so that the collided fuel is scattered in the radial direction of the cavity.

In a twelfth aspect based on the first aspect, there is provided an exhaust gas recirculation device for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage, wherein the inert gas comprises recirculated exhaust gas. . According to a thirteenth aspect, in the twelfth aspect, the exhaust gas recirculation rate during the first combustion is approximately 55% or more,
The exhaust gas recirculation rate when the combustion of
0% or less.

[0023] In the first invention in the 14th invention, the catalyst is an oxidation catalyst, consisting of one at least of the three-way catalyst or _the NO _x absorbent. In the first invention in the 15 th invention, the catalyst consists of _the NO _x absorbent, and air-fuel ratio under the first combustion when releasing the NO _x from the NO _x absorbent to be rich I have.

According to a sixteenth aspect, in the first aspect, the catalyst comprises a NO _x absorbent, and the catalyst comprises a NO _x absorbent.
Additional fuel is injected from the fuel injection valve during the exhaust stroke when O _x is to be released. In the first invention in the 17 th invention, the catalyst consists of _the NO _x absorbent, and the fuel injection valve when releasing the NO _x from the NO _x absorbent so as to inject additional fuel during the expansion stroke I have.

[0025]

FIG. 1 shows a case where the present invention is applied to a four-stroke compression ignition type internal combustion engine. Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Denotes an exhaust valve, and 10 denotes an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to a supercharger, for example, an outlet of a compressor 16 of an exhaust turbocharger 15 via an intake duct 13 and an intercooler 14. Be linked. An inlet of the compressor 16 is connected to an air cleaner 18 via an air suction pipe 17, and a throttle valve 20 driven by a step motor 19 is arranged in the air suction pipe 17.

On the other hand, the exhaust port 10 is connected to the exhaust manifold 2.
1 and the exhaust turbocharger 15 via the exhaust pipe 22
The exhaust gas turbine 23 is connected to a catalytic converter 26 having a built-in catalyst 25 having an oxidizing function via an exhaust pipe 24. The exhaust pipe 28 connected to the outlet of the catalytic converter 26 and the air suction pipe 17 downstream of the throttle valve 20 are connected to the EGR passage 2.
An EGR control valve 31 which is connected to each other via a motor 9 and driven by a step motor 30 is disposed in the EGR passage 29. Further, the EGR passage 29 is provided in the EGR passage 29.
An intercooler 32 for cooling the EGR gas flowing therein is arranged. In the embodiment shown in FIG. 1, the engine cooling water is guided into the intercooler 32, and the engine cooling water cools the EGR gas.

On the other hand, the fuel injection valve 6 is connected to a fuel reservoir, a so-called common rail 34, via a fuel supply pipe 33. Fuel is supplied into the common rail 34 from an electric control type variable discharge fuel pump 35, and the fuel supplied into the common rail 34 is supplied to the fuel injection valve 6 through each fuel supply pipe 33. A fuel pressure sensor 36 for detecting the fuel pressure in the common rail 34 is attached to the common rail 34, and the fuel pump 35 is controlled so that the fuel pressure in the common rail 34 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 36. Is controlled.

The electronic control unit 40 is composed of a digital computer, and has a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45, An output port 46 is provided. The output signal of the fuel pressure sensor 36 is input to the input port 45 via the corresponding AD converter 47. A load sensor 51 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. . Also, input port 4
5 is connected to a crank angle sensor 52 that generates an output pulse each time the crankshaft rotates, for example, by 30 °. On the other hand, the output port 46 is connected to the fuel injection valve 6, the throttle valve control step motor 19, the EGR control valve control step motor 30, and the fuel pump 35 via a corresponding drive circuit 48.

FIG. 2 shows the throttle valve 2 when the engine is operating at a low load.
Change in the output torque when changing the air-fuel ratio A / F (abscissa in FIG. 2) by changing the opening and the EGR rate of 0, and smoke, HC, CO, a change in emission of the NO _x It shows the experimental example shown. As can be seen from FIG. 2, in this experimental example, the smaller the air-fuel ratio A / F, the higher the EGR rate. When the air-fuel ratio A / F is smaller than the stoichiometric air-fuel ratio (≒ 14.6), the EGR rate is 65% or more.

As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the smoke is reduced when the EGR rate becomes close to 40% and the air-fuel ratio A / F becomes about 30. The generation starts to increase. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the amount of smoke generated sharply increases and reaches a peak. Next, when the EGR rate is further increased and the air-fuel ratio A / F is reduced, the smoke is sharply reduced. When the EGR rate is increased to 65% or more and the air-fuel ratio A / F is around 15.0, the smoke becomes almost zero. . That is, almost no soot is generated. At this time, the output torque of the engine slightly decreases, and N
The generation amount of O _x is considerably reduced. On the other hand, at this time, HC,
The amount of generated CO starts to increase.

FIG. 3 (A) shows the change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 21 and the amount of generated smoke is the largest, and FIG. 3 (B) shows the air-fuel ratio A / F. The graph shows the change in the combustion pressure in the combustion chamber 5 when the smoke generation amount is substantially zero when F is around 18. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), in the case of FIG. 3 (B) where the amount of smoke generation is almost zero, FIG.
It can be seen that the combustion pressure is lower than in the case shown in (A).

The following can be said from the experimental results shown in FIGS. That is, first, the air-fuel ratio A / F is 1
FIG. 2 when the smoke generation amount is almost zero at 5.0 or less.
As shown in ₍₁₎ , the generation amount of NOx is considerably reduced. N
That the generation amount of O _x produced falls means that the combustion temperature in the combustion chamber 5 is reduced, thus the combustion temperature in the combustion chamber 5 becomes low when the soot is hardly generated I can say. The same can be said from FIG. That is, in the state shown in FIG. 3B where almost no soot is generated, the combustion pressure is low.
The combustion temperature inside is low.

Second, when the amount of generated smoke, that is, the amount of generated soot becomes almost zero, as shown in FIG.
Emissions increase. This means that hydrocarbons are emitted without growing to soot. That is, the linear hydrocarbons and aromatic hydrocarbons contained in the fuel as shown in FIG. 4 are thermally decomposed when the temperature is increased in a state of lack of oxygen, soot precursors are formed, and then mainly, Soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot production process is complicated, and it is not clear what form the soot precursor takes, but in any case, the hydrocarbon as shown in FIG. It will grow to soot. Therefore, as described above, when the amount of generated soot becomes substantially zero, the emission amounts of HC and CO increase as shown in FIG. 2, but HC at this time is a precursor of soot or a hydrocarbon in a state before it. .

Summarizing these considerations based on the experimental results shown in FIGS. 2 and 3, when the combustion temperature in the combustion chamber 5 is low, the amount of soot generation becomes almost zero. Is discharged from the combustion chamber 5. As a result of further detailed experimental study on this, if the temperature of the fuel and the surrounding gas in the combustion chamber 5 is lower than a certain temperature, the growth process of the soot is stopped halfway, that is, the soot is It was found that no soot was generated, and soot was generated when the temperature of the fuel and its surroundings in the combustion chamber 5 exceeded a certain temperature.

Incidentally, the temperature of the fuel and its surroundings when the process of producing hydrocarbons is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature depends on various factors such as the type of fuel, the air-fuel ratio and the compression ratio. Although the change can not be said that how many times since this certain temperature has a generation amount and the closely related of the nO _x, therefore this certain temperature is defined to a certain degree from the generation amount of the nO _x be able to. That is, the fuel and the gas temperature surrounding it at the time of combustion and the greater the EGR rate, decreases, the amount of the NO _x is reduced. Generation amount at this time NO _x is soot is hardly generated when it is around or less 10 ppm. Therefore, the above certain temperature is NO
It almost coincides with the temperature when the amount of generated _x is about 10 p.pm or less.

Once soot is produced, it cannot be purified by post-treatment using a catalyst having an oxidizing function. On the other hand, the soot precursor or the hydrocarbon in a state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Considering the post-treatment with a catalyst having an oxidation function as described above, it is extremely difficult to discharge hydrocarbons from the combustion chamber 5 in the state of a precursor of soot or in the state before the soot or in the form of soot from the combustion chamber 5. There is a big difference. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a soot precursor or previous state without producing soot in the combustion chamber 5 and removes the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.

Now, in order to stop the growth of hydrocarbons before the soot is generated, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 are set to a temperature lower than the temperature at which the soot is generated. It needs to be suppressed. In this case, it has been found that the endothermic effect of the gas around the fuel when the fuel burns has an extremely large effect on suppressing the temperature of the fuel and the gas around the fuel.

That is, if there is only air around the fuel, the evaporated fuel immediately reacts with oxygen in the air and burns. In this case, the temperature of the air separated from the fuel does not rise so much, and only the temperature around the fuel becomes extremely high locally. That is, at this time, the air separated from the fuel hardly absorbs the heat of combustion heat of the fuel. In this case, since the combustion temperature becomes extremely high locally, the unburned hydrocarbons that have received the heat of combustion will generate soot.

On the other hand, when fuel is present in a mixed gas of a large amount of inert gas and a small amount of air, the situation is slightly different.
In this case, the fuel vapor diffuses to the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, the combustion temperature is not increased so much because the combustion heat is absorbed by the surrounding inert gas. That is, the combustion temperature can be kept low. That is, the presence of the inert gas plays an important role in suppressing the combustion temperature, and the combustion temperature can be kept low by the endothermic effect of the inert gas.

In this case, in order to suppress the temperature of the fuel and the gas around it to a temperature lower than the temperature at which soot is generated, an amount of the inert gas that can absorb a sufficient amount of heat to do so is required. . Therefore, if the fuel amount increases, the required amount of inert gas increases accordingly. In this case, the endothermic effect becomes stronger as the specific heat of the inert gas increases, and therefore, the inert gas preferably has a higher specific heat. In this regard, it can be said that it is preferable to use EGR gas as the inert gas since CO ₂ and EGR gas have relatively large specific heats.

FIG. 5 shows the relationship between the EGR rate and smoke when EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 5, a curve A indicates that the EGR gas temperature is substantially 9
Curve B shows the case where the EGR gas is cooled by a small cooling device, and curve C shows the case where the temperature is maintained at 0 ° C.
Indicates a case where the EGR gas is not forcibly cooled.

As shown by the curve A in FIG. 5, when the EGR gas is cooled strongly, the amount of soot generation peaks at a point where the EGR rate is slightly lower than 50%. Above a percentage, little soot is generated. On the other hand, as shown by the curve B in FIG. 5, when the EGR gas is slightly cooled, the soot generation amount reaches a peak at a point where the EGR rate is slightly higher than 50%. In this case, the EGR rate is increased to about 65% or more. If so, almost no soot is generated.

As shown by the curve C in FIG.
When the R gas is not forcibly cooled, the EGR rate becomes 5
The soot generation amount peaks near 5%, and in this case, if the EGR rate is set to approximately 70% or more, soot is hardly generated. FIG. 5 shows the amount of smoke generated when the engine load is relatively high. When the engine load decreases, the EGR rate at which the amount of soot peaks slightly decreases, and the EGR rate at which soot is hardly generated is reduced. Also lowers slightly. As described above, the lower limit of the EGR rate at which almost no soot is generated varies depending on the degree of cooling of the EGR gas and the engine load.

FIG. 6 shows a mixture of EGR gas and air necessary to make the temperature of fuel during combustion and its surrounding gas lower than the temperature at which soot is generated when EGR gas is used as the inert gas. It shows the gas amount, the ratio of air in the mixed gas amount, and the ratio of EGR gas in the mixed gas. In FIG. 6, the vertical axis indicates the total intake gas amount sucked into the combustion chamber 5, and the dashed line Y indicates the total intake gas amount that can be sucked into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis indicates the required load.

Referring to FIG. 6, the proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air necessary to completely burn the injected fuel. That is, in the case shown in FIG. 6, the ratio between the air amount and the injected fuel amount is the stoichiometric air-fuel ratio. On the other hand, in FIG. 6, the ratio of the EGR gas, that is, the amount of the EGR gas in the mixed gas, is set so that when the injected fuel is burned, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is formed. The required minimum EGR gas amount is shown. This EGR gas amount is approximately 55% or more in terms of the EGR rate. In the embodiment shown in FIG.
0% or more. That is, the total intake gas amount sucked into the combustion chamber 5 is indicated by a solid line X in FIG. 6, and the ratio of the air amount to the EGR gas amount in the total intake gas amount X is shown in FIG.
When the ratio is as shown in the following, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is generated, and thus no soot is generated. Further, the NO _x generation amount at this time is around 10 p.pm or less.
The amount of O _x generated is extremely small.

When the fuel injection amount increases, the amount of heat generated when the fuel burns increases. Therefore, in order to maintain the temperature of the fuel and the surrounding gas at a temperature lower than the temperature at which the soot is generated, the heat generated by the EGR gas is required. Must be increased. Therefore, as shown in FIG. 6, the EGR gas amount must be increased as the injected fuel amount increases.
That is, the EGR gas amount needs to increase as the required load increases.

When supercharging is not performed, fuel
The upper limit of the total intake gas amount X sucked into the firing chamber 5 is Y.
Therefore, in FIG.₀Territory larger than
In the region, the EGR gas ratio increases as the required load increases.
The air-fuel ratio can be maintained at the stoichiometric air-fuel ratio unless reduced.
Can not. In other words, it is necessary when there is no supercharging.
Load demand is L₀Air-fuel ratio in the larger area than theoretical
When trying to maintain the fuel ratio, the required load increases.
As a result, the EGR rate decreases, and thus the required load becomes L ₀Than
In areas where the fuel and the surrounding gas temperature are
It will not be possible to maintain a temperature lower than the temperature produced.

[0048] However through the EGR passage 29 as shown in Figure 1 of the supercharger inlet side, i.e. the required load and recirculate the EGR gas into the air intake pipe 17 of an exhaust turbocharger 15 than L ₀ In large areas, the EGR rate can be maintained at or above 55 percent, for example, 70 percent, and thus the temperature of the fuel and its surrounding gas can be maintained below the temperature at which soot is produced. That is, if the EGR gas is recirculated so that the EGR rate in the air suction pipe 17 becomes, for example, 70%, the EGR rate of the suction gas boosted by the compressor 16 of the exhaust turbocharger 15 also becomes 70%. The temperature of the fuel and the surrounding gas can be maintained at a temperature lower than the temperature at which soot is generated, to the extent that the pressure can be increased by the compressor 16. Therefore, the operating range of the engine that can generate low-temperature combustion can be expanded. In this case, the required load is EGR control valve 31 is fully opened is when the EGR rate more than 55 percent in the region larger than L _0, the throttle valve 20 is closed slightly.

As described above, FIG. 6 shows the case where the fuel is burned under the stoichiometric air-fuel ratio. However, even if the air amount is smaller than the air amount shown in FIG. 6, that is, the air-fuel ratio is made rich. 10p.p. the generation amount of the NO _x even while preventing generation of soot by
m or less, and even if the air amount is larger than the air amount shown in FIG. 6, that is, even if the average value of the air-fuel ratio is 17 to 18 lean, soot generation is prevented. while the generation amount of the NO _x can be around or less 10 ppm.

That is, when the air-fuel ratio is made rich, the fuel becomes excessive, but since the combustion temperature is suppressed to a low temperature, the excess fuel does not grow to soot, and soot is generated. There is no. Further, at this time NO _x even only an extremely small amount of generated. On the other hand, when the average air-fuel ratio is lean, or even when the air-fuel ratio is the stoichiometric air-fuel ratio, a small amount of soot is generated if the combustion temperature increases, but in the present invention, the soot is suppressed to a low temperature, so that the soot is reduced. Not generated at all. Furthermore, NO _x
Only very small amounts are generated.

As described above, when low-temperature combustion is performed, soot is generated regardless of the air-fuel ratio, that is, whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean. Sarezu, the amount of the NO _x becomes extremely small. Therefore, considering the improvement of the fuel consumption rate, it can be said that it is preferable to make the average air-fuel ratio lean at this time.

By the way, the temperature of fuel during combustion in the combustion chamber and its surrounding gas can be suppressed to a temperature below the temperature at which the growth of hydrocarbons stops halfway, only during low load operation in the engine, which generates a relatively small amount of heat by combustion. Can be Therefore, in the embodiment according to the present invention, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas temperature around the same at or below the temperature at which the growth of hydrocarbons stops halfway during the low load operation in the engine. In addition, the second combustion, that is, the combustion that is usually performed conventionally, is performed during the high load operation of the engine. Here, the first combustion, that is, the low-temperature combustion, has a larger amount of the inert gas in the combustion chamber than the amount of the inert gas at which the soot generation amount is at a peak, as is clear from the description so far. The second combustion, that is, the combustion that has been performed normally in the past, is a combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of soot is peaked. Say that.

The solid line in FIG. 7A shows the relationship between the average gas temperature Tg in the combustion chamber 5 and the crank angle when the first combustion is performed, and the broken line in FIG. 2 shows the relationship between the average gas temperature Tg in the combustion chamber 5 and the crank angle when the combustion of No. 2 is performed. The solid line in FIG. 7 (B) represents the fuel and gas temperature Tf around the fuel when the first combustion is performed.
7B shows the relationship between the fuel and the surrounding gas temperature Tf and the crank angle when the second combustion is performed.

When the first combustion, that is, the low-temperature combustion is being performed, the amount of the EGR gas is larger than when the second combustion, that is, the conventional ordinary combustion is being performed.
As shown in (A), before the compression top dead center, that is, during the compression process, the average gas temperature Tg during the first combustion shown by the solid line is better than the average gas temperature Tg during the second combustion shown by the broken line.
Is higher than. At this time, as shown in FIG. 7 (B), the temperature of the fuel and its surrounding gas Tf is substantially the same as the average gas temperature Tg.

Next, combustion is started near the compression top dead center. In this case, when the first combustion is being performed, the temperature of the fuel and the gas Tf around the fuel and its surroundings are reduced as shown by the solid line in FIG. 7B. Not so high. The second
When the combustion is performed, the fuel and the surrounding gas temperature Tf become extremely high as shown by the broken line in FIG. 7B. When the second combustion is performed as described above, the temperature Tf of the fuel and the surrounding gas becomes considerably higher than that of the case where the first combustion is performed, but the temperature of the other gas that occupies most of the temperature Tf. Is lower in the case where the second combustion is performed than in the case where the first combustion is performed. Therefore, as shown in FIG. The average gas temperature Tg in the chamber 5 is higher when the first combustion is being performed than when the second combustion is being performed. As a result, as shown in FIG. 7A, the average gas temperature Tg in the combustion chamber 5 after the combustion is completed, that is, in the latter half of the expansion stroke, in other words, the temperature of the burned gas in the combustion chamber 5 becomes the second temperature. The case where the first combustion is performed is higher than the case where the second combustion is performed.

As described above, when the first combustion, that is, the low-temperature combustion is performed, the temperature of the fuel and the surrounding gas Tf during the combustion is considerably lower than that in the case where the second combustion is performed. The burned gas in the chamber 5 is higher than that in the case where the second combustion is performed. Therefore, the temperature of the exhaust gas discharged from the combustion chamber 5 is also lower than that in the case where the second combustion is performed. Get higher.

FIG. 8 shows a first operation region I in which the first combustion, that is, low-temperature combustion is performed, and a second operation region II in which the second combustion, that is, combustion by the conventional combustion method, is performed. I have. In FIG. 8, the vertical axis L indicates the depression amount of the Alcel pedal 50, that is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 8, X (N) is the first
Shows the first boundary between the operating region I and the second operating region II, and Y (N) represents the first operating region I and the second operating region.
2 shows a second boundary with II. The determination of the change of the operating range from the first operating range I to the second operating range II is made based on the first boundary X (N), and the determination of the change from the second operating range II to the first
The determination of the change of the operation region to the operation region I of the second boundary Y
(N).

That is, when the operating state of the engine is in the first operating region I
When the required load L exceeds a first boundary X (N), which is a function of the engine speed N, during low-temperature combustion, it is determined that the operation region has shifted to the second operation region II, Combustion is performed by a conventional combustion method. Next, when the required load L becomes lower than a second boundary Y (N) which is a function of the engine speed N, it is determined that the operation region has shifted to the first operation region I, and low-temperature combustion is performed again.

The two boundaries of the first boundary X (N) and the second boundary Y (N) on the lower load side than the first boundary X (N) are provided as follows. For three reasons. The first reason is that the combustion temperature is relatively high on the high load side of the second operation region II, and even if the required load L becomes lower than the first boundary X (N), low-temperature combustion cannot be performed immediately. Because. That is, the low-temperature combustion does not immediately start unless the required load L becomes considerably low, that is, when the required load L becomes lower than the second boundary Y (N). The second reason is that hysteresis is provided for a change in the operation range between the first operation range I and the second operation range II.

Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG. FIG. 9 shows the throttle valve 2 with respect to the required load L.
0 indicates the opening degree, the opening degree of the EGR control valve 31, the EGR rate, the air-fuel ratio, the injection timing, and the injection amount. As shown in FIG. 9, in the first operating region I where the required load L is low, the opening of the throttle valve 20 is gradually increased from almost fully closed to about 2/3 opening as the required load L increases. E
The degree of opening of the GR control valve 31 is gradually increased from almost fully closed to fully open as the required load L increases. Also,
In the example shown in FIG. 9, in the first operation region I, the EGR rate is set to approximately 70%, and the air-fuel ratio is set to a slightly lean air-fuel ratio.

In other words, in the first operating region I, the EGR
The opening of the throttle valve 20 and the opening of the EGR control valve 31 are controlled such that the rate becomes approximately 70% and the air-fuel ratio becomes a slightly lean air-fuel ratio. In the first operation region I, fuel injection is performed before the compression top dead center TDC. In this case, the injection start timing θS is delayed as the required load L is increased, and the injection completion timing θE is delayed as the injection start timing θS is delayed.

When the engine is idling, the throttle valve 20 is closed until the valve is almost fully closed. At this time, the EGR control valve 31 is also closed almost completely. Throttle valve 2
If the valve is closed close to 0, the pressure in the combustion chamber 5 at the start of compression decreases, so that the compression pressure decreases. When the compression pressure decreases, the compression work by the piston 4 decreases, so that the vibration of the engine body 1 decreases. That is, at the time of idling operation, the throttle valve 20 is closed to almost fully closed in order to suppress the vibration of the engine body 1.

On the other hand, the operating region of the engine is the first operating region I
From the second operating region II to the second operating region II, the opening of the throttle valve 20 is increased stepwise from about 2/3 opening toward the full opening direction. At this time, in the example shown in FIG. 9, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. That is, the EGR rate at which the EGR rate generates a large amount of smoke
The engine operating range is the first because it jumps over the rate range (Fig. 5).
A large amount of smoke does not occur when changing from the operating region I to the second operating region II.

In the second operation region II, the second combustion, that is, the conventional combustion is performed. In this combustion method generates little soot and NO _x, but the heat efficiency is higher than the low temperature combustion, thus as the operating region of the engine is shown in Figure 9 from the first operation area I changes to the second operating region II Thus, the injection amount is reduced stepwise. In the second operating region II, the throttle valve 20 is held in a fully open state except for a part, and the opening of the EGR control valve 31 is gradually reduced as the required load L increases. In this operating region II, the EGR rate decreases as the required load L increases, and the air-fuel ratio decreases as the required load L increases. However, the air-fuel ratio is a lean air-fuel ratio even when the required load L increases.

On the other hand, in the embodiment according to the present invention, the second operating region II is further divided into a region P on the low load side and a region W on the high load side. As shown in FIG. 9, the second operation area
In the low load side region P of II, the injection start timing θS is set before the compression top dead center TDC, and the second operation region II
In the high-load side region W of FIG.
It is near DC.

FIG. 10 shows the air-fuel ratio A / F in the first operating region I. In FIG. 10, A / F = 15.
The curves indicated by 5, A / F = 16, A / F = 17, and A / F = 18 have air-fuel ratios of 15.5, 16, 17, and 18, respectively.
And the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 10, the air-fuel ratio is lean in the first operating region I, and in the first operating region I, the air-fuel ratio A / F becomes leaner as the required load L decreases.

That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, low-temperature combustion can be performed even if the EGR rate is reduced as the required load L decreases.
When the EGR rate is reduced, the air-fuel ratio increases. Therefore, as shown in FIG. 10, as the required load L decreases, the air-fuel ratio A / F increases. As the air-fuel ratio A / F increases, the fuel consumption rate increases. Accordingly, in order to make the air-fuel ratio as lean as possible, in the embodiment according to the present invention, the air-fuel ratio A / F increases as the required load L decreases.

The target opening degree ST of the throttle valve 20 required for setting the air-fuel ratio to the target air-fuel ratio shown in FIG.
As shown in FIG. 1A, the EGR is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N, and is necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. The target opening SE of the control valve 31 is as shown in FIG.
As shown in (1), a map is previously stored in the ROM 42 as a function of the required load L and the engine speed N.

FIG. 12 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 12, A / F = 24 and A / F = 3.
Curves indicated by 5, A / F = 45 and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. Throttle valve 2 required to set air-fuel ratio to this target air-fuel ratio
As shown in FIG. 13A, a target opening degree ST of 0 is stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N, and the air-fuel ratio is set as the target air-fuel ratio. Opening SE of EGR control valve 31 necessary for
Are stored in the ROM 42 in advance in the form of a map as a function of the required load L and the engine speed N as shown in FIG.

Next, a first embodiment of the combustion chamber structure and the injection method used in the present invention will be described with reference to FIGS. 14 (A) and 14 (B). Referring to FIGS. 14A and 14B, a cavity 60 is formed at the center of the top surface of the piston 4. A raised portion 61 projecting upward is formed at the center of the bottom wall surface of the cavity 60, and a lip portion 62 projecting inward is formed at the upper end of the inner peripheral surface of the cavity 60. . A plurality of fuel sprays F having a small injection angle are injected from the fuel injection valve 6 into the cavity 60. FIG. 14A shows the first operation region I,
FIG. 14B shows fuel injection in the low load side region P of the second operation region II, and FIG. 14B shows fuel injection in the high load side region W of the second operation region II.

As can be seen from FIG. 9, the first operating region I,
In the low-load region P of the second operation region II, the injection start timing θS is set before the compression top dead center TDC. Therefore, at this time, as shown in FIG.
Is at a low position, the fuel F is injected from the fuel injection valve 6, and at this time, the injected fuel F collides tangentially on the inner wall surface of the cavity 60. The impinging fuel then spreads in the form of a fuel film on the inner wall of the cavity 60, as indicated by F '. Next, the fuel gradually evaporates from the fuel thin film F ', and the evaporated fuel is sequentially burned.

[0072] Now, when the first combustion is assumed to take place the gas temperature of the fuel and its surroundings at the time of combustion at this time is kept low, thus the time of soot and NO _x are hardly generated. Instead, unburned hydrocarbons are discharged from the combustion chamber 5 in the form of a soot precursor or previous state. On the other hand, at this time, unburned HC or liquid H
C and aldehydes are generated, and these unburned HC and liquid HC
Aldehydes and aldehydes are also discharged from the combustion chamber 5.

However, as described above, when the first combustion is being performed, the temperature of the exhaust gas is high, and therefore, at this time, the catalyst 25 having an oxidizing function is maintained in an activated state. Therefore, at this time, unburned HC, liquid HC, aldehyde, and the like discharged from the combustion chamber 5 are satisfactorily purified by the catalyst 25. Therefore, emission of harmful components into the atmosphere can be suppressed, and generation of offensive odor can be suppressed.

On the other hand, if the second combustion is performed at this time, since the combustion temperature is higher than during the low engine load operation, the unburned HC and liquid The amount of HC and aldehydes generated is reduced.
However, at this time, since the temperature of the inner wall surface of the cavity 60 does not rise so much, a part of the fuel forming the thin film F 'remains without burning, and the unburned H
Since C and aldehyde are generated, unburned HC, liquid HC and aldehyde are still discharged from the combustion chamber 60.
However, when the second combustion is being performed, the exhaust gas temperature is high due to the large amount of heat generated. Accordingly, at this time, the catalyst 25 is maintained in the activated state, and therefore, the unburned HC, liquid HC, and aldehyde discharged from the engine are satisfactorily purified by the catalyst 25. In addition,
At this time, the fuel evaporated from the fuel thin film F 'is gradually burned, so that the combustion becomes gentle and the combustion noise is considerably reduced. The generation amount of the NO _x and smoke at this time is also reduced.

As can be seen from FIG. 9, in the high load side region W of the second operation region II, fuel F is injected from the fuel injection valve 6 near the compression top dead center TDC. At this time, the pressure in the combustion chamber 5 is high, and part of the injected fuel is split and diffused before reaching the inner wall surface of the cavity 60. Further, at this time, as shown in FIG. 14B, since the position of the piston 4 is high, part of the injected fuel F collides with the inner wall surface of the cavity 60 almost vertically. The impinging fuel then reflects and quickly diffuses into cavity 60.
As described above, in the high-load-side region W of the second operation region II, the fuel is diffused throughout the cavity 60, so that good combustion without smoke is obtained.

The low load side region P of the second operation region II
Alternatively, pilot injection is performed prior to main injection in the high load side region W, and at this time, the injected fuel F at the time of pilot injection tangentially collides with the inner wall surface of the cavity 60 as shown in FIG. In other words, the injected fuel F at the time of the main injection may be caused to collide almost vertically with the inner wall surface of the cavity 60 as shown in FIG.

FIGS. 15A and 15B show a second embodiment of the combustion chamber structure and injection method used in the present invention. Referring to FIGS. 15A and 15B, in the second embodiment, a substantially flat annular collision surface 63 is formed on the top surface of the raised portion 61 of the cavity 60. Note that, also in this embodiment, FIG. 15A shows fuel injection in the low load side region P of the first operation region I and the second operation region II, and FIG. The fuel injection in the high load side region W of the operation region II is shown.

In this embodiment, in the low load side region P of the first operation region I or the second operation region II, as shown in FIG.
Is almost perpendicular to the inner wall of the car. At this time, since the pressure in the combustion chamber 5 is not so high yet, a considerable amount of the injected fuel F collides with the inner wall surface of the cavity 60. Due to this collision action, the cavity 6
An air-fuel mixture is formed in zero.

On the other hand, in the high load region W of the second operation region II, the fuel F is injected from the fuel injection valve 6 near the compression top dead center TDC as shown in FIG. At this time, the injected fuel F collides with the collision surface 63, and the colliding fuel F is scattered in the cavity 60 in the radial direction of the cavity 60. As a result, the fuel is dispersed throughout the cavity 60.

In this case, pilot injection is performed prior to main injection in the low load side region P or the high load side region W of the second operation region II. As shown in FIG. 15 (A), the fuel is caused to collide almost vertically on the inner wall surface of the cavity 60, and the injected fuel F at the time of the main injection is made to collide with the collision surface 63 of the cavity 60 as shown in FIG. 15 (B). You can also

FIGS. 16A and 16B show a third embodiment of the combustion chamber structure and injection method used in the present invention. Referring to FIGS. 15A and 15B, the third embodiment also has a substantially flat annular collision surface 63 formed on the top surface of the raised portion 61 of the cavity 60. Also in this embodiment, FIG. 16A shows the fuel injection in the low load side region P of the first operation region I and the second operation region II, and FIG. The fuel injection in the high load side region W of the operation region II is shown.

In this embodiment, in the low load side region P of the first operation region I or the second operation region II, as shown in FIG.
Tangentially collide with the inner wall surface. Therefore, the colliding fuel spreads on the inner wall surface of the cavity 60 in the form of the fuel thin film F ', and the fuel is gradually evaporated from the fuel thin film F'.

On the other hand, in the high load region W of the second operation region II, the fuel F is injected from the fuel injection valve 6 near the compression top dead center TDC as shown in FIG. At this time, the injected fuel F collides with the collision surface 63, and the colliding fuel F scatters in the cavity 60 in the radial direction of the cavity 60. As a result, the fuel is dispersed throughout the cavity 60.

In this case as well, pilot injection is performed prior to main injection in the low load side region P or the high load side region W of the second operation region II. As shown in FIG. 16 (A), it collides with the inner wall surface of the cavity 60 tangentially,
The injected fuel F during the main injection may be caused to collide with the collision surface 63 of the cavity 60 as shown in FIG.

[0085] By the way as a catalyst 25 may be an oxide catalyst, three-way catalyst, or _the NO _x absorbent. NO _x
Absorber has the function of releasing the average air-fuel ratio is absorbed NO _x when the lean, the average air-fuel ratio becomes rich in the combustion chamber 5 NO _x in the combustion chamber 5. This NO
_{The x} absorbent is, for example, alumina as a carrier. On this carrier, for example, potassium K, sodium Na, lithium Li, alkali metal such as cesium Cs, barium Ba, alkaline earth such as calcium Ca, lanthanum La, yttrium Y At least one selected from such rare earths,
A noble metal such as platinum Pt is supported.

The oxidation catalyst, the three-way catalyst and the NO
_{The x} absorbent also has an oxidizing function, so that a three-way catalyst and a NO _x absorbent can be used as the catalyst 25 as described above. Next, the operation control will be described with reference to FIG. Referring to FIG. 17, first, Step 1
At 00, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, step 10
The program proceeds to 1 to determine whether the required load L has become larger than the first boundary X1 (N). When L ≦ X1 (N), the routine proceeds to step 103, where low-temperature combustion is performed.

That is, in step 103, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 11A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 104, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening of the EGR control valve 31 is set as the target opening SE.
Next, in step 105, FIG.
(A) or fuel injection is performed as shown in FIG. At this time, low-temperature combustion is performed.

On the other hand, in step 101, L> X
When it is determined that (N) has been reached, the routine proceeds to step 102, where the flag I is reset.
And the second combustion is performed. That is, step 108
In FIG. 13A, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 13A, and the opening of the throttle valve 20 is set as the target opening ST. Next, at step 109, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 13B, and the opening of the EGR control valve 31 is set to the target opening SE. Next, at step 110, FIG.
(A), (B) or FIG. 15 (A), (B) or FIG.
Fuel injection is performed as shown in (A) and (B).

When the flag I is reset, in the next processing cycle, the process proceeds from step 100 to step 106, where it is determined whether the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), step 108
And the second combustion is performed. On the other hand, step 106
When it is determined that L <Y (N), the routine proceeds to step 107, where the flag I is set. Then, the routine proceeds to step 103, where low-temperature combustion is performed.

Next, the case where a NO _x absorbent is used as the catalyst 25 will be described. This _the NO _x absorbent 25 as described above has a function average air-fuel ratio in the combustion chamber 5 absorbs NO _x when the lean, the average air-fuel ratio in the combustion chamber 5 is to release the NO _x becomes rich . To put it more precisely, the ratio of air and fuel (hydrocarbon) supplied to the engine intake passage, the combustion chamber 5 and the exhaust passage upstream of the NO _x absorbent 25 is determined by the ratio of the exhaust gas flowing into the NO _x absorbent 25. Toko of the NO _x absorbent 25 is referred to as the air-fuel ratio is the air-fuel ratio of the inflowing exhaust gas absorbs NO _x when the lean air-fuel ratio of the inflowing exhaust gas to release NO _x absorbed to become stoichiometric or rich carry out the absorption and release action of NO _x.

If this NO _x absorbent 25 is disposed in the exhaust passage of the engine, the NO _x absorbent 25 actually performs the absorption and release of NO _x , but the detailed mechanism of this absorption and release is not clear. . However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

In the compression ignition type internal combustion engine shown in FIG. 1, combustion is performed with the air-fuel ratio in the normal combustion chamber 5 being lean. Thus the oxygen concentration in the exhaust gas when the air-fuel ratio is performed is combusted in a lean state is high, these oxygen O ₂ as is shown in FIG. 18 (A) at this time O
₂ ^- or O ^2- shape is deposited on the surface of the platinum Pt. on the other hand,
NO in the inflowing exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of the platinum Pt to become NO ₂ (2NO + O ₂ → 2N).
O ₂ ). Next, a part of the generated NO ₂ is absorbed in the absorbent while being oxidized on the platinum Pt, and the barium oxide BaO
As shown in FIG. 18 (A), it diffuses into the absorbent in the form of nitrate ions NO ₃ ⁻ while being combined. In this way, NO _x is absorbed in the NO _x absorbent 25. NO ₂ is produced on the surface of the platinum Pt so long as the oxygen concentration in the inflowing exhaust gas is high, NO unless absorption of NO _x capacity of the absorbent is not saturated
₂ is absorbed in the absorbent and nitrate ions NO ₃ ^- are produced.

On the other hand, the air-fuel ratio of the inflowing exhaust gas is made rich.
The concentration of oxygen in the incoming exhaust gas decreases,
NO on the surface of gold Pt_TwoIs reduced. NO_Twoof
When the amount of production decreases, the reaction reverses (NO_Three ^-→ NO_Two)
And thus nitrate ion NO in the absorbent_Three ^-Is NO
_TwoReleased from the absorbent in the form of NO at this time_xAbsorbent
NO released from 25_xIs shown in FIG. 18 (B).
A large amount of unburned HC and CO contained in the inflow exhaust gas
It is reduced by reaction. In this way, platinum Pt
NO on surface_TwoWhen no longer exists, the next
NO_TwoIs released. Therefore, the air-fuel ratio of the incoming exhaust gas
Is enriched in a short time, NO _xAbsorbent 25?
NO_xIs released, and the released NO_xIs returned
NO in the atmosphere to be removed_xWill not be released
No.

In this case, the air-fuel ratio of the inflowing exhaust gas is
NO even at stoichiometric air-fuel ratio_xNO from absorbent 25_xIs released
Is done. However, the air-fuel ratio of the inflowing exhaust gas is
NO if ratio_xNO from absorbent 25_xGradually
NO because only _xAbsorbed by the absorbent 25
All NO_xIt takes a slightly longer time to release.

[0095] Incidentally there is a limit to the absorption of NO _x capacity of the NO _x absorbent 25, absorption of NO _x capacity of the NO _x absorbent 25 needs to release the NO _x from the NO _x absorbent 25 before saturation. For this purpose it is necessary to estimate the amount of NO _x is absorbed in the NO _x absorbent 25. Therefore, in this embodiment of the present invention of a map as shown in FIG. 19 (A) as a function of the NO _x absorption amount A of the required load L and engine speed N per unit time when it is performed first combustion is previously obtained in the form of a map as shown in FIG. 19 (B) the absorption of NO _x amount B per unit time as a function of the required load L and engine speed N when the second combustion is being performed It is previously obtained in the form, per these unit time of absorption of NO _x amount a, so that to estimate the amount of NO _x ΣNOX being absorbed in the NO _x absorbent 25 by integrating the B.

[0096] In the embodiment according to the present invention N when exceeding the allowable maximum value that this absorption of NO _x amount ΣNOX reaches a predetermined
NO _x is released from the O _x absorbent 25. Next, this will be described with reference to FIG. Referring to FIG. 20, in the embodiment according to the present invention, there are two allowable maximum values, namely, an allowable maximum value MAX1 and an allowable maximum value MA.
X2 is set. The maximum allowable value MAX1 is NO _x
The maximum absorption amount MAX2 is about 30% of the maximum NO _x absorption amount that the absorbent 25 can absorb, and the allowable maximum value MAX2 is about 80% of the maximum absorption amount that the NO _x absorbent 25 can absorb. NO _x during the first combustion
NO fuel ratio in order to release the NO _x from _x absorbent 25 is made rich, NO _x absorption amount ΣNOX permissible maximum when the second combustion is being performed when the absorption amount ΣNOX has exceeded the allowable maximum value MAX1 When the value exceeds MAX1, the second
Air-fuel ratio in order to release the NO _x from the NO _x absorbent 25 when it is switched from the combustion to the first combustion is made rich,
Absorption of NO _x amount when the second combustion is being performed ΣNOX
_The NO _x absorbent 2 when but exceeding the maximum allowable value MAX2
5 additional fuel during the expansion stroke or during the exhaust stroke so as to release the NO _x is ejected from.

That is, in FIG. 20, the period X is the required load L
Is lower than the first boundary X (N), indicating that the first combustion is being performed. At this time, the air-fuel ratio is a lean air-fuel ratio slightly leaner than the stoichiometric air-fuel ratio. First when combustion is being performed extremely small generation amount of the NO _x is therefore of absorption of NO _x amount ΣNOX as is shown in Figure 20 at this time rises very slowly. Absorption of NO _x amount ΣN when first combustion is being performed
OX is an air-fuel ratio A / F exceeds the allowable maximum value MAX1 is temporarily rich, whereby NO _x from the NO _x absorbent 25 is released. At this time, NO _x absorption amount ΣNOX
Is set to zero.

As described above, when the first combustion is being performed, no soot is generated regardless of whether the air-fuel ratio is lean, the stoichiometric air-fuel ratio, or rich, so that the first combustion is performed. and does not soot generated at this time is also the air-fuel ratio a / F in order to release the nO _x from the nO _x absorbent 25 is made rich when being. Then the required load L at time t ₁ is switched from the first combustion exceeds the first boundary X (N) to the second combustion. As shown in FIG.
When the combustion is performed, the air-fuel ratio A / F becomes considerably lean. When the second combustion is being performed _the amount of NO _x ΣNOX when the generation amount of the NO _x as compared with the case where the first combustion is being performed is large and therefore the second combustion is being performed relatively quickly To rise.

When the second combustion is being performed, the air-fuel ratio A
When / F is made rich, a large amount of soot is generated, and therefore, the air-fuel ratio A / F cannot be made rich during the second combustion. Thus the air-fuel ratio in order to release the NO _x from the NO _x absorbent 25 even absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX1 when the second combustion is being performed as shown in FIG. 20 A / F is not made rich.
The required load L as at time t ₂ in FIG. 20 when the _the NO _x absorbent when is switched from the second combustion is lower in the first combustion than the second boundary Y (N) 25 air-fuel ratio a / F in order to release the NO _x is rich temporarily from.

Next, it is assumed that the first combustion is switched to the second combustion at time t ₃ in FIG. 20, and the second combustion is continued for a while. The time of absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX1, then during the expansion stroke so as to release the NO _x from the NO _x absorbent 25 at this time assuming that exceeds the allowable maximum value MAX2 at time t ₄ or during the exhaust stroke Additional fuel is injected, and the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 25 is made rich.

The additional fuel injected during the expansion or exhaust stroke does not contribute to the generation of engine power, and therefore it is preferable to inject the additional fuel as little as possible. Therefore, when the second combustion is performed, the NO _x absorption amount Σ
When the NOX exceeds the allowable maximum value MAX1 is temporarily rich air-fuel ratio A / F when it is switched to the first combustion from the second combustion, NO _x absorption amount ΣNOX has exceeded the allowable maximum value MAX2 Additional fuel is injected only in special cases.

As shown in FIGS. 14 to 16, in the embodiment according to the present invention, the spray angle of the injected fuel F is small.
Therefore, at the end of the exhaust stroke, the fuel injection valve 6 moves the cavity 60
When the fuel F is injected inward, the injected fuel stays in the cavity 60 without being diffused and atomizes in the cavity 60. Therefore, without NO _x also NO _x from the absorbent 25 from the fuel injection valve 6 during the exhaust stroke in order to release performs fuel injection injected fuel adheres to the inner wall surface of the cylinder,
Thus, there is no danger of lubricating oil being diluted by the fuel.

Further, even if the fuel F is injected from the fuel injection valve 6 into the cavity 60 in the first half of the expansion stroke, the injected fuel remains in the cavity 60 without being diffused. Therefore, without _the NO _x absorbent 25 injected fuel even if the fuel injected from the fuel injection valve 6 during the expansion stroke so as to release the NO _x from adheres to the inner wall surface of the cylinder, lubricating oil by the fuel and thus There is no danger of dilution. Further, in the first half of the expansion stroke, the temperature in the combustion chamber 5 gradually decreases, so that even if fuel injection is performed at this time, the hydrocarbon does not grow to soot, and therefore no smoke is generated. However, since the temperature in the combustion chamber 5 is considerably high, the hydrocarbons are cracked and become hydrocarbons or radicals having a small molecular weight. As a result, good can be released NO _x from the NO _x absorbent 25 to be active as a reducing agent is increased, so that can be favorably reduced the released NO _x.

Next, the NO _x absorbent 25 will be described with reference to FIG.
The processing routine of the NO _x release flag that is set when NO _x should be released from will be described. This routine is executed by interruption every predetermined time. FIG.
Referring to FIG. 1, first, at step 200, it is determined whether or not a flag I indicating that the operation region of the engine is the first operation region I is set. When the flag I is set, that is, when the operation region of the engine is the first operation region I, the routine proceeds to step 201, and FIG.
From the map shown in (A) per unit time of absorption of NO _x amount A
Is calculated. Then A is added to the absorption of NO _x amount ΣNOX step 202. Next, at step 203 NO _x absorption amount ΣNOX whether exceeds the allowable maximum value MAX1 is determined. If ΣNOX> MAX1, the routine proceeds to step 204, where NO is set during the first combustion.
A NO _x release flag 1 indicating that _x should be released is set. On the other hand, when it is determined in step 200 that the flag I has been reset, that is, when the operating region of the engine is in the second operating region II, the routine proceeds to step 205, where the map per unit time is obtained from the map shown in FIG. NO
_x Absorption amount B is calculated. Next, at step 206, N
B is added to the O _x absorption amount .SIGMA.NOX. Next, at step 207 NO _x absorption amount ΣNOX allowable maximum value MAX1
Is determined. Becomes the .SIGMA.NOX> MAX1 proceeds to step 208, NO _x releasing flag 1 indicating that it should release the NO _x is set when the first combustion is being performed.

[0105] On the other hand, in step 209, whether absorption of NO _x amount ΣNOX has exceeded the allowable maximum value MAX2 is determined. Becomes a .SIGMA.NOX> MAX2 proceeds to step 210, NO _x releasing flag 2 which indicates that it should inject additional fuel during the expansion stroke or the exhaust stroke is set. Next, the operation control will be described with reference to FIG.

Referring to FIG. 22, first, in step 300, it is determined whether or not a flag I indicating that the operating state of the engine is in the first operating region I is set. If the flag I is set, that is, if the operating state of the engine is in the first operating region I, step 3
In step 01, it is determined whether the required load L has become larger than the first boundary X1 (N). When L ≦ X1 (N), the routine proceeds to step 303, where low-temperature combustion is performed.

That is, in step 303, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 11A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 304, the target opening degree SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening of the EGR control valve 31 is set as the target opening SE.
Next, at step 305 NO _x releasing flag 1 is whether it is set or not. When the NO _x release flag 1 is not set, the routine proceeds to step 306, where fuel injection is performed as shown in FIG. 14 (A), FIG. 15 (A) or FIG. 16 (A).

[0108] On the other hand, the injection control I is performed proceeds to step 307 when _the NO _x releasing flag 1 is judged as being set in step 305. In this injection control I, the air-fuel ratio is made rich for a predetermined period,
Then ΣNOX is made zero, NO _x releasing flag 1 is reset. On the other hand, in step 301, L> X
When it is determined that (N) has been reached, the routine proceeds to step 302, where the flag I is reset.
And the second combustion is performed.

That is, in step 310, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 13A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 311, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG.
The opening of the EGR control valve 31 is set as the target opening SE.
Then whether _the NO _x releasing flag 2 in step 312 is set or not. When the NO _x release flag 2 is not set, the routine proceeds to step 313, and FIG. 14 (A), (B) or FIG. 15 (A), (B) or FIG.
Fuel injection is performed as shown in FIGS. 6 (A) and 6 (B).

[0110] On the other hand, the injection control II is performed proceeds to step 314 when _the NO _x releasing flag 2 has been determined to have been set in step 312. Period additional fuel required to bring the air-fuel ratio of the exhaust gas flowing into the injection control II, _the NO _x absorbent 25 rich is predetermined for the expansion stroke initial or exhaust stroke end, the cavity from the fuel injection valve 6 injected into the 60, then ΣNOX is made zero, _the NO _x releasing flag I and _the NO _x releasing flag II is reset.

[0111]

Even if the injected fuel is caused to collide with the inner wall surface of the cavity formed on the top surface of the piston, the release of harmful components to the atmosphere and the generation of offensive odors are suppressed regardless of the engine load. Can be suppressed.

[Brief description of the drawings]

FIG. 1 is an overall view of a compression ignition type internal combustion engine.

FIG. 2 is a diagram showing amounts of smoke and NO _x generated, and the like.

FIG. 3 is a diagram showing a combustion pressure.

FIG. 4 is a diagram showing fuel molecules.

FIG. 5 is a diagram showing a relationship between a generation amount of smoke and an EGR rate.

FIG. 6 is a diagram showing a relationship between an injected fuel amount and a mixed gas amount.

FIG. 7 is a diagram showing changes in an average gas temperature Tg in a combustion chamber, and changes in fuel and a gas temperature Tf around the fuel.

FIG. 8 is a diagram showing a first operation region I and a second operation region II.

FIG. 9 is a view showing an opening degree of a throttle valve and the like.

FIG. 10 is a diagram showing an air-fuel ratio in a first operation region I.

FIG. 11 is a diagram showing a map of a target opening degree of a throttle valve and the like.

FIG. 12 is a view showing an air-fuel ratio in a second combustion.

FIG. 13 is a view showing a map of a target opening degree of a throttle valve and the like.

FIG. 14 is a side cross-sectional view of the combustion chamber showing the first embodiment.

FIG. 15 is a side sectional view of a combustion chamber showing a second embodiment.

FIG. 16 is a side sectional view of a combustion chamber according to a third embodiment.

FIG. 17 is a flowchart for controlling operation of the engine.

FIG. 18 is a view for explaining a NO _x releasing action.

FIG. 19 is a diagram showing a map of the NO _x absorption amount per unit time.

FIG. 20 is a diagram for explaining NO _x release control.

FIG. 21 is a flowchart for processing a NO _x release flag.

FIG. 22 is a flowchart for controlling the operation of the engine.

[Explanation of symbols]

 6. Fuel injection valve 20 Throttle valve 31 EGR control valve

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F02D 21/08 301 F02D 21/08 301D 3G301 301H 41/04 355 41/04 355 385 385C 41/38 41/38 B 41 / 40 41/40 C F02M 25/07 570 F02M 25/07 570D 45/08 45/08 Z 61/14 310 61/14 310D F term (reference) 3G023 AA04 AA05 AA18 AB05 AC05 AD02 AD09 AD14 AE05 AF03 AG03 3G062 AA01 AA05 BA02 BA05 BA06 CA06 ED08 GA04 GA05 GA06 GA15 GA21 3G066 AA07 AA11 AA13 AB02 AC09 AD12 BA22 BA24 BA25 BA26 CC34 DA09 DB08 DB09 DC18 3G091 AA02 AA10 AA11 AA18 AB02 AB03 AB06 BA14 BA15 BA19 BA20 CA02 CB02 CB02 CB02 CB02 CB02 CB02 CB02 CB02 EA30 FA07 FA11 FA13 FA14 FB10 FB11 FB12 HB05 HB06 3G092 AA02 AA17 AA18 BA04 BB01 BB06 BB13 BB19 DC03 DC09 DG08 EA07 EA11 FA17 FA18 GA05 GA06 HA11Z HB01X HB01Z HB02X H03Z HD03 HD03 HC03 HD03 HC03 HD03 HC03 HD03 HC03X03 MA0 1 MA19 MA23 MA26 NE13 PE03Z PF03Z

Claims (17)

[Claims] When the amount of inert gas in the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas in the combustion chamber further increases, the amount of soot generated during combustion in the combustion chamber increases. In an internal combustion engine where the temperature of the fuel and its surrounding gas is lower than the soot generation temperature and soot is hardly generated, a catalyst having an oxidizing function is arranged in the engine exhaust passage, and the amount of soot generation peaks The first where the amount of inert gas in the combustion chamber is larger than the amount of inert gas and soot is hardly generated
And the second combustion in which the amount of inert gas in the combustion chamber is smaller than the amount of inert gas at which the amount of generated soot becomes a peak. The fuel is injected from the fuel injection valve toward the inside of the cavity, and the fuel injected from the fuel injection valve collides with the inner wall surface of the cavity at least during the first combustion. Internal combustion engine. 2. A fuel thin film is formed on an inner wall surface of a piston by tangentially colliding fuel injected from a fuel injection valve on an inner wall surface of a cavity, and the fuel is sequentially evaporated from the fuel thin film. Item 2. The internal combustion engine according to Item 1. 3. The internal combustion engine according to claim 1, wherein the fuel injected from the fuel injector collides with the inner wall surface of the cavity almost vertically. 4. A raised portion is formed at the center of the cavity, and a collision surface is formed at the top of the raised portion. The fuel injected from the fuel injection valve collides with the collision surface, and the colliding fuel is moved in the radial direction of the cavity. 2. The internal combustion engine according to claim 1, wherein the internal combustion engine is scattered. 5. An operation region of the engine is divided into a first operation region on a low load side and a second operation region on a high load side, and a first combustion is performed in the first operation region. The internal combustion engine according to claim 1, wherein the second combustion is performed in the region. 6. On the low load side of the second operating region, a fuel thin film is formed on the inner wall surface of the piston by tangentially colliding the fuel injected from the fuel injection valve on the inner wall surface of the cavity. 6. The internal combustion engine according to claim 5, wherein the fuel is sequentially evaporated, and the fuel injected from the fuel injection valve collides with the inner wall surface of the cavity almost vertically on the high load side of the second operation region. 7. A raised portion is formed at the center of the cavity and a collision surface is formed at the top of the raised portion. On the low load side of the second operating region, fuel injected from the fuel injection valve is transferred onto the inner wall surface of the cavity. Wherein the fuel injected from the fuel injector collides with a collision surface on the high load side of the second operating region to scatter the colliding fuel in the radial direction of the cavity. 6. The internal combustion engine according to 5. 8. A raised portion is formed at the center of the cavity, and a collision surface is formed at the top of the raised portion. On the low load side of the second operation region, fuel injected from the fuel injection valve is transferred onto the inner wall surface of the cavity. A fuel thin film is formed on the inner wall surface of the piston by tangentially colliding with the fuel, and the fuel is sequentially evaporated from the fuel thin film. On the high load side of the second operation region, the fuel injected from the fuel injection valve collides. 6. The internal combustion engine according to claim 5, wherein the fuel is caused to collide with the surface and the collided fuel is scattered in a radial direction of the cavity. 9. In the second operation region, pilot injection is performed prior to main injection, and fuel injected from a fuel injection valve at the time of pilot injection tangentially collides with the inner wall surface of the cavity to thereby reduce the inner wall surface of the piston. 6. The internal combustion engine according to claim 5, wherein a fuel thin film is formed on the internal combustion engine, and the fuel is sequentially evaporated from the fuel thin film, so that the fuel injected from the fuel injection valve at the time of the main injection collides with the inner wall surface of the cavity almost vertically. organ. 10. A raised portion is formed at the center of the cavity, and a collision surface is formed at the top of the raised portion. In the second operation region, pilot injection is performed prior to main injection, and during the pilot injection, a fuel injection valve is provided. So that the fuel injected from the fuel injector collides almost vertically on the inner wall surface of the cavity, and the fuel injected from the fuel injection valve at the time of main injection collides with the collision surface so that the colliding fuel is scattered in the radial direction of the cavity. The internal combustion engine according to claim 5, wherein 11. A raised portion is formed at the center of the cavity, and a collision surface is formed at the top of the raised portion. In the second operation region, pilot injection is performed prior to main injection, and the fuel injection valve is used during pilot injection. The fuel injected from the cylinder collides tangentially on the inner wall surface of the cavity to form a thin fuel film on the inner wall surface of the piston so that the fuel is sequentially evaporated from the thin fuel film. 6. The internal combustion engine according to claim 5, wherein the fuel collides with the collision surface, and the colliding fuel is scattered in a radial direction of the cavity. 12. An exhaust gas recirculation device for recirculating exhaust gas discharged from a combustion chamber into an engine intake passage, wherein the inert gas comprises recirculated exhaust gas.
An internal combustion engine according to claim 1. 13. The exhaust gas recirculation rate during the first combustion is substantially 55% or more, and the exhaust gas recirculation rate during the second combustion is substantially 50%.
The internal combustion engine of claim 12, which is less than or equal to percent. 14. The catalyst according to claim 1, wherein said catalyst is an oxidation catalyst, a three-way catalyst or NO.
_2. The internal combustion engine of claim 1, comprising at least one of an _x absorbent. 15. The catalyst according to claim 15, wherein said catalyst comprises a NO _x absorbent.
internal combustion engine according to claim 1 in which the air-fuel ratio under the first combustion to the rich when releasing the NO _x from _x absorbent. 16. The catalyst comprises _the NO _x absorbent, NO
claim and from the fuel injection valve when releasing the NO _x from _x absorbent so as to inject additional fuel during the exhaust stroke 1
An internal combustion engine according to claim 1. 17. The catalyst comprising a NO _x absorbent, wherein the NO
claim to the additional fuel from the fuel injection valve so that injection during the expansion stroke when releasing the NO _x from _x absorbent 1
An internal combustion engine according to claim 1.