JP3555439B2 - Compression ignition type internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a compression ignition type internal combustion engine.
[0002]
[Prior art]
Conventionally, in an internal combustion engine, for example, a diesel engine, NO_XThe engine exhaust passage and the engine intake passage are connected by an exhaust gas recirculation (hereinafter, referred to as EGR) passage in order to suppress the generation of the exhaust gas, that is, the exhaust gas, that is, the EGR gas is introduced into the engine intake passage through the EGR passage. I try to recirculate. In this case, the EGR gas has a relatively high specific heat and can absorb a large amount of heat. Therefore, as the EGR gas amount increases, the EGR rate (EGR gas amount / (EGR gas amount + intake air amount)) Increases, the combustion temperature in the combustion chamber decreases. NO when combustion temperature drops_XThe more the EGR rate increases, the lower the NO_XWill decrease.
[0003]
If the EGR rate is increased as compared with the conventional case, NO_XIt has been known that the amount of generation of phenol can be reduced. However, when the EGR rate is increased, when the EGR rate exceeds a certain limit, the amount of generated soot, that is, smoke starts to increase rapidly. In this regard, it has been conventionally considered that if the EGR rate is further increased, the smoke will increase infinitely. Therefore, the EGR rate at which the smoke starts to increase rapidly is considered to be the maximum allowable limit of the EGR rate. Has been.
[0004]
Therefore, conventionally, the EGR rate is set within a range not exceeding the maximum allowable limit (for example, see Japanese Patent Application Laid-Open No. 4-334750). The maximum allowable EGR rate varies substantially depending on the type of engine and fuel, but is approximately 30 to 50%. Therefore, in the conventional diesel engine, the EGR rate is suppressed to about 30% to 50% at the maximum.
[0005]
[Problems to be solved by the invention]
As described above, conventionally, it has been considered that the maximum allowable limit exists for the EGR rate. Therefore, the EGR rate is conventionally set to a value within the range not exceeding the maximum allowable limit._XAnd the amount of smoke generated was determined to be as small as possible. However, in this way, the EGR rate is set to NO._XNO even if the amount of smoke generated is minimized_XAnd the reduction in the amount of smoke generated is limited, and in practice, a considerable amount of NO_XAt present, smoke is generated.
[0006]
However, if the EGR rate is made larger than the maximum permissible limit in the course of research on the combustion of a diesel engine, the smoke rapidly increases as described above. However, a peak exists in the amount of generated smoke. When the EGR 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 rate is increased to about 55% or more when the EGR gas is cooled strongly, the smoke is almost completely reduced. It was found that it was zero, ie, little soot was generated. In this case, NO_XIt has also been found that the amount of generation is extremely small. After that, based on this finding, the reason why no soot is generated was studied, and as a result, unprecedented soot and NO_XThis has led to the construction of a new combustion system that can simultaneously reduce the combustion. 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 of the process until the hydrocarbons grow into soot.
[0007]
That is, as a result of repeated experimental research, it has been found that when the temperature of the fuel during combustion in the combustion chamber and the gas temperature around it are below a certain temperature, the growth of hydrocarbons stops at a stage before reaching soot, and the fuel When the temperature of the gas surrounding the gas exceeds a certain temperature, hydrocarbons grow to 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.
[0008]
Therefore, if the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is suppressed to a temperature at which the growth of hydrocarbons stops halfway, soot will not be generated, and the temperature of the fuel and the surrounding gas during combustion in the combustion chamber will be reduced. Can be suppressed 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 a catalyst having an oxidation function. This is the basic idea of a new combustion system.
[0009]
An object of the present invention is to provide a compression ignition type internal combustion engine suitable for the new combustion system.
[0010]
[Means for Solving the Problems]
That is, in the first invention, as the amount of inert gas in the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak.However, when the amount of the inert gas supplied into the combustion chamber is further increased, the temperature of the fuel and the surrounding gas during combustion in the combustion chamber becomes lower than the temperature at which soot is generated, and soot is hardly generated.In a compression ignition internal combustion engine, hydrocarbons are oxidized in the presence of_X  Is disposed in the engine exhaust passage, and by increasing the amount of inert gas in the combustion chamber from the amount of inert gas at which the amount of generated soot becomes a peak, fuel and fuel during combustion in the combustion chamber are reduced. The temperature of the surrounding gas is suppressed to a temperature lower than the temperature at which soot is generated.
[0011]
According to a second aspect, in the first aspect, a catalyst having an oxidizing function is arranged in the engine exhaust passage downstream of the selective reduction catalyst.
In a third aspect based on the second aspect, the catalyst having an oxidation function comprises an oxidation catalyst or a three-way catalyst.
In a fourth 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 is recirculated into the engine intake passage. Consists of recirculated exhaust gas.
[0012]
In a fifth aspect based on the fourth aspect, the exhaust gas recirculation rate is approximately 55% or more.
According to a sixth aspect of the present invention, in the first aspect, the 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 becomes a peak and almost no soot is generated, and the amount of generated soot is reduced. There is provided switching means for selectively switching between the second combustion in which the amount of inert gas in the combustion chamber is smaller than the peak amount of inert gas.
[0013]
In a seventh aspect based on the sixth aspect, additional fuel is injected during the second half of the expansion stroke or during the exhaust stroke when the second combustion is being performed.
In an eighth aspect based on the sixth aspect, when the air-fuel ratio of the inflowing exhaust gas is lean, the NO contained in the exhaust gas is reduced._XAnd the NO absorbed when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich._XReleases NO_XAn absorbent is disposed in the engine exhaust passage downstream of the selective catalytic reduction catalyst, and NO during the first combustion is performed._XNO from absorbent_X, The air-fuel ratio in the combustion chamber is temporarily set to the stoichiometric air-fuel ratio or rich.
[0014]
According to a ninth aspect, in the eighth aspect, when the second combustion is being performed, NO_XNO from absorbent_XShould be released by additional fuel injected during the second half of the expansion stroke or during the exhaust stroke._XThe air-fuel ratio of the exhaust gas flowing into the absorbent is set to the stoichiometric air-fuel ratio or rich.
In a tenth aspect based on the sixth aspect, the operating range of the engine is divided into a first operating range on the low load side and a second operating range on the high load side, and the first combustion is performed in the first operating range. In the second operation region, the second combustion is performed.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
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 an air cleaner 14 via an intake duct 13. A throttle valve 16 driven by an electric motor 15 is arranged in the intake duct 13. On the other hand, the exhaust port 10 is connected to a catalytic converter 19a via an exhaust manifold 17 and an exhaust pipe 18, and another catalytic converter 20a is connected to the catalytic converter 19a.
[0016]
In the catalytic converter 19a, hydrocarbons are oxidized in the presence of hydrocarbons in the presence of excess oxygen and NO_XIs disposed, and a catalyst 20 having an oxidizing function is disposed in a catalytic converter 20a.
As shown in FIG. 1, an air-fuel ratio sensor 21 is disposed in the exhaust manifold 17. The exhaust manifold 17 and the surge tank 12 are connected to each other via an EGR passage 22, and an electrically controlled EGR control valve 23 is disposed in the EGR passage 22. Further, a cooling device 24 for cooling the EGR gas flowing in the EGR passage 22 is disposed around the EGR passage 22. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 24, and the engine cooling water cools the EGR gas.
[0017]
On the other hand, each fuel injection valve 6 is connected via a fuel supply pipe 25 to a fuel reservoir, a so-called common rail 26. Fuel is supplied into the common rail 26 from an electric control type variable discharge fuel pump 27, and the fuel supplied into the common rail 26 is supplied to the fuel injection valve 6 through each fuel supply pipe 25. A fuel pressure sensor 28 for detecting the fuel pressure in the common rail 26 is attached to the common rail 26. The fuel pump 27 is controlled so that the fuel pressure in the common rail 26 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 28. Is controlled.
[0018]
The electronic control unit 30 is composed of a digital computer and is connected to each other by a bidirectional bus 31 such as a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an output port 36. Is provided. The output signal of the air-fuel ratio sensor 21 is input to the input port 35 via the corresponding AD converter 37. The output signal of the fuel pressure sensor 28 is also input to the input port 35 via the corresponding AD converter 37. A load sensor 41 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. . Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 30 °. On the other hand, the output port 36 is connected to the fuel injection valve 6, the electric motor 15, the EGR control valve 23, and the fuel pump 27 via a corresponding drive circuit 38.
[0019]
FIG. 2 shows a change in the output torque when the air-fuel ratio A / F (horizontal axis in FIG. 2) is changed by changing the opening degree and the EGR rate of the throttle valve 16 at the time of low load operation of the engine, smoke, and HC. , CO, NO_X4 shows an experimental example showing a change in the emission amount of the gas. 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.
[0020]
As shown in FIG. 2, when the air-fuel ratio A / F is reduced by increasing the EGR rate, the amount of smoke generated when the EGR rate becomes about 40% and the air-fuel ratio A / F becomes about 30 is reduced. Start growing. 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 becomes about 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 NO_XThe amount of generation is considerably low. On the other hand, at this time, the generation amounts of HC and CO begin to increase.
[0021]
FIG. 3A shows a change in the combustion pressure in the combustion chamber 5 when the air-fuel ratio A / F is around 18 and the amount of generated smoke is the largest, and FIG. The graph shows changes in the combustion pressure in the combustion chamber 5 when the amount of generated smoke is almost zero in the vicinity. As can be seen by comparing FIG. 3 (A) and FIG. 3 (B), FIG. 3 (B) in which the amount of smoke generation is almost zero is shown in FIG. 3 (A) where the amount of smoke generation is large. It can be seen that the combustion pressure is lower than in the case.
[0022]
The following can be said from the experimental results shown in FIGS. That is, first, when the air-fuel ratio A / F is 15.0 or less and the amount of generated smoke is almost zero, NO as shown in FIG._XThe amount of generation of methane is considerably reduced. NO_XThe decrease in the amount of the generated gas means that the combustion temperature in the combustion chamber 5 has decreased. Therefore, it can be said that the combustion temperature in the combustion chamber 5 is low when little soot is generated. 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, and the combustion temperature in the combustion chamber 5 is low at this time.
[0023]
Second, when the amount of generated smoke, that is, the amount of generated soot becomes almost zero, the amount of HC and CO emissions increases as shown in FIG. This means that hydrocarbons are emitted without growing to soot. That is, the linear hydrocarbon and the aromatic hydrocarbon contained in the fuel as shown in FIG. 4 are thermally decomposed when the temperature is increased in a state of lack of oxygen, so that a precursor of soot is formed. A soot consisting of a solid aggregate of carbon atoms is produced. In this case, the actual soot generation 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 generation amount of soot becomes almost zero, the emission amounts of HC and CO increase as shown in FIG. 2, but HC at this time is a soot precursor or a hydrocarbon in a state before it. .
[0024]
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 generated soot becomes almost zero. The hydrocarbon will be discharged from the combustion chamber 5. As a result of further detailed experimental research on this fact, when 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. 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.
[0025]
By the way, the temperature of the fuel and its surrounding when the process of producing hydrocarbons is stopped in the state of the soot precursor, that is, the above-mentioned certain temperature varies depending on various factors such as the type of fuel, the air-fuel ratio, the compression ratio, and the like. I can not say how many times, but this certain temperature is NO_XIs closely related to the amount of NOx generated, so that this certain temperature is NO_XCan be defined to some extent from the amount of occurrence of. That is, as the EGR rate increases, the fuel temperature during combustion and the gas temperature around the fuel decrease, and the NO_XGeneration amount decreases. NO at this time_XIs 10 p. p. When it is less or equal to or less than m, almost no soot is generated. Therefore, the above certain temperature is NO_XIs 10 p. p. m The temperature almost coincides with the temperature when the temperature becomes lower or higher.
[0026]
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 the state before the soot can be easily purified by a post-treatment using a catalyst having an oxidation function. Considering the post-treatment with the catalyst having the oxidation function as described above, it is extremely difficult to discharge hydrocarbons from the combustion chamber 5 in the state of the 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 used 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 oxidizes the hydrocarbons. Its core is to oxidize with a functional catalyst.
[0027]
Now, in order to stop the growth of hydrocarbons before soot is generated, it is necessary to suppress the temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 to a temperature lower than the temperature at which soot is generated. There is. 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.
[0028]
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.
[0029]
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 evaporated fuel diffuses to the surroundings, reacts with oxygen mixed in the inert gas, and burns. In this case, since the combustion heat is absorbed by the surrounding inert gas, the combustion temperature does not rise so much. 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.
[0030]
In this case, controlling the temperature of the fuel and its surrounding gas to a temperature lower than the temperature at which soot is generated requires an amount of an inert gas that can absorb a sufficient amount of heat to do so. Therefore, if the amount of fuel 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, so that the inert gas preferably has a higher specific heat. In this regard, CO₂Since EGR gas has a relatively large specific heat, it can be said that it is preferable to use EGR gas as the inert gas.
[0031]
FIG. 5 shows the relationship between the EGR rate and smoke when the EGR gas is used as the inert gas and the degree of cooling of the EGR gas is changed. That is, in FIG. 5, the curve A shows a case where the EGR gas is cooled strongly and the EGR gas temperature is maintained at approximately 90 ° C., and the curve B shows a case where the EGR gas is cooled by a small cooling device. , Curve C shows the case where the EGR gas is not forcibly cooled.
[0032]
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%. In this case, the EGR rate is increased to approximately 55% or more. Then, almost no soot is generated.
On the other hand, as shown by the curve B in FIG. 5, when the EGR gas is slightly cooled, the amount of soot generation peaks at a point where the EGR rate is slightly higher than 50%, and in this case, the EGR rate is increased to about 65% or more. So that almost no soot is generated.
[0033]
As shown by the curve C in FIG. 5, when the EGR gas is not forcibly cooled, the amount of soot generation reaches a peak when the EGR rate is around 55%. Above a percentage, 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 almost no soot is generated 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.
[0034]
FIG. 6 shows a mixed gas amount of the EGR gas and the air necessary for setting the fuel temperature during combustion and the surrounding gas temperature to a temperature lower than the temperature at which soot is generated when EGR gas is used as the inert gas; Further, the ratio of air in the mixed gas amount and the ratio of EGR gas in the mixed gas are shown. In FIG. 6, the vertical axis indicates the total intake gas amount drawn into the combustion chamber 5, and the dashed line Y indicates the total intake gas amount that can be drawn into the combustion chamber 5 when supercharging is not performed. ing. The horizontal axis indicates the required load, and Z1 indicates the low load operation region.
[0035]
Referring to FIG. 6, the proportion of air, that is, the amount of air in the mixed gas, indicates the amount of air required 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 the soot is formed. The minimum required EGR gas amount is shown. This EGR gas amount is approximately 55% or more in terms of the EGR rate, and is 70% or more in the embodiment shown in FIG. 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 between the air amount and the EGR gas amount in the total intake gas amount X is as shown in FIG. The temperature of the fuel and the gas around it will be lower than the temperature at which soot is produced, so that no soot is generated. In this case, NO_XThe amount generated is 10 p. p. m around or below and therefore NO_XIs extremely small.
[0036]
As the amount of fuel injection increases, the amount of heat generated when the fuel burns increases. Therefore, in order to maintain the temperature of the fuel and its surrounding gas at a temperature lower than the temperature at which soot is generated, the amount of heat absorbed by the EGR gas Must be increased. Accordingly, 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.
[0037]
On the other hand, in the load region Z2 in FIG. 6, the total intake gas amount X required to prevent the generation of soot exceeds the total intake gas amount Y that can be sucked. Therefore, in this case, it is necessary to supercharge or pressurize both the EGR gas and the intake air or the EGR gas in order to supply the total intake gas amount X necessary for preventing the generation of soot into the combustion chamber 5. When the EGR gas or the like is not supercharged or pressurized, the total intake gas amount X matches the total intake gas amount Y that can be sucked in the load region Z2. Therefore, in this case, in order to prevent the generation of soot, the amount of air is slightly reduced to increase the amount of EGR gas, and the fuel is burned under a rich air-fuel ratio.
[0038]
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 in the low load operation region Z1 shown in FIG. That is, even if the air-fuel ratio is made rich, NO_XIs 10 p. p. m or less, and even if the air amount is larger than the air amount shown in FIG. 6 in the low load region Z1 shown in FIG. NO while preventing soot generation even when lean_XIs 10 p. p. m can be around or below.
[0039]
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 thus no soot is generated. At this time, NO_XOnly a very small amount is 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 when 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_XOnly a very small amount is generated.
[0040]
Thus, in the engine low load operation region Z1, no soot is generated regardless of the air-fuel ratio, that is, regardless of whether the air-fuel ratio is rich, the stoichiometric air-fuel ratio, or the average air-fuel ratio is lean, and NO_XIs 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, under the new combustion system used in the present invention, soot and NO_XIn order to simultaneously reduce the EGR rate, the EGR rate needs to be at least approximately 55% or more. However, it is possible to make the EGR rate approximately 55% or more when the intake air amount is small, that is, when the engine load is relatively low, and when the intake air amount exceeds a certain limit, that is, when the required load exceeds the certain limit. If it becomes high, the intake air amount cannot be increased unless the EGR rate is reduced. However, in this case, in the experimental example shown in FIG. 2, as the intake air amount increases, that is, as the required load increases, the EGR rate gradually decreases from approximately 65%, that is, as the required load increases, the empty space gradually decreases. When the fuel ratio is increased, a large amount of smoke is generated. Therefore, when the required load exceeds a certain limit, as the required load increases, the EGR rate is gradually reduced from approximately 65%, and the air-fuel ratio cannot be gradually increased.
[0041]
In this case, in order to prevent generation of a large amount of smoke, it is necessary to jump over an EGR rate range of approximately 40% to approximately 65% where a large amount of smoke occurs when the required load exceeds a certain limit. Therefore, in the embodiment according to the present invention, when the required load is low, the EGR rate is maintained at least at about 55% or more. When the required load becomes high and the EGR rate cannot be maintained at about 55% or more, the EGR rate is stepped. It is to be reduced to almost 50% or less. At this time, the air-fuel ratio also increases stepwise.
[0042]
When the EGR rate is approximately 55% or more, the temperature of the fuel and the surrounding gas is lower than the temperature at which soot is generated, as described above. At this time, the first combustion, that is, the low-temperature combustion is performed. I have. On the other hand, when the EGR rate is reduced to about 50% or less, the temperature of the fuel and the surrounding gas becomes higher than the temperature at which the soot is formed, and at this time, the first combustion, that is, the low temperature combustion is no longer performed. Can not. When the low-temperature combustion cannot be performed in the embodiment according to the present invention, the second combustion, that is, the combustion that is conventionally performed conventionally, is performed. 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 generation amount of soot is a peak, as is apparent from the description so far, and almost all the soot is generated. The second combustion, that is, the combustion that has been conventionally performed, is 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 generation peaks. I say
[0043]
FIG. 7 shows the first combustion in which the EGR rate is approximately 55% or more, that is, the first operation region I in which low-temperature combustion is performed, and the second combustion in which the EGR rate is approximately 50% or less, that is, the conventional combustion. 2 shows a second combustion region II in which combustion is performed by a combustion method. In FIG. 7, the vertical axis L indicates the amount of depression of the accelerator pedal 40, that is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 7, X (N) indicates a first boundary between the first operation region I and the second operation region II, and Y (N) indicates the first operation region I and the second operation region. The second boundary with the area II is shown. The determination of the change of the operation region from the first operation region I to the second operation region II is made based on the first boundary X (N), and the change from the second operation region II to the first operation region I is performed. The determination of the change of the operating region is performed based on the second boundary Y (N).
[0044]
That is, when the operating state of the engine is in the first operating region I and the first combustion, that is, the low-temperature combustion is being performed, the required load L is a first boundary X (N ), It is determined that the operation region has shifted to the second operation region II, and the operation is switched to the second combustion. 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 the second combustion is shifted to the first combustion. Is switched.
[0045]
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 for the following two 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 start immediately 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.
[0046]
FIG. 8 shows the output of the air-fuel ratio sensor 21. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 21 changes according to the air-fuel ratio A / F. Therefore, the air-fuel ratio can be known from the output current I of the air-fuel ratio sensor 21.
FIG. 9 shows the target air-fuel ratio when the first combustion, that is, the low-temperature combustion is performed. In FIG. 9, curves A / F = 15.5, A / F = 16, A / F = 17, and A / F = 18 indicate target air-fuel ratios of 15.5, 16, 17, and 18, respectively. Is shown. As shown in FIG. 10A, the target opening degree ST of the throttle valve 16 required for setting the air-fuel ratio to the target air-fuel ratio is stored in the ROM 32 in advance in the form of a map as a function of the required load L and the engine speed N. The target opening SE of the EGR control valve 23 required for setting the air-fuel ratio to the target air-fuel ratio is calculated as a function of the required load L and the engine speed N as shown in FIG. It is stored in the ROM 32 in the form of a map in advance.
[0047]
On the other hand, FIG. 11 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. Note that, in FIG. 11, curves indicated by A / F = 24, A / F = 35, A / F = 45, and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. As shown in FIG. 12A, the target opening degree ST of the throttle valve 16 necessary for setting the air-fuel ratio to the target air-fuel ratio is stored in the ROM 32 in advance in the form of a map as a function of the required load L and the engine speed N. The target opening SE of the EGR control valve 23 required for setting the air-fuel ratio to the target air-fuel ratio is a function of the required load L and the engine speed N as shown in FIG. It is stored in the ROM 32 in the form of a map in advance.
[0048]
By the way, when the operating state of the engine is in the first operating region I and low-temperature combustion is being performed, almost no soot is generated, and instead, the unburned hydrocarbon is in the form of a precursor of soot or a state before it. It is discharged from the combustion chamber 5. At this time, the unburned hydrocarbon discharged from the combustion chamber 5 is oxidized well by the selective reduction catalyst 19, and the NO discharged at this time is discharged._XIs satisfactorily reduced by the selective reduction catalyst 19. Next, this will be described.
[0049]
Various types of catalysts are known as the selective reduction catalyst 19, and a typical catalyst is a Cu-zeolite catalyst or a Pt-zeolite catalyst. These selective reduction catalysts 19 have similar functions. Therefore, the functions of the selective reduction catalyst 19 will be described using a Cu-zeolite catalyst as an example.
That is, in the Cu-zeolite catalyst 19, hydrocarbon HC is converted to oxygen O in pores of the zeolite.₂To form active species (HC + O₂→ active species). This active species is NO on Cu ions_XAnd at this time NO_XIs reduced by the active species (NO_X+ Active species → N₂+ CO + CO₂). Thus, in the selective reduction catalyst 19, the oxidizing action of hydrocarbon HC and NO_XAre performed together. However, in this case, the oxidation action of hydrocarbon HC and NO_XIn order to perform the reduction action together, a relatively large amount of hydrocarbon HC and a relatively large amount of oxygen O are contained in the exhaust gas flowing into the selective reduction catalyst 19.₂Must exist together.
In this regard, when low-temperature combustion is performed in the present invention, a relatively large amount of unburned hydrocarbons is discharged from the combustion chamber 5 as described above, and therefore, a relatively large amount of hydrocarbons is present in the exhaust gas. become. When low-temperature combustion is being performed, as shown in FIG. 9, the air-fuel ratio in the combustion chamber 5 is lean, and therefore, a relatively large amount of oxygen is present in the exhaust gas. Therefore, when low-temperature combustion is being performed, unburned hydrocarbons are oxidized favorably by the selective reduction catalyst 19, and NO_XIs favorably reduced.
[0050]
On the other hand, even when the second combustion is being performed, the air-fuel ratio in the combustion chamber 5 is lean as shown in FIG. 11, and therefore, at this time, a large amount of oxygen exists in the exhaust gas. However, at this time, not much unburned hydrocarbon is discharged from the combustion chamber 5. Accordingly, at this time, in the embodiment according to the present invention, additional fuel is injected from the fuel injection valve 6 in the latter half of the expansion stroke or during the exhaust stroke. That is, when the additional fuel is injected in the latter half of the expansion stroke or during the exhaust stroke, the additional fuel is discharged from the combustion chamber 5 in the form of unburned hydrocarbon without completely burning. Therefore, a relatively large amount of hydrocarbons is contained in the exhaust gas._XIs performed.
[0051]
A catalyst 20 having an oxidation function disposed downstream of the selective reduction catalyst 19 is provided to oxidize unburned HC and CO that could not be oxidized in the selective reduction catalyst 19. The catalyst 20 having the oxidation function is an oxidation catalyst or a three-way catalyst.
Next, a specific example of operation control in the first operation region I and the second operation region II will be described with reference to FIG.
[0052]
FIG. 13 shows the opening degree of the throttle valve 16, the opening degree of the EGR control valve 23, the EGR rate, the air-fuel ratio, the injection timing, and the injection amount with respect to the required load L. As shown in FIG. 13, in the first operating region I where the required load L is low, the opening of the throttle valve 16 is gradually increased from almost fully closed to about half-open as the required load L increases, and the EGR control valve 23 Is gradually increased from near fully closed to fully open as the required load L increases. In the specific example shown in FIG. 13, in the first operation region I, the EGR rate is approximately 70%, and the air-fuel ratio is a lean air-fuel ratio of about 15 to 18.
[0053]
In other words, in the first operation region I, the opening of the throttle valve 16 and the opening of the EGR control valve 23 are controlled such that the EGR rate becomes approximately 70% and the air-fuel ratio becomes a lean air-fuel ratio of about 15 to 18. You. At this time, the air-fuel ratio is controlled to the target lean air-fuel ratio by correcting the opening of the throttle valve 16, the opening of the EGR control valve 23, or the fuel injection amount based on the output signal of the air-fuel ratio sensor 21. 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.
[0054]
As described above, at the time of idling operation, the throttle valve 16 is closed to almost fully closed, and at this time, the EGR control valve 23 is also closed to almost fully closed. When the throttle valve 16 is closed close to the fully closed position, 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 16 is closed to almost fully closed in order to suppress the vibration of the engine body 1.
[0055]
When the operating state of the engine is in the first operating region I, soot and NO_XIs hardly generated, and the soot precursor or the hydrocarbon in a state before the soot contained in the exhaust gas is oxidized well by the selective reduction catalyst 19. Also, a small amount of NO generated at this time_XCan be satisfactorily reduced by the selective reduction catalyst 19.
On the other hand, when the operating region of the engine changes from the first operating region I to the second operating region II, the opening of the throttle valve 16 is increased stepwise from a half-open state to a fully-open state. At this time, in the example shown in FIG. 13, the EGR rate is reduced stepwise from approximately 70% to 40% or less, and the air-fuel ratio is increased stepwise. That is, since the EGR rate jumps over the EGR rate range in which a large amount of smoke is generated, a large amount of smoke is not generated when the operation region of the engine changes from the first operation region I to the second operation region II.
[0056]
In the second operation region II, the second combustion, that is, the conventional combustion is performed. In this combustion method, soot and NO_XIs generated, but the thermal efficiency is higher than that of low-temperature combustion. Therefore, when the operating region of the engine changes from the first operating region I to the second operating region II, the injection amount decreases stepwise as shown in FIG. I'm sullen.
In the second operation region II, the throttle valve 16 is kept in a fully open state, and the opening of the EGR control valve 23 is reduced as the required load L increases. Therefore, 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. In the second operation region II, a main injection Qm for generating engine output and an additional injection Qa for discharging a large amount of unburned hydrocarbons from the engine are performed.
[0057]
As shown in FIG. 13, the injection start timing θS of the main injection Qm is set near the compression top dead center TDC. The injection amount of the additional injection Qa is substantially constant regardless of the required load L, and the injection timing of the additional injection Qa is set in the latter half of the expansion stroke. The unburned hydrocarbon HC is oxidized by the selective reduction catalyst 19 by the fuel from the additional injection Qa, and NO_XIs reduced.
[0058]
Next, the operation control will be described with reference to FIG.
Referring to FIG. 14, first, in step 100, 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, the routine proceeds to step 101, where it is determined whether the required load L has become larger than the first boundary X (N). Is done. When L ≦ X (N), the routine proceeds to step 103, where low-temperature combustion is performed.
[0059]
That is, in step 103, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 10A, and the opening of the throttle valve 16 is set to the target opening ST. Next, at step 104, the target opening SE of the EGR control valve 23 is calculated from the map shown in FIG. 10B, and the opening of the EGR control valve 23 is set to the target opening SE. Next, at step 105, fuel injection is performed so as to attain the air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed under a lean air-fuel ratio.
[0060]
On the other hand, when it is determined in step 101 that L> X (N), the routine proceeds to step 102, where the flag I is reset, and then proceeds to step 108 to perform the second combustion.
That is, in step 108, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 12A, and the opening of the throttle valve 16 is set to the target opening ST. Next, at step 109, the target opening SE of the EGR control valve 23 is calculated from the map shown in FIG. 12B, and the opening of the EGR control valve 23 is set to this target opening SE. Next, at step 110, the main injection Qm (FIG. 13) is performed so as to obtain the lean air-fuel ratio shown in FIG. 11, and the additional injection Qa (FIG. 13) is performed in the latter half of the expansion stroke.
[0061]
When the flag I is reset, the process proceeds from step 100 to step 106 in the next processing cycle, and it is determined whether the required load L has become lower than the second boundary Y (N). When L ≧ Y (N), the routine proceeds to step 108, where the second combustion is performed under the lean air-fuel ratio, and the additional injection Qa is performed in the latter half of the expansion stroke.
On the other hand, when it is determined in step 106 that L <Y (N), the routine proceeds to step 107, where the flag I is set, and then proceeds to step 103 to perform low-temperature combustion.
[0062]
FIG. 15 shows a second embodiment. In this embodiment, NO that could not be reduced in the selective reduction catalyst 19_XNO to the downstream of the selective catalytic reduction catalyst 19 in order to purify_XAn absorbent 50 is provided.
This NO_XThe absorbent 50 is made of, 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 and a noble metal such as platinum Pt are supported. Engine intake passage, combustion chamber 5 and NO_XThe ratio of air and fuel (hydrocarbon) supplied into the exhaust passage upstream of the absorbent 50 is set to NO._XWhen the air-fuel ratio of the exhaust gas flowing into the absorbent 50 is called this NO_XThe absorbent 50 is NO when the air-fuel ratio of the inflowing exhaust gas is lean._XNO when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich._XReleases NO_XPerforms the absorption and release action.
[0063]
This NO_XNO if the absorbent 50 is arranged in the engine exhaust passage_XAbsorbent 50 is actually NO_XHowever, there is a part where the detailed mechanism of the absorption / release action 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 platinum Pt and barium Ba supported on a carrier as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.
[0064]
In the compression ignition type internal combustion engine shown in FIG. 15, combustion is performed with the air-fuel ratio in the normal combustion chamber 5 being lean. When the combustion is performed with the lean air-fuel ratio, the oxygen concentration in the exhaust gas is high. At this time, as shown in FIG.₂Is O₂ ⁻Or O^2-On the surface of platinum Pt. On the other hand, NO in the inflowing exhaust gas becomes O 2 on the surface of platinum Pt.₂ ⁻Or O^2-Reacts with NO₂(2NO + O₂→ 2NO₂). NO generated next₂Is absorbed in the absorbent while being oxidized on the platinum Pt and combined with barium oxide BaO, as shown in FIG.₃ ⁻Diffuses into the absorbent in the form of NO in this way_XIs NO_XIt is absorbed in the absorbent 50. NO on the surface of platinum Pt as long as the oxygen concentration in the inflowing exhaust gas is high₂Is generated, and the NO_XNO unless absorption capacity is saturated₂Is absorbed in the absorbent and nitrate ion NO₃ ⁻Is generated.
[0065]
On the other hand, when the air-fuel ratio of the inflowing exhaust gas is made rich, the oxygen concentration in the inflowing exhaust gas decreases, and as a result, NO on the surface of the platinum Pt is reduced.₂Is reduced. NO₂The reaction proceeds in the reverse direction (NO₃ ⁻→ NO₂) And thus the nitrate ions NO in the absorbent₃ ⁻Is NO₂Released from the absorbent in the form of NO at this time_XNO released from absorbent 50_XIs reduced by reacting with a large amount of unburned HC and CO contained in the inflowing exhaust gas as shown in FIG. Thus, NO on the surface of platinum Pt₂When no longer exists, NO is changed from one absorbent to the next₂Is released. Therefore, if the air-fuel ratio of the inflowing exhaust gas is made rich, NO_XNO from absorbent 50_XIs released, and the released NO_XNO in the atmosphere to be reduced_XIs not emitted.
[0066]
In this case, even if the air-fuel ratio of the inflowing exhaust gas is set to the stoichiometric air-fuel ratio, NO_XNO from absorbent 50_XIs released. However, when the air-fuel ratio of the inflowing exhaust gas is set to the stoichiometric air-fuel ratio, NO_XNO from absorbent 50_XIs released only slowly_XTotal NO absorbed in absorbent 50_XIt takes a slightly longer time to release.
[0067]
By the way, NO_XNO of absorbent 50_XAbsorption capacity is limited, NO_XNO of absorbent 50_XNO before absorption capacity is saturated_XNO from absorbent 50_XMust be released. NO for that_XNO absorbed in the absorbent 50_XThe quantity needs to be estimated. Therefore, in the embodiment according to the present invention, NO per unit time when the first combustion is performed_XThe absorption amount A is determined in advance in the form of a map as shown in FIG. 17A as a function of the required load L and the engine speed N, and the NO per unit time during the second combustion is performed._XThe absorption amount B is previously obtained as a function of the required load L and the engine speed N in the form of a map as shown in FIG._XNO by integrating absorption amounts A and B_XNO absorbed in the absorbent 50_XThe amount ΣNOX is estimated.
[0068]
In the embodiment according to the present invention, this NO_XNO when the absorption amount ΣNOX exceeds a predetermined allowable maximum value MAX._XNO from absorbent 50_XIs to be released. That is, when low-temperature combustion is being performed, NO_XWhen the absorption amount ΣNOX exceeds the permissible maximum value MAX, the air-fuel ratio in the combustion chamber 5 is temporarily made rich, whereby the NO_XNO from absorbent 50_XIs released. As described above, even when the air-fuel ratio is made rich during low-temperature combustion, almost no soot is generated.
[0069]
On the other hand, in the second embodiment, when the second combustion is being performed, NO_XWhen the absorption amount ΣNOX exceeds the allowable maximum value MAX, the fuel amount of the additional injection Qa performed in the latter half of the expansion stroke is temporarily increased. The fuel increase of this additional injection Qa is NO_XThe air-fuel ratio of the exhaust gas flowing into the absorbent 50 is set to be rich, so that if the fuel amount of the additional injection Qa is increased, NO_XNO from absorbent 50_XWill be released.
[0070]
FIG. 18 is NO_XNO from absorbent 50_XSet when to release_XThis shows a routine for processing the release flag, and this routine is executed by interruption every predetermined time.
Referring to FIG. 18, 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, where NO per unit time is obtained from the map shown in FIG._XThe absorption amount A is calculated. Next, at step 202, NO_XA is added to the absorption amount ΣNOX. Next, at step 203, NO_XIt is determined whether or not the absorption amount ＸNOX exceeds the allowable maximum value MAX.と If NOX> MAX, proceed to step 204 and NO for a predetermined time._XA process of setting the release flag is performed, and then in step 205, ΣNOX is made zero.
[0071]
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 206, where the map per unit time is obtained from the map shown in FIG. NO_XThe absorption amount B is calculated. Next, at step 207, NO_XB is added to the absorption amount ΣNOX. Next, at step 208, NO_XIt is determined whether or not the absorption amount ＸNOX exceeds the allowable maximum value MAX.と If NOX> MAX, proceed to step 209 and NO for a predetermined time_XA process for setting the release flag is performed, and then in step 210, ΣNOX is made zero.
[0072]
Next, the operation control in the second embodiment will be described with reference to FIG.
Referring to FIG. 19, first, at 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. When the flag I is set, that is, when the operating state of the engine is in the first operating region I, the routine proceeds to step 301, where it is determined whether or not the required load L has become larger than the first boundary X (N). Is done. When L ≦ X (N), the routine proceeds to step 303, where low-temperature combustion is performed.
[0073]
That is, in step 303, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 10A, and the opening of the throttle valve 16 is set to the target opening ST. Next, at step 304, the target opening SE of the EGR control valve 23 is calculated from the map shown in FIG. 10B, and the opening of the EGR control valve 23 is set to the target opening SE. Next, at step 305, NO_XIt is determined whether the release flag is set. NO_XIf the release flag has not been set, the routine proceeds to step 306, where fuel injection is performed so as to achieve the air-fuel ratio shown in FIG. At this time, low-temperature combustion is performed under a lean air-fuel ratio.
[0074]
On the other hand, in step 305, NO_XWhen it is determined that the release flag has been set, the routine proceeds to step 307, where injection control for enriching the average air-fuel ratio in the combustion chamber 5 is performed. NO at this time_XNO from absorbent 50_XIs released.
On the other hand, when it is determined in step 301 that L> X (N), the routine proceeds to step 302, where the flag I is reset, and then proceeds to step 310 to perform the second combustion.
[0075]
That is, in step 310, the target opening ST of the throttle valve 16 is calculated from the map shown in FIG. 12A, and the opening of the throttle valve 16 is set to the target opening ST. Next, at step 311, the target opening SE of the EGR control valve 23 is calculated from the map shown in FIG. 12B, and the opening of the EGR control valve 23 is set as the target opening SE. Next, at step 312, NO_XIt is determined whether the release flag is set. NO_XWhen the release flag is not set, the routine proceeds to step 313, where the main injection Qm is performed so as to have the air-fuel ratio shown in FIG. 11, and the additional injection Qa is performed in the latter half of the expansion stroke. At this time, the second combustion is performed under the lean air-fuel ratio.
[0076]
On the other hand, in step 312, NO_XWhen it is determined that the release flag is set, the routine proceeds to step 314, and NO_XThe fuel amount of the additional injection Qa is increased so that the air-fuel ratio of the exhaust gas flowing into the absorbent 50 becomes rich. NO at this time_XNO from absorbent 50_XIs released.
As described above, in the second embodiment, when the second combustion is being performed, NO_XNO from absorbent 50_XIs to be released, the fuel amount of the additional injection Qa is increased. However, when the second combustion is being performed, no additional injection Qa is performed, only the main injection Qm is performed, and when the second combustion is being performed, NO is determined._XNO from absorbent 50_XAdditional fuel can be injected during the latter half of the expansion stroke or during the exhaust stroke only when is to be released. In this case, the additional fuel amount is NO_XThe air-fuel ratio of the exhaust gas flowing into the absorbent 50 is determined to be rich.
[0077]
When the additional injection Qa is not performed when the second combustion is being performed and only the main injection Qm is performed, the NO generated in the combustion chamber 5 during the second combustion is used._XIs hardly reduced by the selective reduction catalyst 19, and NO_XAbsorbed by the absorbent 50.
In the embodiment shown in FIG. 15, the oxidation catalyst or the three-way catalyst is replaced with the selective reduction catalyst 19 and NO._XIt can be placed between the absorbents 50, or the oxidation catalyst or the three-way catalyst_XIt can also be located downstream of the absorbent 50.
[0078]
【The invention's effect】
Unburned HC, CO and NO while controlling the generation of soot_XCan be suppressed from being released into the atmosphere.
[Brief description of the drawings]
FIG. 1 is an overall view of a compression ignition type internal combustion engine.
FIG. 2 Smoke and NO_XFIG.
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 a first operation region I and a second operation region II.
FIG. 8 is a diagram showing an output of an air-fuel ratio sensor.
FIG. 9 is a diagram showing a target air-fuel ratio when the first combustion is performed.
FIG. 10 is a diagram showing a map of a target opening degree of a throttle valve and the like.
FIG. 11 is a diagram showing a target air-fuel ratio when a second combustion is performed.
FIG. 12 is a diagram showing a map of a target opening degree of a throttle valve and the like.
FIG. 13 is a diagram showing an opening degree of a throttle valve and the like.
FIG. 14 is a flowchart for controlling operation of the engine.
FIG. 15 is an overall view showing another embodiment of the compression ignition type internal combustion engine.
FIG. 16 NO_XIt is a figure for explaining the absorption-release action of.
FIG. 17: NO per unit time_XIt is a figure showing a map of an amount of absorption.
FIG. 18 NO_XIt is a flowchart for processing a release flag.
FIG. 19 is a flowchart for controlling the operation of the engine.
[Explanation of symbols]
6 ... Fuel injection valve
16 ... Throttle valve
19… Selective reduction catalyst

Claims (10)

As you increase the amount of inert gas in the combustion chamber is peaked increases the amount of soot produced gradually, at the time of combustion in the combustion chamber will further increase the amount of inert gas supplied to the combustion chamber In a compression ignition type internal combustion engine in which the temperature of the fuel and its surrounding gas is lower than the soot generation temperature and soot is hardly generated , hydrocarbons are oxidized in the presence of hydrocarbons in the presence of excess oxygen and NO _X Is disposed in the engine exhaust passage, and the amount of inert gas in the combustion chamber is made larger than the amount of inert gas at which the amount of soot generated becomes a peak, so that fuel and fuel during combustion in the combustion chamber are reduced. A compression ignition type internal combustion engine in which the temperature of the surrounding gas is suppressed to a temperature lower than the temperature at which soot is generated. 2. The compression ignition type internal combustion engine according to claim 1, wherein a catalyst having an oxidation function is arranged in an engine exhaust passage downstream of the selective reduction catalyst. 3. The compression ignition type internal combustion engine according to claim 2, wherein the catalyst having the oxidation function is an oxidation catalyst or a three-way catalyst. 2. 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 recirculated into the engine intake passage. A compression ignition type internal combustion engine according to claim 1. 5. The compression ignition type internal combustion engine according to claim 4, wherein an exhaust gas recirculation rate is approximately 55% or more. The first combustion in which the amount of inert gas in the combustion chamber is larger than the amount of inert gas in which the amount of soot is peaked and little soot is generated, and the combustion chamber is smaller than the amount of inert gas in which the amount of soot is peaked. 2. The compression ignition type internal combustion engine according to claim 1, further comprising switching means for selectively switching between the second combustion and the second combustion having a small amount of inert gas. 7. The compression ignition type internal combustion engine according to claim 6, wherein additional fuel is injected during the second half of the expansion stroke or during the exhaust stroke when the second combustion is being performed. The _the NO _X absorbent air-fuel ratio of the inflowing exhaust gas to release the NO _X when the air-fuel ratio of the exhaust gas absorb and flowing the NO _X contained in the exhaust gas is absorbed and becomes the stoichiometric air-fuel ratio or rich when the lean placed above selective reduction catalyst downstream of the engine exhaust passage, temporarily theoretical air fuel ratio in the combustion chamber to when releasing the NO _X from _the NO _X absorbent when the first combustion is being performed 7. The compression ignition type internal combustion engine according to claim 6, wherein the fuel ratio is made rich. When NO _X is to be released from the NO _X absorbent during the second combustion, the exhaust gas flowing into the NO _X absorbent by the additional fuel injected in the second half of the expansion stroke or during the exhaust stroke. 9. The compression ignition type internal combustion engine according to claim 8, wherein the air-fuel ratio is set to a stoichiometric air-fuel ratio or rich. The operating region of the engine is divided into a first operating region on the low load side and a second operating region on the high load side, and a first combustion is performed in the first operating region, and a second combustion is performed in the second operating region. The compression ignition type internal combustion engine according to claim 6, wherein combustion is performed.

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