JP3551799B2 - Internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in an internal combustion engine, for example, a diesel engine, an engine exhaust passage and an engine intake passage are connected by an exhaust gas recirculation (hereinafter, referred to as EGR) passage in order to suppress generation of NOx, and exhaust gas is passed through the EGR passage. Gas, that is, EGR gas is recirculated into the engine intake passage. 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. When the combustion temperature decreases, the amount of generated NOx decreases. Therefore, the higher the EGR rate, the lower the amount of generated NOx.
[0003]
As described above, it is known that the amount of generated NOx can be reduced by increasing the EGR rate as compared with the related art. 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. 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]
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 so that the generation amount of NOx and smoke is minimized within a range not exceeding the maximum allowable limit. I was However, even if the EGR rate is determined so that the amount of NOx and smoke generated is as small as possible, the reduction of the amount of generated NOx and smoke is limited, and in fact, a considerable amount of NOx and smoke is still generated. The current situation is to do it.
[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 sharply, and when the EGR rate is increased to 70% or more during idling operation, and when the EGR gas is strongly cooled, the smoke is reduced to about 55% or more. Becomes zero. That is, it was found that soot was hardly generated. At this time, it has also been found that the amount of generated NOx is extremely small. After that, the reason why soot was not generated was studied based on this finding, and as a result, a new combustion system capable of simultaneously reducing soot and NOx, which has never been seen before, was constructed. 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 an oxidation catalyst or the like. This is the basic idea of a new combustion system.
[0009]
[Problems to be solved by the invention]
However, in the new combustion system as described above, what should be done when the temperature of the fuel during combustion in the combustion chamber and the gas around it cannot be suppressed below the temperature at which the growth of hydrocarbons stops halfway? Has not yet been disclosed.
[0010]
Therefore, the present invention provides a low-temperature combustion under conditions unsuitable for performing a low-temperature combustion in which almost no soot is generated while simultaneously preventing emission of soot and NOx from the internal combustion engine. It is an object of the present invention to provide an internal combustion engine that can prevent the generation amount of soot from increasing by executing the above.
[0011]
[Means for Solving the Problems]
According to the first aspect of the invention, when the amount of the inert gas supplied into the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and the inert gas supplied into the combustion chamber is increased. When the amount of gas is further increased, the soot is hardly generated in the internal combustion engine in which the temperature of the fuel and the surrounding gas during the combustion in the combustion chamber becomes lower than the soot generation temperature and soot is hardly generated. It is provided with a judging means for judging whether or not the temperature in the combustion chamber rises to the extent that combustion cannot be performed, and it is determined that the temperature in the combustion chamber rises to such an extent that the combustion in which the soot is hardly generated can not be performed. An internal combustion engine is provided which prohibits combustion when the soot is hardly generated.
[0012]
According to the second aspect of the present invention, whether or not the temperature in the combustion chamber rises to such an extent that the combustion in which the soot is hardly generated can not be performed is determined based on the remaining state of the combustion gas in the combustion chamber. Item 1. An internal combustion engine according to item 1 is provided.
[0013]
According to the third aspect of the present invention, the remaining state of the combustion gas is determined in accordance with the output value of the pressure detecting means disposed in the engine exhaust passage in order to detect the pressure in the engine exhaust passage. Item 3. An internal combustion engine according to item 2 is provided.
[0014]
In the internal combustion engine according to any one of claims 1 to 3, the amount of the inert gas supplied into the combustion chamber is larger than the amount of the inert gas at which the amount of generated soot becomes a peak, and the combustion at which soot is hardly generated is performed at a low temperature. Since it is performed below, it is possible to simultaneously prevent the emission of soot and the emission of NOx from the internal combustion engine. Further, when it is determined that the temperature in the combustion chamber rises to such an extent that the combustion in which the soot is hardly generated is not performed, the combustion in which the soot is hardly generated is prohibited. By the way, when the temperature in the combustion chamber rises to such an extent that the combustion in which the soot is hardly generated can not be performed, particularly, the relatively high-temperature internal EGR gas which makes it difficult for the exhaust gas to be discharged from the combustion chamber into the engine exhaust passage is generated. When the temperature in the combustion chamber rises due to stagnation in the combustion chamber, the combustion around the fuel is reduced by increasing the amount of the inert gas supplied into the combustion chamber. It is difficult to absorb heat sufficiently, and hydrocarbons grow into soot, and therefore, the amount of soot generated increases. Therefore, as described above, in the internal combustion engine according to claims 1 to 3, when it is determined that the temperature in the combustion chamber rises to the extent that the combustion in which the soot is hardly generated cannot be performed, the combustion in which the soot is hardly generated is performed. It is forbidden to do so. As a result, it is possible to prevent an increase in the amount of generated soot by performing the combustion in which the soot is hardly generated under conditions inappropriate for performing the combustion in which the soot is hardly generated.
[0015]
According to the invention described in claim 4, the internal combustion engine according to claim 1, wherein a catalyst having an oxidation function is disposed in the engine exhaust passage to oxidize unburned hydrocarbons discharged from the combustion chamber. Provided.
[0016]
According to the fifth aspect of the present invention, there is provided the internal combustion engine according to the fourth aspect, wherein the catalyst comprises at least one of an oxidation catalyst, a three-way catalyst, and a NOx absorbent.
[0017]
In the internal combustion engine according to claims 4 and 5, since unburned hydrocarbons discharged from the combustion chamber are oxidized in the engine exhaust passage, it is possible to prevent unburned hydrocarbons from being discharged from the internal combustion engine. Can be.
[0018]
According to the invention described in claim 6, there is provided an exhaust gas recirculation device for recirculating exhaust gas discharged from the combustion chamber into the engine intake passage, and the inert gas is recirculated into the engine intake passage. An internal combustion engine according to claim 1, comprising circulated recirculated exhaust gas.
[0019]
In the internal combustion engine according to the sixth aspect, the inert gas is supplied from the outside into the combustion chamber by using the recirculated exhaust gas recirculated into the engine intake passage by the exhaust gas recirculation device as the inert gas. The need for special provision of means can be avoided.
[0020]
According to the invention described in claim 7, the amount of the recirculated exhaust gas supplied into the combustion chamber is larger than the amount of the recirculated exhaust gas at which the amount of generated soot becomes a peak, and the first soot is hardly generated. Switching means for selectively switching between combustion and second combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than the amount of recirculated exhaust gas at which the generation amount of soot is at a peak, 7. The internal combustion engine according to claim 6, wherein the exhaust gas recirculation rate is changed stepwise when the first combustion is switched to the second combustion or the second combustion is switched to the first combustion. Agencies are provided.
[0021]
In the internal combustion engine according to the seventh aspect, when the first combustion is switched from the first combustion to the second combustion or from the second combustion to the first combustion, the exhaust gas recirculation rate is changed in a step-like manner, so that the exhaust gas is changed. It is possible to prevent the gas recirculation rate from being set to the exhaust gas recirculation rate at which the generation amount of soot becomes a peak.
[0022]
According to the invention described in claim 8, when it is determined that exhaust gas is difficult to be discharged from the combustion chamber into the engine exhaust passage during execution of the first combustion, the first combustion is performed by the first combustion. When the exhaust gas is determined to be difficult to be discharged from the combustion chamber into the engine exhaust passage during execution of the second combustion, the second combustion is switched to the first combustion. 8. The internal combustion engine according to claim 7, wherein execution of the switching is prohibited.
[0023]
In the internal combustion engine according to claim 8, when it is determined that the exhaust gas is difficult to be discharged from the combustion chamber into the engine exhaust passage during the execution of the first combustion, the first combustion is switched to the second combustion. If it is determined that exhaust gas is not easily discharged from the combustion chamber into the engine exhaust passage during execution of the second combustion, execution of switching from the second combustion to the first combustion is prohibited. Therefore, both when the first combustion is being performed and when the second combustion is being performed, the amount of soot generation is reduced due to the inappropriate execution of the first combustion. It can be prevented from increasing.
[0024]
According to the ninth aspect of the present invention, the exhaust gas recirculation rate during the first combustion is substantially 55% or more, and the exhaust gas during the second combustion is performed. An internal combustion engine according to claim 7, wherein the recirculation rate is less than or equal to about 50 percent.
[0025]
The internal combustion engine according to claim 9, wherein the exhaust gas recirculation rate when the first combustion is performed is approximately 55% or more, and the exhaust gas recirculation rate when the second combustion is performed. Is set to approximately 50% or less, it is possible to prevent the exhaust gas recirculation rate from being set to the exhaust gas recirculation rate at which the generation amount of soot reaches a peak.
[0026]
According to the tenth aspect of the present invention, the operating range of the engine is divided into the first operating range on the low load side and the second operating range on the high load side, and the first operating range in the first operating range. The internal combustion engine according to claim 7, wherein the second combustion is performed in the second operation range.
[0027]
In the internal combustion engine according to claim 10, when the first combustion can be performed, that is, when the temperature of the fuel and the surrounding gas during the combustion in the combustion chamber can be maintained lower than the soot generation temperature, The first combustion is performed in the first operation region on the low load side and the second combustion is performed in the second operation region on the high load side because the heat generation amount is limited to the engine low load operation in which the heat generation is relatively small. I do. Therefore, appropriate combustion can be performed according to the operation range.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0029]
FIG. 1 shows an embodiment in which 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 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. A mass flow detector 21 for detecting the mass flow of the intake air is disposed in the air suction pipe 17 upstream of the throttle valve 20.
[0030]
On the other hand, the exhaust port 10 is connected to an inlet of an exhaust turbine 23 of an exhaust turbocharger 15 via an exhaust manifold 22, and an outlet of the exhaust turbine 23 is provided with a catalyst 25 having an oxidizing function via an exhaust pipe 24. Connected to converter 26. An air-fuel ratio sensor 27 is disposed in the exhaust manifold 22. Further, a pressure sensor 53 is disposed in the exhaust manifold 22 to detect a pressure in the exhaust manifold 22.
[0031]
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 each other via an exhaust gas recirculation (hereinafter, referred to as EGR) passage 29. An EGR control valve 31 driven by a step motor 30 is disposed. In the EGR passage 29, an intercooler 32 for cooling the EGR gas flowing in the EGR passage 29 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.
[0032]
On the other hand, the fuel injection valve 6 is connected via a fuel supply pipe 33 to a fuel reservoir, a so-called common rail 34. 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.
[0033]
The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41 such as a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a CPU (Microprocessor) 44, an input port 45 and an output port 46. Is provided. The output signal of the mass flow detector 21 is input to the input port 45 via the corresponding AD converter 47, and the output signals of the air-fuel ratio sensor 27, the fuel pressure sensor 36, and the pressure sensor 53 are also supplied to the corresponding AD converter 47. The input is input to the input port 45 via the input port 45. A load sensor 51 that generates an output voltage proportional to the depression amount 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. . The input port 45 is connected to a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. The engine speed is calculated based on the output value of the crank angle sensor 52. On the other hand, the output port 46 is connected to the fuel injection valve 6, the step motor 19 for controlling the throttle valve, the step motor 30 for controlling the EGR control valve, and the fuel pump 35 via the corresponding drive circuit 48.
[0034]
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 20 during the low load operation of the engine, and smoke, HC, An experimental example showing a change in CO and NOx emissions is shown. As can be seen from FIG. 2, in this experimental example, the EGR rate increases as the air-fuel ratio A / F decreases, and when the stoichiometric air-fuel ratio is less than (14.6), the EGR rate is approximately 65% or more.
[0035]
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 air-fuel ratio A / F becomes approximately 30% when the EGR rate becomes approximately 40% or so. Begins 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, and the EGR rate is increased to about 65% or more. When the air-fuel ratio A / F is around 15.0, the smoke becomes almost zero. Become. That is, almost no soot is generated. At this time, the output torque of the engine slightly decreases, and the generation amount of NOx becomes considerably low. On the other hand, at this time, the generation amounts of HC and CO begin to increase.
[0036]
FIG. 3A shows a 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. 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.
[0037]
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, the amount of generated NOx is considerably reduced as shown in FIG. The decrease in the amount of generated NOx 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 has decreased 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.
[0038]
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. .
[0039]
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, 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, 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.
[0040]
By the way, 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 varies depending on various factors such as the type of fuel and the compression ratio of the air-fuel ratio. Although it cannot be said how many times, this certain temperature is closely related to the amount of NOx generated, so that this certain temperature can be defined to some extent from the amount of NOx generated. That is, as the EGR rate increases, the temperature of the fuel during combustion and the gas temperature around it decrease, and the amount of generated NOx decreases. At this time, the amount of generated NOx is 10 p. p. When it is less or equal to or less than m, almost no soot is generated. Therefore, at the above-mentioned certain temperature, the amount of generated NOx is 10 p. p. m The temperature almost coincides with the temperature when the temperature becomes lower or higher.
[0041]
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 the catalyst having the oxidation function, it is extremely difficult to discharge the hydrocarbon from the combustion chamber 5 in the state of the precursor of soot or in the state before the soot, or to discharge the hydrocarbon from the combustion chamber 5 in the form of soot. 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.
[0042]
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 is burned has an extremely large effect on suppressing the temperature of the fuel and the gas around the fuel.
[0043]
That is, if there is only air around the fuel, the evaporated fuel immediately reacts with the 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 locally becomes extremely high, the unburned hydrocarbons that have received the combustion heat will generate soot.
[0044]
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, 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 suppressed low by the endothermic effect of the inert gas.
[0045]
In this case, in order to suppress the temperature of the fuel and the surrounding gas to a temperature lower than the temperature at which the soot is generated, an amount of the inert gas is required to be able to absorb enough heat to do so. Therefore, if the fuel amount increases, the required amount of inert gas increases accordingly. In this case, the larger the specific heat of the inert gas, the stronger the endothermic action, and therefore, the inert gas is preferably a gas having a large specific heat. In this regard, since CO ₂ and EGR gas have relatively large specific heats, it can be said that it is preferable to use EGR gas as the inert gas.
[0046]
FIG. 5 shows the relationship between the EGR rate and the 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.
[0047]
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.
[0048]
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.
[0049]
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.
[0050]
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.
[0051]
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.
[0052]
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. At this time, the NOx generation amount is 10 p. p. m or less, so the amount of NOx generated is extremely small.
[0053]
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 the 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.
[0054]
By the way, when the supercharging is not performed, the upper limit of the total intake gas amount X sucked into the combustion chamber 5 is Y, and therefore, in FIG. 6, in the region where the required load is larger than Lo, as the required load increases, Unless the EGR gas ratio is reduced, the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio. In other words, when the supercharge is not performed, and when the required air-fuel ratio is maintained at the stoichiometric air-fuel ratio in a region where the required load is larger than Lo, the EGR rate decreases as the required load increases. In a region where the required load is larger than Lo, the temperature of the fuel and the surrounding gas cannot be maintained at a temperature lower than the temperature at which soot is generated.
[0055]
However, as shown in FIG. 1, when the EGR gas is recirculated through the EGR passage 29 into the inlet side of the supercharger, that is, into the air suction pipe 17 of the exhaust turbocharger 15, the EGR rate is increased in a region where the required load is larger than Lo. 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. When the EGR rate is set to 55% or more in a region where the required load is larger than Lo, the EGR control valve 31 is fully opened and the throttle valve 20 is slightly closed.
[0056]
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. NOx generation is reduced to 10 p. p. m or less, and even if the air amount is larger than the air amount shown in FIG. 6, that is, the average value of the air-fuel ratio is 17 to 18 lean, soot generation is prevented. While the amount of generated NOx is 10 p. p. m can be around or below.
[0057]
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, only a very small amount of NOx 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 if the combustion temperature is high. Not generated at all. Further, only a very small amount of NOx is generated.
[0058]
In this way, when low-temperature combustion is being performed, soot is not 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, The generation amount of NOx 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.
[0059]
By the way, the temperature of the fuel and the surrounding gas at the time of combustion in the combustion chamber can be suppressed to a temperature at or 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. Therefore, in the embodiment according to the present invention, during the low load operation in the engine, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas around it at a temperature below the temperature at which the growth of hydrocarbons stops halfway. 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, as is clear from the above description, the amount of inert gas in the combustion chamber is larger than the amount of inert gas at which the amount of soot is peaked, and soot is almost generated. The second combustion, that is, the combustion that has been performed conventionally, 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 generation peaks. Say that.
[0060]
FIG. 7 shows a first operation region I in which first combustion, that is, low-temperature combustion is performed, and a second operation region II in which second combustion, that is, combustion by a conventional combustion method, is performed. In FIG. 7, the vertical axis L indicates the amount of depression of the accelerator pedal 50, 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).
[0061]
That is, if the required load L exceeds a first boundary X (N), which is a function of the engine speed N, when the operating state of the engine is in the first operating region I and low-temperature combustion is being performed, the operating region Is shifted to the second operation region II, and combustion is performed by the 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.
[0062]
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 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.
[0063]
By the way, when the operation region of the engine is in the first operation region I and low-temperature combustion is being performed, soot is hardly generated, and instead, unburned hydrocarbons are 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 catalyst 25 having an oxidizing function.
[0064]
As the catalyst 25, an oxidation catalyst, a three-way catalyst, or a NOx absorbent can be used. The NOx absorbent has a function of absorbing NOx when the average air-fuel ratio in the combustion chamber 5 is lean, and releasing NOx when the average air-fuel ratio in the combustion chamber 5 becomes rich.
[0065]
The NOx absorbent uses, for example, alumina as a carrier, and on the carrier, for example, alkali metals such as potassium K, sodium Na, lithium Li, cesium Cs, alkaline earths such as barium Ba, calcium Ca, lanthanum La, yttrium Y And at least one noble metal such as platinum Pt.
[0066]
Not only the oxidation catalyst but also the three-way catalyst and the NOx absorbent have an oxidation function. Therefore, the three-way catalyst and the NOx absorbent can be used as the catalyst 25 as described above.
[0067]
FIG. 8 shows the output of the air-fuel ratio sensor 27. As shown in FIG. 8, the output current I of the air-fuel ratio sensor 27 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 27.
[0068]
Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG.
[0069]
FIG. 9 shows the opening degree of the throttle valve 20, the opening degree of the EGR control valve 31, 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. 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 as the required load L increases. The opening degree of the EGR control valve 31 is gradually increased from near full closure to full opening as the required load L increases. In the example shown in FIG. 9, in the first operation region I, the EGR rate is approximately 70%, and the air-fuel ratio is a slightly lean air-fuel ratio.
[0070]
In other words, in the first operating region I, the opening of the throttle valve 20 and the opening of the EGR control valve 31 are controlled such that the EGR 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.
[0071]
At the time of the idling operation, 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. When the throttle valve 20 is closed close to the fully closed state, 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.
[0072]
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 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, since the EGR rate jumps over the EGR rate range (FIG. 5) in which a large amount of smoke is generated, a large amount of smoke is generated when the engine operating region changes from the first operating region I to the second operating region II. There is no.
[0073]
In the second operation region II, the conventional combustion is performed. In the second operation region II, the throttle valve 20 is held in a fully open state except for a part, and the opening degree 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. In the second operation region II, the injection start timing θS is set near the compression top dead center TDC.
[0074]
FIG. 10A shows the target air-fuel ratio A / F in the first operation region I. In FIG. 10 (A), curves indicated by A / F = 15.5, A / F = 16, A / F = 17, and A / F = 18 have target air-fuel ratios of 15.5, 16, and 17, respectively. , 18 and the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 10A, the air-fuel ratio is lean in the first operation region I, and the target air-fuel ratio A / F is made leaner as the required load L decreases in the first operation region I. You.
[0075]
That is, the lower the required load L, the smaller the amount of heat generated by combustion. Therefore, as the required load L decreases, low-temperature combustion can be performed even if the EGR rate is reduced. When the EGR rate is decreased, the air-fuel ratio increases. Therefore, as shown in FIG. 10A, as the required load L decreases, the target air-fuel ratio A / F increases. As the target air-fuel ratio A / F increases, the fuel consumption rate increases. Therefore, in order to make the air-fuel ratio as lean as possible, the embodiment according to the present invention increases the target air-fuel ratio A / F as the required load L decreases. .
[0076]
The target air-fuel ratio A / F shown in FIG. 10A is stored in advance in the ROM 42 in the form of a map as a function of the required load L and the engine speed N as shown in FIG. 10B. . In addition, as shown in FIG. 11A, the target opening ST of the throttle valve 20 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening degree SE of the EGR control valve 31 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 10A is stored in advance in the ROM 42 in the form of a map as a function of N. As shown in FIG. 11 (B), it 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.
[0077]
FIG. 12A shows the target air-fuel ratio A / F when the second combustion, that is, the normal combustion according to the conventional combustion method is performed. In FIG. 12A, curves A / F = 24, A / F = 35, A / F = 45, and A / F = 60 indicate target air-fuel ratios 24, 35, 45, and 60, respectively. ing. The target air-fuel ratio A / F shown in FIG. 12A 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 as shown in FIG. In addition, as shown in FIG. 13A, the target opening ST of the throttle valve 20 necessary for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. The target opening SE of the EGR control valve 31 required for setting the air-fuel ratio to the target air-fuel ratio A / F shown in FIG. 12A is stored in advance in the ROM 42 in the form of a map as a function of N. As shown in FIG. 13 (B), a map is stored in advance in the ROM 42 as a function of the required load L and the engine speed N.
[0078]
Further, when the second combustion is being performed, the fuel injection amount Q is calculated based on the required load L and the engine speed N. The fuel injection amount Q 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 as shown in FIG.
[0079]
Next, the operation control of the present embodiment will be described with reference to FIGS. Referring to FIGS. 15 and 16, first, at 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 105. 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 111 to perform the second combustion.
[0080]
When it is determined in step 100 that the flag I has not been set, that is, when the operating state of the engine is in the second operating region II, the routine proceeds to step 103, where the required load L exceeds the second boundary Y (N). It is determined whether it has become low. When L ≧ Y (N), the routine proceeds to step 111, where the second combustion is performed under a lean air-fuel ratio. On the other hand, when it is determined in step 103 that L <Y (N), the routine proceeds to step 104, where the flag I is set, and then the routine proceeds to step 105.
[0081]
In step 105, it is determined whether the pressure P in the exhaust manifold 22 detected by the pressure sensor 53 is equal to or higher than a predetermined value P1. In the case of YES, it is determined that low-temperature combustion should not be performed because the exhaust gas is unlikely to be discharged from the combustion chamber 5 into the exhaust manifold 22, and the routine proceeds to step 102 ', where the flag I is reset, and then the routine proceeds to step 111. A second combustion takes place. On the other hand, if NO, it is determined that low-temperature combustion can be performed, and the routine proceeds to step 106, where low-temperature combustion is performed.
[0082]
In step 106, 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 107, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 11B, and the opening of the EGR control valve 31 is set as the target opening SE. Next, at step 108, the mass flow rate of the intake air (hereinafter simply referred to as the intake air amount) Ga detected by the mass flow rate detector 21 is taken in. Next, at step 109, the target air-fuel ratio is obtained from the map shown in FIG. A / F is calculated. Next, at step 110, a fuel injection amount Q necessary for setting the air-fuel ratio to the target air-fuel ratio A / F is calculated based on the intake air amount Ga and the target air-fuel ratio A / F.
[0083]
When the required load L or the engine speed N changes during such low-temperature combustion, the opening of the throttle valve 20 and the opening of the EGR control valve 31 are immediately changed to the target according to the required load L and the engine speed N. The opening degrees ST and SE are made to match. Therefore, for example, when the required load L is increased, the amount of air in the combustion chamber 5 is increased immediately, and the generated torque of the engine is immediately increased.
[0084]
On the other hand, when the opening degree of the throttle valve 20 or the opening degree of the EGR control valve 31 changes to change the intake air amount, the change in the intake air amount Ga is detected by the mass flow rate detector 21, and the detected intake air amount The fuel injection amount Q is controlled based on Ga. That is, the fuel injection amount Q is changed after the intake air amount Ga is actually changed.
[0085]
In step 111, the target fuel injection amount Q is calculated from the map shown in FIG. 14, and the fuel injection amount is set as the target fuel injection amount Q. Next, at step 112, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. Next, at step 113, 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 as the target opening SE.
[0086]
Next, at step 114, the intake air amount Ga detected by the mass flow detector 21 is taken. Next, at step 115, the actual air-fuel ratio (A / F) _R is calculated from the fuel injection amount Q and the intake air amount Ga. Next, at step 116, the target air-fuel ratio A / F is calculated from the map shown in FIG. Next, at step 117, it is determined whether or not the actual air-fuel ratio (A / F) _R is larger than the target air-fuel ratio A / F. (A / F) When _R > A / F, the routine proceeds to step 118, where the throttle opening correction value ΔST is decreased by a constant value α, and then the routine proceeds to step 120. On the other hand, when (A / F) _R ≦ A / F, the routine proceeds to step 119, where the correction value ΔST is increased by a constant value α, and then the routine proceeds to step 120. In step 120, the final target opening ST is calculated by adding the correction value ΔST to the target opening ST of the throttle valve 20, and the opening of the throttle valve 20 is used as the final target opening ST. That is, the opening of the throttle valve 20 is controlled such that the actual air-fuel ratio (A / F) _R becomes the target air-fuel ratio A / F.
[0087]
As described above, when the required load L or the engine speed N changes during the second combustion, the fuel injection amount is immediately matched with the target fuel injection amount Q corresponding to the required load L and the engine speed N. For example, when the required load L is increased, the fuel injection amount is immediately increased, and thus the torque generated by the engine is immediately increased.
[0088]
On the other hand, when the fuel injection amount Q is increased and the air-fuel ratio deviates from the target air-fuel ratio A / F, the opening of the throttle valve 20 is controlled so that the air-fuel ratio becomes the target air-fuel ratio A / F. That is, the air-fuel ratio is changed after the fuel injection amount Q changes.
[0089]
In the embodiments described so far, the fuel injection amount Q is subjected to open-loop control during low-temperature combustion, and the air-fuel ratio changes the opening of the throttle valve 20 during second combustion. Is controlled by However, the fuel injection amount Q can be feedback-controlled based on the output signal of the air-fuel ratio sensor 27 when the low-temperature combustion is being performed, and the air-fuel ratio can be controlled by the EGR control when the second combustion is being performed. The control can also be performed by changing the opening of the valve 31.
[0090]
According to the present embodiment, the low-temperature combustion in which the amount of EGR gas supplied into the combustion chamber 5 is larger than the amount of EGR gas at which the generation amount of soot reaches a peak and almost no soot is generated is performed in step 106 to step 110 under low-temperature conditions. Therefore, the emission of soot and the emission of NOx from the internal combustion engine can be simultaneously prevented. Further, when it is determined in step 105 that the exhaust gas is hard to be discharged from the combustion chamber 5 into the exhaust manifold 22, the second combustion is performed in steps 111 to 120, that is, the low temperature combustion is prohibited. Is done. As a result, while the internal EGR gas having a relatively high temperature continues to stagnate in the combustion chamber 5, the exhaust gas is difficult to supply the EGR gas for lowering the temperature in the combustion chamber 5 into the combustion chamber 5. By performing low-temperature combustion under a relatively rich air-fuel ratio when it is difficult for the gas to be exhausted from the combustion chamber 5 into the exhaust manifold 22, it is possible to prevent an increase in soot generation.
[0091]
Further, according to the present embodiment, when it is determined that the temperature in the combustion chamber 5 rises to such an extent that low-temperature combustion cannot be performed, in detail, the required load L in Step 101 or Step 103 becomes larger than a predetermined value. When the engine speed N becomes higher, in other words, when the engine speed N becomes higher than a predetermined value, or because the pressure in the exhaust manifold 22 is high in step 105, the exhaust gas flows from the combustion chamber 5 to the exhaust manifold 22. When it is determined that the second combustion is difficult to be performed, the second combustion is performed in Steps 111 to 120, that is, the low-temperature combustion is prohibited. As a result, when the temperature in the combustion chamber 5 rises and hydrocarbons grow into soot, by performing low-temperature combustion under a relatively rich air-fuel ratio, the amount of soot generation increases. Can be prevented.
[0092]
【The invention's effect】
According to the first to third aspects of the present invention, it is possible to simultaneously prevent the emission of soot from the internal combustion engine and the emission of NOx, and reduce the temperature in the combustion chamber to such an extent that combustion in which almost no soot is generated cannot be performed. When the amount of soot is increased, it is possible to prevent an increase in the amount of generated soot by trying to perform combustion in which almost no soot is generated.
[0093]
According to the fourth and fifth aspects of the invention, it is possible to prevent unburned hydrocarbons from being discharged from the internal combustion engine.
[0094]
According to the invention described in claim 6, it is possible to avoid the necessity of specially providing a means for supplying an inert gas from the outside into the combustion chamber.
[0095]
According to the seventh aspect of the present invention, it is possible to prevent the exhaust gas recirculation rate from being set to the exhaust gas recirculation rate at which the generation amount of soot peaks.
[0096]
According to the invention as set forth in claim 8, the first combustion is performed under inappropriate conditions both when the first combustion is performed and when the second combustion is performed. It is possible to prevent the generation amount of soot from being increased by trying to execute.
[0097]
According to the ninth aspect of the present invention, it is possible to prevent the exhaust gas recirculation rate from being set to the exhaust gas recirculation rate at which the generation amount of soot reaches a peak.
[0098]
According to the tenth aspect, appropriate combustion can be performed according to the operation range.
[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 NOx 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 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 an opening degree of a throttle valve and the like.
FIG. 10 is a diagram showing an air-fuel ratio and the like 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 diagram showing an air-fuel ratio and the like in a second combustion.
FIG. 13 is a diagram showing a map of a target opening degree of a throttle valve and the like.
FIG. 14 is a diagram showing a map of a fuel injection amount.
FIG. 15 is a flowchart for controlling operation of the engine.
FIG. 16 is a flowchart for controlling operation of the engine.
[Explanation of symbols]
5 Combustion chamber 6 Fuel injection valve 20 Throttle valve 22 Exhaust manifold 29 EGR passage 31 EGR control valve 53 Pressure sensor

Claims (10)

As the amount of inert gas supplied into the combustion chamber increases, the amount of soot generated gradually increases and reaches a peak, and when the amount of inert gas supplied into the combustion chamber further increases, the amount of soot increases. In an internal combustion engine in which the temperature of fuel and surrounding gas during combustion in the combustion chamber is lower than the temperature at which soot is generated and soot is hardly generated, the temperature in the combustion chamber is reduced to such an extent that combustion in which soot is hardly generated cannot be performed. Determination means for determining whether or not the temperature rises. When it is determined that the temperature in the combustion chamber rises to such an extent that the combustion in which the soot is hardly generated is not performed, the combustion in which the soot is hardly generated is determined. Internal combustion engine that is prohibited from performing 2. The internal combustion engine according to claim 1, wherein whether or not the temperature in the combustion chamber rises to such an extent that combustion in which the soot is hardly generated is not determined is determined based on a state of remaining combustion gas in the combustion chamber. 3. The internal combustion engine according to claim 2, wherein a remaining state of the combustion gas is determined according to an output value of a pressure detection unit disposed in the engine exhaust passage to detect a pressure in the engine exhaust passage. The internal combustion engine according to claim 1, wherein a catalyst having an oxidizing function is disposed in the engine exhaust passage to oxidize unburned hydrocarbons discharged from the combustion chamber. The internal combustion engine according to claim 4, wherein the catalyst comprises at least one of an oxidation catalyst, a three-way catalyst, and a NOx absorbent. An exhaust gas recirculation device for recirculating exhaust gas discharged from the combustion chamber into an engine intake passage, wherein the inert gas comprises recirculated exhaust gas recirculated into the engine intake passage. 2. The internal combustion engine according to 1. The first combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is larger than the amount of recirculated exhaust gas at which the amount of soot generated at the peak is large and soot is hardly generated, and the amount of generated soot is peaked Switching means for selectively switching between the second combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than the amount of recirculated exhaust gas, wherein the first combustion is changed to the second combustion. 7. The internal combustion engine according to claim 6, wherein the exhaust gas recirculation rate is changed stepwise when the second combustion is switched to the first combustion. If it is determined during the execution of the first combustion that the exhaust gas is difficult to be discharged from the combustion chamber into the engine exhaust passage, the first combustion is switched to the second combustion, and the second combustion is performed. 8. The execution of switching from the second combustion to the first combustion is prohibited when it is determined that exhaust gas is hardly discharged from the combustion chamber into the engine exhaust passage during execution of the combustion. An internal combustion engine according to claim 1. The exhaust gas recirculation rate when the first combustion is performed is approximately 55% or more, and the exhaust gas recirculation rate when the second combustion is performed is approximately 50% or less. Item 8. The internal combustion engine according to Item 7. The operating range of the engine is divided into a first operating range on a low load side and a second operating range on a high load side, and the first combustion is performed in the first operating range, and the second operating range is performed. The internal combustion engine according to claim 7, wherein the second combustion is performed.

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