JP3551771B2 - Internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an 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. 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 to a value within the range not exceeding the maximum allowable limit._xAnd the amount of smoke 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 soot was not generated was examined, and as a result, 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 And when the temperature of the gas around it rises above a certain temperature, the 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. An internal combustion engine employing the new combustion system has already been filed by the present applicant (Japanese Patent Application No. 9-305850).
[0009]
[Problems to be solved by the invention]
By the way, even in this internal combustion engine, if the fuel injection amount increases, the calorific value of the whole injected fuel increases, so that the temperature of the fuel and the surrounding gas during combustion in the combustion chamber is lower than the temperature at which soot is generated. The low temperature can be maintained when the fuel injection amount is relatively small. However, with this new combustion system, soot and NO_xCan be reduced at the same time, and it is therefore preferable to extend the operating range of the engine in which the new combustion system can be used as much as possible.
[0010]
It is an object of the present invention to extend the operating range of an engine that can use this new combustion system.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, in the first invention, as the amount of recirculated exhaust gas supplied to the fuel chamber increases, the amount of soot generated gradually increases and reaches a peak.However, if the amount of recirculated exhaust gas supplied into the combustion chamber is further increased, the temperature of 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 an internal combustion engine, by increasing the amount of recirculated exhaust gas supplied into the combustion chamber from the amount of recirculated exhaust gas at which the generation amount of soot becomes a peak, the temperature of fuel and the surrounding gas during combustion in the combustion chamber is reduced. Is suppressed to a temperature lower than the temperature at which water is generated, and water is supplied to the intake air sent into the combustion chamber. That is, when water is supplied to the intake air, the temperature of fuel and the surrounding gas during combustion in the combustion chamber decrease.
[0012]
According to a second aspect, in the first aspect, the amount of water supplied to the intake air is larger when the engine load is higher than the predetermined load than when the engine load is lower than the predetermined load. Is done.
In a third aspect based on the first aspect, when the air-fuel ratio of the inflowing exhaust gas is lean, NO contained in the exhaust gas is included._xAnd the NO absorbed when the air-fuel ratio of the inflowing exhaust gas becomes stoichiometric or rich._xReleases NO_xThe absorbent is disposed in the engine exhaust passage, and NO_xNO from absorbent_xWhen the air-fuel ratio in the combustion chamber is set to the stoichiometric air-fuel ratio or rich in order to release the water, water is supplied to the intake air.
[0013]
In a fourth aspect based on the first aspect, a means for collecting moisture in the recirculated exhaust gas is provided, and the collected water is supplied to the intake air.
In a fifth aspect based on the first aspect, a catalyst having an oxidizing function is disposed in the engine exhaust passage.
In a sixth aspect based on the fifth aspect, the catalyst is an oxidation catalyst, a three-way catalyst or NO._xConsists of at least one of the absorbents.
[0014]
In a seventh aspect based on the first aspect, the exhaust gas recirculation rate is approximately 55% or more.
In an eighth aspect based on the first aspect, 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 generation amount of soot reaches a peak and soot is hardly generated; There is provided 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 gas at which the amount of generated soot becomes a peak.
[0015]
According to a ninth aspect, in the eighth aspect, the air-fuel ratio in the first combustion is a stoichiometric air-fuel ratio, a lean air-fuel ratio slightly leaner than the stoichiometric air-fuel ratio, or a rich air-fuel ratio. The air-fuel ratio in the combustion is defined as the lean air-fuel ratio.
In a tenth aspect based on the eighth 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.
[0016]
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 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.
[0017]
On the other hand, the exhaust port 10 is connected to an inlet of an exhaust turbine 23 of the exhaust turbocharger 15 via an exhaust manifold 21 and an exhaust pipe 22, and an outlet of the exhaust turbine 23 is connected to a catalyst 25 having an oxidation function through an exhaust pipe 24. Is connected to a catalytic converter 26 having a built-in. An air-fuel ratio sensor 27 is disposed in the exhaust manifold 21.
[0018]
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.
[0019]
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.
[0020]
A water injection valve 37 is attached to each intake branch pipe 11. These water injection valves 37 are connected to a water tank 39 via a water supply pump 38. When performing water injection, water in the water tank 39 is supplied to each water injection valve 37 by the water supply pump 38, and water is supplied from each water injection valve 37 into the corresponding intake port 8. That is, water is injected into the intake air.
[0021]
On the other hand, the EGR gas contains moisture. Therefore, when the EGR gas is cooled by the intercooler 32, the moisture contained in the EGR gas condenses in the intercooler 32. The condensed water flows down in the intercooler 32 and accumulates at the bottom of the intercooler 32. As shown in FIG. 1, the bottom of the intercooler 32 is connected to a water tank 39 via a conduit 40 and an on-off valve 41.
[0022]
In the embodiment shown in FIG. 1, for example, the on-off valve 41 is temporarily opened immediately after the engine is stopped. At this time, the coagulated water accumulated at the bottom of the intercooler 32 is supplied into the water tank 39 via the conduit 40. You. If the amount of water in the water tank 39 is insufficient with only the condensed water, the water is supplied into the water tank 39 as necessary.
The electronic control unit 50 is composed of a digital computer, and is connected to each other by a bidirectional bus 51. A ROM (read only memory) 52, a RAM (random access memory) 53, a CPU (microprocessor) 54, an input port 55, and an output port 56. The output signal of the air-fuel ratio sensor 27 is input to the input port 55 via the corresponding AD converter 57, and the output signal of the fuel pressure sensor 36 is also input to the input port 55 via the corresponding AD converter 57. A load sensor 61 that generates an output voltage proportional to the depression amount L of the accelerator pedal 60 is connected to the accelerator pedal 60, and the output voltage of the load sensor 61 is input to the input port 55 via the corresponding AD converter 57. . The input port 55 is connected to a crank angle sensor 62 that generates an output pulse each time the crankshaft rotates, for example, by 30 °. On the other hand, the output port 56 is connected to the fuel injection valve 6, the throttle valve control step motor 19, the EGR control valve control step motor 30, the fuel pump 35, the water supply pump 38, and the on-off valve 41 via the corresponding drive circuit 58. Is done.
[0023]
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, 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.
[0024]
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 when the air-fuel ratio A / F is around 15.0, the smoke becomes almost zero. . That is, almost no soot is generated. At this time, the output torque of the engine slightly decreases, and 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.
[0025]
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.
[0026]
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.
[0027]
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. .
[0028]
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.
[0029]
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.
[0030]
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, it is extremely difficult to discharge the hydrocarbon soot from the combustion chamber 5 in the state of or before the hydrocarbon soot or in the form of soot from the combustion chamber 5. There is a big difference. The new combustion system employed in the present invention discharges hydrocarbons from the combustion chamber 5 in the form of a precursor or previous soot without producing soot in the combustion chamber 5 and removing the hydrocarbons. The core is to oxidize with a catalyst having an oxidation function.
[0031]
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.
[0032]
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.
[0033]
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.
[0034]
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.
[0035]
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.
[0036]
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.
[0037]
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.
[0038]
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 shows the required load.
[0039]
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.
[0040]
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.
[0041]
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.
[0042]
However, as shown in FIG. 1, when the EGR gas is recirculated through the EGR passage 29 to the inlet side of the supercharger, that is, in the air suction pipe 17 of the exhaust turbocharger 15, the EGR gas is recirculated in a region where the required load is larger than Lo. The rate can be maintained at or above 55 percent, such as 70 percent, so that 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.
[0043]
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.
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. NO while preventing generation of_xIs 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. NO_xIs 10 p. p. m can be around or below.
[0044]
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.
[0045]
Thus, 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, 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.
[0046]
By the way, the temperature of the fuel and the surrounding gas during the combustion in the combustion chamber can be suppressed to a temperature lower than the temperature at which the fuel stops during the growth of hydrocarbons, but is limited to the low load operation in the engine where the amount of heat generated by combustion is relatively small. Therefore, in the embodiment according to the present invention, the first combustion, that is, the low-temperature combustion is performed by suppressing the temperature of the fuel during combustion and the gas temperature around the same at or below the temperature at which the growth of hydrocarbons stops halfway during the low load operation in the engine. In addition, the second combustion, that is, the combustion that has been performed conventionally, is performed during the high load operation of the engine. Here, the first combustion, that is, the low-temperature combustion, has a larger amount of the inert gas in the combustion chamber than the amount of the inert gas at which the 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 performed conventionally, is a combustion in which the amount of the inert gas in the combustion chamber is smaller than the amount of the inert gas at which the amount of soot is peaked. Say that.
[0047]
FIG. 7A 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. I have. In FIG. 7A, the vertical axis L indicates the depression amount of the accelerator pedal 60, that is, the required load, and the horizontal axis N indicates the engine speed. In FIG. 7A, X (N) indicates a first boundary between the first operation region I and the second operation region II, and Y (N) indicates a first boundary between the first operation region I and the second operation region II. 2 shows a second boundary with the second operating region II. 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).
[0048]
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.
[0049]
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.
[0050]
By the way, as described above, when the EGR gas is recirculated to the air suction pipe 17 of the exhaust turbocharger 15, the operating range of the engine that can generate low-temperature combustion can be expanded. In this case, in particular, when water is injected from the water injection valve 37 into the intake port 8 when the calorific value when fuel is burned during low-temperature combustion is large, that is, when the required load L is high in the first operation region I, The temperature of the fuel and the surrounding gas during combustion in the combustion chamber 5 becomes low, and thus the operating range of the engine in which low-temperature combustion can be performed can be further expanded.
[0051]
Therefore, in the first embodiment according to the present invention, when the required load L exceeds the boundary Z (N) shown in FIG. Water is sprayed inside. FIG. 7B shows a first boundary X (N) and a second boundary Y (N) when water injection is performed. When comparing FIG. 7A and FIG. 7B, the first boundary X (N) and the second boundary Y (N) shown in FIG. 7B when water injection is performed are shown in FIG. It can be seen that the load has moved to a higher load than the first boundary X (N) and the second boundary Y (N) when the water injection shown in FIG. 7 (A) is not performed. In other words, it can be seen that when water injection is performed, the operating range in which low-temperature combustion can be performed expands to the high load side.
[0052]
The boundary Z (N) is a function of the engine speed N, and this Z (N) decreases as the engine speed N increases.
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 catalyst 25 having an oxidizing function.
[0053]
As the catalyst 25, an oxidation catalyst, a three-way catalyst, or NO_xAn absorbent can be used. NO_xThe absorbent is NO when the average air-fuel ratio in the combustion chamber 5 is lean._xWhen the average air-fuel ratio in the combustion chamber 5 becomes the stoichiometric air-fuel ratio or rich, NO_xHas the function of releasing.
This NO_xThe absorbent is, for example, alumina as a carrier, and 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 or the like. And at least one selected from rare earths and a noble metal such as platinum Pt.
[0054]
Not only oxidation catalyst, but also three-way catalyst and NO_xThe absorbent also has an oxidizing function, and therefore, as described above, the three-way catalyst and the NO_xAn absorbent can be used as the catalyst 25.
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.
[0055]
Next, the operation control in the first operation region I and the second operation region II will be schematically described with reference to FIG.
FIG. 9 shows the 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 operation 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 1/3 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.
[0056]
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. At this time, the air-fuel ratio is controlled to the target lean air-fuel ratio by correcting the opening of the EGR control valve 31 based on the output signal of the air-fuel ratio sensor 27. 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.
[0057]
In the first operating region I, water is injected from the water injection valve 37 in an operating region where the required load L is high, as indicated by Z in FIG.
In addition, during idling operation, the throttle valve 20 is closed to almost fully closed, and at this time, the EGR control valve 31 is also closed to almost fully closed. 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.
[0058]
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 1/3 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.
[0059]
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.
[0060]
FIG. 10 shows the air-fuel ratio A / F in the first operation region I. In FIG. 10, the curves indicated by A / F = 15.5, A / F = 16, A / F = 17, and A / F = 18 have air-fuel ratios of 15.5, 16, 17, and 18, respectively. And the air-fuel ratio between the curves is determined by proportional distribution. As shown in FIG. 10, the air-fuel ratio is lean in the first operating region I, and the air-fuel ratio A / F is leaner in the first operating region I as the required load L decreases.
[0061]
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 reduced, the air-fuel ratio increases. Therefore, as shown in FIG. 10, the air-fuel ratio A / F increases as the required load L decreases. As the air-fuel ratio A / F increases, the fuel consumption rate increases. Therefore, in order to make the air-fuel ratio as lean as possible, in the embodiment according to the present invention, the air-fuel ratio A / F increases as the required load L decreases.
[0062]
Note that the target opening ST of the throttle valve 20 necessary for setting the air-fuel ratio to the target air-fuel ratio shown in FIG. 10 is obtained as a function of the required load L and the engine speed N as 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 shown in FIG. 10 is stored in advance in the ROM 52 as shown in FIG. And in the form of a map as a function of the engine speed N in the ROM 52 in advance.
[0063]
FIG. 12 shows the target air-fuel ratio when the second combustion, that is, the normal combustion by the conventional combustion method is performed. In FIG. 12, 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. The target opening ST of the throttle valve 20 required for setting the air-fuel ratio to the target air-fuel ratio is stored in the ROM 52 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. The target opening SE of the EGR control valve 31 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 52 in the form of a map in advance.
[0064]
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 the required load L is changed from the first boundary X (N) shown in FIG. Is also determined. When L ≦ X (N), the routine proceeds to step 103, where low-temperature combustion is performed.
[0065]
That is, in step 103, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 11A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 104, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 11B, and the opening of the EGR control valve 31 is set as 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. Next, at step 106, it is determined whether the required load L is larger than the boundary Z (N) shown in FIG. 7B. When L> Z (N), the routine proceeds to step 107, where water is injected from the water injection valve 37.
[0066]
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 110 to perform the second combustion.
That is, in step 110, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 13A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 111, 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. Next, at step 112, fuel injection is performed so as to attain the lean air-fuel ratio shown in FIG.
[0067]
When the flag I is reset, in the next processing cycle, the process proceeds from step 100 to step 108, where it is determined whether or not the required load L has become lower than the second boundary Y (N) shown in FIG. 7B. You. When L ≧ Y (N), the routine proceeds to step 110, where the second combustion is performed under a lean air-fuel ratio.
On the other hand, when it is determined in step 108 that L <Y (N), the routine proceeds to step 109, where the flag I is set. Then, the routine proceeds to step 103, where low-temperature combustion is performed.
[0068]
Next, NO as the catalyst 25_xA second embodiment using an absorbent will be described.
NO as described above_xThe absorbent 25 is NO when the average air-fuel ratio in the combustion chamber 5 is lean._xWhen the average air-fuel ratio in the combustion chamber 5 becomes the stoichiometric air-fuel ratio or rich, NO_xHas the function of releasing. That is, the engine intake passage, the combustion chamber 5, and the NO_xThe ratio of air and fuel (hydrocarbon) supplied into the exhaust passage upstream of the absorbent 25 is set to NO._xWhen the air-fuel ratio of the exhaust gas flowing into the absorbent 25 is called this NO_xThe absorbent 25 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.
[0069]
This NO_xIf the absorbent 25 is arranged in the engine exhaust passage, NO_xAbsorbent 25 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.
[0070]
In the compression ignition type internal combustion engine shown in FIG. 1, combustion is performed in a state where the air-fuel ratio in the normal combustion chamber 5 is lean. As described above, when combustion is performed with a 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 25. 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.
[0071]
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 25_xIs reacted with a large amount of unburned HC and CO contained in the inflowing exhaust gas and reduced 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 25_xIs released, and the released NO_xNO in the atmosphere to be reduced_xIs not emitted.
[0072]
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 25_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 25_xIs released only slowly_xTotal NO absorbed in absorbent 25_xIt takes a slightly longer time to release.
[0073]
By the way, NO_xNO of absorbent 25_xAbsorption capacity is limited, NO_xNO of absorbent 25_xNO before absorption capacity is saturated_xNO from absorbent 25_xMust be released. NO for that_xNO absorbed by absorbent 25_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 amount of absorption A is determined in advance in the form of a map as shown in FIG. 16A 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 obtained in advance 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 by absorbent 25_xThe amount ΣNOX is estimated.
[0074]
In the second embodiment, this NO_xNO when the absorption amount ΣNOX exceeds a predetermined allowable maximum value._xNO from absorbent 25_xIs to be released. Next, this will be described with reference to FIG.
Referring to FIG. 17, in the second embodiment, two allowable maximum values, that is, an allowable maximum value MAX1 and an allowable maximum value MAX2 are set. Maximum allowable value MAX1 is NO_xMaximum NO that can be absorbed by the absorbent 25_xIt is about 30% of the absorption amount, and the allowable maximum value MAX2 is NO_xIt is about 80% of the maximum absorption amount that the absorbent 25 can absorb. NO when the first combustion is being performed_xNO when the absorption amount ΣNOX exceeds the allowable maximum value MAX1._xNO from absorbent 25_xWhen the air-fuel ratio is made rich and the second combustion is performed, NO_xWhen the absorption amount ΣNOX exceeds the permissible maximum value MAX1, when the second combustion is switched to the first combustion, NO_xNO from absorbent 25_xWhen the air-fuel ratio is made rich and the second combustion is performed, NO_xNO when the absorption amount ΣNOX exceeds the allowable maximum value MAX2._xNO from absorbent 25_xAdditional fuel is injected during the second half of the expansion stroke or during the exhaust stroke to release.
[0075]
That is, FIG. 17 shows a case where the required load L is lower than the first boundary X (N) and the first combustion is performed in the period X, and the air-fuel ratio at this time is slightly smaller than the stoichiometric air-fuel ratio. It has a lean air-fuel ratio. NO when first combustion is being performed_xIs extremely small, and therefore, at this time, as shown in FIG._xThe absorption amount ΣNOX rises very slowly. NO when the first combustion is being performed_xWhen the absorption amount ΣNOX exceeds the allowable maximum value MAX1, the air-fuel ratio A / F is temporarily made rich, whereby the NO_xNO from absorbent 25_xIs released. NO at this time_xThe absorption amount ΣNOX is set to zero.
[0076]
As described above, no soot is generated during the first combustion. However, NO_xNO from absorbent 25_xIf the air-fuel ratio is made considerably rich to release the fuel, there is a danger that soot will be generated due to a rapid increase in the amount of heat generated when the fuel burns. Therefore, in the second embodiment, when the air-fuel ratio is made rich, water is injected from the water injection valve 37 to lower the gas temperature in the combustion chamber 5.
[0077]
Returning again to FIG.₁When the required load L exceeds the first boundary X (N), the first combustion is switched to the second combustion. As shown in FIG. 17, when the second combustion is being performed, the air-fuel ratio A / F becomes considerably lean. NO is performed when the second combustion is performed, compared to when the first combustion is performed._xIs large when the second combustion is being performed._xThe amount ΣNOX rises relatively quickly.
[0078]
If the air-fuel ratio A / F is made rich while the second combustion is being performed, a large amount of soot is generated. Therefore, it is difficult to make the air-fuel ratio A / F rich when the second combustion is being performed. Can not. Therefore, when the second combustion is being performed as shown in FIG._xEven if the absorption amount ΣNOX exceeds the allowable maximum value MAX1, NO_xNO from absorbent 25_xThe air-fuel ratio A / F is not made rich in order to release the fuel. In this case, time t in FIG.₂When the required load L becomes lower than the second boundary Y (N) and the second combustion is switched to the first combustion as in_xNO from absorbent 25_xThe air-fuel ratio A / F is temporarily made rich to release the air. Also at this time, water is injected from the water injection valve 37 in order to avoid the danger of generating soot.
[0079]
Next, at time t in FIG.₃Is switched from the first combustion to the second combustion, and the second combustion is continued for a while. NO at this time_xThe absorption amount ΣNOX exceeds the allowable maximum value MAX1, and then the time t₄In this case, if the allowable maximum value MAX2 is exceeded, then NO_xNO from absorbent 25_xAdditional fuel is injected during the second half of the expansion stroke or during the exhaust stroke to release_xThe air-fuel ratio of the exhaust gas flowing into the absorbent 25 is made rich.
[0080]
The additional fuel injected during the second half of the expansion stroke or during the exhaust stroke does not contribute to the generation of engine power, so it is preferable to inject the additional fuel as little as possible. Therefore, when the second combustion is performed, NO_xWhen the absorption amount ΣNOX exceeds the allowable maximum value MAX1, the air-fuel ratio A / F is temporarily made rich when the second combustion is switched to the first combustion, and NO_xAdditional fuel is injected only in special cases where the absorption amount ΣNOX exceeds the allowable maximum value MAX2.
[0081]
FIG. 18 is NO_xNO from absorbent 25_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_xThe absorption amount ΣNOX is added to A. Next, at step 203, NO_xIt is determined whether or not the absorption amount ＸNOX has exceeded the allowable maximum value MAX1. If ΣNOX> MAX1, the routine proceeds to step 204, where NO is set during the first combustion._xNO indicating that the gas should be released_xThe release flag I is set.
[0082]
On the other hand, when it is determined in step 200 that the flag I has been reset, that is, when the operating region of the engine is in the second operating region II, the routine proceeds to step 205, where the map per unit time is obtained from the map shown in FIG. NO_xThe absorption amount B is calculated. Next, at step 206, NO_xB is added to the absorption amount ΣNOX. Next, at step 207, NO_xIt is determined whether or not the absorption amount ＸNOX has exceeded the allowable maximum value MAX1. When ΣNOX> MAX1, the routine proceeds to step 208, where NO is set when the first combustion is being performed._xNO indicating that the gas should be released_xThe release flag I is set.
[0083]
On the other hand, in step 209, NO_xIt is determined whether or not the absorption amount ＸNOX has exceeded the allowable maximum value MAX2. When ΣNOX> MAX2, the routine proceeds to step 210, where NO during the second combustion_xNO indicating that the gas should be released_xThe release flag II is set.
Next, the operation control will be described with reference to FIG.
[0084]
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 the required load L is changed from the first boundary X (N) shown in FIG. Is also determined. When L ≦ X (N), the routine proceeds to step 303, where low-temperature combustion is performed.
[0085]
That is, in step 303, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 11A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 304, the target opening 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 305, NO_xIt is determined whether or not the release flag I is set. NO_xIf the release flag I 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.
[0086]
On the other hand, in step 305, NO_xWhen it is determined that the release flag I has been set, the routine proceeds to step 307, where the rich processing I shown in FIG. 20 is performed.
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.
[0087]
That is, in step 310, the target opening ST of the throttle valve 20 is calculated from the map shown in FIG. 13A, and the opening of the throttle valve 20 is set to the target opening ST. Next, at step 311, the target opening SE of the EGR control valve 31 is calculated from the map shown in FIG. 13B, and the opening of the EGR control valve 31 is set as the target opening SE. Next, at step 312, NO_xIt is determined whether or not the release flag II has been set. NO_xIf the release flag II has not been set, the routine proceeds to step 313, where fuel injection is performed so as to achieve the air-fuel ratio shown in FIG. At this time, the second combustion is performed under the lean air-fuel ratio.
[0088]
On the other hand, in step 312, NO_xWhen it is determined that the release flag II has been set, the routine proceeds to step 314, where the rich processing II shown in FIG. 21 is performed.
Next, the rich processing I will be described with reference to FIG.
Referring to FIG. 20, first, in step 400, NO_xTotal NO presumed to be absorbed by absorbent 25_xリ ッ チ Rich time t required to release NOX_rIs calculated. Next, at step 401, the elapsed time t after the start of the rich processing I is equal to the rich time t._rIs determined. t ≦ t_rIn step 402, the routine proceeds to step 402, where the fuel injection amount is increased, and the air-fuel ratio is made rich. Next, at step 403, water is injected from the water injection valve 37.
[0089]
On the other hand, in step 401, t> t_rIf it is determined that the condition has been reached, the process proceeds to step 404 and NO_xThe release flag I is reset, and then ス テ ッ プ NOX is made zero in step 405.
Next, the rich process II will be described with reference to FIG.
Referring to FIG. 21, first, in step 500, NO_xTotal NO presumed to be absorbed by absorbent 25_xリ ッ チ Rich time t required to release NOX_rIs calculated. Next, at step 501, the elapsed time t after the start of the rich process II is equal to the rich time t._rIs determined. t ≦ t_rIn step 502, the routine proceeds to step 502, where the main injection is performed so that the air-fuel ratio A / F shown in FIG._xAdditional fuel required to make the air-fuel ratio of the exhaust gas flowing into the absorbent 25 rich is injected in the latter half of the expansion stroke or during the exhaust stroke.
[0090]
On the other hand, in step 501, t> t_rIf it is determined that the answer has been reached, the process proceeds to step 503 and the determination is NO._xThe release flags I and II are reset, and then ΣNOX is made zero in step 504.
In the second embodiment, similarly to the first embodiment, when the required load L exceeds the boundary Z (N) shown in FIG. 7B during low-temperature combustion, water is injected from the water injection valve 37. Can be fired.
[0091]
【The invention's effect】
The low temperature combustion area can be expanded.
[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 an opening degree of a throttle valve and the like.
FIG. 10 is a diagram showing an air-fuel ratio in a first operation region I.
FIG. 11 is a diagram showing a map of a target opening degree of a throttle valve and the like.
FIG. 12 is a view showing an air-fuel ratio in a second combustion.
FIG. 13 is a diagram showing a map of a target opening degree of a throttle valve and the like.
FIG. 14 is a flowchart for controlling operation of the engine.
FIG. 15 NO_xIt is a figure for explaining the release operation of.
FIG. 16: NO per unit time_xIt is a figure showing a map of an amount of absorption.
FIG. 17 NO_xIt is a figure for explaining discharge control.
FIG. 18 NO_xIt is a flowchart for processing a release flag.
FIG. 19 is a flowchart for controlling the operation of the engine.
FIG. 20 is a flowchart for executing a rich process I.
FIG. 21 is a flowchart for executing a rich process II.
[Explanation of symbols]
6 ... Fuel injection valve
15 Exhaust turbocharger
20 ... Throttle valve
29… EGR passage
37 ... water injection valve

Claims (10)

Combustion As we increase the recirculated exhaust gas amount supplied to the combustion chamber the amount of soot produced is peaked gradually increased, and gradually the recirculated exhaust gas amount further increases to be supplied into the combustion chamber In an internal combustion engine in which the temperature of the fuel and the surrounding gas during combustion in the room becomes lower than the soot generation temperature and soot is hardly generated , the amount of soot generation is more in the combustion chamber than the recirculated exhaust gas amount where the amount of soot is peaked. By increasing the amount of recirculated exhaust gas that is supplied, the temperature of fuel and surrounding gas during combustion in the combustion chamber is suppressed to a temperature lower than the temperature at which soot is generated, and the intake air that is sent into the combustion chamber contains An internal combustion engine that supplies water. 2. The internal combustion engine according to claim 1, wherein the amount of water supplied to the intake air is larger when the engine load is higher than a predetermined load than when the engine load is lower than the predetermined load. organ. 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 place the engine exhaust passage, according to claim 1 which is adapted to supply water to the intake air when the air-fuel ratio in the combustion chamber so as to release the NO _x from the NO _x absorbent the stoichiometric air-fuel ratio or rich Internal combustion engine. 2. The internal combustion engine according to claim 1, further comprising means for collecting moisture in the recirculated exhaust gas, and supplying the collected water to intake air. The internal combustion engine according to claim 1, wherein a catalyst having an oxidizing function is disposed in the engine exhaust passage. Internal combustion engine according to claim 5 in which said catalyst comprises one at least of the oxidation catalyst, three-way catalyst or _the NO _x absorbent. The internal combustion engine of claim 1, wherein the exhaust gas recirculation rate is greater than or equal to about 55 percent. First combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is larger than the amount of recirculated exhaust gas at which the amount of soot is peaked and little soot is generated, and the recirculated gas at which the amount of soot generated is peaked 2. The internal combustion engine according to claim 1, further comprising a switching means for selectively switching between a second combustion in which the amount of recirculated exhaust gas supplied into the combustion chamber is smaller than an amount of the second combustion. The air-fuel ratio in the first combustion is a stoichiometric air-fuel ratio, a lean air-fuel ratio slightly leaner than the stoichiometric air-fuel ratio, or a rich air-fuel ratio, and the air-fuel ratio in the second combustion is a lean air-fuel ratio. An internal combustion engine according to claim 8. 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 internal combustion engine according to claim 8, wherein combustion is performed.

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