JP3680637B2 - Diesel engine exhaust purification system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for a diesel engine.
[0002]
[Prior art]
NOx in the exhaust is adsorbed in the range of lean air-fuel ratio (the air-fuel ratio leaner than the stoichiometric air-fuel ratio), and the exhaust air-fuel ratio becomes the catalyst at the stoichiometric air-fuel ratio or rich air-fuel ratio (air-fuel ratio richer than the stoichiometric air-fuel ratio). A NOx catalyst that desorbs the adsorbed NOx and reduces and purifies the desorbed NOx using HC and CO present in a stoichiometric or rich air-fuel ratio atmosphere as a reducing agent is provided in the exhaust passage. Some are provided (see Japanese Patent Publication No. 2600492).
[0003]
Here, since this NOx catalyst can purify (regenerate the catalyst) NOx adsorbed on the catalyst by changing (fluctuating) the excess air ratio λ, this catalyst is hereinafter referred to as “λ variable catalyst”. That's it.
[0004]
[Problems to be solved by the invention]
By the way, since the above-mentioned λ-variable catalyst is intended for a gasoline engine, this λ-variable catalyst is applied to a diesel engine that is operated in a lean state with an air-fuel ratio of approximately 20 or more in the entire operation range. Is difficult. This is because if the air-fuel ratio is made rich in a diesel engine, smoke will be worsened.
[0005]
However, since the common rail fuel injection device is provided and performed in a limited operating range such as a high load range, the deterioration of smoke can be suppressed by promoting atomization of sprayed fuel by high pressure injection, so the air-fuel ratio is made rich. Is possible. In other words, it is difficult to perform rich combustion while suppressing the deterioration of smoke in a practical operation range such as a low and medium load range. As described above, in the conventional diesel engine, NOx discharged in the practical operation range cannot be treated with the λ fluctuation type catalyst, and therefore, EGR (exhaust gas recirculation) is relied on to reduce NOx in the practical operation range. It is inevitable.
[0006]
Now, when the HC concentration in the exhaust gas is almost constant in the lean air-fuel ratio region, NOx in the exhaust gas is adsorbed, and when the HC concentration at the catalyst inlet changes (fluctuates) in the same lean air-fuel ratio region, it adsorbs to the catalyst. The same applicant as the present applicant previously proposed a NOx catalyst that desorbs the NOx that had been removed and reduced and purified the desorbed NOx using HC and CO in the atmosphere as reducing agents. (Refer to Japanese Patent Application Nos. 10-215881 and 10-319689). If this catalyst is used, the catalyst can be regenerated in a practical operation range. Since this catalyst can be regenerated by changing (fluctuating) the HC concentration, this catalyst is hereinafter referred to as “HC fluctuation type catalyst”.
[0007]
Therefore, the present invention uses a combination of a λ-variable catalyst and an HC-variable catalyst for an engine that performs exhaust gas recirculation in the low-medium load region as an EGR region and stops EGR (exhaust gas recirculation) in the high-load region. When the NOx adsorption amount of the HC variable catalyst reaches saturation, the HC variable catalyst is regenerated by changing the HC concentration in the exhaust gas flowing into the HC variable catalyst in the EGR region. When the NOx adsorption amount of the λ fluctuation type catalyst reaches saturation, the air / fuel ratio of the exhaust gas flowing into the λ fluctuation type catalyst is enriched in a region other than the EGR region (high load region). The purpose is to regenerate the catalyst while preventing the deterioration of smoke.
[0008]
On the other hand, the low-medium load region is a low-temperature premixed combustion region, the fuel injection timing until after the compression top dead center is delayed, and the oxygen ignition concentration reduction due to exhaust gas recirculation increases the fuel ignition delay period. An engine that forms a premixed mixture in which the fuel is sufficiently vaporized during the period to perform low-temperature premixed combustion, and shifts to diffusion-based combustion in a high load range where this low-temperature premixed combustion becomes difficult (Refer to Japanese Patent Laid-Open No. 7-4287), this engine has a smaller amount of NOx emission than an engine that performs the EGR described above.
[0009]
Therefore, the present invention is also intended for this engine and uses a combination of a λ fluctuation type catalyst and an HC fluctuation type catalyst. When the NOx adsorption amount of the HC fluctuation type catalyst reaches saturation, The HC fluctuation type catalyst is regenerated by changing the HC concentration in the exhaust gas flowing into the HC fluctuation type catalyst, and when the NOx adsorption amount of the λ fluctuation type catalyst reaches saturation, the low temperature premixed combustion region By regenerating the λ-variable catalyst by enriching the air-fuel ratio of the exhaust gas flowing into the λ-variable catalyst in a region other than the high-load region, this further promotes the purification of NOx in the entire operation region. Objective.
[0010]
[Means for Solving the Problems]
As shown in FIG. 25, the first invention includes a λ fluctuation type catalyst 71, an HC fluctuation type catalyst 72, means 73 for determining whether or not an EGR region (low / medium load region), and the determination result. Means 74 for controlling the exhaust amount (EGR amount) recirculated into the intake air in the EGR region, and when the NOx adsorption amount of the HC variable catalyst 72 reaches saturation, the HC variable catalyst 72 in the EGR region. 75 for varying the HC concentration in the exhaust gas flowing into the exhaust gas, and when the NOx adsorption amount of the λ-variable catalyst 71 reaches saturation, the λ-variable catalyst is not in the EGR region (high load region). Means 76 for enriching the air-fuel ratio of the exhaust gas flowing into 71 (including the theoretical air-fuel ratio).
[0011]
According to a second aspect, in the first aspect, the λ variation type catalyst and the HC variation type catalyst are arranged in this order from the upstream side of the exhaust passage (in series arrangement), and HC adsorption is performed on the upstream λ variation type catalyst. Give ability.
[0012]
According to a third invention, in the second invention, the exhaust temperature raising means is provided, and HC sufficient to regenerate the HC variable catalyst in the EGR region is adsorbed on the λ variable catalyst, and When the NOx adsorption amount of the HC variable catalyst reaches saturation when the temperature condition is not such that HC desorbs from the λ variable catalyst, the exhaust temperature increasing means reaches the temperature at which HC is desorbed from the λ variable catalyst. Increase the exhaust temperature.
[0013]
According to a fourth invention, in the second invention, the HC concentration variation means is provided, and HC sufficient to regenerate the HC variation catalyst in the EGR region is not adsorbed on the λ variation catalyst, and The HC concentration in the exhaust gas flowing through the HC variation type catalyst by the HC concentration variation means when the NOx adsorption amount of the HC variation type catalyst reaches saturation when the temperature condition is not desorbing HC from the λ variation type catalyst. Fluctuate.
[0014]
According to a fifth aspect of the invention, in the first aspect of the invention, the exhaust passage is branched to arrange the λ-variable catalyst in one branch passage and the HC-variable catalyst in the other branch passage (parallel arrangement). Means for switching the exhaust flow to the branch passage is provided. By this switching means, the exhaust gas is caused to flow to the HC variable catalyst in the EGR region, and when the region is not the EGR region (high load region), the λ variable catalyst is Flow exhaust.
[0015]
As shown in FIG. 26, the sixth invention includes a λ fluctuation type catalyst 71, an HC fluctuation type catalyst 72, a means 81 for determining whether or not the low temperature premixed combustion zone, and a low temperature premixing result from the determination result. In the combustion zone, the fuel injection timing until after the compression top dead center is delayed, and the oxygen concentration is reduced by exhaust gas recirculation, so that the fuel ignition delay period is lengthened, and the fuel is sufficiently vaporized during this ignition delay period. When the NOx adsorption amount of the HC fluctuation type catalyst 72 reaches saturation, the means 82 for forming the gas and performing the low temperature premix combustion burns into the HC fluctuation type catalyst 72 in the low temperature premix combustion region. When the NOx adsorption amount of the means 83 for varying the HC concentration in the exhaust gas and the λ variable catalyst 71 reaches saturation, the exhaust gas flowing into the λ variable catalyst 71 in a region that is not in the low temperature premixed combustion region. Rich air / fuel ratio And means 84 for) of including an air-fuel ratio.
[0016]
According to a seventh aspect, in the sixth aspect, the λ variation type catalyst and the HC variation type catalyst are arranged in this order from the upstream side of the exhaust passage (in series arrangement), and HC adsorption is performed on the upstream λ variation type catalyst. Give ability.
[0017]
In an eighth aspect of the invention, the exhaust temperature raising means is provided in the seventh aspect of the invention, and HC sufficient to regenerate the HC variable catalyst is adsorbed on the λ variable catalyst in the low temperature premixed combustion zone. When the NOx adsorption amount of the HC variable catalyst reaches saturation when the temperature condition is not such that HC desorbs from the λ variable catalyst, HC is desorbed from the λ variable catalyst by the exhaust temperature raising means. Increase the exhaust temperature to the desired temperature.
[0018]
In a ninth aspect, the HC concentration variation means according to the seventh aspect is provided, and HC sufficient to regenerate the HC variation type catalyst in the low temperature premixed combustion zone is adsorbed to the λ variation type catalyst. And when the NOx adsorption amount of the HC variable catalyst reaches saturation when the temperature condition is not desorbed from the λ variable catalyst, the exhaust gas flowing through the HC variable catalyst by the HC concentration changing means The HC concentration is varied.
[0019]
According to a tenth aspect, in the sixth aspect, the exhaust passage is branched, the λ-variable catalyst is arranged in one branch passage, and the HC-variable catalyst is arranged in the other branch passage (parallel arrangement). A means for switching the exhaust flow to the branch passage is provided, and by this switching means, exhaust gas flows to the HC variable catalyst in the low-temperature premixed combustion region, and when the region is not in the low-temperature premixed combustion region (high load region). Exhaust gas is allowed to flow through the λ variable catalyst.
[0020]
In an eleventh aspect of the invention, in the third or eighth aspect, when the exhaust temperature raising means includes post-injection, retarded fuel injection timing, intake throttle, and the λ-variable catalyst includes a heater, at least heating of the heater is performed. A means to do one.
[0021]
In a twelfth aspect, in the fourth or ninth aspect, the HC concentration changing means is means for performing at least one of post injection, delay of fuel injection timing, and early pilot injection.
[0022]
As shown in FIG. 27, the thirteenth invention includes a λ fluctuation type catalyst 71, a means 81 for determining whether or not the low temperature premixed combustion region, and a compression top dead center in the low temperature premixed combustion region based on the determination result. The fuel injection timing until later is delayed, the oxygen concentration is reduced by exhaust gas recirculation, the fuel ignition delay period is lengthened, and during this ignition delay period, a premixed gas in which the fuel is sufficiently vaporized is formed, and the low temperature pre- When the NOx adsorption amount of the means 82 for performing mixed combustion and the λ-variable catalyst 71 reaches saturation, it flows into the λ-variable catalyst 71 in a region (high load region) that is not the low-temperature premixed combustion region. Means 84 for enriching the air-fuel ratio of the exhaust (including the stoichiometric air-fuel ratio).
[0023]
In a fourteenth aspect of the invention, the supercharging pressure control means according to any one of the first to thirteenth aspects is provided, and means for enriching the air-fuel ratio of exhaust (including the stoichiometric air-fuel ratio) includes the supercharging pressure control. Means for reducing the supercharging pressure by means.
[0024]
According to a fifteenth aspect, in any one of the first to thirteenth aspects, a common rail fuel injection device, a common rail pressure control unit, and a supercharging pressure control unit are provided, and the exhaust air-fuel ratio is rich ( Means for increasing the common rail pressure by the common rail pressure control means and delaying the fuel injection timing to promote atomization of the spray. In this case, the fuel injection timing is retarded. The fuel injection amount is increased in order to compensate for the torque reduction due to the above, and the supercharging pressure is controlled by the supercharging pressure control means.
[0025]
【The invention's effect】
In contrast to the λ fluctuation type catalyst, which cannot be regenerated under lean air-fuel ratio conditions (normal diesel engine exhaust conditions), the HC fluctuation type catalyst changes the HC concentration at the catalyst inlet to change the HC fluctuation type catalyst. Can be played. According to the first aspect of the present invention, the HC variable catalyst is regenerated in the EGR range (low and medium load range), which is a lean air-fuel ratio condition, and the air-fuel ratio is made rich (including stoichiometric). When the region is outside the possible EGR region (high load region), the λ fluctuation type catalyst is regenerated. By differentiating the catalyst to be regenerated for each region (EGR region and other regions) where the NOx emission amount is greatly different, it is possible to regenerate the two catalysts together while preventing the deterioration of smoke. Since the enrichment is performed only in a region (high load region) that is not in the EGR region, it is possible to minimize deterioration in fuel consumption due to enrichment of the air-fuel ratio.
[0026]
According to the second and seventh inventions, at the time of low load in the EGR region and the low temperature premixed combustion region, HC sufficient to enable regeneration of the subsequent HC variable catalyst is adsorbed on the previous λ variable catalyst. Then, when the exhaust gas temperature rises due to acceleration in the EGR region or the low temperature premixed combustion region and the temperature condition is such that HC is desorbed, a sufficient amount of HC is desorbed from the preceding λ fluctuation type catalyst. Therefore, the subsequent HC fluctuation type catalyst can be regenerated without bothering to supply secondary HC. In addition, when the exhaust air-fuel ratio is enriched outside the EGR region and the low temperature premixed combustion region (high load region), not only the previous λ variation type catalyst but also the subsequent HC variation type catalyst can be regenerated. Yes (because the NOx adsorbed by the HC variable catalyst at the latter stage is also desorbed and reduced when the atmosphere is in the vicinity of the stoichiometric air-fuel ratio (three-way region) due to the rise in exhaust temperature accompanying regeneration of the λ variable catalyst.) .
[0027]
NOx adsorption of the HC variable catalyst when HC sufficient to regenerate the HC variable catalyst at the rear stage is adsorbed to the λ variable catalyst at the front stage when the load is low in the EGR region or the low temperature premixed combustion region. Even if the amount reaches saturation, if the low load operation is continued, desorption of HC from the λ-variable catalyst cannot be expected. According to the third, eighth, and eleventh inventions, Since the HC adsorbed on the λ fluctuation type catalyst can be desorbed by the exhaust temperature raising means, when the NOx adsorption amount of the HC fluctuation type catalyst reaches saturation, the low load operation is continued. Even if there is, the HC fluctuation type catalyst can be regenerated.
[0028]
Even if the NOx adsorption amount of the HC variable catalyst reaches saturation in the EGR region or the low temperature premixed combustion region, HC sufficient to regenerate the HC variable catalyst is not adsorbed to the preceding λ variable catalyst. Even if the exhaust temperature is raised to a temperature at which HC is desorbed from the λ fluctuation type catalyst by the exhaust temperature raising means, the HC concentration in the exhaust flowing through the HC fluctuation type catalyst cannot be sufficiently varied, and the HC fluctuation type Although the regeneration of the catalyst is incomplete, according to the fourth, ninth, and twelfth inventions, the HC that can regenerate the HC variable catalyst by the HC concentration changing means is secondary. Therefore, when the NOx adsorption amount of the HC variable catalyst reaches saturation in the EGR region or the low temperature premixed combustion region, HC sufficient to regenerate the HC variable catalyst is accumulated in the λ variable catalyst. HC fluctuation even if not The catalyst can be reproduced.
[0029]
Sulfur is contained in the fuel, and the λ fluctuation type catalyst is affected by poisoning due to the sulfur, but according to the fifth and tenth inventions, it is not an EGR region or a low temperature premixed combustion region. Since it is only necessary to flow the exhaust through the λ variable catalyst only in the region (high load region), it is not necessary to be affected by poisoning due to sulfur (the exhaust temperature is sufficiently high in the high load region, so the λ variable catalyst has sulfur As a result, the durability of the λ-variable catalyst is improved.
[0030]
The amount of NOx adsorbed and desorbed and reduced by the HC variable type catalyst is currently considerably smaller than that of the λ variable type catalyst. When the target is a normal diesel engine (without EGR) mainly based on diffusion combustion, the catalyst Since the NOx concentration at the inlet is higher than that at low temperature premixed combustion, the NOx adsorption amount of the HC fluctuation type catalyst immediately reaches saturation, and the regeneration of the catalyst that has reached the saturation causes the HC concentration at the catalyst inlet to be considerably increased. It is necessary to fluctuate with. For this reason, if the change in the HC concentration at the catalyst inlet is performed by the secondary HC supply, the fuel efficiency and drivability are deteriorated, but the sixth invention performs the low temperature premixed combustion. This is a combination with an engine. According to low temperature premixed combustion, the NOx concentration at the catalyst inlet is originally low, so the time to regenerate the HC variable catalyst is greatly delayed. Such a reduction can suppress deterioration of fuel consumption and drivability.
[0031]
According to the low temperature premixed combustion, the NOx in the exhaust can be reduced to about 1/50 of that of a conventional diesel engine (without EGR). It is an operating range where it is difficult to perform, that is, a high load range. In this high load region, it is possible to enrich the air-fuel ratio of the exhaust without degrading the smoke performance. According to the thirteenth aspect, it becomes possible to purify NOx discharged in the high load region by using the λ fluctuation type catalyst, thereby suppressing the NOx emission amount in the entire operation region.
[0032]
According to the fourteenth aspect of the invention, the charging efficiency is lowered due to the reduction of the supercharging pressure, thereby making it possible to enrich the air-fuel ratio of exhaust.
[0033]
According to the fifteenth aspect, the air-fuel ratio of the exhaust gas can be enriched while preventing the deterioration of smoke and without reducing the torque.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic configuration diagram of a diesel engine.
[0035]
In the combustion of a diesel engine, the amount of NOx produced greatly depends on the combustion temperature, and it is effective to lower the combustion temperature relatively for the reduction. In the low temperature premixed combustion system, the oxygen concentration is reduced by an exhaust gas recirculation system (EGR), thereby realizing low temperature combustion. For this reason, the exhaust passage 2 and the intake passage 3 are connected by an EGR passage 4, and a diaphragm type EGR valve 6 that operates according to the control negative pressure from the negative pressure control valve 5 is provided in the middle of the EGR passage 4. A part of the exhaust is recirculated into the intake air.
[0036]
The negative pressure control valve 5 is driven by a duty control signal from the control unit 41 so as to obtain an appropriate EGR rate according to the operating conditions of the engine. For example, the EGR rate is set to a maximum of 100 percent (the intake air flow rate and the EGR gas flow rate are the same amount) in a low rotation and low load range, and the EGR rate is decreased as the rotation speed and load increase. Since the exhaust gas temperature rises on the high load side, when a large amount of EGR gas is recirculated, the intake air temperature rises, which in turn causes the combustion temperature to rise relatively, reducing the effect of reducing NOx, and igniting the injected fuel. The delay period is shortened and premixed combustion cannot be realized. For this reason, the EGR rate is decreased as the load becomes higher.
[0037]
An EGR gas cooling device 7 is provided in the middle of the EGR passage 4. This is formed around the EGR passage 4 and has a water jacket 8 in which a part of the engine cooling water is circulated, and the circulation amount of this cooling water is a flow rate provided at the cooling water inlet 7a. It can be adjusted by the control valve 9. The degree of cooling of the EGR gas increases as the opening degree of the control valve 9 increases according to a command from the control unit 41.
[0038]
The intake passage near the intake port of the engine is provided with a swirl control valve (not shown). When the opening degree of the swirl control valve is controlled by the control unit 41 and is closed in the low engine speed and low load range (the opening degree is decreased), the flow rate of the intake air sucked into the combustion chamber is increased and the swirl strong against the combustion chamber Is generated. However, when the swirl becomes strong, the heat exchange rate of the working gas in the cylinder increases, and the working gas temperature relatively decreases.
[0039]
A hollow combustion chamber (not shown) formed in the piston is a large-diameter toroidal combustion chamber. In this, the piston cavity is formed in a cylindrical shape from the crown to the bottom of the piston without restricting the inlet, and a conical part is formed in the center of the bottom, and this conical part enters the piston cavity later in the compression stroke. In order not to give resistance to the swirl that flows while swirling, the mixing of air and fuel is further improved.
[0040]
Thus, the swirl generated by the swirl control valve is diffused from the inside of the piston cavity to the outside of the cavity as the piston descends during the combustion process, due to the cylindrical piston cavity that does not restrict the inlet. The swirl is maintained outside the cavity.
[0041]
The exhaust passage 2 is provided with a turbocharger downstream of the branch point of the EGR passage 4. This turbocharger is provided with a variable vane 53 driven by a step motor 54 at the scroll inlet of the exhaust turbine 52. The variable vane 53 is controlled by the control unit 41, and is controlled to a vane angle that increases the flow rate of the exhaust gas introduced into the exhaust turbine 52 on the low rotation side so that a predetermined supercharging pressure is obtained from the low engine rotation range. On the high rotation side, the vane angle (full open state) that allows exhaust to be introduced into the exhaust turbine 52 without resistance is controlled. Further, the variable vane 53 is controlled to a vane angle at which a desired supercharging pressure is obtained depending on the operating conditions.
[0042]
The engine is equipped with a common rail fuel injection device.
[0043]
This is mainly composed of a fuel tank (not shown), a supply pump 14, a common rail (accumulation chamber) 16, and a fuel injection nozzle 17 provided for each cylinder, and the high-pressure fuel generated in the high-pressure supply pump 14 is stored in the common rail 16. The start and end of the injection can be freely controlled by opening and closing the nozzle needle by the three-way valve 25 in the fuel injection nozzle 17. The fuel pressure in the common rail 16 is always controlled to an optimum value required by the engine by a pressure sensor (not shown) and a discharge amount control mechanism (not shown) of the supply pump 14.
[0044]
The control of the fuel injection amount, the injection timing, the fuel pressure, and the like is performed by a control unit 41 constituted by a microprocessor. For this reason, the control unit 41 receives signals from an accelerator opening sensor 33, a sensor 34 for detecting the engine speed and crank angle, a sensor (not shown) for cylinder discrimination, and a water temperature sensor 38. Based on this, the control unit 41 calculates the target fuel injection amount and the fuel injection timing according to the engine speed and the accelerator opening, and sets the ON time of the three-way valve 25 in the nozzle corresponding to the target fuel injection amount. In addition, the ON timing of the three-way valve 25 is controlled corresponding to the target injection timing. Further, the fuel pressure of the common rail 16 is feedback-controlled through the discharge amount control mechanism of the supply pump 14 so that the common rail pressure detected by a pressure sensor (not shown) matches the target pressure.
[0045]
The fuel injection timing is delayed from the normal injection timing in order to realize low temperature premixed combustion. For example, the fuel injection is set to start within a predetermined range after compression top dead center at the crank angle. As a result, the ignition delay period of the injected fuel is lengthened, during which the fuel vaporization is promoted, and it is possible to ignite in a state sufficiently mixed with air. As a result, low-temperature premixed combustion is performed under a low oxygen concentration due to exhaust gas recirculation, and NOx can be reduced without increasing particulates.
[0046]
On the other hand, a λ fluctuation type catalyst 55 and an HC fluctuation type catalyst 56 are provided in the exhaust passage 2 downstream of the exhaust turbine 52 from the upstream side.
[0047]
Here, the λ fluctuation type catalyst 55 adsorbs NOx in the exhaust in the lean air-fuel ratio region, and desorbs the NOx adsorbed on the catalyst when the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio. In addition, the λ fluctuation type catalyst is a catalyst that reduces and purifies the desorbed NOx by using HC and CO present in a stoichiometric air-fuel ratio atmosphere or a rich air-fuel ratio atmosphere as a reducing agent. It is known by the number etc. For example, the NOx adsorbent contains at least one selected from an alkali metal consisting of potassium, sodium, lithium and cesium, an alkaline earth consisting of barium and calcium, a rare earth consisting of lanthanum and yttrium, and platinum.
[0048]
As will be described later, the λ variation type catalyst 55 is regenerated in a region other than the low temperature premixed combustion region, but the λ variation type catalyst 55 also carries alumina, zeolite (ZSM5, β, USY) and the like. Therefore, it has HC adsorption capacity.
[0049]
On the other hand, the HC fluctuation type catalyst adsorbs NOx in the exhaust when the HC concentration in the exhaust gas is substantially constant in the lean air-fuel ratio region, and the HC concentration at the catalyst inlet changes in the same lean air-fuel ratio region ( The NOx catalyst that desorbs NOx adsorbed on the catalyst and reduces and purifies the desorbed NOx using HC and CO in the atmosphere as reducing agents. The details have been previously proposed by the same applicant as the present applicant (see Japanese Patent Application Nos. 10-295881 and 10-319689).
[0050]
Specifically, alkali metals consisting of potassium, sodium, lithium and cesium, alkaline earth metals consisting of barium, magnesium, calcium and strontium, rare earths consisting of lanthanum, cerium, praseodymium, neodymium and samarium, manganese and iron , A catalyst containing at least one selected from transition metals consisting of nickel and cobalt, zirconium and yttrium and at least one selected from platinum, palladium, rhodium and iridium. The NOx adsorption process is shown on the left side of FIG. NOx is NO_Three ^-It is adsorbed in the state of (nitrate ions), and in the desorption reduction process, as shown on the right side of FIG._Three ^-Is N₂It is thought to be.
[0051]
When the concentration of HC and CO at the catalyst inlet is increased stepwise, the NOx concentration at the catalyst outlet changes as shown in FIG. 4 with reference to the EOE level (the NOx concentration level when there is no catalyst). In the figure, NOx is adsorbed to the catalyst in the region A below the EOE level, NOx is desorbed from the catalyst in the region B exceeding the EOE level due to the step increase in the HC concentration, and from the EOE level after the step increase in the HC concentration. NOx is reduced and purified in the lower region C. As a result, A + B−C (≧ 0) is the amount of NOx purified by the total catalyst.
[0052]
In this case, the NOx reduction rate is compared between the case where the atmospheric oxygen concentration in the desorption reduction process is 3% (a condition close to rich) and the case where the atmospheric oxygen concentration is 10% (a lean condition where the air-fuel ratio is 18 or more). When the atmospheric oxygen concentration is 3%, 8% and 3% NOx are reduced in the interval between t1 and t2 when the atmospheric oxygen concentration is 3%, whereas the interval between t1 and t2 when the atmospheric oxygen concentration is 10%. 35% and 2% NOx are reduced. In other words, while there is no difference between the two in the steady t2 interval, the lean condition actually reduces NOx four times or more in the lean condition. In other words, in the HC variable catalyst, NOx can be desorbed and reduced by giving HC concentration fluctuations under lean conditions with an air-fuel ratio of 18 or more.
[0053]
However, at present, the amount of NOx that can be desorbed and reduced by the HC variable catalyst is much smaller than that of the λ variable catalyst. Therefore, in the present embodiment, low-temperature premixed combustion is performed using the low-medium load region as the low-temperature premixed combustion region, and the high-load region where the low-temperature premixed combustion becomes difficult is shifted to the combustion based on diffusion combustion. For an engine, a λ variable catalyst 55 having an HC adsorption function and an HC variable catalyst 56 are arranged in this order from the upstream side of the exhaust passage. At this time, the two types of NOx catalysts 55 and 56 are regenerated as follows.
[0054]
1) Low temperature premixed combustion zone:
(1) When HC sufficient to enable regeneration of the HC variable catalyst is changed to the HC desorption region from a state where the HC is adsorbed on the λ variable catalyst: Is the temperature condition at which is desorbed. If HC that can regenerate the HC variable catalyst is adsorbed to the λ variable catalyst under a temperature condition that does not desorb HC from the λ variable catalyst, the exhaust temperature will increase with acceleration in the low and medium load range. When the HC desorption region is reached, the HC concentration in the exhaust gas flowing through the HC variation type catalyst is sufficiently varied by the HC desorbing from the λ variation type NOx catalyst. Can play.
[0055]
(2) NOx adsorption of the HC variable catalyst when the HC variable catalyst is adsorbed to the λ variable catalyst and the temperature is not desorbed from the λ variable catalyst. When the amount reaches saturation, the exhaust temperature is raised to a temperature at which HC is desorbed from the λ-variable catalyst by the exhaust temperature raising means. When the λ fluctuation type catalyst rises to a temperature at which HC is desorbed, the HC concentration of the exhaust gas flowing through the HC fluctuation type catalyst fluctuates due to the HC desorbing from the λ fluctuation type NOx catalyst, thereby regenerating the HC fluctuation type catalyst. . Here, in order to raise the temperature of the exhaust, this heater heating in the case where the post injection, the delay of the fuel injection timing, the intake throttle, and the λ variable NOx catalyst are provided with a heater can be considered.
[0056]
(3) NOx of the HC variable type catalyst when the HC variable type catalyst is not adsorbed by the λ variable type catalyst and the temperature condition does not desorb HC from the λ variable type catalyst. When the adsorption amount reaches saturation, the HC concentration in the exhaust flowing through the HC variable catalyst is changed by the HC concentration changing means. The HC concentration of the exhaust gas flowing through the HC fluctuation type catalyst fluctuates due to secondary HC supply by the operation of the HC concentration fluctuation means, and the HC fluctuation type catalyst is regenerated. Here, in order to change (increase or increase / decrease) the HC concentration in the exhaust, post injection, delay of fuel injection timing, early pilot injection, and the like are conceivable.
[0057]
2) High load range (regions other than the low temperature premixed combustion range):
The λ fluctuation NOx catalyst is regenerated by the rich spike process.
[0058]
The contents of this control executed by the control unit 41 will be described according to the following flowchart.
[0059]
FIG. 6 is for performing the regeneration process of the two catalysts 55 and 56, and is executed at regular intervals.
[0060]
In step 1, operating conditions such as the engine speed Ne and the accelerator opening (or engine torque) are read. In step 2, the HC adsorption amount a1 of the λ-variable catalyst is calculated. This calculation will be described with reference to the flowchart of FIG.
[0061]
In FIG. 7, the engine speed Ne and the catalyst temperature Tcat1 (detected by the temperature sensor 57) of the λ fluctuation type catalyst are read in step 21, and a map containing FIG. (HC adsorption amount per predetermined time (calculation cycle)) aa1 is calculated, and in step 23, this is the previous HC adsorption amount a1._-1Is added as the current HC adsorption amount a1. In FIG. 8, the region where the catalyst temperature Tcat1 is lower than the predetermined value T1 is the HC adsorption region, and when the catalyst temperature Tcat1 becomes equal to or higher than the predetermined value T1, HC is desorbed. T1 which is a temperature for defining this boundary is a temperature of about 200 to 300 ° C., and the HC desorption temperature is lower than the NOx desorption temperature (400 to 500 ° C. or more).
[0062]
When the HC adsorption amount a1 is calculated in this way, the process returns to FIG. 6, and in steps 3 and 4, the NOx adsorption amounts b1 and b2 of the two catalysts are calculated. The calculation of these NOx adsorption amounts b1 and b2 will be described with reference to FIGS.
[0063]
In FIG. 9, the engine speed Ne and the catalyst temperature Tcat1 of the λ variable catalyst are read in step 31, and the maps containing the contents of FIG. 11 are retrieved in steps 32 and 33, thereby the NOx adsorption of the λ variable catalyst. Speed (NOx adsorption amount per predetermined time) bb1, and the previous NOx adsorption amount b1_-1From FIG. 12, the adsorption coefficient k1 is calculated by searching a table having the contents shown in FIG.
[0064]
[Expression 1]
b1 = b1_-1+ Bb1 × k1
The NOx adsorption amount b1 of the λ fluctuation type catalyst is updated by the following equation.
[0065]
FIG. 10 is similar to FIG. That is, in step 41, the engine speed Ne and the catalyst temperature Tcat2 (detected by the temperature sensor 58) of the HC variable catalyst are read, and from these, the map having the same contents as in FIG. NOx adsorption speed (NOx adsorption amount per predetermined time) bb2 of the type catalyst, and b2 which is the previous NOx adsorption amount_-1From FIG. 12, a suction coefficient k2 is calculated by searching a table having the contents shown in FIG.
[0066]
[Expression 2]
b2 = b2_-1+ Bb2 × k2
The NOx adsorption amount b2 of the HC variable catalyst is updated by the following equation.
[0067]
Under the condition that the NOx in the exhaust gas is hardly absorbed by the catalysts 55 and 56, the NOx in the exhaust gas is well adsorbed by the catalyst. On the other hand, when the NOx adsorption amount approaches a saturated state, It will not be adsorbed. This is represented by the adsorption coefficients k1 and k2. Therefore, the adsorption coefficients k1 and k2 are the conditions under which NOx is hardly absorbed as shown in FIG. 12 (that is, b1_-1≒ 0, b2_-1≒ 0), which is 1.0, and becomes smaller as the NOx adsorption amount increases. In addition, since the λ variation type catalyst is better adsorbed, k1> k2.
[0068]
When the calculation of the NOx adsorption amounts b1 and b2 is completed in this manner, the process returns to FIG. 6 and it is checked in step 5 whether or not the operating point determined from the engine speed Ne and the engine torque is in the low temperature premixed combustion region. The operating range in which low-temperature premixed combustion can be performed is determined in advance by engine specifications such as the compression ratio. Here, as shown in FIG. 13, a description will be given of a case where low temperature premixed combustion can be performed in a low and medium load region and low temperature premixed combustion cannot be performed in a high load region. This is because low-temperature premixed combustion can be performed by a large amount of EGR in the low and medium load range, but in the high load range, combustion cannot be controlled by EGR, and the low-temperature premixed combustion is changed to the combustion mainly from diffusion combustion. This is because it moves.
[0069]
If the operating point is not in the low temperature premixed combustion region (MK region in the figure), the process proceeds to step 6 where the NOx adsorption amount b1 of the λ variable catalyst is compared with the predetermined value b01. This is a part for determining whether or not it is the regeneration time of the λ variable catalyst. If b1 <b01, it is determined that the NOx adsorption amount of the λ variable catalyst has not yet reached saturation (not the regeneration time). The current process is terminated as it is.
[0070]
If b1 ≧ b01 in the non-low temperature premixed combustion zone, it is determined that the regeneration time has come, and the routine proceeds from step 6 to step 7 where rich spike processing is performed to regenerate the λ-variable catalyst. In the rich spike processing, HC and CO are supplied to the λ variable catalyst by enriching the air / fuel ratio (including the theoretical air / fuel ratio), and NOx is supplied from the λ variable catalyst in this rich atmosphere (reducing atmosphere). While desorbing, the desorbed NOx is purified using HC and CO in the atmosphere as reducing agents.
[0071]
The rich spike process will be specifically described with reference to the flow of FIG. 14. In step 51, the time trs after the rich spike process is entered is compared with a predetermined value trs0. The predetermined value trs0 determines the end time of the rich spike processing. By proceeding to step 52 while trs <trs0, the fuel injection timing is retarded by a predetermined amount while the atomization of the spray is promoted by increasing the common rail pressure by a predetermined value to prevent the deterioration of smoke in the high load range. Enhance vaporization of atomized spray. In this case, since the torque generated by the engine decreases with the delay of the fuel injection timing, the fuel injection amount is increased by a predetermined amount to compensate for the torque decrease. Further, the intake vane efficiency is lowered by opening the variable vane 53 by a predetermined amount to lower the supercharging pressure, thereby creating a rich air-fuel ratio state.
[0072]
In this case, although not shown, it is possible to further purify the desorbed NOx by installing a three-way catalyst downstream of the λ fluctuation type catalyst.
[0073]
If the rich spike process continues for a while (trs ≧ trs0), all NOx adsorbed on the λ-variable catalyst is desorbed and reduced (that is, regeneration is complete), so the process proceeds from step 51 to step 53, where After the NOx adsorption amount b1 is returned to 0, in step 54, the common rail pressure, fuel injection timing, fuel injection amount, and variable vane angle are returned to their original values.
[0074]
Further, the temperature of the λ variable catalyst rises with the regeneration of the λ variable catalyst, and all the HC adsorbed on the λ variable catalyst is oxidized by this temperature increase. Return to zero.
[0075]
Further, the NOx adsorbed on the downstream HC variable catalyst is also reduced and purified (regenerated) when the atmosphere is in the vicinity of the stoichiometric air-fuel ratio (three-way region) due to the rise in exhaust temperature accompanying the regeneration of the λ variable catalyst. Therefore, in step 56, the NOx adsorption amount b2 is returned to zero.
[0076]
Returning to FIG. 6, when it is the low temperature premixed combustion region, the process proceeds from step 5 to step 8, where the HC desorption region (HC adsorbed on the λ variation type catalyst is desorbed from the catalyst temperature Tcat1 of the λ variation type catalyst). Check if the temperature condition is coming). The HC desorption region is a region in which the catalyst temperature Tcat1 is equal to or higher than a predetermined value T1 in FIG. When in the HC desorption region, the process proceeds to step 9 and subsequent steps.
[0077]
In steps 9 and 10, the natural regeneration flag (initially set to “0”) is checked, and the HC adsorption amount a1 of the λ fluctuation type catalyst is compared with a predetermined value a0. Here, the predetermined value a0 is set to an amount of HC that causes a change in the HC concentration necessary for regeneration of the HC variable catalyst. When a1 ≧ a0 at the timing of entering the HC desorption region (natural regeneration flag = 0), the HC variable catalyst can be regenerated using HC desorbed from the λ variable catalyst, so step 11 Then, the natural reproduction flag is set (natural reproduction flag = 1). If the natural regeneration flag is set and still in the HC desorption region, the process proceeds from step 9 to step 12 from the next time, and the time td in the HC desorption region is compared with a predetermined value td0. The predetermined value td0 determines the reproduction end time. Therefore, the process is terminated as long as td <td0, and the regeneration of the HC variable catalyst ends when td ≧ td0 is reached. Therefore, the process proceeds to steps 13 and 14, and the NOx adsorption amount b2 of the HC variable catalyst is reduced to 0. In addition, since the HC adsorption amount of the λ-variable catalyst disappears due to HC desorption, the HC adsorption amount a1 is returned to zero.
[0078]
On the other hand, when it is not in the HC desorption region, the process proceeds from step 8 to step 15 to compare the NOx adsorption amount b2 of the HC variable catalyst with a predetermined value b02. This is a part for determining whether or not it is the regeneration timing of the HC variable catalyst. If b2 <b02, it is determined that the NOx adsorption amount of the HC variable catalyst has not yet reached saturation (not the regeneration timing), The current process is terminated as it is.
[0079]
On the other hand, when b2 ≧ b02, it is determined that the regeneration time has come, and the routine proceeds from step 15 to step 16 where the HC adsorption amount a1 of the λ-variable catalyst is compared with the predetermined value a0. When a1 ≧ a0, it is possible to regenerate the HC variable catalyst as long as HC is desorbed from the λ variable catalyst. Therefore, the process proceeds to step 17 to perform a process for raising the temperature of the exhaust.
[0080]
If there is a sufficient amount of desorbed HC in the HC desorption region than the λ-variable catalyst, supply of this desorbed HC can cause fluctuations in the HC concentration in the exhaust gas flowing through the HC variable-type catalyst. When an operation that causes frequent load fluctuations in the low-temperature premixed combustion region is performed (the catalyst temperature Tcat1 is equal to or higher than T1), the flow from Steps 9 and 10 to Steps 11 to 14 is performed. The HC fluctuation type catalyst is regenerated without supplying basic HC. However, when low load continuous operation continues, the catalyst temperature Tcat1 does not become T1 or higher, and HC desorption from the λ-variable catalyst does not occur, so the NOx adsorption amount of the HC-variable catalyst is saturated. May be reached. Therefore, in this case, a sufficient amount of HC accumulated in the λ fluctuation type catalyst is forcibly desorbed by the exhaust temperature raising means (exhaust temperature raising means).
[0081]
This temperature rising process will be described with reference to the flow of FIG. 15. The time toz after the temperature rising process is started in step 61 is compared with a predetermined value toz0. The predetermined value toz0 determines the reproduction end time. Therefore, while toz <toz0, the routine proceeds to step 62 where (1) post-injection, (2) delay of fuel injection timing, (3) intake throttle, and (4) λ variable NOx catalyst has a heater. By performing at least one of the heater heating, the temperature is raised to the above-described T1, which is a temperature at which the λ variable catalyst desorbs HC.
[0082]
When toz ≧ toz0, all of the NOx adsorbed on the HC variable catalyst is desorbed and purified (regeneration is completed), so the process proceeds from step 61 to steps 63, 64 and 65, where the NOx adsorption amount b2 of the HC variable catalyst is After returning the HC adsorption amount a1 of the λ-variable catalyst to 0, the post-injection, fuel injection timing retardation, intake throttle, and heater heating processes are stopped.
[0083]
Returning to FIG. 6, when a1 <a0 in step 16, the HC fluctuation of the exhaust gas flowing through the HC fluctuation type catalyst becomes insufficient with only the HC adsorption amount of the λ fluctuation type catalyst, and the HC fluctuation type catalyst is regenerated. Therefore, the process of forcibly changing the HC concentration at the inlet of the HC fluctuation type catalyst is performed.
[0084]
This HC concentration fluctuation process will be described with reference to the flow of FIG. 16. In step 71, the time tks after the start of the HC concentration fluctuation process is compared with a predetermined value tks0. The predetermined value tks0 determines the playback end time. Therefore, while tks <tks0, the routine proceeds to step 72, where at least one of (1) post-injection, (2) delay of fuel injection timing, (3) early pilot injection, etc. is performed to achieve the HC variable catalyst. Increase the supply of HC and CO. Here, the post-injection (1) is to discharge the fuel to the engine-out unburned by performing a small amount of injection in an exhaust stroke or the like. The early pilot injection (3) is different from the pilot injection used for reducing the vibration caused by the combustion excitation force, and uses the vicinity of the intake bottom dead center as the injection timing (see Japanese Patent Laid-Open No. 8-218920). ) According to experiments, it has been confirmed that engine-out HC increases.
[0085]
As a result of this process, HC is adsorbed to the λ fluctuation type catalyst. Therefore, in step 73, the HC adsorption speed (HC adsorption amount per predetermined time) aa2 is set to the previous HC adsorption amount a1._-1Is added as the current HC adsorption amount a1. The HC adsorption speed aa2 can also be given by the same map value as in FIG.
[0086]
When tks ≧ tks0, all NOx adsorbed on the HC variable catalyst is desorbed and purified (regeneration is completed), so the process proceeds from Step 71 to Steps 74 and 75, and the NOx adsorption amount b2 of the HC variable catalyst is set to 0. After returning, processing such as post injection, delay of fuel injection timing, and early pilot injection is stopped.
[0087]
Here, the function and effect of the first embodiment will be described.
[0088]
The amount of NOx adsorbed and desorbed and reduced by the HC variable type catalyst is currently considerably smaller than that of the λ variable type catalyst. When the target is a normal diesel engine (without EGR) mainly based on diffusion combustion, the catalyst Since the NOx concentration at the inlet is higher than that at low temperature premixed combustion, the NOx adsorption amount of the HC fluctuation type catalyst immediately reaches saturation, and the regeneration of the catalyst that has reached the saturation causes the HC concentration at the catalyst inlet to be considerably increased. It is necessary to fluctuate with. For this reason, if the fluctuation of the HC concentration at the catalyst inlet is performed by the secondary HC supply, the fuel efficiency and the drivability are deteriorated, but this embodiment performs the low temperature premixed combustion. The target engine is low temperature premixed combustion, because the NOx concentration at the catalyst inlet is originally low, the time to regenerate the HC variable catalyst is greatly delayed, and the chances of regeneration of this HC variable catalyst are greatly reduced. Thus, deterioration of fuel consumption and drivability can be suppressed.
[0089]
Further, according to the present embodiment, when the HC sufficient to regenerate the subsequent HC variable catalyst is adsorbed to the previous λ variable catalyst at a low load in the low temperature premixed combustion region (a1 ≧ a0) When the exhaust gas temperature rises due to acceleration in the low temperature premixed combustion zone and the temperature condition is such that HC is desorbed (Tcat1 ≧ T1), a sufficient amount of HC is desorbed from the preceding λ fluctuation type catalyst. Therefore, the latter HC variable catalyst can be regenerated. That is, by using the HC accumulated in the λ variable catalyst, the HC variable catalyst can be regenerated without supplying secondary HC.
[0090]
Further, when the exhaust air-fuel ratio is enriched in a region outside the low temperature premixed combustion region (high load region), not only the previous λ variable catalyst but also the subsequent HC variable catalyst can be regenerated (λ Due to the rise in the exhaust gas temperature accompanying the regeneration of the variable catalyst, NOx adsorbed on the subsequent HC variable catalyst is also desorbed and reduced when the atmosphere is in the vicinity of the stoichiometric air-fuel ratio (three-way region).
[0091]
Further, when HC sufficient to regenerate the HC variable catalyst at the subsequent stage is adsorbed to the λ variable catalyst at the previous stage (a1 ≧ a0) at the time of low load in the low temperature premixed combustion region, the HC variable type Even if the NOx adsorption amount of the catalyst reaches saturation (b2 ≧ b02), if the low-load operation is continued, desorption of HC from the λ-variable catalyst cannot be expected. According to the above, the λ fluctuation type is achieved by the operation of the exhaust gas temperature raising means (that is, performing at least one of the post-injection, the fuel injection timing delay, the intake throttle, and the heater heating when the λ fluctuation NOx catalyst includes a heater). Since the HC adsorbed on the catalyst can be desorbed, even if the low load operation may be continued even when the NOx adsorption amount of the HC variable catalyst reaches saturation, the HC variable catalyst Can play That.
[0092]
Further, even if the NOx adsorption amount of the HC variable catalyst reaches saturation in the low temperature premixed combustion region (b2 ≧ b02), HC sufficient to regenerate the HC variable catalyst is adsorbed to the preceding λ variable catalyst. If not (a1 <a0), even if the exhaust temperature is raised to a temperature at which HC is desorbed from the λ fluctuation type catalyst by the exhaust temperature raising means, the HC concentration in the exhaust gas flowing through the HC fluctuation type catalyst is sufficiently fluctuated. However, according to the present embodiment, the operation of the HC concentration changing means (that is, post injection, retarded fuel injection timing, early pilot, etc.) is not possible. The amount of NOx adsorbed by the HC variable type catalyst in the EGR region or the low temperature premixed combustion region is supplied secondarily by HC that enables the regeneration of the HC variable type catalyst by performing at least one of injection and the like. But When saturation is reached, the HC variable catalyst can be regenerated even if HC sufficient to regenerate the HC variable catalyst does not accumulate in the λ variable catalyst.
[0093]
The control system of FIG. 17 is a second embodiment and corresponds to FIG. 1 of the first embodiment.
[0094]
In this embodiment, the exhaust passage 2 is branched, a λ variable catalyst 63 is disposed in one branch passage 61, and an HC variable catalyst 64 is disposed in the other branch passage 62, and the exhaust flow to the branch passages 61, 62 is performed. Are provided upstream of the catalysts 63 and 64, and as shown in FIG. 18, in the region other than the low-temperature premixed combustion region (high load region), the control valve 65 is provided. When the control valve 66 is fully opened and the control valve 66 is fully closed, the entire amount of the exhaust gas is caused to flow through the λ fluctuation type catalyst 63 to enter the low temperature premixed combustion region (low and medium load region), and then the control valve 65 is fully closed and the control valve 66 is closed. Is set to fully open so that the entire amount of exhaust gas flows through the HC variable catalyst 64.
[0095]
In this embodiment, since the two catalysts 63 and 64 are arranged in parallel, even if HC is adsorbed to the λ fluctuation type catalyst 63, the adsorbed HC cannot be used for regeneration of the HC fluctuation type catalyst 64. It is not necessary for the mold catalyst 63 to have HC adsorption capability. For this reason, the regeneration process of each catalyst when the NOx adsorbed to each catalyst 63, 64 reaches saturation is simpler than that of the first embodiment, and this is shown in FIG. 19, FIG. 20, and FIG. 19, 20, and 21 replace FIG. 6, FIG. 14, and FIG. 16 of the first embodiment. 19, the same parts as those in FIG. 6, the same parts as those in FIG. 14 in FIG. 20, and the same parts in FIG.
[0096]
The fuel contains sulfur, and the sulfur variation catalyst is affected by poisoning. However, according to the second embodiment, a region that is not a low temperature premixed combustion region (high load region). Because it is only necessary to flow the exhaust through the λ fluctuation type catalyst, it is not necessary to be affected by poisoning due to sulfur (the exhaust temperature is sufficiently high in the high load region, so it is difficult for sulfur to accumulate on the λ fluctuation type catalyst), This improves the durability of the λ variable catalyst.
[0097]
In the embodiment, the combination of the λ variation type catalyst and the HC variation type catalyst has been described. However, the λ variation type NOx catalyst alone and an engine capable of performing low temperature premixed combustion may be combined (see FIG. 22). . Flow charts for this (third embodiment) are shown in FIGS. 23 and 24 replace FIG. 6 and FIG. 14 of the first embodiment. 23, the same parts as those in FIG. 6 and the same parts as those in FIG. 14 in FIG. 24 are denoted by the same step numbers, and the description thereof is omitted.
[0098]
According to the low temperature premixed combustion, the NOx in the exhaust can be reduced to about 1/50 of that of a conventional diesel engine (without EGR). It is an operating range where it is difficult to perform, that is, a high load range. In this high load region, it is possible to enrich the air-fuel ratio of the exhaust without degrading the smoke performance. According to the third embodiment, it is possible to purify NOx discharged in the high load region using the λ fluctuation type catalyst, and thereby it is possible to suppress the NOx emission amount in the entire operation region.
[0099]
In the first embodiment, the case where the λ variation type catalyst and the HC variation type catalyst are arranged in this order from the upstream side of the exhaust passage has been described. In fact, the same result is obtained even if the HC variation type catalyst and the λ variation type catalyst are arranged in this order from the upstream side of the exhaust passage. However, since only the catalyst containing iron and the catalyst containing lanthanum have the characteristic that the amount of NOx adsorption decreases when the HC concentration is high (experimental results), only these catalysts need to be arranged downstream.
[0100]
In the embodiment, the engine capable of performing low temperature premixed combustion has been described as an object, but the present invention is not limited to this. For example, when the low and middle load range is set in advance as the EGR range and the operating condition is in this EGR range, the exhaust amount recirculated during intake (EGR amount) is controlled, and when the EGR range is deviated from this, It is also possible to target an engine that stops EGR.
[0101]
In the embodiment, the case where the HC concentration is increased as the HC concentration fluctuation processing has been described. However, the increase in the HC concentration and the subsequent decrease may be repeated in a short cycle.
[0102]
In the second embodiment, two control valves are provided for switching the exhaust flow, but the present invention is not limited to this. For example, one flow control valve may be provided at the branch portion of the branch passage or at the assembly portion of the two branch passages.
[Brief description of the drawings]
FIG. 1 is a control system diagram of a first embodiment.
FIG. 2 is a characteristic diagram of NOx emission amount of an engine that performs low-temperature premixed combustion.
FIG. 3 is a model diagram showing a NOx adsorption process and a NOx desorption reduction process of an HC variable catalyst.
FIG. 4 is a waveform diagram showing changes in the NOx concentration at the catalyst outlet of the HC variable catalyst when the HC concentration at the catalyst inlet is increased stepwise.
FIG. 5 is a table showing NOx reduction rates due to HC concentration fluctuations under two oxygen concentration conditions.
FIG. 6 is a flowchart for explaining catalyst regeneration processing;
FIG. 7 is a flowchart for explaining calculation of an HC adsorption amount.
FIG. 8 is a map characteristic diagram of the HC adsorption rate.
FIG. 9 is a flowchart for explaining the calculation of the NOx adsorption amount of the λ variable catalyst.
FIG. 10 is a flowchart for explaining the calculation of the NOx adsorption amount of the HC variable catalyst.
FIG. 11 is a map characteristic diagram of NOx adsorption speed.
FIG. 12 is a map characteristic diagram of an adsorption coefficient.
FIG. 13 is an operation region diagram.
FIG. 14 is a flowchart for explaining rich spike processing;
FIG. 15 is a flowchart for explaining a temperature raising process;
FIG. 16 is a flowchart for explaining HC concentration fluctuation processing;
FIG. 17 is a control system diagram of the second embodiment.
FIG. 18 is a flowchart for explaining exhaust flow switching processing according to the second embodiment;
FIG. 19 is a flowchart for explaining playback processing according to the second embodiment;
FIG. 20 is a flowchart for explaining rich spike processing according to the second embodiment;
FIG. 21 is a flowchart for explaining HC concentration fluctuation processing according to the second embodiment;
FIG. 22 is a control system diagram of the third embodiment.
FIG. 23 is a flowchart for explaining playback processing according to the third embodiment;
FIG. 24 is a flowchart for explaining rich spike processing according to the third embodiment;
FIG. 25 is a diagram corresponding to claims of the first invention.
FIG. 26 is a diagram corresponding to claims of the sixth invention.
FIG. 27 is a view corresponding to claims of the thirteenth invention.
[Explanation of symbols]
6 EGR valve
33 Accelerator position sensor
34 Crank angle sensor
41 Control unit
52 Exhaust turbine
53 variable vanes
55 λ variable catalyst
56 HC variable catalyst
57, 58 Temperature sensor

Claims (15)

NOx in the exhaust is adsorbed in the lean air-fuel ratio region, NOx adsorbed on the catalyst at the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or rich air-fuel ratio, and the desorbed NOx is removed from the stoichiometric air-fuel ratio or rich air-fuel ratio. A λ variable catalyst that is a NOx catalyst that reduces and purifies HC and CO present in an air-fuel ratio atmosphere as a reducing agent ;
When the HC concentration in the exhaust gas is almost constant in the lean air-fuel ratio region, NOx in the exhaust gas is adsorbed. When the HC concentration at the catalyst inlet fluctuates in the same lean air-fuel ratio region, the NOx adsorbed on the catalyst is removed. An HC variable catalyst that is a NOx catalyst that reduces and purifies the desorbed NOx using HC and CO in the atmosphere as a reducing agent ,
Means for determining whether it is in the EGR range;
Means for controlling the amount of exhaust gas recirculated into the intake air in the EGR region from the determination result;
Means for varying the HC concentration in the exhaust gas flowing into the HC variable catalyst in the EGR region when the NOx adsorption amount of the HC variable catalyst reaches saturation;
A diesel engine comprising: means for enriching the air-fuel ratio of the exhaust gas flowing into the λ-variable catalyst when the NOx adsorption amount of the λ-variable catalyst reaches saturation. Exhaust purification equipment. 2. The λ variation type catalyst and the HC variation type catalyst are arranged in this order from the upstream side of the exhaust passage, and the λ variation type catalyst on the upstream side is provided with HC adsorption capability. Diesel engine exhaust purification system. A temperature at which HC is adsorbed to the λ-variable catalyst and HC is desorbed from the λ-variable catalyst; The exhaust gas temperature is increased to a temperature at which HC is desorbed from the λ variable catalyst by the exhaust temperature increasing means when the NOx adsorption amount of the HC variable catalyst reaches saturation when the conditions are not satisfied. Item 3. An exhaust emission control device for a diesel engine according to Item 2. HC concentration variation means is provided, and HC sufficient to regenerate the HC variation type catalyst in the EGR region is not adsorbed on the λ variation type catalyst, and HC is desorbed from the λ variation type catalyst. 3. The HC concentration in exhaust flowing through the HC variable catalyst is varied by the HC concentration variation means when the NOx adsorption amount of the HC variable catalyst reaches saturation when the temperature condition is not satisfied. 2. An exhaust emission control device for a diesel engine according to 1. The exhaust passage is branched, the λ variation type catalyst is disposed in one branch passage, the HC variation type catalyst is disposed in the other branch passage, and the exhaust flow to the two branch passages can be switched. 2. The exhaust gas purification apparatus for a diesel engine according to claim 1, wherein exhaust gas flows through the HC variable catalyst in the EGR region by switching means, and exhaust gas flows through the λ variable catalyst in a region other than the EGR region. . NOx in the exhaust is adsorbed in the lean air-fuel ratio region, NOx adsorbed on the catalyst at the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or rich air-fuel ratio, and the desorbed NOx is removed from the stoichiometric air-fuel ratio or rich air-fuel ratio. A λ variable catalyst that is a NOx catalyst that reduces and purifies HC and CO present in an air-fuel ratio atmosphere as a reducing agent ;
When the HC concentration in the exhaust gas is almost constant in the lean air-fuel ratio region, NOx in the exhaust gas is adsorbed. When the HC concentration at the catalyst inlet fluctuates in the same lean air-fuel ratio region, the NOx adsorbed on the catalyst is removed. An HC variable catalyst that is a NOx catalyst that reduces and purifies the desorbed NOx using HC and CO in the atmosphere as a reducing agent ,
Means for determining whether it is a low temperature premixed combustion zone;
From this determination result, the fuel injection timing until after the compression top dead center is delayed in the low temperature premixed combustion region, and the oxygen concentration is reduced by exhaust gas recirculation, so that the fuel ignition delay period is lengthened. Means for forming a sufficiently vaporized premixed gas to perform low temperature premixed combustion,
Means for varying the HC concentration in the exhaust gas flowing into the HC variable catalyst in the low temperature premixed combustion zone when the NOx adsorption amount of the HC variable catalyst reaches saturation;
Means for enriching the air-fuel ratio of the exhaust gas flowing into the λ-variable catalyst when the NOx adsorption amount of the λ-variable catalyst reaches saturation. Diesel engine exhaust purification system. 7. The λ fluctuation type catalyst and the HC fluctuation type catalyst are arranged in this order from the upstream side of the exhaust passage, and the λ fluctuation type catalyst on the upstream side is provided with HC adsorption capability. Diesel engine exhaust purification system. Exhaust temperature raising means is provided, HC sufficient to regenerate the HC variable catalyst in the low temperature premixed combustion zone is adsorbed to the λ variable catalyst, and HC is desorbed from the λ variable catalyst. When the NOx adsorption amount of the HC variable catalyst reaches saturation when the temperature condition is not separated, the exhaust temperature is increased to a temperature at which HC is desorbed from the λ variable catalyst by the exhaust temperature increasing means. An exhaust emission control device for a diesel engine according to claim 7. HC concentration variation means is provided, and HC sufficient to enable regeneration of the HC variation type catalyst in the low temperature premixed combustion region is not adsorbed by the λ variation type catalyst, and HC varies from the λ variation type catalyst. When the NOx adsorption amount of the HC variable catalyst reaches saturation when it is not a desorbing temperature condition, the HC concentration in the exhaust gas flowing through the HC variable catalyst is changed by the HC concentration changing means. The exhaust emission control device for a diesel engine according to claim 7. The exhaust passage is branched, the λ variation type catalyst is disposed in one branch passage, the HC variation type catalyst is disposed in the other branch passage, and the exhaust flow to the two branch passages can be switched. The exhaust gas is caused to flow to the HC variable catalyst in the low temperature premixed combustion region by switching means, and the exhaust gas is flowed to the λ variable catalyst when the region is not the low temperature premixed combustion region. Diesel engine exhaust purification system. The exhaust temperature raising means is means for performing at least one of post-injection, retardation of fuel injection timing, intake throttle, and heater heating when the λ-variable catalyst includes a heater. The exhaust emission control device for a diesel engine according to 3 or 8. The diesel engine exhaust gas purification apparatus according to claim 4 or 9, wherein the HC concentration changing means is means for performing at least one of post injection, delay of fuel injection timing, and early pilot injection. NOx in the exhaust is adsorbed in the lean air-fuel ratio region, NOx adsorbed on the catalyst at the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or rich air-fuel ratio, and the desorbed NOx is removed from the stoichiometric air-fuel ratio or rich air-fuel ratio. A λ variable catalyst that is a NOx catalyst that reduces and purifies HC and CO present in an air-fuel ratio atmosphere as a reducing agent ;
Means for determining whether it is a low temperature premixed combustion zone;
From this determination result, the fuel injection timing until after the compression top dead center is delayed in the low temperature premixed combustion region, and the oxygen concentration is reduced by exhaust gas recirculation, so that the fuel ignition delay period is lengthened. Means for forming a sufficiently vaporized premixed gas to perform low temperature premixed combustion,
Means for enriching the air-fuel ratio of the exhaust gas flowing into the λ-variable catalyst when the NOx adsorption amount of the λ-variable catalyst reaches saturation. Diesel engine exhaust purification system. The means for enriching the air-fuel ratio of the exhaust gas provided with a supercharging pressure control means is a means for reducing the supercharging pressure by the supercharging pressure control means. 2. An exhaust emission control device for a diesel engine according to 1. A means for enriching the air-fuel ratio of the exhaust gas, comprising a common rail fuel injection device, a common rail pressure control means, and a supercharging pressure control means, increases the common rail pressure by the common rail pressure control means, and By delaying the timing, atomization of the spray is promoted. In this case, the fuel injection amount is increased to compensate for the torque decrease due to the delay of the fuel injection timing, and the boost pressure is reduced by the boost pressure control means. The diesel engine exhaust gas purification device according to any one of claims 1 to 13, wherein the exhaust gas purification device is a means for causing the exhaust gas to flow.

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