JP2010168927A - Exhaust emission control method and exhaust emission control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control method and an exhaust emission control system which enable the catalyst of an exhaust emission control device installed in an exhaust passage to quickly reach an activation temperature zone during the warm-up of an engine after the starting, can form a reduction atmosphere, as necessary, on the catalyst of the exhaust emission control device while suppressing the deterioration of fuel consumption after the warm-up of the engine, and can easily achieve a high EGR rate in EGR control. <P>SOLUTION: It is configured to selectively supply a high oxygen-concentration gas A1 or a low oxygen-concentration gas A2 to the gas supply line of a combustor 13 for raising the temperature of the exhaust gas G which is disposed in the exhaust passage 11 of an internal combustion engine 10. While the exhaust gas G is raised in temperature, the high oxygen-concentration gas A2 is supplied to the combustor 13. While the temperature rise of the exhaust gas G is not required, the low oxygen-concentration gas A2 is supplied to the exhaust passage 11. Further, during the EGR, the low oxygen-concentration gas A2 is added to an EGR gas Ge. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a combustor used for raising the exhaust gas temperature until the catalyst of the exhaust gas purification device provided in the exhaust passage reaches the activation temperature region after starting the internal combustion engine. The present invention relates to an exhaust gas purification method and an exhaust gas purification system for supplying a high oxygen concentration gas having a concentration several times higher than that to increase the combustion speed in a combustor.

  In an internal combustion engine mounted on an automobile or the like, in order to purify the exhaust gas of the internal combustion engine, an exhaust gas purification device (post-treatment device) is provided in the exhaust passage of the internal combustion engine to purify the exhaust gas in the exhaust passage. This exhaust gas purifying device includes an oxidation catalyst (DOC) that oxidizes unburned hydrocarbons (HC) and carbon monoxide (CO), a NOx occlusion reduction catalyst (LNT) that purifies NOx, and particulate matter (PM). For example, a DPF that purifies water or a DPF with a catalyst (CSF) is used.

  In these exhaust gas purifying devices, the internal combustion engine is in an operating state where the catalyst temperature of the exhaust gas purifying device is low and has not reached the activation temperature region (operating temperature region) of the exhaust gas purification device, such as immediately after the start of the internal combustion engine. Since the amount of unburned HC discharged from the engine is large, the reduction of unburned HC is indispensable in order to satisfy the exhaust gas regulation value.

  As a countermeasure, a combustor that burns fuel is provided in the exhaust passage, and when the exhaust gas needs to be heated, the fuel is burned by the combustor and the exhaust gas flowing into the exhaust gas purification device by the combustion gas. It is effective to raise the temperature by heating the gas. For example, there has been proposed an exhaust system control system for an internal combustion engine in which a spray combustor is provided upstream of the exhaust purification means and the exhaust temperature is raised by fuel combustion. (For example, refer to Patent Document 1).

  However, immediately after starting the internal combustion engine, even if combustion is performed by a combustor or the like for heating and raising the temperature of the exhaust gas purifying device, it takes about several minutes to ignite the fuel and burn the fuel. In addition, even if the exhaust gas heated to high temperature by the combustion gas from the combustor or the like flows into the exhaust gas purification device, the temperature rises to a temperature at which the catalyst is activated by the heat capacity of the exhaust gas purification device. , It takes a few minutes.

  Therefore, even if equipped with catalyst heating means such as a combustor, there is no solution for HC reduction for a few minutes after the start of the internal combustion engine until the catalyst temperature rises by the catalyst heating means, suppressing HC emissions There was a problem that I could not.

  That is, when a combustor is used as a means for heating the catalyst of the exhaust gas purification device, after the internal combustion engine is started, the time until the catalyst temperature rises by the combustor is shortened as much as possible so that the unburned HC is exhausted. It is necessary to suppress discharge to the downstream side of the purification device.

  In relation to this, a method for promoting combustion using oxygen-enriched air in a combustor has been proposed, for example, a DPF regeneration device for guiding oxygen-enriched air from an intake passage to a regeneration burner for DPF regeneration is proposed. (For example, see Patent Document 2). In addition, oxygen or oxygen-enriched air is supplied to the exhaust gas purifying catalyst at the time of low temperature starting from the start of the internal combustion engine to the warm-up operation, and the oxidation reaction of the unburned matter is promoted by the catalyst, and the reaction heat It has been proposed to promote warm-up and simultaneously add auxiliary fuel for combustion and install an ignition source (see, for example, Patent Document 3).

JP 2004-257323 A JP-A-6-25508 JP-A-5-141229

  The present invention has been made in view of the above situation, and its purpose is to supply a high oxygen concentration gas to a combustor for raising the temperature of exhaust gas after the engine is started. By increasing the combustion speed, the catalyst of the exhaust gas purification device provided in the exhaust passage can be quickly reached the activation temperature region, and after warming up the engine, a low oxygen concentration gas is supplied from the combustor. Provided is an exhaust gas purification method and an exhaust gas purification system that can form a reducing atmosphere in the control for recovering the exhaust gas purification capacity of the exhaust gas purification device, and that can easily achieve a high EGR rate in the control for EGR. There is to do.

  In order to achieve the above object, an exhaust gas purification method of the present invention provides an exhaust gas purification system including a combustor for raising the temperature of exhaust gas in an exhaust passage of an internal combustion engine, to a gas supply line of the combustor. An oxygen enricher is provided to selectively supply a high oxygen concentration gas and a low oxygen concentration gas, and when the exhaust gas is heated, the high oxygen concentration gas is supplied to the combustor, and the exhaust gas is exhausted. A low oxygen concentration gas is supplied to the exhaust passage when the temperature of the gas is not raised, and the low oxygen concentration gas is added to the EGR gas when performing EGR.

  In order to achieve the above object, an exhaust gas purification system of the present invention is an exhaust gas purification system including a combustor for raising the temperature of exhaust gas in an exhaust passage of an internal combustion engine. An oxygen enrichment device is provided to provide gas supply means for selectively supplying a high oxygen concentration gas and a low oxygen concentration gas. When the gas supply means raises the temperature of the exhaust gas, the high oxygen concentration gas is The low oxygen concentration gas is supplied to the exhaust passage when the exhaust gas is not heated and supplied to the combustor, and the low oxygen concentration gas is added to the EGR gas when EGR is performed.

  According to the exhaust gas purification method and the exhaust gas purification system according to the present invention, when the exhaust gas is heated, the high oxygen concentration gas is supplied to the combustor to promote the temperature rise of the exhaust gas. The time until the catalyst temperature of the inflowing exhaust gas purification device rises can be shortened. As a result, the catalyst temperature can reach the activation temperature region in a shorter time than when only the intake air from the atmosphere is used, so that the amount of HC emission downstream of the exhaust gas purification device can be reduced. it can.

  When exhaust gas temperature rise is not required, a low oxygen concentration gas (high nitrogen concentration gas) is supplied to the exhaust passage so that the exhaust gas in the exhaust gas can be repeatedly controlled in the rich air-fuel ratio control for regenerating the purification capacity of the exhaust gas purification device. It is possible to increase the concentration of unburned hydrocarbons and promote the regeneration of the purification capacity. For example, when a NOx occlusion reduction type catalyst is used, atomization of fuel droplets necessary for reduction processing of released NOx is performed in the rich air-fuel ratio control for recovery of the NOx occlusion capability performed periodically. NOx occlusion and purification performance is improved because it can be promoted with a low oxygen concentration gas and the oxygen on the catalyst can be consumed in a very short time to restore the NOx occlusion capability. .

  Further, during the EGR (exhaust gas recirculation) performed to reduce NOx generated in the combustion process (inside cylinder) of the internal combustion engine, the EGR rate is significantly increased by adding a low oxygen concentration gas to the EGR gas. Therefore, the slow combustion reaction can be promoted, and the amount of NOx generated can be reduced.

It is the figure which showed the structure of the exhaust-gas purification system of embodiment of this invention. It is the figure which showed typically an example of the gas mixing type fuel injection valve. It is the figure which showed the gas flow at the time of high oxygen concentration gas filling in a nitrogen oxygen separation unit. It is the figure which showed the flow of the gas at the time of low oxygen concentration gas filling in a nitrogen oxygen separation unit. It is the figure which showed an example of the control flow for filling control of high oxygen concentration gas and low oxygen concentration gas. It is the figure which showed an example of the control flow for switching of the assist gas in a combustor. It is an equilibrium isothermal adsorption diagram showing the characteristics of a synthetic zeolite. It is the figure which showed the relationship between the adsorption pressure of gas at the time of using activated carbon, and adsorption amount. It is the figure which showed the relationship between the adsorption time of gas at the time of using activated carbon, and an equilibrium achievement rate.

  Hereinafter, an exhaust gas purification method and an exhaust gas purification system according to embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration of an exhaust gas purification system 1 according to an embodiment of the present invention.

  In the exhaust gas purification system 1, an exhaust gas purification device 12 is disposed in an exhaust passage 11 of an engine (internal combustion engine) 10. A combustor 13 that can supply combustion gas and sprayed fuel is disposed upstream of the exhaust gas purification device 12. In addition, as an oxygen enrichment system, an oxygen enrichment compressor 20, a nitrogen separation unit 21, a high oxygen concentration gas storage device 22, a low oxygen concentration gas storage device 23, and the like are arranged.

  The exhaust gas purification device 12 is formed by a combination of several exhaust gas purification units such as a NOx purification catalyst unit carrying a catalyst that purifies harmful components in the exhaust gas G. When a NOx purification catalyst unit carrying a NOx storage reduction catalyst is used, the NOx purification catalyst unit is formed of a monolith catalyst in order to purify NOx in the exhaust gas. A catalyst coat layer of aluminum oxide, titanium oxide or the like is provided on a carrier such as a cordierite honeycomb of the monolith catalyst. This catalyst coat layer is configured to carry a NOx occlusion reduction catalyst comprising a catalyst metal such as platinum (Pt) or palladium (Pd) and a NOx occlusion material (NOx occlusion material) such as barium (Ba).

  This NOx occlusion reduction type catalyst purifies NOx in the exhaust gas by the NOx occlusion material storing NOx in the exhaust gas when the oxygen concentration is high, that is, in the lean air-fuel ratio state, When the oxygen concentration is low, the air / fuel ratio is less than 1 or the air / fuel ratio is 1 or the stoichiometric air / fuel ratio is 1, the stored NOx is released and the released NOx is converted to catalytic metal catalyst. By reducing with NO, the outflow of NOx to the atmosphere is prevented.

  In this NOx occlusion reduction type catalyst, if the lean air-fuel ratio state continues, the NOx occlusion material changes to nitrate, so that the regeneration control to make the exhaust gas G rich in the air-fuel ratio state before the NOx occlusion capacity is saturated. The NOx occlusion capacity is restored by releasing and reducing the occluded NOx.

  In this embodiment, an example in which a NOx purification unit carrying a NOx occlusion reduction type catalyst is used as the exhaust gas purification device 12 is shown. However, the present invention is not limited to this, and the exhaust gas is recovered in order to recover the purification performance for the exhaust gas. Any exhaust gas purifying apparatus that needs to perform air-fuel ratio control such as rich air-fuel ratio control temporarily may be used. For example, an exhaust gas purification unit such as an oxidation catalyst (DOC), a selective reduction type NOx catalyst (SCR), or a filter with catalyst (CSF) that needs to recover sulfur poisoning may be used.

  The combustor 13 is configured using, for example, an external mixing type two-fluid injection valve as shown in FIG. As shown in FIG. 1, this configuration includes an injector fuel injection unit 13a, a fuel supply pipe 13b, a gas supply pipe 13c, a gas switching valve 13d, and an ignition device (not shown). The fuel supply pipe 13b is connected to the fuel supply pipe 18 into the cylinder. The gas switching valve 13d is connected to the high oxygen concentration gas supply pipe 24 and the low oxygen concentration gas supply pipe 25a, and selects one of the high concentration oxygen gas A1 and the low concentration oxygen gas A2 as the gas supply pipe 13c. Configured to supply. The ignition device is formed by a heater such as a glow plug or a heat source such as an ignition plug, and these are heated to high temperatures when energized.

  In this combustor 13, a high-pressure gas (high oxygen concentration gas A 1 or low oxygen concentration gas A 2) is injected around the injector type fuel injection unit 13 a to generate a mixed gas of this gas and fuel f droplets. To do. The generation of this mixed gas promotes ignition when the fuel f is burned. In the case of supplying unburned fuel, the fuel f in the exhaust gas is evenly dispersed.

  Next, an oxygen enrichment system will be described. As shown in FIG. 1, the inlet 20 a of the oxygen-enriching compressor 20 is connected to a connecting portion 15 a of an intake passage 15 on the outlet side of the compressor of the turbocharger 14 via a flow path switching valve 26. The outlet 20 b of the oxygen enriching compressor 20 is connected to the air intake pipe 19.

  As shown in FIGS. 1, 3, and 4, the nitrogen separation unit 21 is configured by connecting an air intake pipe 19, a high oxygen concentration supply pipe 21b, and a low oxygen concentration gas supply pipe 21c to an adsorption vessel 21i. The The air intake pipe 19 is connected to the outlet 20b of the oxygen enriching compressor 20, and a flow path switching valve 21a is disposed. The high oxygen concentration supply pipe 21 b connects between the adsorption container 21 i and the on-off valve 22 a of the storage container 22 i of the high oxygen concentration gas storage device 22. The low oxygen concentration gas supply pipe 21c connects between the adsorption vessel 21i and the open / close valve 23a of the storage vessel 23i of the low oxygen concentration gas storage device 23, and a decompression pump 21e is disposed. Further, a cooling water pipe 21f for cooling the adsorbing vessel 21i by flowing the cooling water W is connected.

  In the high oxygen concentration gas storage device 22, the storage container 22i is provided with on-off valves 22a, 22b, 22c, a first oxygen concentration sensor 22d, and a first pressure sensor 22e. Further, in the low oxygen concentration gas storage device 23, the storage container 23i is provided with on-off valves 23a, 23b, 23c, a second oxygen concentration sensor 23d, and a second pressure sensor 23e.

  When these arrangement relationships are summarized, the oxygen-enriching compressor 20 is connected to the adsorption vessel 21i of the nitrogen separation unit 21 via the flow path switching valve 21a by the air intake pipe 19. Further, the nitrogen separation unit 21 is connected to a storage container 22i of the high oxygen concentration gas storage device 22 by a high oxygen concentration gas supply pipe 21b via an on-off valve 22a, and low oxygen concentration by a low oxygen concentration gas supply pipe 21c. The concentration gas storage device 23 is connected to a storage container 23i through a decompression pump 21e and an on-off valve 23a.

  Further, the storage container 22i of the high oxygen concentration gas storage device 22 is connected to the gas switching valve 13d of the combustor 13 by the high oxygen concentration gas supply pipe 24 connected to the on-off valve 22c, and the low oxygen concentration gas storage device 23 The storage container 23i is also connected to the gas switching valve 13d by the low oxygen concentration gas supply pipe 25a through the on-off valve 23c.

  Further, the open / close valve 23b of the low oxygen concentration gas storage device 23 and the flow path switching valve 26 are connected by a low oxygen concentration gas supply pipe 25b, and excess low oxygen concentration is supplied to the intake passage 15 on the outlet side of the compressor of the turbocharger 14. The concentration gas A2 can be released. Further, the branch pipe 27 of the low oxygen concentration gas supply pipe 25b is connected to the EGR valve 17 of the EGR passage 16 so that the low oxygen concentration gas A2 can be supplied during EGR.

  Next, oxygen enrichment in the nitrogen separation unit 21 will be described. The nitrogen separation unit 21 uses synthetic zeolite or molecular sieve activated carbon for oxygen enrichment.

  When synthetic zeolite is used, the pore diameter is about 0.0005 μm to 0.001 μm, and as shown in FIG. 7, electrically polar nitrogen is selectively adsorbed, and this tendency increases as the pressure increases. Therefore, if the processing gas A is cooled and kept at a temperature near room temperature while repeating the operation of pressurizing from atmospheric pressure to about 3 atmospheres, it can be separated into nitrogen and oxygen. Gases A1 and A2 generated during this time are pressurized and stored in storage containers 22i and 23i, respectively. In this case, nitrogen is selectively adsorbed in the process of being adsorbed while being pressurized, so that oxygen remaining without being adsorbed is obtained, and nitrogen is obtained by a depressurization process for returning from the pressurized state to the original pressure.

  In the nitrogen separation unit 21 using this synthetic zeolite, when the high oxygen concentration gas is filled, the flow path switching valve 21a is switched, the air A of the oxygen enriching compressor 20 is taken in, and the adsorption vessel 21i filled with a nitrogen adsorbent. Pressure is applied to the nitrogen absorber, and the oxygen concentration of the gas is increased to about 95%, and the high oxygen concentration gas A1 is supplied to the storage container 22i of the high oxygen concentration gas storage device 22. Store.

  On the other hand, in order to secure a necessary high oxygen concentration gas amount, it is necessary to perform oxygen separation treatment again. As this pretreatment, a decompression process for desorbing and releasing nitrogen that has already been adsorbed is performed using the decompression pump 21e. The nitrogen-rich low oxygen concentration gas A2 released in this process is supplied into the storage container 23i of the low oxygen concentration gas storage device 23 and filled under reduced pressure.

  In the method using the synthetic zeolite, in order to adsorb nitrogen at a high pressure (for example, 180 kPa), oxygen is selected from the air by a pressurizing step for increasing the pressure in the adsorption vessel 21i and adsorption of nitrogen. The high-pressure maintenance step for obtaining the concentration and the adsorption in the adsorption vessel 21i were reduced to a low pressure (for example, 48 kPa) in order to prevent the nitrogen adsorption from reaching saturation and the oxygen sorting ability from being lowered. The depressurization step for releasing nitrogen from the nitrogen adsorbent and the low pressure maintaining step for maintaining the pressure in the adsorption vessel 21i in a low pressure state are repeated in order to sufficiently release the adsorbed nitrogen.

  Further, when molecular sieve activated carbon is used, as shown in FIG. 8, selective adsorption to nitrogen by adsorption pressure cannot be expected. However, as shown in FIG. 9, there is a large difference in adsorption rate between nitrogen and oxygen. The adsorption rate depends on the pressure. Therefore, if the processing gas A is cooled and kept at a temperature near room temperature while repeating the operation of pressurizing from atmospheric pressure to about 3 atmospheres, it can be separated into nitrogen and oxygen. Gases A1 and A2 generated during this time are pressurized and stored in storage containers 22i and 23i, respectively. In this case, in the adsorption process under a constant pressure, oxygen having a high adsorption rate is adsorbed to separate nitrogen, and oxygen is released in a subsequent decompression process to obtain oxygen.

  In the nitrogen separation unit 21 using the molecular sieve activated carbon, when the low oxygen concentration gas is charged, the flow path switching valve 21a is switched to take in the air A of the oxygen enriching compressor 20 and fill the oxygen adsorbent (activated carbon). The pressure is increased in the adsorption vessel 21i so that oxygen is adsorbed by the oxygen absorber, the oxygen concentration of the gas is lowered to about 95%, and the low oxygen concentration gas A2 is stored in the storage vessel 23i of the low oxygen concentration gas storage device 23. To supply and store.

  On the other hand, in order to secure a necessary low oxygen concentration gas amount, it is necessary to perform nitrogen separation again. As this pretreatment, a decompression process for desorbing and releasing oxygen that has already been adsorbed is performed using a decompression pump. In this case, the decompression pump 21e is arranged not in the high oxygen concentration gas supply pipe 21b but in the low oxygen concentration gas supply pipe 21c. The oxygen-rich high oxygen concentration gas A1 released in this decompression process is supplied into the storage container 22i of the high oxygen concentration gas storage device 22 and filled under reduced pressure.

  In this method using molecular sieve activated carbon, in order to adsorb oxygen at a high pressure (for example, 690 kPa), nitrogen is selected from the air by a pressurizing step for increasing the pressure in the adsorption vessel 21i and adsorption of oxygen. The high pressure maintaining step for obtaining the oxygen concentration and the adsorption in the adsorption vessel 21i are set to a low pressure (for example, 48 kPa) in order to prevent the adsorption of oxygen from reaching saturation and reducing the nitrogen sorting ability. The depressurization step for releasing the oxygen from the oxygen adsorbent and the low pressure maintaining step for maintaining the pressure in the adsorption vessel 21i in a low pressure state are repeated in order to sufficiently release the adsorbed oxygen.

  Below, in order to avoid the complexity of explanation, the case where synthetic zeolite is used is explained. When molecular sieve activated carbon is used, “nitrogen” and “oxygen” may be interchanged, and “high oxygen concentration” and “low oxygen concentration” may be interchanged.

  That is, in the oxygen enrichment in the nitrogen separation unit 21, the air A taken in by the engine contains nitrogen and oxygen, and contains a small amount of argon. Therefore, the volume concentration in the air A is about 21%. Is separated from nitrogen and argon. A low-pressure adsorption container (tank) 21i for storing the separated oxygen at a constant pressure is arranged, and when the pressure rises to a necessary value, the oxygen separation operation is stopped. The low oxygen concentration gas A2 having a large amount of nitrogen discharged in this process is also stored in the low oxygen concentration gas storage device 23 separately from the high oxygen concentration gas storage device 22. This low oxygen concentration gas A2 is also stored up to the required pressure value, and unnecessary low oxygen concentration gas A2 generated in the oxygen separation process is discharged into the atmosphere from the pipe 21d by switching the flow path switching valve 21a.

  Next, the valve operation of each valve will be described. When the high oxygen concentration gas is filled, the on-off valve 22a is opened, and the other on-off valves 22b, 22c, 23a, 23b, 23c are closed. The flow path switching valve 21a is operated so that the gas supply pipe 19 and the adsorption container 21i of the nitrogen separation unit 21 are communicated with each other. The flow path switching valve 26 is operated so as to suck air from the compressor inlet 15a. When the pressure in the storage container 22i increases, the on-off valve 22b is opened to discharge the high oxygen concentration gas A1 to the outside so that the filling pressure of the high oxygen concentration gas A1 can be adjusted.

  When the low oxygen concentration gas is filled, the on-off valve 23a is opened, and the other on-off valves 22a, 22b, 22c, 23b, 23c are closed. The flow path switching valve 21a is operated so that the pipe 21d opened to the atmosphere communicates with the adsorption container 21i of the nitrogen separation unit 21. The flow path switching valve 26 is operated so that the compressor inlet 15a and the low oxygen gas storage device 23 communicate with each other. When the pressure in the storage container 23i increases, the on-off valve 23b is opened to discharge the low oxygen concentration gas A2 to the intake passage 15 so that the filling pressure of the low oxygen concentration gas A2 can be adjusted.

  Next, the control at the time of filling with the high oxygen concentration gas A1 and the low oxygen concentration gas A2 will be described with reference to the control flow of FIG. In this control flow, starting from an advanced control flow, operation of the engine 10 is confirmed in step S11. If the engine 10 is not in operation, the process is stopped in step 12 and each on-off valve is controlled to a state suitable for the stop state, and then the process goes to return and the control is terminated.

  When the operation of the engine 10 is confirmed in step S11, a high oxygen concentration gas filling process is performed in step S13. In the next step S14, it is determined whether or not the first pressure Po detected by the first pressure sensor 22c of the storage container 22i of the high oxygen concentration gas storage device 22 exceeds a preset first upper limit pressure Pfo.

  If it is determined in step S14 that the first pressure Po does not exceed the first upper limit pressure Pfo (NO), the process returns to step S13 and repeats the high oxygen concentration gas filling process until it exceeds. If the first pressure Po exceeds the first upper limit pressure Pfo in the determination of step S14 (YES), the process goes to step S15, and the first oxygen concentration sensor 22d of the storage container 22i of the high oxygen concentration gas storage device 22 is reached. It is determined whether or not the first oxygen concentration Co detected in step S1 exceeds a preset first oxygen concentration Cfo (for example, set to 95%).

  If it is determined in step S15 that the first oxygen concentration Co does not exceed the first oxygen concentration Cfo (NO), the process returns to step S13 and repeats the high oxygen concentration gas filling process until it exceeds (NO). When the pressure of the storage container 22i of the high oxygen concentration gas storage device 22 is increased, the stored high oxygen concentration gas A1 is released from the on-off valve 22b as a safety valve, and a new high oxygen concentration gas A1 is supplied. The oxygen concentration of the high oxygen concentration gas A1 in the storage container 22i of the concentration gas storage device 22 is increased.

  If it is determined in step S15 that the first oxygen concentration Co exceeds the first oxygen concentration Cfo (YES), the process goes to step S16 to perform a low oxygen concentration gas filling process. In the next step S17, it is determined whether or not the second pressure Pn detected by the second pressure sensor 23e of the storage container 23i of the low oxygen concentration gas storage device 23 has exceeded a preset second upper limit pressure Pfn.

  If the second pressure Pn does not exceed the second upper limit pressure Pfn in the determination in step S17 (NO), the process returns to step S16 until it exceeds, and the low oxygen concentration gas filling process is repeated. If the second pressure Pn exceeds the second upper limit pressure Pfn in the determination of step S17 (YES), the process goes to step S18, and the second oxygen concentration sensor 23d of the storage container 23i of the low oxygen concentration gas storage device 23 is reached. It is determined whether or not the second oxygen concentration Cn detected in step 2 is lower than a second oxygen concentration Cfn set in advance (for example, set to 5%).

  If it is determined in step S18 that the second oxygen concentration Cn does not exceed the second oxygen concentration Cfn (NO), the process returns to step S16 and repeats the low oxygen concentration gas filling process until it exceeds (NO). When the pressure in the storage container 23i of the low oxygen concentration gas storage device 23 is increased, the stored low oxygen concentration gas A2 is released from the on-off valve 23b as a safety valve, and a new low oxygen concentration gas A2 is supplied. The oxygen concentration of the low oxygen concentration gas A2 in the storage container 23i of the concentration gas storage device 23 is lowered.

  If it is determined in step S18 that the second oxygen concentration Cn exceeds the second oxygen concentration Cfn (YES), the process returns to step S11, and steps S11 to S18 are repeated. If the engine is stopped in the middle of each step, the processing of step 12 is stopped due to the occurrence of an interrupt, and each on-off valve is controlled to be in a state that matches the stopped state, and then the control is returned to return. Exit.

  Next, an exhaust gas purification method in the exhaust gas purification system 1 will be described. In this exhaust gas purification method, immediately after starting the engine, the ignition device is energized and heated to burn the fuel f supplied to the combustor 13, and the high-concentration oxygen gas A1 is used as the high-pressure gas. Concentration of oxygen increases the oxidation reaction rate and promotes fuel ignition. As a result, the temperature of the catalyst of the exhaust gas purification device 13 can be quickly reached in the activation temperature region sufficient for the exhaust gas purification reaction. As a result, the amount of fuel for warming up can be reduced, and the exhaust gas purification performance can be exhibited in a short time, so that the exhaust gas purification performance is improved.

  On the other hand, the engine is warmed up and the catalyst of the exhaust gas purification device 13 is also heated to the activation temperature or higher, and in the temperature range where the exhaust gas temperature increasing process using the combustor 13 is unnecessary, that is, the combustor 13. In the temperature range where no heat of oxidation reaction is required, the supply of the high oxygen concentration gas A1 is switched to the supply of the low oxygen concentration gas A2, and the supply of the low oxygen concentration gas A2 depends on the state of the exhaust gas purification device 12. Do it. For example, by supplying the low oxygen concentration gas A2, rich air-fuel ratio control in the case of NOx regeneration control of the NOx occlusion reduction type catalyst of the exhaust gas purification device 12 is performed. By using this low oxygen concentration gas A2, the oxygen concentration in the exhaust gas is lowered and the exhaust gas is made rich (low oxygen state) while avoiding deterioration of fuel consumption. Thereby, it can be set as a reducing atmosphere in a catalyst, and NOx occlusion ability can be recovered efficiently.

  The switching between the gases A1 and A2 is performed based on a control flow as shown in FIG. 6, for example. When the control flow of FIG. 6 is called from the advanced control flow and started, the operation of the engine is confirmed in step S21. If the engine is not in operation, the process goes to step 22 to stop the process and control each on-off valve to a state that matches the stop state, then goes to return and ends the control.

  When the engine operation is confirmed in step S21, it is determined in step S23 whether or not a gas supply start signal is received. When the gas supply start signal has not been received, after a preset time (time related to the start signal reception determination interval) has elapsed, the process returns to step S23.

  If it is determined in step S23 that a gas supply start signal has been received, the inlet exhaust gas temperature Tb detected by the inlet side temperature sensor 12a provided at the inlet of the exhaust gas purification device 12 is set in advance in step S24. It is determined whether it is lower than the set temperature threshold value Tf.

  If it is determined in step S24 that the inlet exhaust gas temperature Tb is lower than the temperature threshold Tf (YES), in step S25, the high oxygen concentration gas A1 is supplied, and the inlet exhaust gas temperature Tb is equal to or higher than the temperature threshold Tf. In this case (NO), the low and high oxygen concentration gas A2 is supplied in step S26. The supply of these gases A1 and A2 is performed until a supply stop signal is received, and then the gas supply is stopped in step S26.

  After stopping the gas supply in step S26, the process returns to step S21, and steps S21 to S26 are repeated. If the engine operation is stopped in the middle of each step, the processing of step 22 is stopped due to the occurrence of an interrupt, and each on-off valve is controlled to a state suitable for the stopped state, and then the return is performed. Exit.

  Next, the low oxygen concentration gas supply during EGR will be described. At the time of EGR performed to reduce NOx generated in the combustion process in the cylinder of the engine, the EGR valve 17 is connected from the open / close valve 23b of the low oxygen concentration gas storage device 23 via the low oxygen concentration gas supply pipe 25b and the branch pipe 27. By supplying the low oxygen concentration gas A2 to the oxygen concentration in the cylinder, the oxygen concentration can be lowered and the EGR rate can be increased as compared with the fresh air A and the EGR gas Ge. The combustion reaction in the cylinder can be made a slow combustion reaction, and the amount of NOx generated can be reduced.

  According to the exhaust gas purification method and the exhaust gas purification system 1 described above, when it is necessary to raise the temperature of the exhaust gas, such as when the engine is started, the high oxygen concentration gas A1 is supplied to the combustor 13 to The temperature rise can be promoted, and the rise time to the activation temperature region of the catalyst temperature of the exhaust gas purification device 12 into which the exhaust gas flows can be shortened. As a result, the amount of unburned HC discharged at the start of the engine to the downstream side of the exhaust gas purification device 13 can be reduced, and the exhaust gas purification capability of the exhaust gas purification device 13 can be increased in a short time. As a result, the exhaust gas purification performance can be improved.

  Further, when the temperature of the exhaust gas does not need to be raised, the low oxygen concentration gas A2 is supplied to the exhaust passage 11 so that the unburned HC in the exhaust gas can be obtained in the rich air-fuel ratio control that is repeatedly performed to regenerate the purification capacity of the exhaust gas purification device 12. The concentration can be increased to promote regeneration of the purification capacity. For example, when a NOx occlusion reduction type catalyst is used, in the rich air-fuel ratio control for recovering the NOx occlusion ability that is performed periodically, the atomization of fuel required for the reduction treatment of released NOx is reduced by low oxygen. The concentration gas A2 can be promoted, and the oxygen on the catalyst can be consumed in a very short time to restore the NOx storage capacity in a reducing atmosphere, so that the NOx storage and purification performance is improved. improves.

  Furthermore, the EGR rate can be remarkably increased by adding the low oxygen concentration gas A2 to the EGR gas Ge during EGR performed to reduce NOx generated in the combustion process in the cylinder of the engine. In this case, the slow combustion reaction can be promoted and the amount of NOx generated can be reduced.

  The exhaust gas purification method and the exhaust gas purification system according to the present invention achieve the exhaust gas purification by reaching the activation temperature region of the catalyst temperature in a short time due to the effect of promoting the temperature rise of the exhaust gas when the temperature of the exhaust gas is raised. The amount of HC discharged to the downstream side of the apparatus can be reduced. When exhaust gas temperature rise is not required, low oxygen concentration gas (high nitrogen concentration gas) is supplied to the exhaust passage and unburned in the exhaust gas in rich air-fuel ratio control for regenerating the purification capacity of the exhaust gas purification device. It is possible to increase the hydrocarbon concentration and promote the regeneration of the purification capacity. Furthermore, at the time of EGR, by adding a low oxygen concentration gas to the EGR gas, the EGR rate can be remarkably increased, and the amount of NOx generated can be reduced.

  Therefore, the exhaust gas purification method and the exhaust gas purification system of the present invention can be used as an exhaust gas purification method and an exhaust gas purification system in an exhaust passage of an internal combustion engine or the like mounted on an automobile.

1 Exhaust gas purification system 10 Engine (internal combustion engine)
DESCRIPTION OF SYMBOLS 11 Exhaust passage 12 Exhaust gas purification apparatus 13 Combustor 13c Gas supply piping 13d Gas switching valve 16 EGR passage 17 EGR valve 19 Gas supply piping 20 Oxygen-enriching compressor 21 Nitrogen separation unit 21b High oxygen concentration gas supply piping 21c Low oxygen Concentration gas supply pipe 22 High oxygen concentration gas storage device 22i Storage container 22d First oxygen concentration sensor 22e First pressure sensor 23 Low oxygen concentration gas storage device 23i Storage container 23d Second oxygen concentration sensor 23e Second pressure sensor 24 High oxygen concentration Gas supply piping 25a, 25b Low oxygen concentration gas supply piping 26 Flow path switching valve A Air (fresh air)
A1 High concentration oxygen gas A2 Low concentration oxygen gas Cfo 1st oxygen concentration Cfn 2nd oxygen concentration Cn 2nd oxygen concentration Co 1st oxygen concentration f Fuel G Exhaust gas Ge EGR gas Pfn 2nd upper limit pressure Po 1st pressure Pfo 1st Upper limit pressure Pn Second pressure Tb Inlet exhaust gas temperature Tf Temperature threshold W Cooling water

Claims (2)

  In an exhaust gas purification system provided with a combustor for raising the temperature of exhaust gas in an exhaust passage of an internal combustion engine, an oxygen enrichment device is provided in a gas supply line of the combustor so that a high oxygen concentration gas and a low oxygen concentration gas are provided. The high oxygen concentration gas is supplied to the combustor when the temperature of the exhaust gas is raised, and the low oxygen concentration gas is supplied to the exhaust passage when the temperature of the exhaust gas is not raised. And an exhaust gas purification method characterized by adding a low oxygen concentration gas to the EGR gas when performing EGR.   In an exhaust gas purification system provided with a combustor for raising the temperature of exhaust gas in an exhaust passage of an internal combustion engine, an oxygen enrichment device is provided in a gas supply line of the combustor so that a high oxygen concentration gas and a low oxygen concentration gas are provided. The gas supply means supplies a high oxygen concentration gas to the combustor when raising the temperature of the exhaust gas, and the low oxygen concentration when not raising the temperature of the exhaust gas. An exhaust gas purification system, characterized in that a gas is supplied to an exhaust passage and a low oxygen concentration gas is added to EGR gas when EGR is performed.

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