WO2013005341A1

WO2013005341A1 - Exhaust gas purifier for internal combustion engine

Info

Publication number: WO2013005341A1
Application number: PCT/JP2011/065642
Authority: WO
Inventors: 佳久塚本; 中山　茂樹; 優一祖父江; 寛真西岡; 大地今井; 克彦押川; 寛大月; 潤一松尾; 菅原　康
Original assignee: トヨタ自動車株式会社
Priority date: 2011-07-01
Filing date: 2011-07-01
Publication date: 2013-01-10

Abstract

The present invention relates to an exhaust gas purifier for an internal combustion engine installed with a diesel particulate filter (DPF) at an exhaust system of the internal combustion engine. According to the present invention, ash accumulation on the DPF, a long-term increase in pressure drop and particulate matter (PM) regeneration temperature, and a decrease in fuel efficiency may be controlled. A solid acid whose acid strength is larger than an acid strength of SO₃ and smaller than an acid strength of SO₄is coated onto a surface of the DPF, and a SO_xinhalation and release catalyst device is installed at an upstream of the DPF of the exhaust system of the internal combustion engine to conduct a control for raising a temperature of the DPF, a control of a fuel-air ratio of an atmosphere in the DPF, and a control for supplying SO₄equivalent to the amount of the ash to be released from the SO_xinhalation and release catalyst device.

Description

Exhaust gas purification device for internal combustion engine

The present invention relates to an exhaust purification device for an internal combustion engine.

In order to reduce the number of particles of particulate matter (hereinafter referred to as “PM”) in the exhaust gas of the internal combustion engine, a diesel particulate filter (hereinafter referred to as “DPF”) is installed in the exhaust gas passage of the internal combustion engine, Generally, PM in exhaust gas is collected and removed.

In this case, since the PM collected in the DPF gradually accumulates, regeneration (hereinafter referred to as “PM regeneration”) is performed periodically or by detecting a decrease in the performance of the DPF and burning and removing the PM collected in the DPF. ”).

PM regeneration operation is usually performed by heating the DPF while supplying a reducing agent such as hydrocarbon (HC) to the DPF.

Various improvements have been proposed to improve the performance and reduce the cost of the PM regeneration operation that collects PM in the exhaust gas using the DPF and burns and removes the PM collected in the DPF. Has been.

However, in the conventional DPF, if the use of the DPF is continued, even if the PM regeneration operation is performed, the pressure loss of the DPF gradually increases, and if the PM regeneration temperature is not gradually increased, sufficient regeneration is achieved. There is a problem that it will not be performed, and fuel consumption deteriorates. This problem is caused by the accumulation of ash inside the DPF.

Ash is generated when the engine oil mixed in the cylinder of the engine burns, and the generated ash particles are covered with PM in the DPF. The ash particles covered with PM are exposed to high temperature conditions during the PM regeneration operation in the DPF, and the PM covering the ash particles is burned and removed. Ash deposition occurs because the ash particles are agglomerated and increased in size by further applying heat to the ash particles from which the PM has been burned and removed.

However, there is no effective solution to the accumulation of ash so far, and in order to minimize the influence of the accumulation of ash on the DPF, for example, a large-capacity DPF is installed in advance. Measures were taken.

That is, the improvement to the conventional DPF and the improvement to the regeneration operation of the DPF are intended to improve the collection efficiency of the DPF and improve the performance of the PM regeneration operation, and not to the accumulation of ash. As an object for improving the performance of the PM regeneration operation, for example, there is an invention disclosed in Patent Document 1, and Patent Document 1 shows a configuration of a DPF capable of burning PM at a relatively low temperature. Yes.

The structure of the DPF disclosed in Patent Document 1 is characterized in that, in the DPF and the exhaust gas purification method using the DPF, a catalyst made of a solid superacid having an active metal supported on the DPF is held on the filter surface. is there.

That is, the invention of Patent Document 1 reduces the combustion temperature of PM with a solid super strong acid carrying an active metal, and regenerates DPF at a lower temperature than before, preferably continuously, and CO, HC, NO, NO ₂ can be removed at the same time.

Therefore, the invention of Patent Document 1 is intended to improve the performance of the PM regeneration operation, and does not correspond to the accumulation of ash. If the use of the DPF is continued, the PM regeneration operation is performed. However, this does not solve the problem that the pressure loss of the DPF gradually increases, and unless the PM regeneration temperature is gradually increased, sufficient regeneration cannot be performed and the fuel consumption deteriorates.

Further, as a disclosure of a catalyst structure similar to the invention of Patent Document 1, there is an invention of Patent Document 2, which is selected from platinum, palladium and rhodium as a catalyst for a diesel engine exhaust gas purification device. By using a catalyst having at least one kind of noble metal and a solid super strong acid, it is possible to purify SOF (Soluable Organic Fraction), unburned hydrocarbons, etc. contained in particulate matter in diesel engine exhaust gas from a low temperature range. Further, it is described that the effect of suppressing oxidation of sulfur dioxide is exhibited even in a high temperature range, and the invention of Patent Document 2 aims at an effect similar to the invention of Patent Document 1 and does not relate to DPF. Therefore, it does not correspond to the accumulation of ash on the DPF. If the use of the DPF is continued, the pressure loss of the DPF gradually increases and the PM regeneration temperature gradually increases even if the PM regeneration operation is performed. If this is not done, it will not solve the problem that sufficient regeneration will not be performed and fuel consumption will deteriorate.

JP 2006-289175 A Japanese Patent Laid-Open No. 10-033985

The present invention provides an exhaust emission control device for an internal combustion engine that can suppress the accumulation of ash on the DPF and suppress an increase in pressure loss, an increase in PM regeneration temperature, and a decrease in fuel consumption over a long period of time. It is aimed.

That is, the present invention provides a configuration in which the ash deposited on the DPF is discharged with a reduced particle size, and the DPF is regenerated (hereinafter referred to as “ash regeneration”). It is an object of the present invention to provide an epoch-making DPF that has an advantageous effect of suppressing an increase in temperature and a decrease in fuel consumption.

According to the present invention, the accumulated ash can be discharged with a reduced particle size. As a further effect, a DPF that is smaller than the conventional DPF can be used from the beginning of the installation of the DPF. Not only cost reduction, but also energy cost of PM regeneration operation can be reduced. In addition, the fact that a small DPF can be used means that the space for mounting the DPF on the vehicle can be reduced, and the weight of the vehicle on which the DPF is mounted can be reduced.

By the way, when the ash regeneration operation is performed in the present invention, SO ₄ needs to be present when the ash is discharged with a reduced particle size. As will be described below, SO ₄ exists under the condition of air-fuel ratio lean, so control is performed to make the exhaust gas lean to air-fuel ratio. However, if the amount of accumulated ash is large, A problem arises in that the amount of SO ₄ required for the release of ash is not sufficient relative to the amount, and the ash release rate is low.

The inventor of the present application studied the problem of ash accumulation inside the DPF, analyzed the cause of ash accumulation, and the main components of ash were calcium (Ca) contained in engine oil and SOx in exhaust gas. It was found that ash is ion-bonded, CaSO ₄ is the main component, and Ca salt has a high melting point, so that in the exhaust gas, ash flows into the DPF as a solid and aggregates to increase the particle size.

Furthermore, the inventors of the present application have confirmed by experiments that the size of ash is on the order of submicrons, and that the ash slips through the DPF when the ash size is reduced to the order of nanomicrons.

Furthermore, the inventors of the present application, a CaSO ₄ that large grain size to the size of submicron, when placed in a reducing atmosphere, it becomes SO ₃ SO ₄ of CaSO ₄ is reduced, the bond between Ca weakened, At this time, if an acid stronger than SO ₃ is present on the surface of the DPF, the bond between Ca and SO _{3 in} the CaSO ₃ is cleaved, and the Ca ions are stronger than the SO ₃ on the surface of the DPF. It was confirmed by experiments that the atoms were dispersed and bonded in an atomic form.

Furthermore, the inventors of the present application, Ca ions associated with stronger acid than SO ₃ on the surface of the DPF is different from the stronger acid than SO ₃ on the surface of the DPF, if a stronger acid is present in the atmosphere It was confirmed by an experiment that it binds to a stronger acid in the atmosphere, is released from the DPF, and passes through the DPF to be discharged.

To summarize the above, if the acid strength of this acid is stronger than SO ₃ on the surface of the DPF and the acid strength of this acid is stronger than SO ₃ and weaker than SO ₄ , the particle size will be submicron. CaSO ₄ deposited in the DPF turned into, in a reducing atmosphere, becomes CaSO ₃ SO ₄ is reduced in CaSO _4, Ca ions CaSO ₃ is bonded with the acid on the surface of the DPF, on the surface of the DPF Disperse in atomic form. Next, if SO ₄ is present in the atmosphere, the Ca on the surface of the DPF combines with the SO _{4 in} the atmosphere and becomes sub-nanometer-sized CaSO ₄ and is released from the DPF.

When the exhaust gas atmosphere is a stoichiometric or rich atmosphere, it is the above-described reducing atmosphere, and when it is a lean atmosphere, the lean atmosphere contains SO ₄ . Therefore, if control for making the atmosphere stoichiometric or rich and control for making the lean atmosphere next are performed on the above-mentioned DPF, ash Ca ions deposited on the DPF in the stoichiometric or rich atmosphere are converted to DPF. Then, in a lean atmosphere, Ca on the surface of the DPF is combined with SO ₄ in the lean atmosphere and released from the DPF, and the fine particle size is reduced to a sub-nanometer size. CaSO ₄ is converted to pass through the DPF and discharged.

That is, in the above process, the first CaSO ₄ having a large particle size of submicron and deposited on the DPF is finally released again from the DPF as CaSO _4. No. ₄ is reduced in size to a sub-nanometer size and passes through the DPF and is discharged.

However, when performing the above-described ash regeneration operation, if the amount of accumulated ash is large, the amount of SO ₄ required for releasing the ash is not sufficient with respect to the amount of accumulated ash, and the ash release rate is low. The problem occurs.

In order to solve this problem, the present invention provides a configuration that provides the amount of SO ₄ required when ash is released. That is, according to the present invention, an optimum amount of SO ₄ is supplied in accordance with the amount of accumulated ash, and the ash regeneration operation proceeds effectively.

According to the first aspect of the present invention, there is provided an exhaust purification device for an internal combustion engine in which a DPF is disposed in an exhaust system of the internal combustion engine, wherein the DPF is a DPF whose surface is coated with a solid acid, The acid strength is larger than the acid strength of SO ₃ and smaller than the acid strength of SO ₄ , and further, in the exhaust system of the internal combustion engine, an SOx absorption / release catalyst device is provided upstream of the DPF whose surface is coated with a solid acid. An exhaust purification device for an internal combustion engine is provided in which the SOx absorption / release catalyst device has a characteristic of releasing SO ₄ by increasing the temperature.

That is, in the invention of claim 1, the DPF is constituted by applying a solid acid having an acid strength stronger than SO _{3 and} weaker than SO ₄ on the surface of the DPF. Relative thus constituted DPF, when passing the exhaust gas in a reducing atmosphere, CaSO ₄ deposited on the DPF with large grain size is in a reducing atmosphere, SO ₄ of CaSO ₄ is reduced CaSO ₃ If the Ca ions of CaSO ₃ bind to the solid acid on the surface of the DPF, and then SO ₄ is present in the atmosphere, the Ca on the surface of the DPF binds to SO _{4 in} the atmosphere. , CaSO ₄ is released from the DPF. Since the CaSO ₄ released through this process has a reduced particle size, the first large-sized CaSO ₄ is released from the DPF as the reduced particle size CaSO ₄ and passes through the DPF. Discharged. The invention of claim 1 includes an SOx absorption / release catalyst device, and the SOx absorption / release catalyst device has a characteristic of releasing SO ₄ by raising the temperature. According to the invention of claim 1, Depending on the amount of accumulated ash, the amount of SO ₄ required to release ash can be supplied from the SOx absorption / release catalyst device, and the ash is removed at a high release rate. An exhaust purification device for an internal combustion engine that can suppress an increase in regeneration temperature and a decrease in fuel consumption is provided.

According to the second aspect of the present invention, the ash regeneration operation control for removing the ash accumulated in the DPF is provided, and the control of the ash regeneration operation includes the control for increasing the temperature of the DPF, and the atmosphere in the DPF. The control of the air-fuel ratio of the atmosphere in the DPF includes a stoichiometric or air-fuel ratio rich atmosphere first and then changes to an air-fuel ratio lean atmosphere during the control to increase the temperature of the DPF. Further, in the control for changing to an air-fuel ratio lean atmosphere during the control for increasing the temperature of the DPF, the temperature increase of the SOx adsorption / release catalyst device is controlled according to the amount of ash to be released from the DPF, The exhaust emission control device for an internal combustion engine according to claim 1, wherein the emission amount of SO ₄ released from the SOx absorption / release catalyst device is adjusted.

That is, in the invention of claim 2, the ash regeneration operation is performed on the DPF configured in claim 1, and the ash regeneration operation is performed between the control for increasing the temperature of the DPF and the control for increasing the temperature of the DPF. Control of the air-fuel ratio of the atmosphere in the DPF, and the control of the air-fuel ratio of the atmosphere in the DPF is a control that first changes to a stoichiometric or air-fuel ratio rich atmosphere and then changes to an air-fuel ratio lean atmosphere, and a lean atmosphere The amount of SO _{4 in} the catalyst is supplied from the SOx absorption / release catalyst device by a necessary amount by controlling the temperature rise of the SOx absorption / release catalyst device according to the amount of ash to be released from the DPF. Therefore, CaSO ₄ having a large particle size is reduced to HC, CO, or the like in a stoichiometric or air-fuel ratio rich atmosphere to become CaSO ₃ , and the Ca ions of CaSO ₃ are combined with the solid acid on the surface of the DPF. Next, the air-fuel ratio is changed to a lean atmosphere. In the lean atmosphere, SO ₄ corresponding to the amount of ash to be released from the DPF exists, and Ca on the surface of the DPF However, it combines with SO ₄ in a lean atmosphere with high efficiency and becomes CaSO ₄ and is released from the DPF. CaSO ₄ released through this process, because it is fine diameter, the first, CaSO ₄ deposited on the DPF with large grain size is, finally, becomes CaSO ₄ that is fine diameter It is released from the DPF and passes through the DPF to be discharged. Accordingly, there is provided an exhaust emission control device for an internal combustion engine that can remove ash at a high release rate in ash regeneration operation, and can suppress an increase in pressure loss, an increase in PM regeneration temperature, and a decrease in fuel consumption over a long period of time. .

According to the invention described in each claim, an ash regeneration configuration is provided, and the ash is completely removed in the ash regeneration operation, and an increase in pressure loss, an increase in PM regeneration temperature, and a decrease in fuel consumption are suppressed over a long period of time. The present invention provides a common effect of providing an exhaust gas purification device for an internal combustion engine.

FIG. 1 is a diagram illustrating a schematic configuration of an embodiment when the present invention is applied to an exhaust gas purification apparatus for an internal combustion engine.
FIG. 2 is a view for explaining ash release in the embodiment of control of the SOx adsorption / release catalyst device of the present invention.
FIG. 3 is a diagram illustrating ash release in another embodiment of the control of the SOx adsorption / release catalyst device of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the plurality of accompanying drawings, the same or corresponding members are denoted by the same reference numerals.

FIG. 1 is a diagram showing a basic configuration of the present invention. A solid acid corresponding to an acid strength of SO ₃ or more and SO ₄ or less is formed on the surface of DPF 2, specifically, on the surface of a DPF substrate of DPF 2. Apply. Further, an SOx absorption / release catalyst device 30 is provided upstream of the DPF 2 in the exhaust system of the internal combustion engine 1. The exhaust gas of the internal combustion engine 1 is guided to the DPF 2 via the SOx absorption / release catalyst device 30, SOx in the exhaust gas is collected and removed by the SOx absorption / release catalyst device 30, and PM in the exhaust gas is captured by the DPF 2. The exhaust gas that has been collected and removed and from which SOx and PM have been removed is discharged. Since PM collected in the DPF 2 is gradually accumulated, a PM regeneration operation is performed periodically or by detecting a decrease in the performance of the DPF 2 and burning and removing the PM collected in the DPF 2.

However, if the PM regeneration operation is repeated, ash 3 accumulates in the DPF 2, and even if the PM regeneration operation is performed, the pressure loss of the DPF 2 gradually increases, and it is sufficient if the PM regeneration temperature is not increased gradually. There is a problem that proper regeneration is not performed, and fuel consumption deteriorates.

In the present invention, in the ash regeneration operation of the DPF 2, the ash 3 deposited in the DPF 2 is supplied from the SOx adsorption / release catalyst device 30 with an amount of SO ₄ corresponding to the amount of the ash 3 to reduce the particle size. The particle size particles 4 pass through the filter gap of the DPF 2 at a high release rate and are discharged together with the exhaust gas.

FIG. 3 is a diagram for explaining ash release in an embodiment in which the temperature increase control of the SOx adsorption / release catalyst device 30 of the present invention is performed so as to increase to a certain temperature for a certain time. The four graphs are graphs for explaining each event for the same time, and the horizontal axis is time. The top graph shows the temperature rise of the SOx absorption / release catalyst device 30 (FIG. 1), and the vertical axis T (30) is the temperature of the SOx absorption / release catalyst device 30. The second graph from the top shows the periods Z ₁ and Z ₃ for capturing SOx and the period Z ₂ for releasing SO ₄ of the SOx adsorption / release catalyst device 30, and the vertical axis SO ₄ (L ₂ ) is shown in FIG. It shows SO ₄ emission at the position of 1 in _{L 2.} The third graph from the top is a graph showing the ash discharge state, and the vertical axis ash (L ₃ ) indicates the ash discharge amount at the position L ₃ in FIG. The lowermost graph is a graph showing the amount of SO ₄ released at the position of L ₃ , and the vertical axis SO ₄ (L ₃ ) is the amount of SO ₄ released at the position of L ₃ . That is, in this embodiment, the lower two graphs show that although ash regeneration is sufficiently performed, surplus SO ₄ is generated and surplus SO ₄ is discharged downstream of the DPF 2.

FIG. 2 shows an embodiment in which the drawbacks in the control of FIG. 3 are improved. The four graphs in FIG. 2 correspond to the four graphs in FIG. 3 respectively. In the uppermost graph, the temperature increase of the SOx adsorption / release catalyst device 30 is controlled in stages, and ash regeneration is performed. In the initial stage, the temperature rise of the SOx adsorption / release catalyst device 30 is controlled to a relatively low temperature as compared with FIG. That is, as shown in the second graph from the top in FIG. 2, the amount of SO ₄ released at the position L ₂ is T (30) so that the unreacted SO ₄ slip-through does not occur in the ash release reaction. To control. Note that the SO ₄ (L ₂ ) peak in the _second graph from the top in FIG. 2 is lower than the peak in the corresponding graph in FIG. Further, Adj in the graph indicates the range of the upper limit value and the lower limit value of the SO ₄ release amount that can maintain the necessary ash release rate appropriately. That is, if the temperature rise control of the SOx adsorption / release catalyst device 30 is performed and kept at a constant temperature rise value, the SO ₄ release amount gradually decreases. Therefore, when a lower limit is set and the lower limit is approached, The temperature T (30) of the SOx absorption / release catalyst device 30 is further raised to recover the SO ₄ release amount. The effects by adjusting the discharge amount per ashes unit time, the ash playback period Z _A in FIG. 2, the longer than ash playback period Z _A in FIG. 3, the reaction with SO ₄ needed for ash discharge Can be done automatically. The relationship between these temperatures rise T (30) and ash playback period Z _A is the characteristic of the catalyst and to be used for the catalytic converter output SOx absorbing, because it depends on the processing amount of ash, to grasp the optimum relationship experimentally, It is preferably incorporated into the control system as a map.

Doing appropriate control as in FIG. 2, as shown in the third graph from the top, with obtaining ash emissions at the position of L _3, as shown in the bottom graph, in the position of L ₃ The amount of SO ₄ slip-through can be made almost zero. That is, in this embodiment, the lower two graphs indicate that ash regeneration is sufficiently performed, no surplus SO ₄ is generated, and SO ₄ is not discharged downstream of the DPF 2.

Therefore, a solid acid corresponding to an acid strength of SO ₃ or higher and SO ₄ or lower is applied on the DPF substrate, and the air-fuel ratio of the atmosphere in the DPF is set to the stoichiometric or rich air-fuel ratio first during the ash regeneration operation. When the atmosphere is changed to an air-fuel ratio lean atmosphere, and an appropriate amount of SO ₄ corresponding to the amount of ash to be released is controlled to be supplied from the SOx adsorption / release catalyst device as shown in FIG. The ash having a large particle size in the DPF 2 is completely removed, and an exhaust purification device for an internal combustion engine having a DPF whose performance does not deteriorate indefinitely can be configured. The performance of the DPF 2 can be dramatically improved over a long period of time. There is an advantageous effect that it can be improved. Furthermore, as a further effect that accompanies this effect, a DPF smaller than the conventional one can be used from the beginning of the installation of the DPF, which not only reduces the manufacturing cost of the DPF but also reduces the energy cost of the PM regeneration operation. be able to. Furthermore, the fact that a small DPF can be used has the effect that the space for mounting the DPF on the vehicle can be reduced, and the weight of the vehicle on which the DPF is mounted can be reduced. It should be noted.

1 Internal combustion engine 2 DPF
3 Ash 4 Fine particle 5 DPF base material 6 Solid acid 30 SOx absorption / release catalyst device L ₁ : SOx absorption / release catalyst device inlet L ₂ : DPF inlet L ₃ : DPF outlet T (30): SOx absorption / release catalyst device 30 temperature _SO 4 in _(L 2): SO ₄ emission at the position of _{_{_{L 2 SO 4 (L 3)}}} : SO 4 emission ash _(L 3) at the position of _{L 3:} ash emission at the position of _{L 2} Z _A : Ash regeneration Z ₁ : SOx capture period Z ₂ : SO ₄ release period Z ₃ : SOx capture period

Claims

An exhaust purification device for an internal combustion engine in which a DPF is disposed in an exhaust system of the internal combustion engine,
The DPF is a DPF having a surface coated with a solid acid,
The acid strength of the solid acid is greater than the acid strength of SO 3 and less than the acid strength of SO 4 ;
Further, in the exhaust system of the internal combustion engine, an SOx absorption / release catalyst device is provided upstream of the DPF whose surface is coated with a solid acid,
The SOx absorption / release catalyst device has a characteristic of releasing SO 4 by raising the temperature;
An exhaust purification device for an internal combustion engine.
An ash regeneration operation control for removing ash deposited in the DPF;
The control of the ash regeneration operation is
Control to increase the temperature of the DPF;
An air-fuel ratio control of the atmosphere in the DPF,
The control of the air-fuel ratio of the atmosphere in the DPF is a control for changing the atmosphere to the stoichiometric or air-fuel ratio rich atmosphere first and then changing to the air-fuel ratio lean atmosphere during the control to increase the temperature of the DPF.
Further, in the control to change the air-fuel ratio lean atmosphere during the control to increase the temperature of the DPF, the temperature increase of the SOx adsorption / release catalyst device is controlled according to the amount of ash to be released from the DPF, Adjusting the amount of SO 4 released from the SOx absorption / release catalyst device,
The exhaust emission control device for an internal combustion engine according to claim 1.