WO2013005338A1

WO2013005338A1 - Exhaust purification apparatus for internal combustion engine

Info

Publication number: WO2013005338A1
Application number: PCT/JP2011/065637
Authority: WO
Inventors: 潤一松尾; 中山　茂樹; 優一祖父江; 寛真西岡; 大地今井; 克彦押川; 佳久塚本; 寛大月; 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

Provided is an exhaust purification apparatus for an internal combustion engine with a DPF disposed in the exhaust system of the internal combustion engine, such that accumulation of ash in the DPF can be suppressed, and increases in pressure loss and PM regeneration temperature as well as a decrease in fuel efficiency can be suppressed over a long period. A surface of the DPF, which includes a wall portion parallel to the flow of exhaust gas and a bottom portion on the opposite side to an exhaust gas inlet, is coated with a solid acid with an acid strength greater than the acid strength of SO₃ and smaller than the acid strength of SO₄ such that the amount of coating is greater toward the bottom portion than around the exhaust gas inlet on the parallel wall portion of the DPF (2).

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.

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.

By the way, DPF usually has a wall part parallel to the flow of exhaust gas and a bottom part opposite to the exhaust gas inlet of DPF, and ash is deposited near the DPF inlet. The amount of deposition is small, the deposition amount gradually increases along the flow direction of the exhaust gas on the parallel wall portion, and deposition is performed so that the deposition amount is the largest at the bottom.

Therefore, it is necessary to further decompose the accumulated ash from the vicinity of the DPF entrance toward the bottom in accordance with the amount of accumulation.

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 parallel to the flow of exhaust gas, and the DPF A DPF having a surface coated with a solid acid, the acid strength of the solid acid being greater than the acid strength of SO _{3 and} the acid strength of SO ₄ There is provided an exhaust gas purification apparatus for an internal combustion engine, which is smaller and has a coating amount of solid acid at the bottom portion than in the vicinity of the exhaust gas inlet of the parallel wall portion of the DPF.

That is, in the invention of claim 1, the DPF is constituted by coating the surface of the DPF with a solid acid having an acid strength stronger than SO _{3 and} weaker than SO _4. The coating is performed so that the coating amount is larger at the bottom portion than in the vicinity of the exhaust gas inlet of the parallel wall portion. When exhaust gas in a reducing atmosphere is passed through the DPF configured as described above, the amount of ash deposited is small in the vicinity of the DPF inlet, and gradually increases along the flow direction of the exhaust gas on the parallel walls. Since the amount of deposit increases and the deposit is deposited so that the amount of deposit is the largest at the bottom, CaSO ₄ having a large particle size and deposited on the DPF is reduced in a reducing atmosphere to CaSO ₃ , and the Ca ions of CaSO ₃ However, when it binds to the solid acid on the surface of the DPF, it becomes easy to bind to the solid acid on the surface of the DPF according to the distribution of the amount of ash deposited. Next, if SO ₄ is present in the atmosphere, , Ca on the surface of the DPF is combined with SO _{4 in} the atmosphere to become CaSO ₄ and 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. Therefore, the ash is efficiently removed according to the distribution of the accumulation amount in the DPF, and the exhaust gas purification of the internal combustion engine can suppress the increase in pressure loss, the increase in PM regeneration temperature, and the decrease in fuel consumption over a long period of time. An apparatus is provided.

According to the invention described in claim 2, the coating amount of the solid acid increases from the vicinity of the exhaust gas inlet of the parallel wall portion of the DPF toward the bottom portion, and the coating amount of the solid acid increases most at the bottom portion. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is an increased number of coatings.

That is, in the invention of claim 2, the DPF is constituted by coating the surface of the DPF with a solid acid having an acid strength stronger than that of SO _{3 and} weaker than that of SO _4. Coating is performed so that the coating amount increases from the vicinity of the exhaust gas inlet of the parallel wall portion toward the bottom, and the coating amount is maximized at the bottom. When exhaust gas in a reducing atmosphere is passed through the DPF configured as described above, the amount of ash deposited is small in the vicinity of the DPF inlet, and gradually increases along the flow direction of the exhaust gas on the parallel walls. Since the amount of deposit increases and the deposit is deposited so that the amount of deposit is the largest at the bottom, CaSO ₄ having a large particle size and deposited on the DPF is reduced in a reducing atmosphere to CaSO ₃ , and the Ca ions of CaSO ₃ However, when combined with the solid acid on the surface of the DPF, it becomes easier to bind with the solid acid on the surface of the DPF depending on the distribution of the amount of ash deposited, and then SO ₄ is present in the atmosphere. Then, Ca on the surface of the DPF combines with SO _{4 in} the atmosphere to become CaSO ₄ and 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. Therefore, the ash is efficiently removed according to the distribution of the accumulation amount in the DPF, and the exhaust gas purification of the internal combustion engine can suppress the increase in pressure loss, the increase in PM regeneration temperature, and the decrease in fuel consumption over a long period of time. An apparatus is provided.

According to the invention described in each claim, the ash regeneration configuration is provided, and the ash is efficiently 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 has 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 a DPF, (a) is a diagram illustrating the entire DPF, and (b) is a diagram illustrating a state inside the DPF. It is a figure expanded and demonstrated.
FIG. 2 is a diagram illustrating a schematic configuration of the embodiment when the present invention is applied to an exhaust gas purification apparatus for an internal combustion engine.

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. 2 is a diagram for explaining a schematic configuration of the embodiment when the present invention is applied to an exhaust gas purification apparatus for an internal combustion engine. On the surface of the DPF 2, specifically, on the surface of the DPF base material of the DPF 2, A solid acid corresponding to an acid strength of SO ₃ or higher and SO ₄ or lower is applied. The exhaust gas from the internal combustion engine is guided to the DPF 2, and the PM in the exhaust gas is collected and removed by the DPF 2, and the exhaust gas from which the PM has been removed is discharged. Since the PM collected in the DPF gradually accumulates, PM regeneration operation is performed periodically or by detecting a decrease in the performance of the DPF and burning and removing the PM collected in the DPF.

However, if the PM regeneration operation is repeatedly performed, the ash 3 accumulates in the DPF, and even if the PM regeneration operation is performed, the pressure loss of the DPF 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, since the ash 3 deposited in the DPF is reduced in size, the reduced size particles 4 pass through the filter gap of the DPF and are discharged together with the exhaust gas.

In this case, as shown in FIG. 1B, the DPF 2 has a wall portion 11 that is parallel to the flow of the exhaust gas, and a bottom portion 12 on the opposite side of the DPF from the exhaust gas inlet. The ash 3 is deposited so that the amount of accumulation is small near the entrance of the DPF 2, the amount of accumulation gradually increases along the flow direction of the exhaust gas in the parallel walls 11, and the amount of accumulation is the largest at the bottom 12. .

Therefore, it is necessary to further decompose the accumulated ash 3 according to the amount of accumulation from the vicinity of the DPF entrance toward the bottom 12.

Therefore, in the present invention, when the DPF 2 is configured by coating the surface of the DPF 2 with the solid acid 6 having an acid strength stronger than that of SO _{3 and} weaker than that of SO ₄ , as shown in FIG. On the surface, the coating amount of the solid acid 6 is coated so that the bottom portion 12 is larger than the vicinity of the exhaust gas inlet of the parallel wall portion 11 of the DPF 2. For example, in one embodiment, the solid gas is not coated in the vicinity of the exhaust gas inlet of the parallel wall portion 11 of the DPF 2 and only the bottom portion is coated, or in another embodiment, the parallel wall portion 11 of the DPF 2 is coated. The solid acid is coated with a thickness t ₁ from the exhaust gas inlet to a predetermined distance a, and then solid with a thickness t ₂ greater than t ₁ from the distance a to the bottom (ie, t ₁ <t ₂ ). In another embodiment, the coating amount is gradually increased from the vicinity of the exhaust gas inlet of the parallel wall portion 11 of the DPF 2 toward the bottom portion 12, and the coating amount is maximized at the bottom portion 12. Coating with solid acid. Although FIG. 1A schematically illustrates the coating amount of the solid acid 6, the solid acid 6 is actually coated on the inner surface of the DPF 2.

Therefore, the solid acid 6 having an acid strength of SO ₃ or higher and SO ₄ or lower is formed on the base material on the inner surface of the DPF 2, as shown in FIG. Coating is performed so that the bottom 12 is larger than in the vicinity of the gas inlet, and during the ash regeneration operation, the air-fuel ratio of the atmosphere in the DPF 2 is first changed to a stoichiometric or air-fuel ratio rich atmosphere and then changed to an air-fuel ratio lean atmosphere. As a result of the control, the ash 3 having a large particle size in the DPF 2 is decomposed more from the vicinity of the entrance of the DPF 2 toward the bottom 12 in accordance with the distribution of the accumulation amount of the ash 3, and an efficient ash regeneration operation is performed. It can be carried out.

In addition, as shown in FIG. 1A, the solid acid 6 is coated such that the bottom 12 is larger than the vicinity of the exhaust gas inlet of the parallel wall 11 of the DPF 2, which means that the exhaust gas passing through the DPF 2 is exhausted. Since the pressure loss of the flow of gas passing through the wall portion 11 can be reduced, there is also an effect that the pressure loss can be reduced as a whole of the DPF 2.

As described above, according to the present invention, it is possible to effectively configure an exhaust gas purification apparatus for an internal combustion engine having a DPF whose performance does not deteriorate indefinitely, and to dramatically improve the performance of the DPF over a long period of time. There is an advantageous effect of being able to. 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 6 Solid acid 11 Wall 12 Bottom

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 has a wall portion parallel to the flow of exhaust gas, and a bottom portion opposite to the exhaust gas inlet of the DPF;
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 ;
The coating is characterized in that the coating amount of the solid acid is larger at the bottom than in the vicinity of the exhaust gas inlet of the parallel wall of the DPF.
An exhaust purification device for an internal combustion engine.
The coating is a coating in which the coating amount of the solid acid increases from the vicinity of the exhaust gas inlet of the parallel wall portion toward the bottom portion of the DPF, and the coating amount of the solid acid increases at the bottom portion. Characterized by the
The exhaust emission control device for an internal combustion engine according to claim 1.