WO2013005342A1 - Exhaust purification device for internal combustion engine - Google Patents

Abstract

Provided is an exhaust purification device for an internal combustion engine having a DPF disposed in an exhaust system of the internal combustion engine, wherein the accumulation of ash in the DPF is minimized, enabling increases in pressure loss, increases in PM regeneration temperature, and reductions in fuel consumption to be minimized over the long term. In the DPF, which is coated with a solid acid, the acid strength of which, on the surface of the DPF, is greater than acid strength of SO₃ but less than the acid strength of SO₄, a PM regeneration operation is carried out before an ash regeneration operation is carried out.

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 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, when performing the above ash reproduction | regeneration operation | movement, the ash is normally in the state buried in PM deposited in DPF. Therefore, even trying to ash reproduced in this state, in order to CaSO ₄ deposited in the DPF with large grain size to the size of the sub-micron can not be in contact with a reducing atmosphere, SO ₄ of CaSO ₄ is reduced Not. Alternatively, the ash reduced to CaSO ₃ cannot contact the solid acid on the surface of the DPF. Therefore, there is a problem that the ash cannot be decomposed.

In order to solve this problem, in the present invention, PM accumulated in the DPF is burned and removed by performing the PM regeneration operation before performing the ash regeneration operation. Therefore, CaSO ₄ having a large particle size that has been buried in PM is exposed to a reducing atmosphere, and the ash that has been reduced to CaSO ₃ becomes solid acid on the surface of the DPF. The ash regeneration operation effectively proceeds.

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 includes an ash regeneration operation control that removes ash accumulated in the DPF. The control for increasing the temperature and the 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 performed before the control for increasing the temperature of the DPF. Provided is an exhaust gas purification apparatus for an internal combustion engine, which is controlled to change to an atmosphere and then to an air-fuel ratio lean atmosphere, and performs PM regeneration operation before performing ash regeneration operation.

That is, according to the first aspect of the present invention, the PM regeneration operation is performed before the ash regeneration operation. Therefore, CaSO ₄ having a large particle size that has been buried in PM is exposed to a reducing atmosphere, and the ash that has been reduced to CaSO ₃ becomes solid acid on the surface of the DPF. The ash regeneration operation following the PM regeneration operation effectively proceeds. As a result, an exhaust gas purification apparatus for an internal combustion engine is provided in which ash is completely removed and an increase in pressure loss, an increase in PM regeneration temperature, and a decrease in fuel consumption can be suppressed over a long period of time.

According to the first aspect of the present invention, the ash regeneration operation proceeds effectively, the ash is completely removed in the ash regeneration operation, and the pressure loss increases, the PM regeneration temperature increases, and the fuel consumption decreases over a long period of time. This provides an effect of providing an exhaust gas purification device for an internal combustion engine that can suppress the above-described problem.

FIG. 1 is a diagram illustrating contact of ash with a solid acid in an embodiment in which the present invention is applied to a DPF of the present invention.
FIG. 2 is a diagram for explaining the presence state of ash before the present invention is carried out on the DPF of the present invention.
FIG. 3 is a diagram illustrating contact of ash with a solid acid in another embodiment in which the present invention is applied to the DPF of the present invention.
FIG. 4 is a diagram for explaining similarities and differences between a regeneration (hereinafter referred to as “S regeneration”) operation condition and an ash regeneration operation condition of a sulfur-poisoned NOx storage reduction catalyst (hereinafter referred to as “NSR”). (A) is a figure explaining the atmosphere in S reproduction | regeneration, (b) is a figure explaining the atmosphere in ash reproduction | regeneration.
FIG. 5 is a diagram for explaining the timing of PM regeneration and S regeneration of ash regeneration according to 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. 2 is a diagram for explaining the presence state of ash before the present invention is carried out on the DPF of the present invention. Usually, the ash is buried in the PM deposited in the DPF as shown in FIG. Therefore, even trying to ash reproduced in this state, in order to CaSO ₄ deposited in the DPF with large grain size to the size of the sub-micron can not be in contact with a reducing atmosphere, SO ₄ of CaSO ₄ is reduced Not. Alternatively, the ash reduced to CaSO ₃ cannot contact the solid acid on the surface of the DPF. Therefore, the ash cannot be decomposed as it is.

FIG. 1 is a diagram illustrating contact of ash with a solid acid in an embodiment in which the present invention is applied to a DPF of the present invention. The state in which the solid acid is coated on the surface of the DPF will be described in detail. The carrier 61 is distributed on the DPF substrate 5, and the acid points 62 of the solid acid are scattered on the carrier 61. The ash Ca ions reduced to CaSO ₃ in the reducing atmosphere are bonded to the acid sites 62 of the solid acid and dispersed atomically on the surface of the DPF.

Therefore, in the present invention, when the PM regeneration operation is performed before the ash regeneration operation, as shown in FIG. 1, the CaSO ₄ having a large particle size that was buried in the PM is exposed to a reducing atmosphere. In addition, the ash Ca ions reduced to CaSO ₃ can bind to the acid sites 62 of the solid acid on the surface of the DPF. Therefore, the ash regeneration operation following the PM regeneration operation effectively proceeds.

FIG. 4 illustrates, as an example, similarities and differences between the NSR S regeneration operation condition and the ash regeneration operation condition when the NSR and the DPF are separately installed and a DPR is provided downstream of the NSR. (A) is a figure explaining the atmosphere in S reproduction | regeneration, (b) is a figure explaining the atmosphere in ash reproduction | regeneration. The state of the NSR entrance is indicated by IN, and the state of the NSR exit is indicated by OUT. That is, OUT represents the state of the DPR entrance. Reference numeral 20 denotes a reducing agent, and (a) indicates that the reducing agent 20 is injected.

That is, the conditions for the S regeneration are that the temperature is 600 ° C. or higher, the air-fuel ratio is rich, and the presence of a reducing agent is essential. The control trigger is the S accumulation amount.

On the other hand, the conditions for the ash regeneration are that the temperature is 600 ° C. or higher and that the atmosphere is a reducing atmosphere, and if it is an oxygen-free atmosphere, a reducing agent may be present but it is not necessary. The control trigger is the ash deposition amount.

Therefore, when the ash playback condition and the S playback condition are compared, if the ash playback and the S playback trigger timing match, the S playback can be performed and the ash playback can be omitted.

Note that the PM regeneration condition requires that the temperature is 600 ° C. or higher, the air-fuel ratio is lean, and no reducing agent is required. The control trigger is the PM accumulation amount.

An example of the relationship between these control timings is shown in FIG. FIG. 5 exemplifies the required timings for PM regeneration, ash regeneration, and S regeneration with respect to the travel distance. Circle marks indicate the necessary timings, which are implemented among the circle marks. Things are painted black. P is PM regeneration, A is ash regeneration, and S is S regeneration. At the timing indicated by I in FIG. 5, PM regeneration is first performed, and then S regeneration is performed. At the timing indicated by II in FIG. 5, PM regeneration is first performed, and then ash regeneration is performed. At the timing indicated by III in FIG. 5, all trigger timings of PM regeneration, ash regeneration, and S regeneration coincide with each other. In this case, PM regeneration is performed first, and then S regeneration is performed. The ash is removed from the DPF by the S regeneration operation without performing the ash regeneration control.

FIG. 3 is a diagram illustrating contact of ash with a solid acid in another embodiment in which the present invention is applied to the DPF of the present invention. That is, in the present invention, when performing PM regeneration operation before performing ash regeneration operation, CaSO ₄ having a large particle size that was buried in PM is exposed to a reducing atmosphere, Further, the ash reduced to CaSO ₃ comes into contact with the acid sites 62 of the solid acid on the surface of the DPF, but as shown in FIG. 3, the ash is exposed to a reducing atmosphere, and the ash If it comes into contact with the acid point 62 of the solid acid, PM may remain without completely removing PM, and the ash regeneration operation following the PM regeneration operation effectively proceeds.

1 Internal combustion engine 2 DPF
3 Ash 4 Fine particle 5 DPF base 6 Solid acid 10 PM
20 Reducing agent 61 Carrier 62 Solid acid point A Ash regeneration P PM regeneration S S regeneration

Claims (1)

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 ;
Furthermore, the ash regeneration operation control for removing the ash accumulated in the DPF is provided,
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.
Before performing the ash regeneration operation, PM regeneration operation is performed,
An exhaust purification device for an internal combustion engine.

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