JP2004060494A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of removing NOx and particulate matter while the number of filters or catalysts is decreased. <P>SOLUTION: The exhaust emission control device of the internal combustion engine is equipped with particulate filters 5 installed in an exhaust passage 4 of the internal combustion engine 1 and capable of temporarily capturing the particulate matter contained in the exhaust gas and carrying an ammonia selecting reductive catalyst and a urea supplying means 10 to supply urea from upstream of the particulate filter. According to this constitution in which the ammonia selecting reductive catalyst is carried by the particulate filter 5, capturing the particulate matter and reducing the NOx can be performed using one filter, it is possible to decrease the number of catalysts and the filters. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine.
[0002]
[Prior art]
While diesel engines are excellent in economic efficiency, it is important to remove particulate matter (PM) represented by soot, which is a suspended particulate matter contained in exhaust gas. Has become. For this reason, a technique is known in which a particulate filter (hereinafter, simply referred to as a “filter”) for trapping PM is provided in an exhaust system of a diesel engine so that PM is not released into the atmosphere.
[0003]
This filter can prevent PM in exhaust gas from being once collected and released into the atmosphere. However, when the PM collected by the filter accumulates on the filter, the filter may be clogged. When the clogging occurs, the pressure of the exhaust gas upstream of the filter increases, which may cause a decrease in the output of the internal combustion engine or damage to the filter. In such a case, the PM deposited on the filter can be ignited and burned to remove the PM. Removing PM accumulated on the filter in this way is called filter regeneration.
[0004]
On the other hand, lean NOx catalysts such as a selective reduction type NOx catalyst and a storage reduction type NOx catalyst are known as one of means for reducing nitrogen oxides (NOx) contained in exhaust gas of an internal combustion engine capable of lean combustion.
[0005]
The selective reduction type NOx catalyst is a catalyst that reduces nitrogen oxides (NOx) when a reducing agent is present in an oxygen-excess atmosphere.
[0006]
In order to purify nitrogen oxides (NOx) using this selective reduction type NOx catalyst, an appropriate amount of a reducing agent is required. Techniques using hydrocarbon (HC), ammonia-derived compounds, and the like as the reducing agent have been developed.
[0007]
For example, in the technique described in Japanese Patent Application Laid-Open No. 2000-8833, a filter capable of collecting particulate matter and supporting an oxidation catalyst is provided in an exhaust passage, and urea is further added to the filter. Urea is hydrolyzed to produce ammonia, which is oxidized by an oxidation catalyst to form NO.₂It becomes. This NO₂The material on the particles collected by the filter is removed by the above. NOx flowing out of the filter is removed by a NOx catalyst provided downstream of the filter.
[0008]
[Problems to be solved by the invention]
However, since it is necessary to provide a filter and a NOx catalyst, it is difficult to secure a mounting space in a vehicle, and the cost increases.
[0009]
The present invention has been made in view of the above-described problems, and provides a technique capable of removing NOx and particulate matter while reducing the number of filters or catalysts in an exhaust gas purification device for an internal combustion engine. The purpose is to do.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention employs the following means. That is,
A particulate filter provided in an exhaust passage of the internal combustion engine, capable of temporarily collecting particulate matter in exhaust gas, and carrying an ammonia selective reduction catalyst;
Urea supply means for supplying urea from upstream of the particulate filter,
It is characterized by having.
[0011]
The greatest feature of the present invention is that, in an exhaust gas purifying apparatus for an internal combustion engine, NOx reducing ability is added to a particulate filter, and collection of particulate matter in exhaust gas and purification of NOx are performed by one filter. .
[0012]
In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, when the exhaust gas passes through the particulate filter, the particulate matter contained in the exhaust gas is collected by the particulate filter. Further, NOx in the exhaust gas is reduced by the ammonia selective reduction catalyst. Here, by supporting the particulate selective filter with the ammonia selective reduction catalyst, the contact area between the ammonia selective reduction catalyst and the exhaust gas is increased, so that the chance of NOx in the exhaust gas contacting the ammonia reduction catalyst is increased. Therefore, the NOx reduction rate by the ammonia reduction catalyst can be improved. In this way, it is possible to remove particulate matter in exhaust gas and purify NOx with one filter.
[0013]
In the present invention, a urea hydrolysis catalyst may be further provided.
[0014]
Urea is easily converted to ammonia by the urea hydrolysis catalyst, and ammonia can be used as a reducing agent to reduce NOx in the ammonia selective reduction catalyst.
[0015]
In the present invention, the urea hydrolysis catalyst may be at least one of alumina, titania, silica, zirconia, and zeolite.
[0016]
By using such a material, urea can be efficiently hydrolyzed.
[0017]
In the present invention, the ammonia selective reduction catalyst may be at least one of titania-vanadium, zeolite, chromium, manganese, molybdenum, and tungsten.
[0018]
By using such a material, NOx can be efficiently reduced.
[0019]
In the present invention, the ammonia selective reduction catalyst may be carried more in the partition wall than in the partition wall surface of the particulate filter.
[0020]
In the wall surface of the particulate filter, there are countless pores serving as exhaust passages. As the exhaust gas passes through the pores, particulate matter contained in the exhaust gas is collected. Here, by supporting the ammonia selective reduction catalyst in the partition, it is possible to widen the surface of the ammonia selective reduction catalyst in contact with the exhaust gas, thereby facilitating the reduction of NOx. In addition, it is possible to support another type of catalyst on the wall surface of the partition.
[0021]
In the present invention, a large amount of the ammonia selective reduction catalyst may be carried in a central portion of the particulate filter.
[0022]
By supporting a large amount of the ammonia selective reduction catalyst in the central portion of the particulate filter, it becomes possible to support another type of catalyst on the upstream side and the downstream side of the particulate filter.
[0023]
In the present invention, the particulate filter may carry an ammonia oxidation catalyst.
[0024]
By carrying the ammonia oxidation catalyst in this way, even if urea is excessively supplied to the ammonia selective reduction catalyst, urea can be oxidized by the ammonia oxidation catalyst, so that the release of urea into the atmosphere can be reduced. It can be suppressed.
[0025]
In the present invention, an ammonia oxidation catalyst may be provided downstream of the particulate filter.
[0026]
By doing so, it is possible to oxidize the urea flowing out of the particulate filter by the downstream ammonia oxidation catalyst and suppress the release of urea to the atmosphere.
[0027]
In the present invention, the urea hydrolysis catalyst may be supported more on the upstream side than on the downstream side of the particulate filter.
[0028]
Since the exhaust gas passing through the filter first passes on the upstream side of the filter, if urea is hydrolyzed at this location, it becomes possible to supply ammonia to the ammonia selective reduction catalyst downstream therefrom.
[0029]
In the present invention, the urea hydrolysis catalyst may be carried more on the wall surface of the partition wall of the particulate filter facing upstream than the wall surface of the partition wall of the particulate filter facing downstream.
[0030]
Since the exhaust gas flowing into the partition wall of the particulate filter first passes through the wall surface facing the upstream side, if urea is hydrolyzed at this location, the ammonia generated when passing therethrough can be converted into an ammonia selective reduction catalyst. Can be supplied to
[0031]
In the present invention, the ammonia oxidation catalyst may be carried more on the downstream side than on the upstream side of the particulate filter.
[0032]
Since the exhaust gas reaches the ammonia oxidation catalyst after passing through the ammonia selective reduction catalyst, the ammonia flowing out of the ammonia selective reduction catalyst can be oxidized and removed by the ammonia oxidation catalyst.
[0033]
In the present invention, the ammonia oxidation catalyst may be carried more on the wall surface of the partition wall of the particulate filter facing downstream than the wall surface of the partition wall of the particulate filter facing upstream.
[0034]
Since the exhaust gas flowing out of the partition wall of the particulate filter always passes through the wall surface facing the downstream side, by carrying an ammonia oxidation catalyst on this wall surface, the ammonia flowing out of the ammonia selective reduction catalyst is oxidized and removed. It is possible to do.
[0035]
In the present invention, the particulate matter trapping amount estimating means for estimating the amount of particulate matter trapped by the particulate filter, and the amount of particulate matter estimated by the particulate matter trapping amount estimating means And a temperature increasing means for increasing the temperature of the particulate filter when the temperature of the particulate filter becomes equal to or more than a predetermined amount.
[0036]
When the amount of the particulate matter trapped in the filter is large, there is a possibility that the output of the engine is reduced or the filter is damaged. When the trapping amount of the particulate matter estimated by the trapping amount estimating means becomes equal to or more than a predetermined amount, the temperature of the particulate filter is increased by the temperature increasing means. As a result, the oxidation of the particulate matter can be promoted and removed.
[0037]
BEST MODE FOR CARRYING OUT THE INVENTION
<First embodiment>
Hereinafter, specific embodiments of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings. Here, an example in which the exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described.
[0038]
FIG. 1 is a diagram showing a schematic configuration of an engine according to the present embodiment and an intake and exhaust system thereof.
[0039]
The engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0040]
An exhaust branch pipe 3 is connected to the engine 1, and each branch pipe of the exhaust branch pipe 3 communicates with a combustion chamber of each cylinder 2 via an exhaust port (not shown). An exhaust pipe 4 is connected to the exhaust branch pipe 3.
[0041]
In the middle of the exhaust pipe 4, a particulate filter (hereinafter, simply referred to as a filter) 5 is provided. An exhaust temperature sensor 6 that outputs an electric signal corresponding to the temperature of the flowing exhaust gas is attached upstream of the filter 5.
[0042]
In the exhaust system configured as described above, the air-fuel mixture (burned gas) burned in each cylinder 2 of the engine 1 is discharged to the exhaust branch pipe 3 through the exhaust port, and then from the exhaust branch pipe 3 to the filter 5. Inflow. In the filter 5, PM in the exhaust gas is collected, and NOx is reduced.
[0043]
Next, the filter 5 according to the present embodiment will be described.
[0044]
FIG. 2 is a sectional view of the filter 5. FIG. 2A is a diagram illustrating a cross section in the lateral direction of the filter 5. FIG. 2B is a diagram illustrating a vertical cross section of the filter 5.
[0045]
As shown in FIGS. 2A and 2B, the filter 5 is a so-called wall flow type including a plurality of exhaust passages 50 and 51 extending in parallel with each other. These exhaust passages include an exhaust inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust outflow passage 51 whose upstream end is closed by a plug 53. In FIG. 2A, hatched portions indicate plugs 53. Accordingly, the exhaust inflow passages 50 and the exhaust outflow passages 51 are alternately arranged with the thin partition walls 54 interposed therebetween. In other words, the exhaust inflow passage 50 and the exhaust outflow passage 51 are arranged such that each exhaust inflow passage 50 is surrounded by four exhaust outflow passages 51 and each exhaust outflow passage 51 is surrounded by the four exhaust inflow passages 50.
[0046]
The filter 5 is made of, for example, a porous material such as cordierite, and has countless pores. Therefore, the exhaust gas that has flowed into the exhaust inflow passage 50 passes through the surrounding partition wall 54 and flows out into the adjacent exhaust outflow passage 51 as indicated by an arrow in FIG.
[0047]
Here, in the conventional exhaust gas purification device for an internal combustion engine, an ammonia oxidation catalyst is separately provided downstream of the ammonia selective reduction catalyst. When a urea hydrolysis catalyst was provided, a urea hydrolysis catalyst was separately provided upstream of the ammonia selective reduction catalyst. In addition, a filter may be provided to trap PM in the exhaust gas. As described above, when a plurality of catalysts and filters are separately provided, a space for mounting each of the catalysts and the filters is required, and there is a possibility that some restrictions may be imposed on mounting on a vehicle. In addition, installing a plurality of catalysts and filters increases costs. The higher the purification rate, the greater the catalyst capacity, the worse the mountability and the higher the cost. Further, when the catalyst capacity increases, the heat capacity of the catalyst also increases. Therefore, when it is necessary to raise the temperature of the catalyst and the filter at the time of PM regeneration or the like, for example, if the temperature of the filter is increased by supplying fuel, the fuel consumption is increased. As the amount increases, fuel economy will deteriorate.
[0048]
Therefore, in the present embodiment, the ammonia selective reduction catalyst is supported in the partition wall 54 of the filter 5, and the urea hydrolysis catalyst is further supported on the surface of the partition wall 54 on the exhaust inflow passage 50 side. Ammonia oxidation catalyst was carried on the surface of 54 to reduce the number of catalysts and filters. Thus, by reducing the number of catalysts and filters, a decrease in exhaust gas temperature can be suppressed.
[0049]
FIG. 3 is an enlarged view of a cross section of the partition wall (X portion in FIG. 2B) of the filter.
[0050]
Exhaust flows in the direction of the arrow. A urea hydrolysis catalyst 501 is supported on the wall surface of each exhaust inflow passage 50 on the side where exhaust gas flows, and an ammonia selective reduction catalyst 502 is supported on a pore surface inside the partition wall 54 of the filter. An ammonia oxidation catalyst 503 is supported on the wall surface of the exhaust outlet passage 51. Therefore, the exhaust gas passing through the partition 54 passes through the urea hydrolysis catalyst 501, the ammonia selective reduction catalyst 502, and the ammonia oxidation catalyst 503 in this order.
[0051]
The filter 5 according to the present embodiment can be manufactured, for example, as follows. First, the entire filter 5 is immersed in a tank filled with the ammonia selective reduction catalyst, and the ammonia selective reduction catalyst is carried in the pores. Next, the pores of the filter 5 are filled with a filler so that gas and liquid cannot pass through the partition wall 54. The filler used at this time has the property of sublimating at a high temperature. Thereafter, only the wall surface of each exhaust inflow passage 50 on the side where exhaust gas flows in is dipped in the urea hydrolysis catalyst, and then only the wall surface of each exhaust outflow passage 51 on the side where exhaust gas flows out is dipped in the ammonia oxidation catalyst. Finally, the temperature of the filter 5 is raised to sublime the filler in the pores.
[0052]
In this way, the urea hydrolysis catalyst 501 is supported on the wall surface of each exhaust inflow passage 50 on the side where the exhaust gas flows, and the ammonia selective reduction catalyst 502 is supported on the pore inner wall surface inside the partition wall 54 of the filter. The ammonia oxidation catalyst 503 can be carried on the wall surface of each exhaust outflow passage 51 on the side from which water flows out.
[0053]
Here, the urea hydrolysis catalyst 501 is at least one of alumina, titania, silica, zirconia, and zeolite.
[0054]
The ammonia selective reduction catalyst 502 is at least one of titania-vanadium, zeolite, chromium, manganese, molybdenum, and tungsten.
[0055]
In the filter 5 configured as described above, the urea aqueous solution that has reached the urea hydrolysis catalyst 501 is hydrolyzed to generate ammonia. The ammonia flows into the partition wall 54 together with the exhaust gas, and the NO and NO in the exhaust gas are exhausted by the ammonia selective reduction catalyst 502.₂To reduce. Ammonia not reacted by the ammonia selective reduction catalyst 502 is oxidized by the ammonia oxidation catalyst 503 when flowing out of the partition wall 54.
[0056]
Such a reaction suppresses the emission of ammonia into the atmosphere while purifying NOx in the exhaust gas.
[0057]
In this embodiment, a urea addition mechanism for adding an aqueous urea solution to the filter 5 is provided. The urea addition mechanism includes a tank 7 for storing an aqueous urea solution, a supply pipe 8 as a flow path for the aqueous urea solution, a pump 9 provided in the flow path, and an injection nozzle 10 for injecting the aqueous urea solution into the exhaust pipe 4. It is configured.
[0058]
In the urea addition mechanism configured as described above, an aqueous urea solution adjusted in advance to a predetermined concentration is stored in the tank 7, and when the pump 9 operates, the aqueous urea solution is pumped out of the tank 7. Then, the urea aqueous solution reaches the injection nozzle 10 via the supply pipe 8. The urea aqueous solution that has reached the injection nozzle 10 is injected into the exhaust pipe 4 when the injection nozzle 10 is opened, and flows downstream together with exhaust flowing from the upstream of the exhaust pipe 4. The injection amount of the aqueous urea solution injected at this time is adjusted by the valve opening time of the injection nozzle 10.
[0059]
The urea aqueous solution that has reached the urea hydrolysis catalyst 501 is hydrolyzed to generate ammonia as in the following equation.
[0060]
(NH₂)₂CO + H₂O → CO₂+ 2NH₃
When this ammonia reaches the ammonia selective reduction catalyst 502, the NO, NO₂Is reduced.
[0061]
6NO + 4NH₃→ 5N₂+ 6H₂O
6NO₂+ 8NH₃→ 7N₂+ 12H₂O
By the way, even if the injection amount of the aqueous urea solution is controlled so that the equivalent ratio between the amount of NOx flowing into the ammonia selective reduction catalyst 502 and the urea in the aqueous urea solution becomes 1, not all the NOx can be reduced. Here, the NOx reduction rate can be improved by excessively supplying the urea aqueous solution. However, when the urea aqueous solution is supplied in excess, excess ammonia is adsorbed on the ammonia selective reduction catalyst 502. The ammonia thus adsorbed flows out of the ammonia selective reduction catalyst 502 when the flow rate of the exhaust gas increases at a high load or the like, so that it is necessary to treat the ammonia.
[0062]
In the present embodiment, ammonia is oxidized and removed by the ammonia oxidation catalyst 503. That is, in an oxygen-excess atmosphere, NO is generated from a part of ammonia by the following equation.
[0063]
4NH₃+ 5O₂→ 4NO + 6H₂O
The NO generated in this way reacts with the remaining ammonia as shown in the following equation.
[0064]
4NH₃+ 4NO + 5O₂→ 4N₂+ 6H₂O
By such a reaction, ammonia is removed and emission into the atmosphere is suppressed.
[0065]
The engine 1 configured as described above is provided with an electronic control unit (ECU: Electronic Control Unit) 11 for controlling the engine 1. The ECU 11 is a unit that controls the operating state of the engine 1 according to the operating conditions of the engine 1 and the driver's requirements.
[0066]
Various sensors are connected to the ECU 11 via electric wiring, and output signals of the various sensors are input to the ECU 11. On the other hand, the pump 9, the injection nozzle 10, and the like are connected to the ECU 11 via electric wiring, so that these can be controlled. Further, the ECU 11 can store various application programs and various control maps and control the above-described urea addition mechanism.
[0067]
By the way, when the PM collected by the filter 5 accumulates on the filter 5, the filter 5 may be clogged. When the clogging occurs, the pressure of the exhaust gas upstream of the filter 5 increases, which may cause a decrease in the output of the engine 1 or damage to the filter 5. In such a case, it is necessary to regenerate the filter 5 for removing PM accumulated on the filter 5. In order to regenerate such a filter, it is necessary to increase the temperature of the filter 5.
[0068]
The regeneration of the filter 5 is performed when the amount of PM collected by the filter 5 becomes larger than a predetermined allowable amount. The allowable value is a value that can prevent the output of the engine 1 from lowering and the filter 5 from being damaged, and is determined by experiments or the like. Further, the amount of PM collected by the filter 5 is determined, for example, by attaching a differential pressure sensor (not shown) for detecting a differential pressure between the front and rear of the filter 5 and performing an experiment on the PM amount according to the detection value of the differential pressure sensor in advance. It can be obtained by obtaining in advance. In addition, a map of the PM generation amount according to the operating state may be obtained in advance by experiments or the like, and the PM generation amount obtained from this map may be integrated to obtain the PM collection amount. Further, the amount of accumulated PM may be estimated according to the traveling distance or traveling time of the vehicle.
[0069]
As a method of regenerating such a filter 5, as a method of adding fuel to exhaust gas or increasing the amount of recirculated EGR gas to increase the amount of generated soot to a maximum, the EGR gas amount is further reduced. Methods of increasing low-temperature combustion (Japanese Patent No. 3116876), a method of injecting fuel again during an expansion stroke or an exhaust stroke after a main injection for injecting fuel for engine output, and the like are conceivable.
[0070]
For example, the fuel injected by the sub-injection burns in the cylinder 2 to increase the gas temperature in the cylinder 2 and decrease the oxygen concentration in the cylinder 2. The gas whose temperature has risen by burning in the cylinder 2 becomes exhaust gas, reaches the filter through the exhaust pipe 4, and increases the temperature of the filter. Thereby, the PM is burned and removed. Note that the temperature of the filter 5 is estimated based on the output signal of the exhaust temperature sensor 6, and is raised to a predetermined temperature while preventing the filter 5 from overheating.
[0071]
Here, the relationship between the accelerator opening, the engine speed, and the sub-injection amount or the sub-injection timing is obtained in advance through experiments or the like, mapped and stored in the ECU 11. The amount and timing of the sub-injection can be calculated from the map, the accelerator opening, and the engine speed.
[0072]
Further, when urea is added to the filter 5 by the urea addition mechanism, heat is generated by a chemical reaction. Therefore, if the PM is regenerated at this time, the temperature of the filter can be easily increased.
[0073]
As described above, according to the present embodiment, the ammonia selective reduction catalyst 502 is supported in the partition wall 54 of the filter 5, and the urea hydrolysis catalyst 501 is further supported on the surface of the partition wall 54 on the side where exhaust gas flows. The number of catalysts and filters can be reduced by supporting the ammonia oxidation catalyst 503 on the surface of the partition wall 54 on the side from which exhaust gas flows. Then, PM in the exhaust gas can be collected by the filter 5, and NOx can be purified by the ammonia selective reduction catalyst 502.
<Second embodiment>
This embodiment differs from the first embodiment in the following points. That is, in the present embodiment, the urea hydrolyzate is formed on the peripheral wall surfaces of the exhaust inflow passages 50 and the exhaust outflow passages 51 on the upstream side of the filter, that is, on both side surfaces of the upstream partition walls 54 and on the inner wall surfaces of the pores in the partition walls 54. The decomposition catalyst is supported, and ammonia is selected on the peripheral wall surfaces of the exhaust inflow passages 50 and the exhaust outflow passages 51 at the center of the filter, that is, on both side surfaces of the partition walls 54 at the center and on the inner wall surfaces of the pores in the partition walls 54. The reduction catalyst is supported, and ammonia oxidation is performed on the peripheral wall surfaces of the exhaust inflow passages 50 and the exhaust outflow passages 51 on the downstream side of the filter, that is, on both side surfaces of the partition walls 54 on the downstream side and on the inner wall surfaces of the pores in the partition walls 54. The catalyst is supported. In the present embodiment, although the positional relationship of the catalyst carried on the filter 5 is different from that of the first embodiment, the basic configuration of the engine 1 and other hardware to be applied is as follows. The description is omitted because it is common to the first embodiment.
[0074]
FIG. 4 is a diagram showing an arrangement relationship of the catalyst carried on the filter according to the present embodiment. In the figure, a range A carries a urea hydrolysis catalyst, a range B carries an ammonia selective reduction catalyst, and a range C carries an ammonia oxidation catalyst.
[0075]
The filter according to the present embodiment can be manufactured, for example, as follows. First, after filling the pores in the range A with the filler, the ranges A and B are immersed in a tank filled with the ammonia selective reduction catalyst. This filler has a property of sublimating due to an increase in temperature. Thereby, the ammonia selective reduction catalyst is supported in the range of B. Next, the temperature of the filter is raised to sublime the filler in the pores in the range of A. Thereafter, only the range A is dipped in the urea hydrolysis catalyst, and then only the range C is dipped in the ammonia oxidation catalyst. Thus, the urea hydrolysis catalyst can be supported in the range A, the ammonia selective reduction catalyst can be supported in the range B, and the ammonia oxidation catalyst can be supported in the range C.
[0076]
In the filter configured as described above, the aqueous urea solution injected from the injection nozzle first passes through the range A. Here, the urea aqueous solution is hydrolyzed to generate ammonia. The generated ammonia flows downstream with the exhaust gas and passes through the range B. At that time, NO, NO₂To reduce.
[0077]
Then, when the flow rate of the exhaust gas increases at a high load or the like, the ammonia flowing out of the ammonia selective reduction catalyst is oxidized when passing through the range of C. Thereby, ammonia is removed, and emission to the atmosphere is suppressed.
[0078]
The method of removing PM trapped by the filter is the same as in the first embodiment, and a description thereof will be omitted.
[0079]
As described above, according to the present embodiment, the number of catalysts and filters can be reduced by supporting the urea hydrolysis catalyst, the ammonia selective reduction catalyst, and the ammonia oxidation catalyst in this order from the upstream side of the filter 5. it can. Then, PM in the exhaust gas can be collected by the filter 5, and NOx can be purified by the ammonia selective reduction catalyst.
<Third embodiment>
FIG. 5 is a diagram showing an arrangement relationship between the catalyst and the filter according to the present embodiment.
[0080]
This embodiment differs from the first embodiment in the following points. That is, in the present embodiment, the urea hydrolysis catalyst 12, the particulate filter 5 carrying the ammonia selective reduction catalyst, and the ammonia oxidation catalyst 13 are provided in the exhaust pipe in this order from the upstream. The present embodiment is different from the first embodiment in that the urea hydrolysis catalyst 12 and the ammonia oxidation catalyst 13 are separated, but the engine 1 and other hardware to be applied are different. The basic configuration is common to that of the first embodiment and will not be described.
[0081]
In the exhaust gas purifying apparatus for an internal combustion engine thus configured, the aqueous urea solution injected from the injection nozzle 10 first passes through the urea hydrolysis catalyst 12. Here, the urea aqueous solution is hydrolyzed to generate ammonia.
[0082]
This ammonia flows out of the urea hydrolysis catalyst 12 together with the exhaust gas. The ammonia that has flowed downstream passes through NO and NO in the exhaust gas when passing through the particulate filter 5 carrying the ammonia selective reduction catalyst.₂To reduce. Further, PM in the exhaust gas is collected by the filter 5.
[0083]
Then, when the flow rate of the exhaust gas increases at the time of a high load or the like, the ammonia flowing out of the ammonia selective reduction catalyst is oxidized when passing through the ammonia oxidation catalyst 13 at the most downstream. Thereby, ammonia is removed, and emission to the atmosphere is suppressed.
[0084]
Note that the method of removing PM trapped by the filter 5 is the same as that of the first embodiment, and will not be described.
[0085]
As described above, according to the present embodiment, the urea hydrolysis catalyst 12, the filter 5 carrying the ammonia selective reduction catalyst, and the ammonia oxidation catalyst 13 are provided in the middle of the exhaust pipe 4 in order from the upstream side. The number of filters can be reduced. Then, PM in the exhaust gas can be collected by the filter 5, and NOx can be purified by the ammonia selective reduction catalyst.
<Fourth embodiment>
FIG. 6 is a diagram showing an arrangement relationship between the catalyst and the filter according to the present embodiment.
[0086]
This embodiment differs from the first embodiment in the following points. That is, in the present embodiment, the oxidation catalyst 14 is provided in the exhaust pipe upstream of the filter. Although the present embodiment differs from the first embodiment in that an oxidation catalyst is provided upstream of the filter, the basic configuration of the engine 1 and other hardware to be applied is different from the first embodiment. The description is omitted because it is common to the first embodiment.
[0087]
In the exhaust gas purifying apparatus for an internal combustion engine thus configured, NO in the exhaust gas is oxidized by the oxidation catalyst 14 and NO₂It becomes. This NO₂Is more liable to react on the ammonia selective reduction catalyst than NO. Therefore, the reduction rate of NOx is improved, and the amount of NOx released into the atmosphere can be reduced.
[0088]
Further, the oxidation catalyst 14 can suppress the hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas from being oxidized and released into the atmosphere. Since heat is generated when carbon (CO) is oxidized, the downstream filter 5 can be heated. Here, the ammonia selective reduction catalyst cannot sufficiently reduce NOx unless the temperature reaches, for example, 350 ° C. or higher. However, since the temperature of the filter 5 can be increased by the heat generated by the oxidation catalyst 14 even at the time of starting the engine, NOx can be reduced.
[0089]
Incidentally, the oxidation catalyst 14 shown in the present embodiment can be provided upstream of the filter 5 shown in the second and third embodiments, and the same effect can be obtained.
[0090]
【The invention's effect】
In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the collection of particulate matter and the purification of NOx are performed in one filter by carrying the ammonia selective reduction catalyst, the urea hydrolysis catalyst, and the ammonia oxidation catalyst on the particulate filter. Can be easily mounted on a vehicle.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an engine according to a first embodiment and an intake / exhaust system thereof.
FIG. 2A is a diagram illustrating a cross section of a particulate filter in a lateral direction. (B) is a figure which shows the longitudinal cross section of a particulate filter.
FIG. 3 is an enlarged view of a cross section of a partition wall (X part in FIG. 2B) of the filter.
FIG. 4 is a diagram showing an arrangement relationship of a catalyst carried on a filter according to a second embodiment.
FIG. 5 is a diagram showing an arrangement relationship between a catalyst and a filter according to a third embodiment.
FIG. 6 is a diagram showing an arrangement relationship between a catalyst and a filter according to a fourth embodiment.
[Explanation of symbols]
1. Engine
2 .... cylinder
3 ... Exhaust branch pipe
4 ... Exhaust pipe
5 ... Particulate filter
6. Exhaust gas temperature sensor
7. Tank
8 ··· Supply pipe
9 Pump
10 ・ ・ ・ Injection nozzle
11 ・ ・ ・ ECU
12 ・ ・ ・ Urea hydrolysis catalyst
13 ... Ammonia oxidation catalyst
14 ... oxidation catalyst
50 ・ ・ ・ Exhaust inflow passage
51 ・ ・ ・ Exhaust outflow passage
52 ... stopper
53 ... stopper
54 ... partition wall
501 ・ ・ Urea hydrolysis catalyst
502..Ammonia selective reduction catalyst
503..Ammonia oxidation catalyst

Claims (13)

A particulate filter provided in an exhaust passage of the internal combustion engine, capable of temporarily collecting particulate matter in exhaust gas, and carrying an ammonia selective reduction catalyst;
Urea supply means for supplying urea from upstream of the particulate filter,
An exhaust gas purification device for an internal combustion engine, comprising: The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, further comprising a urea hydrolysis catalyst. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the urea hydrolysis catalyst is at least one of alumina, titania, silica, zirconia, and zeolite. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the ammonia selective reduction catalyst is at least one of titania-vanadium, zeolite, chromium, manganese, molybdenum, and tungsten. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the ammonia selective reduction catalyst is carried in the partition wall more than the wall surface of the partition wall of the particulate filter. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein a large amount of the ammonia selective reduction catalyst is carried in a central portion of the particulate filter. The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 6, wherein an ammonia oxidation catalyst is carried on the particulate filter. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 6, further comprising an ammonia oxidation catalyst provided downstream of the particulate filter. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein a larger amount of the urea hydrolysis catalyst is carried on the upstream side than on the downstream side of the particulate filter. The urea hydrolysis catalyst is more supported on the wall surface of the partition wall of the particulate filter facing upstream than the wall surface of the partition wall of the particulate filter facing downstream. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. The exhaust gas purification apparatus for an internal combustion engine according to claim 7, wherein a larger amount of the ammonia oxidation catalyst is carried on a downstream side than on an upstream side of the particulate filter. The said ammonia oxidation catalyst is carried more on the wall surface of the partition of the said particulate filter which faced downstream rather than the wall surface of the partition of the said particulate filter which faced the upstream, The claim 7 characterized by the above-mentioned. Exhaust purification device for internal combustion engine. Particulate matter trapping amount estimating means for estimating the amount of particulate matter trapped in the particulate filter, and the amount of particulate matter estimated by the particulate matter trapping amount estimating means is more than a predetermined amount 13. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, further comprising: a temperature increasing unit configured to increase a temperature of the particulate filter when the temperature of the particulate filter increases.

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