Diesel particulate filter

Abstract

To suppress an increase of a pressure loss of a diesel particulate filter.SOLUTION: A diesel particulate filter of the present embodiment comprises an inlet end face located on an upstream side of an exhaust gas flow direction, an outlet end face located on a downstream side of the exhaust gas flow direction, a porous bulkhead for defining a plurality of flow passages for introducing an exhaust gas to the outlet end face side from the inlet end face side, and a sealing part for closing one-side end parts of the plurality of flow passages. The plurality of flow passages include a first flow passage having one end opened at the inlet end face and the other end closed thereat, and a second flow passage having one closed end and the other end which is opened at the outlet end face, being a second flow passage adjoining the first flow passage via the bulkhead. A surface of the bulkhead at the first flow passage side is covered with a film-shaped catalyst layer containing a particulate NOx adsorption material.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a diesel particulate filter.

Background Art

[0002] Devices for purifying exhaust gas discharged from internal combustion engines such as diesel engines are known. For example, Patent Document 1 below describes a device for regenerating a diesel particulate filter (DPF) that collects particulate matter (PM) in exhaust gas and burns and removes the PM collected in the DPF with NO2 having a high oxidation power. This DPF includes an inner layer portion that holds ceramic fibers carrying an HC adsorption catalyst and an outer layer portion that holds ceramic fibers carrying a reduction component concentration fluctuation type NOx purification catalyst, and collects PM contained in the exhaust gas flowing from the inner layer portion to the outer layer portion with the ceramic fibers held in the inner layer portion and the outer layer portion.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above exhaust gas purification device, PM contained in the exhaust gas is collected by the ceramic fibers when passing through the DPF and accumulates inside. When the amount of PM accumulated inside the ceramic fibers increases, the ceramic fibers become clogged and the pressure loss of the DPF increases. In particular, at the initial stage when PM collection is started from the unused state, PM easily enters the inside of the ceramic fibers and the pressure loss easily rises rapidly. The increase in the pressure loss of the DPF causes deterioration of the vehicle's fuel efficiency.

[0005] Therefore, the purpose of this disclosure is to provide a DPF that can suppress the increase in pressure loss. [Means for solving the problem]

[0006] In one embodiment, a diesel particulate filter is provided that is installed in the exhaust passage of an engine and collects particulate matter contained in the exhaust gas from the engine. This diesel particulate filter comprises an inlet end face located upstream in the direction of exhaust gas flow, an outlet end face located downstream in the direction of exhaust gas flow, a porous partition wall that defines a plurality of flow paths that guide the exhaust gas from the inlet end face side to the outlet end face side, and a sealing portion that closes one end of the plurality of flow paths. The plurality of flow paths include a first flow path having one end opening to the inlet end face and the other end being closed, and a second flow path having one end being closed and the other end opening to the outlet end face, and the second flow path adjacent to the first flow path via the partition wall, and the surface of the partition wall on the first flow path side is covered with a film-like catalyst layer containing a particulate NOx adsorbent.

[0007] In the exhaust gas purification device according to this embodiment, the surface of the partition wall on the first flow path side is covered with a film-like catalyst layer containing particulate NOx adsorbent. The NOx adsorbent effectively adsorbs NOx contained in the exhaust gas even when the exhaust gas temperature is low, such as during cold starts, thus improving the NOx purification rate at low temperatures. In addition, the film-like catalyst layer containing particulate NOx adsorbent also functions as a filter that suppresses particulate matter (PM) from entering the interior of the partition wall. By covering the surface of the partition wall on the first flow path side with the catalyst layer, PM in the exhaust gas tends to accumulate in front of the partition wall, suppressing its entry into the interior of the partition wall. As a result, the pressure loss of the diesel particulate filter can be suppressed.

[0008] In one embodiment, the average particle size of the NOx adsorbent contained in the catalyst layer may be between 10 nm and 1000 nm. By setting the average particle size of the NOx adsorbent to the above-mentioned particle size, the entry of PM into the partition wall can be more reliably suppressed, and PM can be accumulated in front of the partition wall. As a result, a rapid increase in pressure loss can be suppressed.

[0009] In one embodiment, the catalyst layer may contain ZrO2 as a NOx adsorbent. Since ZrO2 is a NOx adsorbent with high bulk density, the amount (mass) of NOx adsorbent supported on the diesel particulate filter can be increased. Therefore, NOx in the exhaust gas can be effectively adsorbed, and the NOx reduction performance can be improved. [Effects of the Invention]

[0010] According to one aspect and various embodiments of the present invention, it is possible to suppress the increase in pressure loss of the DPF. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing an exhaust gas purification device including a diesel particulate filter according to one embodiment. [Figure 2] This is a longitudinal cross-section of a diesel particulate filter. [Figure 3] This is a cross-sectional view along line III-III in Figure 2. [Modes for carrying out the invention]

[0012] Various embodiments will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts will be denoted by the same reference numerals, and redundant descriptions of the same or corresponding parts will be omitted. In this specification, the terms "upstream" and "downstream" refer to the direction of exhaust gas flow.

[0013] Figure 1 is a schematic diagram showing an exhaust gas purification device including a diesel particulate filter according to one embodiment. The exhaust gas purification device 10 is installed in a vehicle having an engine (internal combustion engine) 1 and purifies the exhaust gas discharged from the vehicle's engine 1.

[0014] Engine 1 is a diesel engine, for example, installed in a vehicle such as a truck, and generates driving force by burning fuel. An exhaust passage 2 is connected to Engine 1 via an exhaust manifold. Exhaust gas discharged from the exhaust manifold by the operation of Engine 1 is supplied to the exhaust gas purification device 10 through the exhaust passage 2.

[0015] The exhaust gas emitted from engine 1 contains pollutants such as particulate matter (PM), nitrogen oxides (NOx), and carbon monoxide (CO). PM is soot (dry soot) whose main component is carbon. NOx includes nitric oxide (NO), nitrogen dioxide (NO2), etc., which are generated by the combustion of fuel. The exhaust gas purification device 10 removes the pollutants contained in the exhaust gas and releases the purified exhaust gas outside the vehicle.

[0016] As shown in Figure 1, the exhaust gas purification device 10 includes an oxidation catalyst (DOC) 11, a diesel particulate filter (DPF) 12, a selective catalytic reduction (SCR) 13, and an ammonia slip catalyst (ASC) 14. These DOC 11, DPF 12, SCR 13, and ASC 14 are connected to the exhaust passage 2 in this order from the upstream side.

[0017] DOC11 oxidizes chemical substances contained in exhaust gas. DOC11 includes an alumina carrier supporting a precious metal catalyst such as platinum, rhodium, or palladium. DOC11 oxidizes and purifies hydrocarbons (HC) and carbon monoxide (CO) contained in exhaust gas, for example. In addition, DOC11 oxidizes NO contained in exhaust gas to NO2.

[0018] The DPF 12 is provided downstream of the DOC 11. The DPF 12 is a porous ceramic filter having a honeycomb structure, and collects PM contained in the exhaust gas. The DPF 12 supports a NOx adsorbent that adsorbs NOx. The NOx adsorbent is a catalyst that adsorbs NOx when the exhaust gas is at a low temperature and releases the adsorbed NOx when the exhaust gas is at a high temperature. The NOx adsorbent contains zirconia (ZrO2). For example, an oxide in which iron (Fe) is added to zirconia is used as the NOx adsorbent. Details of the DPF 12 will be described later.

[0019] The SCR 13 is provided downstream of the DPF 12. The SCR 13 reduces NOx contained in the exhaust gas using a reducing agent. For example, ammonia is used as the reducing agent. The SCR 13 contains, for example, copper or iron as a NOx reduction catalyst that reduces NOx. The NOx reduction catalyst is supported on an oxide carrier such as alumina or zirconia. The SCR 13 is activated at 200°C or higher and reduces NOx contained in the exhaust gas.

[0020] The ASC 14 is provided downstream of the SCR 13. The ASC 14 contains, for example, a zeolite catalyst, and oxidizes excess ammonia that has passed through the SCR 13.

[0021] As shown in FIG. 1, the exhaust gas purification device 10 further includes a fuel injection valve 15, a reducing agent injection valve 16, and a control device 20. The fuel injection valve 15 injects fuel into the exhaust passage 2 at a position between the engine 1 and the DOC 11. The fuel injected from the fuel injection valve 15 is a liquid fuel such as light oil. The fuel injection valve 15 can adjust the supply amount of fuel to the exhaust passage 2 by adjusting the opening degree of the valve. The supply amount of fuel from the fuel injection valve 15 to the exhaust passage 2 is controlled by the control device 20.

[0022] The reducing agent injection valve 16 injects aqueous urea into the exhaust passage 2 at a position between the DPF 12 and the SCR 13. The aqueous urea injected into the exhaust passage 2 is decomposed into ammonia by the heat of the exhaust gas and supplied to the SCR 13. The ammonia supplied to the SCR 13 reduces NOx on the SCR 13.

[0023] The control device 20 is an electronic control unit having a CPU [Central Processing Unit], a ROM [Read Only Memory], a RAM [Random Access Memory], a CAN [Controller Area Network] communication circuit, etc., and controls the operation of the entire exhaust gas purification device 10. The control device 20 realizes various functions described later by, for example, loading a program stored in the ROM into the RAM and executing the program loaded into the RAM by the CPU.

[0024] The control device 20 is communicably connected to the fuel injection valve 15 and the reducing agent injection valve 16. The control device 20 sends control signals to the fuel injection valve 15 and the reducing agent injection valve 16 to control the injection amounts of the fuel and the aqueous urea from the fuel injection valve 15. For example, when clogging of the DPF 12 is detected, the control device 20 controls the fuel injection valve 15 to add fuel to the exhaust gas. The fuel added to the exhaust gas is supplied to the DOC 11 and raises the temperature of the exhaust gas flowing into the DPF 12 to 500°C to 600°C by an oxidation reaction. Thereby, the PM collected by the DPF 12 is burned and removed, and the DPF is regenerated.

[0025] Furthermore, if the temperature of the exhaust gas in the exhaust passage 2 is low (for example, below 200°C), the control device 20 stops supplying urea solution. At this time, NOx contained in the exhaust gas is adsorbed by the NOx adsorbent supported on the DPF 12. On the other hand, if the temperature of the exhaust gas in the exhaust passage 2 is high (for example, above 200°C), the control device 20 controls the reducing agent injection valve 16 to supply urea solution into the exhaust passage 2. The urea solution supplied to the exhaust passage 2 is decomposed into ammonia by the heat of the exhaust gas and supplied to the SCR 13. The ammonia supplied to the SCR 13 reduces the NOx contained in the exhaust gas to nitrogen (N2) and water (H2O) through the action of the NOx reduction catalyst.

[0026] Next, the DPF12 will be described in detail with reference to Figures 2 and 3. Figure 2 is a schematic longitudinal section of the DPF12 along the direction of exhaust gas flow, and Figure 3 is a cross-sectional view along line III-III in Figure 2. The DPF12 is a cylindrical honeycomb structure with multiple passages through which exhaust gas flows. The DPF12 is a wall-flow type filter and is made of porous ceramic having a large number of pores.

[0027] The DPF12 comprises an outer wall 21, an inlet end face 22, an outlet end face 23, a partition wall 24, and a sealing portion 25. These outer wall 21, inlet end face 22, outlet end face 23, partition wall 24, and sealing portion 25 are made of, for example, porous cordierite or silicon carbide (SiC) and are integrally formed.

[0028] The outer wall portion 21 is cylindrical in shape and defines a space through which exhaust gas flows. The outer wall portion 21 may be cylindrical or elliptical in shape. The inlet end face 22 is connected to the upstream end of the outer wall portion 21. The outlet end face 23 is connected to the downstream end of the outer wall portion 21. That is, the inlet end face 22 is located on the upstream side in the direction of exhaust gas flow, and the outlet end face 23 is located on the downstream side in the direction of exhaust gas flow. The inlet end face 22 and the outlet end face 23 face each other in the direction of exhaust gas flow.

[0029] The partition wall 24 is a honeycomb structure and is joined to the outer wall portion 21. The partition wall 24 defines a plurality of flow paths 30 inside the outer wall portion 21. The plurality of flow paths 30 extend parallel to each other between the inlet end face 22 and the outlet end face 23, and guide exhaust gas from the inlet end face 22 side to the outlet end face 23 side. The plurality of flow paths 30 are arranged radially in the DPF 12. As shown in Figure 3, each of the plurality of flow paths 30 has a rectangular cross-sectional shape. The cross-sectional shape of the plurality of flow paths 30 may be a polygon such as a circle, ellipse, or hexagon.

[0030] The multiple flow paths 30 include multiple first flow paths 31 and multiple second flow paths 32. Each first flow path 31 has one end 31a that opens to the inlet end face 22 and the other end 31b that is closed by a sealing portion 25. The one end 31a of the first flow path 31 is the exhaust gas inlet. Each second flow path 32 has one end 32a that is closed by a sealing portion 25 and the other end 32b that opens to the outlet end face 23. The other end 32b of the second flow path 32 is the exhaust gas outlet.

[0031] Multiple first channels 31 are defined by the first surface 24a of the partition wall 24. Multiple second channels 32 are defined by the second surface 24b of the partition wall 24. That is, the first surface 24a of the partition wall 24 is the surface on the first channel 31 side and constitutes the inner wall surface on the first channel 31 side. Similarly, the second surface 24b of the partition wall 24 is the surface on the second channel 32 side and constitutes the inner wall surface on the second channel 32 side. These first channels 31 and second channels 32 are arranged adjacent to each other via the porous partition wall 24. As shown in Figure 3, the first channels 31 and second channels 32 are arranged alternately in the radial direction of the DPF 12.

[0032] As shown in Figure 3, the opening area of ​​the first channel 31 may be larger than the opening area of ​​the second channel 32. Here, the opening areas of the first channel 31 and the second channel 32 refer to the cross-sectional areas of the first channel 31 and the second channel 32 along a plane perpendicular to the first channel 31 and the second channel 32.

[0033] The sealing portion 25 closes one end of each of the multiple flow paths 30. As shown in Figure 2, the sealing portion 25 seals the other end 31b of the first flow path 31 on the outlet end face 23 side of the multiple flow paths 30. The sealing portion 25 also seals one end 32a of the second flow path 32 on the inlet end face 22 side of the multiple flow paths 30.

[0034] The first surface 24a of the partition wall 24 is covered with a catalyst layer 34 that adsorbs NOx in the exhaust gas. The catalyst layer 34 contains particulate NOx adsorbent and is formed in a film-like (membrane) form. The NOx adsorption capacity of the catalyst layer 34 is temperature-dependent. The catalyst layer 34 has a high NOx adsorption capacity at low temperatures and its NOx adsorption capacity decreases as the temperature increases.

[0035] As the NOx adsorbent, for example, a NOx adsorbent with a higher bulk density than zeolite is used. Zirconia (ZrO2) is an example of a NOx adsorbent with a higher bulk density than zeolite. The NOx adsorbent contained in the catalyst layer 34 has an average particle size of, for example, 10 nm to 1000 nm. The average particle size of the NOx adsorbent may be 100 nm or more, 200 nm or more, or 300 nm or more, and may be 900 nm or less, 800 nm or less, or 700 nm or less. The NOx adsorbent is dispersed in the catalyst layer 34. In addition to ZrO2, the catalyst layer 34 may also contain palladium.

[0036] In one embodiment, the thickness of the catalyst layer 34 may be 10 μm or more and 100 μm or less. The thickness of the catalyst layer 34 may also be 20 μm or more, 30 μm or more, or 40 μm or more, and may be 90 μm or less, 80 μm or less, or 70 μm or less.

[0037] The catalyst layer 34 is formed to cover substantially the entire area of ​​the first surface 24a. Covering substantially the entire area of ​​the first surface 24a means that the majority of the first surface 24a is covered by the catalyst layer 34, and includes, for example, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more of the surface area of ​​the first surface 24a being covered by the catalyst layer 34. On the other hand, the second surface 24b of the partition wall 24 is not covered by the catalyst layer 34.

[0038] Conventionally, when manufacturing DPFs with NOx adsorbents, a common method is to immerse the DPF in a slurry containing NOx adsorbents to load the NOx adsorbents into the pores within the partition walls. However, when NOx adsorbents are loaded into the pores of the partition walls in this way, the amount of NOx adsorbent that can be loaded is limited, and the pressure loss of the DPF increases.

[0039] In contrast, the catalyst layer 34 of the DPF12 is formed by coating the first surface 24a of the partition wall 24 with a paste containing particulate NOx adsorbent having the above-mentioned average particle size. By forming a film-like catalyst layer 34 containing particulate NOx adsorbent on the first surface 24a in this way, it is suppressed that the NOx adsorbent penetrates into the interior of the partition wall 24 and clogs the pores. As a result, the increase in pressure loss of the DPF12 is suppressed. Furthermore, compared to the conventional method of supporting NOx adsorbent in the pores inside the partition wall, forming a film-like catalyst layer 34 on the first surface 24a makes it possible to support more NOx adsorbent in the DPF12. As a result, the NOx reduction performance can be improved.

[0040] Next, let's explain the exhaust gas flow. As shown by the arrows in Figure 2, the exhaust gas G discharged from the engine 1 and passing through the DOC 11 flows into the DPF 12 from one end 31a of the first flow path 31.

[0041] In this case, when the exhaust gas temperature is low, such as during a cold start (for example, below 200°C), NOx in the exhaust gas is adsorbed onto the NOx adsorbent in the catalyst layer 34 as the exhaust gas flows through the first passage 31. As the temperature of the exhaust gas rises, the NOx adsorbed on the catalyst layer 34 is released from the catalyst layer 34, and the exhaust gas containing NOx is discharged from the DPF 12. The exhaust gas containing NOx is supplied to the SCR 13 through the exhaust passage 2, where it reacts with ammonia and is reduced and removed.

[0042] Since the other end 31b of the first flow path 31 is blocked, the exhaust gas G flowing through the first flow path 31 passes through the partition wall 24 and moves to the second flow path 32. PM in the exhaust gas is removed as it passes through the partition wall 24. The exhaust gas from which the PM has been removed flows through the second flow path 32 and is discharged from the other end 32b.

[0043] If a catalyst layer 34 is not formed on the first surface 24a, PM in the exhaust gas enters the pores of the partition wall 24 and accumulates inside the partition wall 24. As the amount of PM accumulated inside the partition wall 24 increases, clogging occurs in the partition wall 24, and the pressure loss of the DPF 12 increases. In particular, in the initial stages when PM collection is started using an unused DPF, PM easily enters the pores of the partition wall 24, and the pressure loss of the DPF 12 rises sharply. Subsequently, as PM collection continues, PM tends to accumulate in front of the first surface 24a of the partition wall 24, and the rate of increase in pressure loss slows down.

[0044] In contrast, in one embodiment of the DPF12, the catalyst layer 34 formed on the first surface 24a of the partition wall 24 functions as a filter that suppresses the entry of PM into the interior of the partition wall 24. Due to the filtering effect of the catalyst layer 34, PM in the exhaust gas accumulates in front of the first surface 24a of the partition wall 24 (for example, on the catalyst layer 34), and its entry into the interior of the partition wall 24 is suppressed. In particular, by setting the average particle size of the NOx adsorbent contained in the catalyst layer 34 to 1000 nm or more, the entry of PM into the interior of the partition wall 24 can be effectively suppressed.

[0045] Furthermore, if PM enters the interior of the partition wall 24, the pressure difference between the first channel 31 and the second channel 32 may cause the PM collected in the pores to pass through the partition wall 24 and move to the second channel 32, where it may be released to the outside of the DPF 12. In contrast, with the DPF 12 described above, it is difficult for PM to enter the interior of the partition wall 24, so the release of PM to the outside can be suppressed. Therefore, the filter performance of the DPF 12 can be improved. As explained above, according to one embodiment of the DPF 12, it is possible to improve the PM removal performance while suppressing an increase in pressure loss.

[0046] Although various embodiments of the DPF have been described above, various modified forms can be constructed without being limited to the embodiments described above, as long as the gist of the invention is not altered.

[0047] For example, in the above-described embodiment, the catalyst layer 34 is formed only on the first surface 24a of the partition wall 24, but the catalyst layer 34 may also be formed on both the first surface 24a and the second surface 24b of the partition wall 24. In this case, the amount of NOx adsorbent can be increased, thereby improving the NOx removal performance. In one embodiment, NOx adsorbent may also be supported on the DOC 11 in addition to the DPF 12. [Explanation of symbols]

[0048] 1...Engine, 2...Exhaust passage, 12...Diesel particulate filter (DPF), 22...Inlet end face, 23...Outlet end face, 24...Partition wall, 25...Sealing section, 30...Flow path, 31...First flow path, 31a...One end of the first flow path, 31b...Other end of the first flow path, 32...Second flow path, 32a...One end of the first flow path, 32b...Other end of the second flow path, 34...Catalyst layer.

Claims

1. A diesel particulate filter provided in the exhaust passage of an engine, which collects particulate matter contained in the exhaust gas from the engine, The inlet end face located on the upstream side in the flow direction of the exhaust gas, The outlet end face located downstream in the flow direction of the exhaust gas, A porous partition wall that defines multiple flow paths for guiding the exhaust gas from the inlet end face side to the outlet end face side, A sealing portion that closes one end of the plurality of flow paths, Equipped with, The plurality of channels include a first channel having one end opening to the inlet end face and the other end being closed, and a second channel having one end being closed and the other end opening to the outlet end face, and the second channel being adjacent to the first channel via the partition wall. The surface of the partition wall on the first channel side is covered with a film-like catalyst layer containing particulate NOx adsorbent, The catalyst layer contains ZrO₂ as the NOx adsorbent, The average particle size of the NOx adsorbent contained in the catalyst layer is 100 nm or more and 1000 nm or less. The thickness of the catalyst layer is 10 μm or more and 100 μm or less. The catalyst layer is a layer coated on the surface of the partition wall on the first channel side. Diesel particulate filter.

2. The diesel particulate filter according to claim 1, wherein the catalyst layer covers 90% or more of the surface of the partition wall on the first flow path side.

Images