KR20070000044A - Filter for an apparatus for purifying exhaust gas from a diesel engine - Google Patents

Abstract

A filter device for an exhaust gas purifying apparatus of a diesel engine is provided to reduce back pressure and improve particulate matter collecting efficiency by arranging a metallic foam filter in a horizontal or vertical direction in a filter assembly. A filter device(50) comprises a can(10), a filter assembly(20), and an exhaust gas flow channel(40). The can has an inlet port(11) for inflow of exhaust gas emitted from an engine, and an outlet port(12) for discharging exhaust gas passed through a filter. The filter assembly is arranged in the can, and mounted with a stacked or rolled type metallic foam filter(30) for passage of introduced exhaust gas. The filter assembly has a top where a conical lid(33) is coupled to improve flow of exhaust gas introduced in the inlet port. The exhaust gas flow channel is formed in the can so as to permit the exhaust gas introduced through the inlet port to pass through the metallic foam filter and exit through the outlet port.

Description

Filter device for purifying exhaust gas from a diesel engine

The present invention relates to a filter device for an exhaust gas purification device of a diesel engine, and more particularly, in the case of replacing a diesel particulate filter (DPF) made of a conventional ceramic with a metal, The pore size is 200-1000 μm, which is coarse than the ceramic filter having an average pore size of 30 μm, resulting in a poor collection efficiency. To improve this problem, a filter shape and a layout design are required to improve the collection efficiency while reducing the back pressure. The present invention relates to a filter device for exhaust gas purification apparatus of a diesel engine having.

In general, the exhaust gas of a vehicle refers to a gas in which a mixture combusted from an engine is released into the atmosphere through an exhaust pipe, and the exhaust gas mainly includes harmful substances such as carbon monoxide (CO), nitrogen oxides (NOx), and unburned hydrocarbons (HC). This is included. Such exhaust gas regulation is inevitably tightened. Accordingly, an exhaust gas control device including an exhaust gas recirculation device, a three-way catalyst, an MPI device, and an evaporative gas control device including a canister, a purge control solenoid valve, etc. The back is applied to a vehicle.

On the other hand, although diesel engine vehicles are excellent in fuel economy and power output, unlike gasoline engines, nitrogen gas and particulate matter (PM) are significantly contained in exhaust gas. In diesel vehicles, CO and HC are emitted much less than gasoline vehicles because the air is combusted in most operating conditions, but NOx and particulate matter (soot) are emitted.

Therefore, the main targets of diesel vehicle emission regulation are NOx and particulate matter (PM). As a countermeasure technique, the delay of fuel injection time and the concentration of NOx by Exhaust Gas Recirculation As a technique for reducing and improving the combustion performance of an engine for reducing particulate matter, the trend is being developed with an emphasis on the technology. In other words, as a concrete countermeasure for diesel vehicle exhaust regulation, engine improvement and after-treatment technology are classified into diesel engines. First, engine improvement technology of diesel vehicles is improved fuel chamber, intake system (turbocharger + intercooler), and fuel injection system ( Electronically controlled high pressure fuel injection devices) and exhaust gas recirculation devices are being applied or under development. In addition, as a post-treatment technique, firstly, an oxidation catalyst for purifying high-boiling hydrocarbons in particulate matter (PM), secondly, a DeNOx catalyst which decomposes or reduces nitrogen oxides (NOx) in an excess oxygen atmosphere, and thirdly, particulate matter (PM). Diesel Particulate Filter (DPF) system. However, the particulate filter (PM) removal filter system of the post-treatment technology has the advantage of reducing the emissions by reliably capture soot, but the back pressure of the exhaust gas increases due to the increase of particulate matter trapped in the DPF over time There is a problem that the burden on the engine becomes large.

For this reason, the regeneration method of burning and removing the particulate matter collected by the reduction of the back pressure of the DPF itself is an important factor that determines the performance of the DPF.

Currently, as the material of the DPF, silicon carbide (SiC) attracts attention due to problems such as thermal expansion and durability at the time of regeneration by combustion of the collected particulate matter, as shown in FIGS. 1 and 2. The unit cell 110 is made of silicon, and the unit cell 110 is bonded with an adhesive similar to that of silicon carbide to manufacture a DPF 100 having a desired size. At present, the DPF 100 is configured of a unit cell 110 having the same cell density and porosity of the unit cell 110 to manufacture a DPF 100 having a desired size. The DPF 100 having a density and porosity has a larger DPF (100) than the diameter of the exhaust gas exhaust pipe because the size of the DPF 100 is determined based on particulate matter discharge to collect particulate matter discharged from the engine. ) Or a DPF 100 having the same diameter as the exhaust pipe, the DPF 100 having a very long length is installed, so that the back pressure of the exhaust gas is very high, so that the operation of the engine is impossible. Therefore, it is inevitable to install the DPF 100 larger than the diameter of the exhaust pipe in order to remove particulate matter while suppressing the increase in the discharge pressure with respect to the exhaust gas of the diesel engine. As a result, a phenomenon in which the flow of exhaust gas is concentrated only at the center portion of the DPF 100 occurs, and particulate matter collected at the edge thereof is not smoothly flowed during the regeneration mode due to the rise of the exhaust gas temperature. At some point, there is a problem in that the exhaust gas passage area of the DPF 100 is reduced by the loss of function, thereby increasing the exhaust gas pressure of the engine, thereby providing a cause of engine failure.

Meanwhile, the material of the conventional diesel particulate filter (DPF) is a ceramic made of cordierite or silicon carbide (SiC), which is brittle and easily damaged by a weak impact, thus producing a process design. In the mass production design, special care is required and productivity is low due to poor assembly. In addition, ceramics have very poor thermal conductivity, which prevents rapid release of heat generated when particulate matter is regenerated to the outside, causing a sharp increase in local temperature, which causes the ceramic filter to melt itself or concentrate heat, resulting in a coefficient of thermal expansion with the surroundings. It may be broken by the difference. However, in the case of the metal filter, due to the superior ductility characteristics of the ceramic, there is less damage due to impact, higher assembly and productivity, and superior thermal conductivity than the ceramic, thereby rapidly transferring local heat generated during regeneration. Although there is little damage due to localized heat concentration or a difference in coefficient of thermal expansion, the pore size of the metal foam is 200 to 1000 μm and coarse than that of a ceramic filter having an average pore size of 30 μm.

Accordingly, the present invention has been conceived to solve the above problems, when replacing the conventional diesel particulate filter (DPF) made of ceramic with a metal, the pore size of the metal foam is 200 to 1000㎛ There is a problem in that the collection efficiency is lower than that of the ceramic filter having an average pore size of 30 μm, and the exhaust gas purifying apparatus of the diesel engine having a filter shape and a layout design that requires a low back pressure and improves the collection efficiency is improved. It is an object to provide a filter device for.

Another object of the present invention is to provide a filter device for an exhaust gas purification device of a diesel engine that can improve the flow of exhaust gas entering the inlet port by fastening a conical lid to the upper end of the filter ass'y.

In addition, another object of the present invention is to install a metal foam filter in the horizontal or vertical direction in the filter ass'y, for the exhaust gas purification device of the diesel engine that can improve the trapping efficiency of particulate matter (PM) while reducing the back pressure To provide a filter device.

Another object of the present invention is to form a through-hole in the center of the nickel foam filter or the nickel foam filter stacked vertically in the direction of the exhaust gas flow direction or the exhaust gas flow direction is formed in the center of the nickel foam filter All of them are available without a through hole or in the form of a plurality of grooves that allow exhaust gas to flow into the outlet port in the middle of the holder formed at the center of the nickel foam filter. The present invention provides a filter device for an exhaust gas purification device of a gel engine, which is easy to apply.

In order to achieve the above object, there is provided a filter apparatus for an exhaust gas purifying apparatus of a diesel engine according to a preferred embodiment of the present invention, including an inlet through which exhaust gas combusted from an engine is introduced, and an outlet through which the exhaust gas is passed through a filter. A can; It is mounted inside the can and is equipped with a laminated or rolled metal foam filter through which the inflow exhaust gas passes, and a conical cap is fastened to the upper end to improve the flow of the exhaust gas into the inlet. A filter ass'y; An exhaust gas flow path formed inside the can to allow exhaust gas introduced into the inlet to pass through the metal filter to be discharged to the outlet; Characterized by including.

In the present invention, the metal foam filter is stacked perpendicular to the direction in which the exhaust gas flow, and includes all the through holes are formed in the center of the nickel foam filter or there is no through hole in the center of the nickel foam filter. It is characterized by.

In the present invention, the metal foam filter is formed by rolling horizontally in the direction of the exhaust gas flow, and the holder is formed in the center of the nickel foam filter to form a through hole or there is no holder in the center of the nickel foam filter It is characterized by including.

In the present invention, it characterized in that it comprises a plurality of grooves are formed in the middle of the holder is formed in the center of the nickel foam filter to be discharged to the discharge port.

Hereinafter, with reference to the accompanying drawings, a filter device for an exhaust gas purification device of a diesel engine according to a preferred embodiment of the present invention will be described in detail.

Figure 3 is a cross-sectional view showing the internal configuration of the filter apparatus for exhaust gas purification apparatus of a diesel engine according to an embodiment of the present invention, Figure 4 is a filter for exhaust gas purification apparatus of a diesel engine according to another embodiment of the present invention. Figure 5 is a cross-sectional view showing an internal configuration having a can holder in the device, Figures 5a and 5b is a case where there is a through hole constituting the filter ass'y in the filter device for the exhaust gas purification device of a diesel engine according to an embodiment of the present invention and 6A and 6B are a perspective view illustrating the shape of a metal foam filter of a stacked type in the absence of a stacked type, and FIGS. It is a perspective view which shows the shape of the rolling metal foam filter with and without a hole. In addition, Figure 7 is a cross-sectional view showing the internal configuration of the filter apparatus for the exhaust gas purification apparatus of the diesel engine according to an embodiment of the present invention, Figure 8 is an exhaust gas purification apparatus of the diesel engine according to another embodiment of the present invention. It is sectional drawing which shows the internal structure of a filter apparatus.

As shown in Figures 3 to 8, the filter device 50 for the exhaust gas purification device of a diesel engine is an inlet 11 through which the exhaust gas combusted from the engine is introduced, and the exhaust gas is discharged through the filter. A can 10 having an outlet 12 formed therein; It is mounted inside the can is equipped with a laminated or rolled metal foam filter 30 in which the inlet exhaust gas passes, and conical in the upper end to improve the flow of the exhaust gas entering the inlet 11 A filter assay 20 to which the lid 33 is fastened; An exhaust gas channel 40 formed inside the can to allow exhaust gas introduced into the inlet 11 to pass through the metal foam filter 30 and to be discharged to the outlet 12; It is provided.

Looking at the function of the main technical means of the filter device for an exhaust gas purification device of a diesel engine according to an embodiment of the present invention with reference to the bar shown in Figs.

The can 10 includes an inlet 11 through which exhaust gas combusted from an engine flows in, and an outlet 12 through which the exhaust gas passes through a filter.

The metal filter ass'y 20 is mounted inside the can, and is equipped with a stacked or rolled metal foam filter 30 through which the introduced exhaust gas passes, and the exhaust gas entering the inlet 11. In order to improve the flow of the conical lid 33 is fastened to the upper end. As shown in FIGS. 5A and 5B, the metal foam filter 30 configured in the metal filter ass'y 20 has a lamination type. The lamination type has a through hole 31 formed at the center of a nickel foam. ) And a structure in which the buried layer is pressurized and canned by a pressurization method, and a structure without a through hole in the center of the nickel foam filter, and also a metal foam filter constituted in the metal filter ass'y (20). 6A and 6B, there is a rolling method, wherein the rolling type shows a structure in which a nickel alloy foam is rolled around the holder 32 and a rolling structure without the holder. . The porosity of the surface and the side of the conventional metal alloy is almost the same, but the pore size of the side is 50% of the porosity of the surface, so that the pores are small and the porosity can increase the collection efficiency. Surface porosity of the metal alloy is 400 to 700㎛, side pore is 100 to 300㎛, porosity is 86% ± 5%. In addition, the metal foam filter 30 is alloyed by adding chromium and iron to the Ni base. In addition, the conical lid 33 is fastened to the upper end of the metal filter ass'y 20 to improve the flow of the exhaust gas entering the inlet 11. In addition, the conical lid 33 for improving the flow of exhaust gas is fastened to the upper end of the filter ass'y 20, and attached to the lower end of the outer can 10. The attachment method is welding, cocking, brazing, Tightening with bolts and the entire bottom of the filter's assy can be threaded. During fabrication, no leakage should occur at the conical cap 33 and the filter ass'y (20) and at the joining position of the filter ass'y (20) and the lower end of the can (10). When the exhaust gas flows into the filter device thus manufactured, the conical lid 33 smoothly flows in and prevents the exhaust gas from shifting to one side with an even distribution, and the exhaust gas flows from the outside of the filter ass'y 20 to the inside. It has a structure using a metal foam filter to allow the inlet to maximize the initial contact area to reduce the back pressure.

The flow path 40 is formed inside the can to allow the exhaust gas introduced into the inlet 11 to pass through the metal foam filter 30 to the outlet 12.

Figure 9 is a photograph of the surface of the nickel foam filter in the filter device for exhaust gas purification device of a diesel engine according to an embodiment of the present invention observed with a scanning electron microscope.

As shown in Fig. 9, there are many holes on the surface of the nickel foam filter so that the exhaust gas is discharged through the holes through the holes.

10 is a perspective view illustrating a flow pattern of exhaust gas in a radial type metal foam diesel particulate filter (DPF) in a filter device for an exhaust gas purification device of a diesel engine according to an embodiment of the present invention, and FIG. 12 is a view showing a difference in pressure drop with time between flow modes in a filter device for an exhaust gas purification device of a diesel engine according to an embodiment of the present invention, and FIG. 12 is an exhaust gas of a diesel engine according to an embodiment of the present invention. In the filter device for purifiers as the process of the flow between the collection process is a view showing a change in the collection efficiency of the filter for each particle diameter, Figure 13 is an exhaust gas purification device of a diesel engine according to an embodiment of the present invention Is a view showing the change of particle density distribution between the flow modes in the filter device. 14 is a view showing the total collection efficiency of the filter between the flow in the filter device for the exhaust gas purification apparatus of the diesel engine according to an embodiment of the present invention, Figure 15 is a view of the diesel engine according to an embodiment of the present invention In the filter device for the exhaust gas purification apparatus is a view showing the distribution of the mass of the soot collected in the filter as the collection process between the flow method, Figure 16 is an exhaust gas purification apparatus of a diesel engine according to an embodiment of the present invention Figure 15 is a view showing the change in mass distribution inside the filter according to the time and the foam thickness in the plane of the filter device for cutting the length of 15cm, which is half the length of the filter in the axial direction, Figure 17 is a diesel according to an embodiment of the present invention Figure showing the thickness change of soot layer growing on the surface of the exhaust gas inlet as the flow between the flow methods is collected in the filter device for the exhaust gas purification device of the engine. .

10 to 17 illustrate the flow and capture process analysis according to the flow direction of the radial type metallic foam DPF. The flow and capture process of the radial type metallic foam DPF with an increased initial exhaust gas inflow area compared to the axial type metallic foam DPF. A prediction technique was developed and applied to the prediction of the effects of flow and capture processes according to flow direction changes in DPF.

As shown in FIG. 10, the analysis target is a radial type metallic foam DPF, and the flow method in the DPF is an inward flow method and an inner surface flowing inward from the outer surface of the foam according to the direction in which the exhaust gas flows through the DPF. It can be distinguished by the outward flow method flowing outward from. The inward flow method has a relatively larger initial exhaust gas inflow area than the outflow flow method, so the concentration and flow rate of soot per area are small.

FIG. 11 shows the influence of the flow method difference on the pressure drop, and a small diagram in the drawing shows an enlarged pressure drop at the beginning of the collecting process. In the early stage of the collection process, the inward flow method, which was expected to have a large pressure drop from the fluid flow point of view, was calculated somewhat higher than the outward flow method, but this trend was reversed as the collection process proceeded. This indicates that the pressure drop as the flow area is narrowed is smaller than the pressure drop generated as the collecting process proceeds. In addition, the outward flow method showed a larger change in pressure drop over time than the inward flow method.

12 is a diagram showing the change in the filter collection efficiency for each particle diameter as the collection process proceeds. In the early stage of the collection process (1 hr), the collection efficiency was similar for both methods. As the process progressed, the outward flow method was found to have a somewhat higher collection efficiency than the inward flow method for all particle sizes. However, in FIG. 13, which shows a decrease in soot particles as the collection process proceeds, the two methods do not show much difference. Both the inward flow method and the outward flow method showed high particle capture performance when the particle diameter was less than 0.1mm, and the particle capture performance was deteriorated due to the low collection efficiency for particles with diameter larger than 0.1mm.

14 shows the total collection efficiency of the filter. In the case of outward flow, the collection efficiency is not significantly different even though it causes a higher pressure drop than in the case of inward flow. The reason for this phenomenon is that in the outward flow method, the flow velocity through the foam at the exhaust gas inlet side is larger than that of the inward flow method. Also, the narrow inlet side increases the inlet mass of the soot, increasing the soot penetration length. I think because. Increasing the flow velocity at the inflow side results in low diffusion efficiency and increasing the penetration length results in an increase in the probability of particle passing through the filter.

FIG. 15 shows the distribution of mass of soot collected inside the filter as the collecting process proceeds. In the case of the inward flow method, soot particles are collected from an upper surface into which exhaust gas is introduced and gradually become inward as time passes. The soot penetrates and shows a high distribution on the upper side and a low distribution toward the inside. It can also be seen that most of the soot mass is concentrated on the upper surface. On the other hand, in the outward flow method, the soot particles are collected from the lower side where the exhaust gas flows and the soot penetrates outward as time passes and shows a high soot mass distribution on the lower side. This aspect is also shown in Fig. 16, which shows the change of mass distribution inside the filter with time in a plane in which the 15 cm point, which is half the length of the filter, is cut perpendicular to the axial direction. In the figure, the coordinate of the surface into which the exhaust gas flows was set to x = 0. In the inward method, as the exhaust gas passes through the filter from the inlet side, a large part of the soot is collected at the inlet side, and the amount of soot mass collected increases over time, whereas the amount of soot introduced into the filter is large. As it decreases proportionally, the increase in trapped soot mass inside the filter decreases as it moves away from the inlet. In the outward method, the soot mass distribution was similar to that of the inward method, but the increase in soot mass collected on the inflow side was smaller than that of the inward method, and the increase in the soot mass collected near the discharge surface where the exhaust gas leaves the filter was inward. Larger than that. It is thought that this is because in the outward method, since the inflow area of the exhaust gas is smaller than that of the inward method, a significant amount of the soot introduced does not collect around the inlet surface but penetrates into the filter. The mass collected on the exhaust gas inlet is smaller than the inward flow method, but the inlet area is only half of the inward area, so the porosity and permeability of the slab forming the inlet is reduced, resulting in a relatively high pressure. It is considered to have shown a drop.

Figure 17 shows the change in thickness of the soot layer growing on the surface of the exhaust gas inlet surface as the collection process proceeds, the outward method was faster than the inward method. Therefore, the outward method, which has a rapid growth rate of the soot layer, has a thicker soot layer than the inward method.

Therefore, it can be seen from the result of the three-dimensional flow analysis that the back pressure is low and the collection efficiency of particulate matter (PM) is good.

As described above, various substitutions, modifications, and changes can be made by those skilled in the art without departing from the technical spirit of the present invention, and thus, the embodiments and the accompanying drawings are limited. It doesn't happen.

As described above, the filter device for exhaust gas purification device of the diesel engine according to the present invention has the following effects.

First, the present invention, when replacing the diesel particulate filter (DPF) made of conventional ceramics with a metal, the pore size of the metal foam is 200 to 1000 ㎛ with a pore size of 30 ㎛ on average There is a problem in that the collection efficiency is lower than that of the filter, the filter shape and arrangement design that can increase the collection efficiency while taking a back pressure to improve this problem.

Second, the present invention can improve the flow of the exhaust gas entering the inlet by fastening the conical lid to the upper end of the filter ass'y.

Third, in the present invention, by installing the metal foam filter in the horizontal or vertical direction in the filter ass'y, it is possible to improve the trapping efficiency of particulate matter (PM) while reducing the back pressure.

Fourth, in the present invention, all through holes are formed in the center of the nickel foam filter stacked vertically in the direction in which the exhaust gas flows or the nickel foam filter is formed in the direction in which the exhaust gas flows. It can be used in various forms according to the installation environment and conditions, because there are no holes or a plurality of grooves are formed in the middle of the holder formed at the center of the nickel foam filter to allow the exhaust gas to flow into the outlet. This is easy.

1 is a perspective view showing a filter system for removing particulate matter of a general diesel engine.

2 is a cross-sectional view showing a filter for removing particulate matter of a conventional diesel engine.

Figure 3 is a cross-sectional view showing the internal configuration of the filter device for exhaust gas purification device of a diesel engine according to an embodiment of the present invention.

Figure 4 is a cross-sectional view showing the internal configuration having a can holder in the filter device for exhaust gas purification device of a diesel engine according to another embodiment of the present invention.

Figures 5a and 5b shows the shape of the laminated metal foam filter with and without the through-holes constituting the filter ass'y in the filter device for the exhaust gas purifier of the diesel engine according to an embodiment of the present invention. Perspective view.

6A and 6B are shapes of a rolling metal foam filter with and without a through hole constituting the filter ass'y in the filter device for an exhaust gas purifier of a diesel engine according to another embodiment of the present invention. Perspective view.

7 is a cross-sectional view showing an internal configuration of a filter device for an exhaust gas purification device of a diesel engine according to an embodiment of the present invention.

8 is a cross-sectional view showing the internal configuration of a filter device for an exhaust gas purification device of a diesel engine according to another embodiment of the present invention.

Figure 9 is a photograph of the surface of the nickel foam filter in the filter device for exhaust gas purification device of a diesel engine according to an embodiment of the present invention observed with a scanning electron microscope.

10 is a perspective view showing the flow pattern of the exhaust gas in the radial type metal foam diesel particulate filter (DPF) in the filter device for exhaust gas purification device of a diesel engine according to an embodiment of the present invention.

11 is a view showing a difference in pressure drop over time between flow modes in a filter device for an exhaust gas purification device of a diesel engine according to an embodiment of the present invention.

12 is a view showing a change in the collection efficiency of the filter for each particle diameter as the collection process between the flow type in the filter device for exhaust gas purification device of the diesel engine according to an embodiment of the present invention.

13 is a view showing the change in the particle density distribution between the flow in the filter device for the exhaust gas purification device of a diesel engine according to an embodiment of the present invention.

14 is a view showing the total collection efficiency of the filter between the flow in the filter device for the exhaust gas purification device of a diesel engine according to an embodiment of the present invention.

15 is a view showing the distribution of the mass of soot collected in the filter as the collection process between the flow in the filter device for the exhaust gas purification device of the diesel engine according to an embodiment of the present invention.

16 is a mass distribution in the filter according to the time and foam thickness in a plane cut perpendicular to the axial direction of the 15cm point of the filter length in the filter device for the exhaust gas purification device of the diesel engine according to an embodiment of the present invention Figure showing change.

17 is a view showing the thickness change of the soot layer grows on the surface of the exhaust gas inlet as the collection process between the flow in the filter device for exhaust gas purification apparatus of the diesel engine according to an embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

10 ... can 11 ... inlet

12 ... outlet 20 ... filter ass'y

30 ... metal foam filter 31 ... through hole

32 holder 33 conical lid

       34 home 40 euros

       50 ... filter unit

Claims (4)

In the filter device for exhaust gas purification device of a diesel engine, A can having an inlet through which an exhaust gas combusted from an engine flows in and an outlet through which the exhaust gas passes through a filter; It is mounted inside the can and is equipped with a laminated or rolled metal foam filter through which the inflow exhaust gas passes, and a conical cap is fastened to the upper end to improve the flow of the exhaust gas into the inlet. A filter ass'y; An exhaust gas flow path formed inside the can to allow exhaust gas introduced into the inlet to pass through the metal filter to be discharged to the outlet; Filter apparatus for exhaust gas purification device of a diesel engine comprising a. The method of claim 1, The metal foam filter may be stacked perpendicular to the direction in which the exhaust gas flows, and the through-holes may be formed in the center of the nickel foam filter, or the diesel engine may include no through-holes in the center of the nickel foam filter. Filter apparatus for exhaust gas purification equipment. The method of claim 1, The metal foam filter is formed by rolling horizontally in a direction in which the exhaust gas flows, and a holder is formed in the center of the nickel foam filter, so that a through hole is formed or there is no holder in the center of the nickel foam filter. Filter device for exhaust gas purification device of diesel engine. The method of claim 1, And a plurality of grooves are formed in the middle of the holder formed at the center of the nickel foam filter to allow the exhaust gas to flow into the outlet.